GroupDIY

Project Specific Discussions => Preamplifiers => Topic started by: gemini86 on January 08, 2013, 10:09:03 PM

Title: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 08, 2013, 10:09:03 PM
Docs:

Original Schematic (https://docs.google.com/open?id=0B6s_klsk9wMDQXMzV1NOOEFDS2M)

Schematic with mods and added filtering (https://docs.google.com/file/d/0B6s_klsk9wMDM3VpRF9UVHdNa00/edit?usp=sharing) :: NEW

Layout (https://docs.google.com/file/d/0B6s_klsk9wMDV3M0RGg1cUlJdDA/edit)

BOM (https://docs.google.com/open?id=0B6s_klsk9wMDMlpHSVVTSDJoak0) :: UPDATED 4/13/2013

Toure14's Mouser cart (http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=e5aaab842a) This cart has not yet been verified (as of 5/13/20013). Please use at your own discretion.

This is (mostly) a straight forward build, but here are a few tips for you guys geeks are building the GIX-51X preamp for a 51X rack.

I shouldn't have to say this, but to some of you: Use a new soldering tip. If it's got black spots where no solder will stick, or the tip isn't sharp, you need a new one. This will help eliminate cold solder joints and make everything go faster.



Place the 1mm pin sockets onto a tube, like so:
(https://lh5.googleusercontent.com/-Q8I2vLrCVt4/UOy97ZonmLI/AAAAAAAAAmE/vsai4EbFGiM/s640/%255BUNSET%255D.jpg)
They shouldn't be a super snug fit.

Place the sockets and tube into the tube PCB, set it on its side on the table just to tack solder on of the pins so it stays put. This next part is a little tricky, I like to place the tube in my hand upside down and reflow the solder tack as i level the pin sockets.

Make sure all the sockets are flat to the top side of the board:
(https://lh6.googleusercontent.com/-SHvaeO6FCRw/UOy98R4g0pI/AAAAAAAAAmM/9glIAMAhINI/s640/%255BUNSET%255D.jpg)
I usually tack a socket on the opposite side to make sure it stays flat where I want it, then put the pcb in a third-hand clamp.

Solder all the sockets, double check the top to make sure everything is level.
(https://lh4.googleusercontent.com/-I-w2up2bdKw/UOy99tupuBI/AAAAAAAAAmU/XSR-e8d0Ebw/s640/%255BUNSET%255D.jpg)
They look so happy! That's because they know how awesome they are.

Who's the idiot who let "1PIN" get through to the final gerber? I AM!
(https://lh4.googleusercontent.com/-XhEe1c8I3Ro/UOy9-Z2SgNI/AAAAAAAAAmc/9HB0Y8TLxS0/s640/IMG_20130108_160850.jpg)
Oh well. This board can be set aside for now.



Now the control board-
READ ME!!! This is important! There are two SPDT toggles, one of them is on-off-on, the other is on-on. The one with only two position is SW4. It goes on the right side. The on-off-on is for the HPF and goes in the middle.

Also make sure to have all the notches on the switch bushings going the same way, so it doesn't drive you crazy later. ...because it will.

Stuff all the resistors and the two HPF caps FIRST. This PCB will hold all our front panel controls, so there's really no need for any of the anti-rotation locating tabs that come on the pot and rotary switch. Just snip em off.

That little round peg needs to go.
(https://lh4.googleusercontent.com/-BDGljqrEb54/UOy9_9zUBrI/AAAAAAAAAms/wF_gjRpKnBM/s640/%255BUNSET%255D.jpg)
You will ruin everything if you don't do this and I'm not going to feel bad for you.

[Note: The alpha switch version of this switch will also work. It's from Taiwan, but personally, I've been seeing better quality with them than with the Lorlin switches.]

Now, I had soldered the big rotary switch in first, but you could probably do them all at once. AGAIN, stuff the resistors first, despite what you see in these photos. It's not a game ender, but some of the resistors are close to the rotary switch. You'll end up melting some plastic, and that will make you look dumb if you ever want to show off your handy-work.)

Remove all the nuts and washers from the toggles, except for one, use that one as a stopper to get the right clearance between the pcb and faceplate.

Bolt the faceplate to the switch, this will help you line up all the toggles in their holes.
(https://lh5.googleusercontent.com/-nHVMhxHjOds/UOy-A9vxtKI/AAAAAAAAAm0/BZ9bxhMdEsw/s640/%255BUNSET%255D.jpg)
Double check everything (triple check that the on-off-on switch is in the middle, not the right side!) Solder them in.

Remove the faceplate from the switches. Grab your metal bracket (if you have one) and place the potentiometer (sans locating tab) through it and into the faceplate hole. I made these hold snug on purpose, BUT- it appears that the fab house won't be winning any awards for precision there. Some of them are very snug, so you can actually thread the faceplate onto the pot bushing. I actually prefer this but this will possible create a NEW problem: While the main board will be serviceable and removable, the controls board will be stuck onto the faceplate and bracket permanently. I'd double check your gain resistors for errors and check the soldering joints. If this is something you don't want to worry about, you have to open up the hole a tiny bit with a drill (just use it as a reamer) or a small round file.

Get the pot flush to the faceplate or bracket, you will see that the pins look like they're too short. Stop whining, they're not too short.
(https://lh5.googleusercontent.com/-usd8IZWtGtU/UOy-B8iZnyI/AAAAAAAAAm8/AmoDm1yn8sE/s640/%255BUNSET%255D.jpg)
Okay they're kindof short, but they're just about flush with the back of the control pcb. Solder them in place with plenty of solder. A cold joint here would be easy to accomplish if you have a dirty tip.

Not pictured (because I forgot to take a picture of it) is the SIL connector on the control board. It goes on the back side facing the rear of the unit, in case that was not obvious. Now you're done with the control board.



Populate the main board with all the small components- caps, resistors, relays, for now just ignore the two pads marked "FIL". Also, do not solder in the instrument jack just yet.

I cut all my leads very very short after soldering but this is especially needed in the power cap section, more specifically c26 and c27. They will be awful close to the bracket mounting legs and while they do not touch on my build, they can and WILL cause a dead short to ground if you have a long lead sticking out into it.

See here:
(https://lh6.googleusercontent.com/-Ai3U5JDPeec/UOzMDvsPegI/AAAAAAAAAns/R-XnyrC23Yg/s640/%255BUNSET%255D.jpg)
Nothing touches, no shorts. Make sure all the leads are cut as short as possible! Double check with an ohm meter on all the power rails to be sure you have no continuity to the bracket.

Now, before you solder the instrument jack to the board, make sure it's perfectly flush with the front edge of the PCB. Bend the leads so it will hold itself to the board, and tack one of the leads closest to the bottom edge. You may want to test fit it in the bracket/faceplate now. Don't use any of the supplied black plastic washers, just the one bezel for the front. Just mount it hand tight, then check PCB alignment.
(https://lh5.googleusercontent.com/-P6x8xbFSz_A/UOy-DWiLnvI/AAAAAAAAAnM/XQV03HSLJPM/s640/%255BUNSET%255D.jpg)
The mounting holed should all line up perfectly. You may go as far as screwing down the rear of the board to the bracket. Then if an adjustment is needed, just reflow the one tack you did and get it all straight and legit, son. The board should be flush to the bottom of the jack.

Everything all lined up:
(https://lh6.googleusercontent.com/-2AmUWNc3B5w/UOy-Emmj88I/AAAAAAAAAnU/NikuM9OorqI/s640/%255BUNSET%255D.jpg)
The mounting holes in the bracket on the rear legs are just the right size to hand thread a 4-40 screw without a nut needed on the backside. Thread it through and cut the excess off so they don't interfere with other modules in your rack.

A couple notes on the main board:

1) Mounting the tube board to the main board: The outline on the main board shows exactly where the tube board should be located. It needs to be very flush to the main board, no space under it or you'll be penalized for going out of bounds. A SIL12 90 degree header could work here, but the plastic retaining block will get in the way. I just used solid core wire, or a bunch of little resistor leads off the floor.

2) The pin head under the main board, which connects to the control board IS meant to be a 90 degree SIL12 header. Plug it into the header socket on the control board, THEN move the main board into position and make sure everything is fit correctly. Also make sure you've stuffed C10 first, and that it's leads have been clipped as short as possible or you'll run into trouble.

:: NEW NEW NEW NEW NEW NEW NEW NEW NEW NEW ::
3) Add a 200R resistor at "HV JUMPER" on the main board. Add the new 100nF/250V ceramic cap to the underside of the board as shown in this photo by bruce0:

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/NewCapPic_zps01b4c4b0.jpg)

It goes from the L503/HV JUMPER junction to ground and adds another filtering stage to the HV supply before it hits the output tubes.



The HV converter is very straight forward. I didn't take any pics, because there's not much to see.

1) Solder down the MAX1771CPA+ first. If you've never hand soldered SOIC8 parts, check youtube, plenty of videos that show you how to do it.

2) Solder the current sense resistor. Make sure it's flat to the pcb, tack one side, solder the other, then add solder to the first side.

3) Solder down the inductor. Same as anything else.

4) Solder the surface mount diode. You may need to move it a tad closer to the inductor than is laid out on the pcb, to make room for the electrolytic cap next to it.

5) Solder in all resistors and caps, except C501.

6) Solder in Q501, which goes on the bottom of the board, bent at 90 degrees, leaving some space under it so it's not touching anything. It's not required, but a good idea to place some electrical tape or heatshrink on the back of the tab, so nothing shorts to the bottom of the board.

7) Solder in U502 and C501.

8) Solder in the two pin headers. I put the pin sockets on the converter board and the pins on the main board but in this case it doesn't matter much. The unit will be pretty much drained of HV when removed from the rack so you don't have to worry about zapping yourself on exposed pins. (just, please don't stick it to your tongue.)

:: NEW NEW NEW NEW NEW NEW NEW NEW ::
9) Add a 100nF wima cap across R504/R503 to ground. This will stabilize the HV output and prevent oscillations.
(http://i.imgur.com/3poOPeJ.png)

That's all for now. Here's my finished unit:
(https://lh3.googleusercontent.com/-f8h9PDlraT0/UOzeng94pKI/AAAAAAAAAn8/hChxMbCU0cI/s640/%255BUNSET%255D.jpg)
Andoids are great, but my camera sucks compared to an Iphone. Let's get it together, Motorola.

(https://lh3.googleusercontent.com/-MdUHmxqqm0k/UOzeoi5UXDI/AAAAAAAAAoE/pUFj-pmMFVk/s640/%255BUNSET%255D.jpg)
Love this knob combo on the white faceplate.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: JamesW on January 08, 2013, 10:39:42 PM
wow

 whats the ship date
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 08, 2013, 10:53:30 PM
Some have shipped already, but I'm out of boxes... :( I'm not exactly...experienced when it comes to shipping, so I've been doing what I can as I go. Will be restocking and shipping this week. I will hopefully have everyone shipped out by end of next week.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: baadc0de on January 09, 2013, 08:55:03 AM
Some have shipped already, but I'm out of boxes... :( I'm not exactly...experienced when it comes to shipping, so I've been doing what I can as I go. Will be restocking and shipping this week. I will hopefully have everyone shipped out by end of next week.

Well, this looks schweet! Can't wait to make mine!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on January 09, 2013, 10:31:36 AM
Great timing!  Just finished making my first 51x rack.

I can't wait to build this,  thanks for making it available.

Ian

 8)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruno2000 on January 09, 2013, 10:40:12 AM
Very nice!  Is there a BOM?
Thanks!
Best,
Bruno2000
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on January 09, 2013, 11:24:37 AM
let's hear some audio clips!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: [silent:arts] on January 09, 2013, 12:21:53 PM
all actual documents would be a good in the first post 8)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: dmp on January 09, 2013, 12:50:48 PM
That looks great!
How is the noise floor? Clean? No buzz / hum?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on January 09, 2013, 03:23:29 PM
does it make me weird, that i felt a little sexually excited when i saw this? or am i just officially becoming a full fledged geek ? Either way, i'm going through some changes i don't fully understand ??? ;) ;D


Awsome Rodney!! I cant wait to build these, thanx again
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on January 09, 2013, 03:26:24 PM
Hey Rodney, your pictures are just fine, except you never posted a shot of the front panel of the finished unit? :)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on January 09, 2013, 03:39:07 PM
The above link shows Face plate

Received the boards today. Unique Face plates, they are P.C.B.
Copper back; grounds unit to chassis ground?
Great job putting this together. Fast production and delivery.
Anybody got a Mouser Order B.O.M.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 09, 2013, 05:08:57 PM
Trying to limit my time on my phone while at work, will update first post with all docs including bom.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on January 09, 2013, 05:37:22 PM
 thanks for posting the face plate pic  , Looks good !
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 09, 2013, 10:21:49 PM
Updated the first post with BOM and schematic.

I'll work on getting some recordings done, but for now I've only been doing some noise tests and freq plots just to make sure everything is happy.

I don't have any hum or buzz, since I don't have any 60HZ anywhere in the build... That's the nice thing about the 51X rack, if you have a clean power rail, no hum. The only kind of power supply noise to be had would be around 100Khz where the HV converter is switching, but it's pretty well filtered out. I can't find a trace of it in the signal.

So, this build is basically working just as the prototype did, minus the errors that were on the prototype, of course.

I also just updated the BOM, had the wrong lorlin rotary switch part # on it.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on January 09, 2013, 10:51:43 PM
What sort of heat does this guy put out?   is it gonna set the rack on fire if you have several?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 09, 2013, 10:56:10 PM
naw, the little au7s just get warm. You can pull them out with bare fingers while they're still glowing.

Now, if you had a full rack of them, I imagine they would draw quite a bit on the -24V rail as the heaters warm up. I didn't think to put current limiting on the heater circuit, but now that you mention it... :/ I guess wel'll see...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 09, 2013, 11:11:55 PM
Do i understand correctly that when finished the control board will be removable by was of the SIL socket, but the tube board will be soldered onto the main board due to clearance considerations?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 10, 2013, 01:54:09 AM
Yes, the control board plugs into the main board underneath, and separates, but the tube board does not unplug from the main board, this is for rigidity. Once everything is bolted together, the tubes can be pulled out and put in without anything flexing or breaking.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 10, 2013, 06:47:33 AM
Thanks.


Note: Further researching at Gyraf site BOM:  They have C2, C5 and C10 at 250V and C11 at 16V.
I was just wondering if there are conditions under which the grid can connect to the cathode in a failing tube, and arc across the C2 to ground when someone is plugging into the DI.  I should say also that I did look at my Scott Hampton LCMP schematic and it has no cap at all there, so I guess I should worry about that too... or do Tubes just not do that?

My question was/is:

Also what voltage rating should c5 and C11 have, they are not specified?

And a question on safety: C2/C10 are speced at 63 V but C2 connects to the DI jack.  Is 63V enough margin of saftey from "grid" to "guitarist hand"? 

What B+ voltages does this thing generate?

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 10, 2013, 11:42:34 PM
Sorry, Bruce, I've been busy tonight.

Looks like I'll need to update the BOM,

C5 and C2, Those should be 100V parts at least, best to go 250V. The original G9 BOM says 250, but it also specifies 250V for C10, which doesn't have any dc on it. In the 51X world, real estate is expensive, but I left footprints for 5mm,7.5mm, and 10mm  (I accidentally grouped C2 and C10 together on the BOM.)

The input stage is a cathodyne type, where the tube has a 47k resistor on plate and cathode, then a biasing resistor to bring the grid down below the cathode. The grid is actually up at around 80V relative to ground, or, your guitar. In a normal gain stage, with a grounded grid, there would be no need for a cap at all, as you see in your LCMP circuit.

Also need to sort out some HV converter details in the BOM- I did the math for the feedback resistors to give an output of 240V. When I did stuff those resistors, I ended up with something more like 265V, which is too high. I had to dial back the resistors some to compensate. (I'll have to look to see what's I ended up with there, I'm unable to get to my work bench right now.) The original had a trim pot which was nixed due to possible instability problems.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 11, 2013, 02:19:17 AM
Hey.. it is DIY... no apology necessary ever (the Y in DIY is me)!

Thank you for the clear explanation, I looked at the LCMP schematic and this one, and I understand a bit better.

I will wait to hear on the HV board change, I assume that is affecting the R502,R503,R504 divider?  At 265 Volts it puts several caps beyond their ratings (speaking of which... do we have to allow for tolerance on the voltage rating or does that just apply to the capacitance?  Is a 20% 250V Electrolytic potentially only rated for 200V?)
.
I already ordered from Mouser today for the 4 kits, and I did order high voltage parts for C5 and C2.


b

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 11, 2013, 02:33:52 AM
The tolerance is for the capacitance. I would like to use 400V caps in these places, since they're cheap and will last longer (less stress on the dielectric), but they're huge. If you can find a 300V cap that will fit, go ahead and use it. The 250V caps will work great for quite a long time.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 11, 2013, 02:50:25 AM
Yet another warning:

C3 I ordered works but I really had to bend the leads to make it not touch the bottoms of the tube sockets which can get hot.  So another choice would be better.  I noted this in the attached partial BOM but left my part number in because it did fit.

Another Warning:
This is an update to the list, stuffing boards and ...

I ordered BFC230348474 for C5.  Unfortunately I misread the lead spacing, and it is 15mm instead of 10.  So without bending the leads this won't fit.  Sorry.  I have removed it from the list attached.  In my case I plan on trying to form the leads to make it fit. If you have not already, don't order BFC230348474 .



Warning:
This is an update to the list, I just got my order and ...

You want switches ending in 2QE-EVX (PCB pin) not 1QE-EVX (solder lug)
SW4 in this list wrong in my original list.


Sorry (SW4 still reaches, you just need to clip the lug in half so it fits in the hole.) Sheepish


In case it helps...
Here is a mouser list of what I ordered -  use at your own risk.
There may be typo's
I ordered flat bat handle switches  (don't know if they fit, bushing is shorter)
I chose PP film over PET if I thought it would fit.
The list excludes all the common resistors, I had most of them, and anything I had (certain caps).  Not sure the parts I chose will fit.

It is an excel file in tab delimited text format.  I couldn't figure how to upload excel.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 11, 2013, 02:55:18 AM
Warning:

You want switches ending in 2QE-EVX (PCB pin) not 1QE-EVX (solder lug)
SW4 in this list wrong in my original list, I will try to update.


Sorry (it still reaches, you just need to clip the lug in half so it fits in the hole.)


The text file looks like a mess, here is a pdf.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bkbirge on January 11, 2013, 01:16:47 PM
Beautiful start to this thread. I'm going to go put together a mouser BOM now...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on January 14, 2013, 08:43:12 PM
hi Rodney, will we be notified of shipment, or should we keep an eye on the mailbox? No pressure, just wondering

Thanx
T
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 15, 2013, 08:28:35 PM
I'll try to notify you as I send them out. I've been busy doing some intensive job hunting, since my current boss has decided to start treating my wife and I (we work together) less like people, and more like shop equipment. I'm still hoping to get everything shipped by the end of the week, but no promises there. (sorry)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mitsos on January 15, 2013, 11:28:02 PM
Hey! nothing to add to the build info, but I wanted to say that my kits arrived safely, and the PCBs and metal look great. Good job overall, can't wait to get them done.  Like you, I'm super busy for the next month or so but I should have everything here, so I'll try to sneak in some DIY at nighttime!! Thanks again for getting this done, if it sounds like it looks, it'll be awesome!

cheers!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 16, 2013, 12:38:30 AM
Rodney

I am holding off populating the Hi Volt board resistors till you let us know what tweaks you made to get it below 265 Volts...

thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 16, 2013, 01:49:41 AM
Crap I forgot about that...

Looking again, at it, it seems that I actually did correct the schematic. My final resistors are:

R502 - 1M
R503 - 5.6K
R504 - 560R

This has me at about 245 volts. (I am using 5% resistors, though, so you may want to measure before you stuff them, so you don't end up with a net gain of 5% low, which would end up causing a higher Vout)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 16, 2013, 03:59:33 AM
ok, I will check. 

I don't really understand how the voltage is set, but if it is too high I will consult the Max_1771 datasheet again, or ask here.

bb

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 16, 2013, 09:31:13 PM
The feedback resistor network (r502,503,504) form a voltage divider that send 1.5V to the FB pin, pin3. This FB pin must always see 1.5V and will adjust the output until it's happy.

On a related note, I went to do some quick recording with my GIX when I got home from work, only to find a loud 7hz noise on the HV output. I don't know what's changed, or if my chip has gone bad, or what... I'm looking into it, but not sure if I'll have time to tonight.

I really wish we had an SMPS guy on the forum...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on January 19, 2013, 04:53:14 PM
Hi Rodney,

I'm looking forward to getting stuck into this once my stuff arrives.

Have you had any luck with the 7Hz issue?  I'm happy to offer help but it did take me a few seconds to work out what SMPS was...  :-\


Thanks again for sharing the project.

Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mitsos on January 20, 2013, 12:48:23 PM
7Hz? Does this make it into the audio?  Can we put a HPF filter on the DC-DC output? 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 20, 2013, 02:19:40 PM
I messed with it a bit last night. I thought maybe I had over-volted a cap or something, so I started adding parallel caps to the output. This changed the frequency of the ripple, and also the amplitude. I'm still investigating. There's not a ton of room on the converter pcb, but there's a filter cap after L503 that you may be able to fit something bigger like 47uF there.

I'm going to build up another converter today and make some comparisons.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mitsos on January 20, 2013, 02:34:58 PM
cool, thanks for the info.  I'll try to do some tests when I start mine, but I probably won't be able to touch it this week.

Did the extra capacitance lower the F?  Shooting from the hip here, maybe we can add an LC or RC filter? 

But again, is this thing audible (not clear from your first post about it)?  Does it affect the audio or are you just seeing it by scoping the converter output?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 20, 2013, 02:44:05 PM
Yes it's audible.

Increasing C increases the ripple frequency. A diode and a large cap would kill most of it.

I'd really like to find the source of the problem, rather than trying to put a band-aid on it.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on January 20, 2013, 03:59:17 PM
Hi,

I've done a bit of blind searching (I don't really know what I'm looking for) but a recurring theme seems to be the inductor/zener combination.

eg: http://www.electro-tech-online.com/repairing-electronics/113123-repairing-smps-i-lost-component.html

My apologies if this is hindering rather than helping.

Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 20, 2013, 04:11:05 PM
This is just a simple boost converter, no zener diodes.

The basic principle is this:

24 is applied to one side of the inductor (the big one), which flows through the diode and on to the output. The feedback resistors are connected to the output and feed a scaled down voltage to the feedback pin3 on the controller. The controller sees the voltage and if that voltage is low, it pulses the FET on. This redirects the 24V supply through the inductor to ground. The inductor builds a magnetic field in the core and starts to saturate. The controller IC has a current sense pin that reads the voltage drop across the 0.25 ohm resistor. When this voltage builds high enough to overcome the controllers internal comparitor, the fet is turned off and all that stored energy is the inductor is released into the diode in one huge blast. The voltage is dumped in the output capacitor and the voltage is again read by the feedback pin. This process repeats until the output is constant.

Right now I'm thinking the problem may be in the current sense resistor. I'll have to do some experimenting because there's not a good answer for what this value should be.

Another cause could be the feedback is getting radiated interference from the inductor. This design has been condensed into a tight space, so some filtering may be needed on the feedback pin.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 20, 2013, 07:55:39 PM
Okay, I've done 2 things which has fixed the LF oscillation.

This is a no-no when it comes to trouble shooting- because now I don't know which thing I did was actually necessary and now I'm too lazy to go back and try one or the other.

1) Added .1uF cap from FB pin3 to ground (across R503,504)

2) Lowered impedance of feedback network. R502=270k R503=680R, R504=1k

Try the cap first. If that doesn't stabilize the output, try changing the feedback network.

With this combo I'm running at about 238V, only noise is about 20mV at around 79Khz, which is knocked down to a couple milivolts after L503.

Science be praised!

Update on shipping: I was planning to have everything shipped out Saturday, but my boss called me into work. Monday is a federal holiday for the post office. So Tuesday will be the final exodus.

Thanks for your patience, everyone.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on January 21, 2013, 08:26:26 AM
Rodney,

Thanks for updating so quickly.

Glad to see my unhelpful 'help' didn't derail you!

I'm looking forward to this!


Regards,
Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 24, 2013, 06:24:49 AM
I used R502=332K R503=249R, R504=1.8K which I think gets me to the same place you are.  I built it without the cap to stabilize FB (I know you told me to try the other thing first, but lets just consider this diagnostic).  Finished build on unit 1 except transformers, I will strap in a couple of transformers I have laying around and fire it up tomorrow, and let you know.

I have to say the fit and finish on this board, metalwork and faceplate is outstanding, no issues other than drilling the faceplate.  The tube RA mount is really solid.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 24, 2013, 08:30:50 PM
that should be about right, bruce.

I'm glad you're pleased with the boards...I spent quite a lot of time getting everything to line up just right. Well worth the effort, I think.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 24, 2013, 11:56:40 PM
You need the cap I think.

With no cap, I also got a slow hunting behavior of a couple of hundred milliamps in the B+ supply, in addition to noise at the 109K, 300K ish, and 1+mhz range.

I have 4 boards, so I made 4 different HV Boards using different size caps, and tested them on the bench.

I think the cap value must be related to the R502+R504 value which in my case is 2049 Ohms (yours was 1680, and you used .1uf).

Unboxed (so I don't know if there is any issue from shielding) my results were.

I tried .01uf, .047uf, .22uf and .67uf value caps.

I got the slow hunting except for the .22 and the .67, and I could even get the .22 to do it sometimes (it seems to be ok, and then "lock in" to that Low frequency noise and get stuck there.  I could kick it off by putting a signal through and turning the gain up. It would remain even when I turned it down.

So for my case I think I am putting a .67uf cap in there (i used polyester), I might try a 1UF.

Note that i also did some tests generating low frequency signal output at approximately 1.2V RMS (0dbu) and I found that at any frequency below around 60 Hz it is easy to see the sag in the B+ supply, so maybe it would be good to up the caps on the B+ rail (or maybe the drain of the lower value resistors in the voltage divider is a bad idea.  Any thoughts on this?

My current config is
R502=332K R503=249R, R504=1.8K with a .67uf film cap across R503, R504.

The cards generate between 247V and 245V (1% resistors, hand matched).  So I am getting about 0.7milliamps across the feedback divider.  What current can the card put out at 245 Volts?

Gemini86:  What about larger caps for C507 and C25? Any thoughts on which one needs to be expanded to avoid the power supply getting sagging at low frequencies (it doesnt exactly sag, it matches the output side wave in frequency but looks more triangular.) At low output levels it is not such a problem, this may be because I wired the transformer at 3:1 to get more inductance.  At 2:1 it would have to output less.  Even wired this way it can crank out a pretty big undistorted signal, but I am worried about what the PSU is doing.

Any thoughts on the feedback stabilization cap, and how big it can be? A .1uf cap in parallel with a 1680R resistor has a corner frequency around 900hz, so I can't figure out why it helps at all. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 25, 2013, 01:46:34 AM
Build PICs.

I got to use my hot air rework station to assemble these.  I put the big inductor down first, because it takes so long to heat, but you really have to shift it to make room for the diode, so the big electrolytic fits (as gemini86 notes, but did i listen?) and I didn't, but I got it all on the card.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1416_zpsb4cab72d.jpg)

4 little High Voltage cards, with different bypass caps tacked on. 

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/HVcardswithvariousbypasscaps_zpsd327b3f7.jpg)

Card set up to test,  I don't plan to leave these makeshift transformers, but I made Lundahl adapter cards for some scavenged transformers (and worked very well actually) 1:11 step up Altec on the input, 3:1 step down on the output, got good response all the way down to 20HZ with about 1 db rolloff, although I got some rolloff on high frequencies when the line switch was in LINE position, worked fine in MIC.  Maybe the test generator? I will look into that.

I could permanently fit the output tranny but I would have to carve up the card... and it is such a pretty card, so not going to do that.  The input however fits, and I might use that on some cards.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/DummiedupsomeLundahladaptersfortest_zpsa0ad09b9.jpg)

Note that I lucked out on the gain resistors.  I had to use a 1/2 watt one in there, and it fit with some trouble, but only because of it's position.  Some of them must be 1/4 watt where the main card comes close to the control card, or it won't fit.  You can see one sticking up off the back of the control card.

Also note my choice of Polyprop for C3 fits, but I had to shift it, and I suggest using something smaller.  Also you can see that I wedged in a 24mm output pot, works fine, and feels nice, I have the spec'd part on order.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Ihadsome24mmpotstheyfitwithabitofbending_zps0287b091.jpg)

Big honking 4.7uf Polyprop on output barely fits, I had to shift the electrolytic cap some (that cap has 250 volts on it so be careful with the leads).

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/47ufpolypropmademenudgetheothercaps_zps97d70120.jpg)

Set the Lorlin for 11 positions, 10 clicks or ticks.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Setthestopat11_zpse17e6143.jpg)

I needed to drill out the faceplate output hole, this may be because it is too small but it may be because I used a 24mm pot.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Potholeistoosmall_zps5b851ff2.jpg)

In insulated the back mounted MOSFET with foam tape, not sure this is such a good idea, hard to remove things once this is on, and it does soak up the flux cleaner.  But it is secure.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/FoamDoublestickforbackmountedMOSFET_zps325087ba.jpg)
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1410_zps6fa6e147.jpg)

Here is how I mounted the socket for the board mating.  Because my sockets were a bit too long i thought, I bent the bins a bit and mounted it elevated, which worked out fine (but lowers the above board clearance a hair, so if you are putting some tall transformer  or cap on then lookout.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Ileaveabitofspacebelowthesocket_zpsd9b8a285.jpg)

You can see the socket peeking out here from below the board.  you can see my C3 is too big (and I had to bend the pins on it to keep it from contacting the tube sockets.  Also note that C10 could interfere with soldering the bottom socket if you install it early (as I did).

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Noteevenwiththepinbenditextendsabit_zpse7c26d1d.jpg)

Another view of the socket.  Note C10, if it was a WIMA I would have had to remove it.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Especiallyifitiswima_zps8dce345c.jpg)

Bent pins on the socket, to help it stay back under the board, hope it doesn't mess up the reliability of the socket, not sure it was necessary.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IbendthepinsbecausemysocketsareIthinktoolong_zps83ac6cb1.jpg)

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/bentbackgivesmeacoupleofmmifImountthesocketraisedofftheboard_zpsaf0c3d71.jpg)

Here is how it goes together, and with standoffs and screws it stay firmly supported.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Hereishowitplustogether_zpsf165b7bc.jpg)

On the second build I used OEP's, and cans.  The cans come disassembled, and I tacked to ground pin to the bottom plate and the plate to the case for solid grounding.  Not sure it is needed.  Note... label the trafo's or you might have to take em apart to see which one is input.  Also not sure I am going to stick with these Trafo's they were cheap (15 bucks a piece) but I am getting really wacky stuff with the low frequency and the frequency response I am measuring is not very flat. Maybe I need to terminate them differently?  Should these work down to 50 Hz in a reasonable sine wave at 0.5Vrms?  Mine don't ... I might have some other problem.

Also NOTE on the BOM the Input and Output are switched.  They are correct on the schematic.  The A2E is output the A3E is input.


(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Marktheoutsidesoyouknowwhatyouputinside_zps67ceddee.jpg)


It looks nice, even with Radio Shack knobs.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/RSknobs_zpsc60ef63e.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: braeden on January 25, 2013, 02:35:43 AM
Very cool, good job!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on January 25, 2013, 09:48:24 AM
In retrospect , was your Bom good ?  not that there's room but would the converter benefit from heatsinking ?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 25, 2013, 03:39:00 PM
I did some testing with my unit. I'm using OEPs input and out, which are small and don't have a huge low end.

I've measured only a 200mV sag in the HV when putting out a little over 20v peak to peak @ 100Hz, terminated into 1k. Of course the sign wave is totally distorted at that point, but this should be a worse than worst case scenario for the output stage.

I wasn't able to get the converter to start oscillating, but I started messing with my other converter to see if we can make things better.

The fet and the inductor are the biggest sources of noise. Try this and see what happens.

-Moved the feedback network to the underside of the PCB
-Moved the FET to the top side of the pcb (cut the mounting tab off)

I want to experiment with separating the control side from the high current side, but that's to come later. I'll need to have a new proto pcb made and I just don't have the cash flow right now. I also want to try the maxim 668 chip for my next designs. tech support tells me it's much more stable and less sensitive to feedback contamination.

Bruce, I think the inductance on the output transformer you're using is maybe a bit much to drive for this output circuit. The G9 historically has a hard time driving heavy loads... It's been recommended elswhere to use a 3:1 or even 4:1 output for better impedance matching when driving low Z inputs, but I can't remember who said that. I personally love the sound of this pre. Mine is not totally flat, and has some low end roll-off, but it suits the source materials that are used for this pre to really shine.

Also, bruce. you've set the gain switch to 10 ticks... should be 11. I used a '0-10' scale on the faceplate, because I prefer that for the output pot and wanted them to match.

okgb, the bom has been updated today to reflect what I've used for my dc converter. Also, the converter itself is doing some pretty light lifting. There is very little heat generated (I've selected the FET to be as low RDS on resistance as possible) and the inductor will be the only thing warming up due to core losses. A heatsink is not needed.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 25, 2013, 05:14:24 PM
In retrospect , was your Bom good ?  not that there's room but would the converter benefit from heatsinking ?

The bom had some problems, but I have been correcting them and updating as i gain experience.  I will make another correction today.

Here is a sheet with comments from my build, it is based upon the layout that was posted.  Does anyone have an up to date PCB layout PDF?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 25, 2013, 05:22:22 PM
Here's an updated layout

https://docs.google.com/file/d/0B6s_klsk9wMDV3M0RGg1cUlJdDA/edit (https://docs.google.com/file/d/0B6s_klsk9wMDV3M0RGg1cUlJdDA/edit)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 25, 2013, 05:24:50 PM
I did some testing with my unit. I'm using OEPs input and out, which are small and don't have a huge low end.

I've measured only a 200mV sag in the HV when putting out a little over 20v peak to peak @ 100Hz, terminated into 1k. Of course the sign wave is totally distorted at that point, but this should be a worse than worst case scenario for the output stage.


 I just got some of those OEP's I will try that out. 

Was your sag in "time" with the music?  I was only putting out 1.2V rms

Looking at the schematic it looks like maybe the issue might be the 1K resistor with 10uF low pass filter in the B+ rail.  That has a rolloff at 15hz, and maybe what is happening is that the HV supply cant keep up with the load of the second stage and that is varying B+ in the first stage, and that gets amplified thus the oscillation.

I have ordered the Lundahls and I have the OEP's I will try them out and see what gives, and report back.

The big G9's have a plentiful B+ supply and the 10uf cap C25 is not called upon to stabilize large audio band noise I think.  I am considering a larger C25, maybe a larger R31, I can't fit a larger C507 or C503, but might be able to replace C506 with something.

I will report back



Also, bruce. you've set the gain switch to 10 ticks... should be 11. I used a '0-10' scale on the faceplate, because I prefer that for the output pot and wanted them to match.

okgb, the bom has been updated today to reflect what I've used for my dc converter. Also, the converter itself is doing some pretty light lifting. There is very little heat generated (I've selected the FET to be as low RDS on resistance as possible) and the inductor will be the only thing warming up due to core losses. A heatsink is not needed.

I set it for 10 clicks which is 11 positions. I think that is what you want.

Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 25, 2013, 06:07:42 PM
Sorry my mistake, set the switch on 11, for 10 clicks.. You are correct, I will remove the incorrect note.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 25, 2013, 07:06:59 PM
I did some testing with my unit. I'm using OEPs input and out, which are small and don't have a huge low end.

I've measured only a 200mV sag in the HV when putting out a little over 20v peak to peak @ 100Hz, terminated into 1k. Of course the sign wave is totally distorted at that point, but this should be a worse than worst case scenario for the output stage.

I wasn't able to get the converter to start oscillating, but I started messing with my other converter to see if we can make things better.

The fet and the inductor are the biggest sources of noise. Try this and see what happens.

-Moved the feedback network to the underside of the PCB
-Moved the FET to the top side of the pcb (cut the mounting tab off)

I want to experiment with separating the control side from the high current side, but that's to come later. I'll need to have a new proto pcb made and I just don't have the cash flow right now. I also want to try the maxim 668 chip for my next designs. tech support tells me it's much more stable and less sensitive to feedback contamination.


I think a generic HV card for 51X tube projects is a great idea, maybe with some right angle tube socket boards.  I would spring to make those cards, pm me if you are interested.

To clarify my situation, I don't think I was clear, and I don't think moving the cap helps.

I should explain that the oscillation I was getting I measured at 4hz, 5Hz and 7 Hz ish, my scope isn't that clear, and there was other noise, and the scale of the oscillation in some cases was only 100mv or 200mv, sometimes larger.

It occurred before I put a large enough cap in.  And when I put in the .22uf cap, I could cause it to start by turning up the volume on a low sine wave, but it wouldn't stop when I turned it off.

I think the kinds of noise that might radiate to my cap antennae would be high frequency where I think things are under control.  With the .68uf cap in there all is well.


Separately I had a "sag" problem.
As far as the HV "sag".  I saw the HV voltage at the HV jumper vary substantially in time to a 20-60HZ sine wave while the unit was putting out 1.2vRMS.  THe filter made by R31/C25 has a corner frequency of 18 (assuming that the electrolytic is only 10% under it's stated value... they rarely are better).  That would only attenuate the variation in HV supply by about 3db, and I think the remaining signal could be being amplified and causing distortion.  (And incidentally this is just the kind of long feedback loop that would causie a  Low Frequency oscillation like what we are seeing, but I have no proof of that). 


I am building a unit with OEP's and will test it.  I will build it with C25 as 150uf for a low pass with a 1 Hz corner (it's pretty tall!, but it fits for testing).  I will report back.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 25, 2013, 09:58:39 PM
Thanks for the explanation.

I read in another forum about somebody developing a HV converter using this chip, and that the HF noise causes this low frequency instability. In their design they simply put more space between the inductor and the controller, which obviously isn't a choice for this application. But, just like us, they were a bunch of amateurs poking things with sticks until the desired result is achieved.

What I did was run a sign through my unit @ 100hz (even tried it at 50hz) and cranked the gain and output up to max. The clipping on the output was a very weird, non square wave. Sort of like a double sine, or something like a camel hump on the sine. I'll post pics maybe tomorrow. I'll also look for a signal appearing on the HV supply, see if the overall DC voltage is dropping or if it's moving in sync with the signal.

But for tonight, I sleep... I have a cold and I'm trying to be as big a baby about it as I can so my wife will take care of me. (Already scored some tasty soup for dinner and got out of doing the dishes...)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 26, 2013, 05:44:55 AM
I built a unit with OEP transformers.  They are very small.

I also saw the weird distorted wave on output, anywhere below 60 HZ or so it begins to go sour.  I think that is a result of the OEP 262A2E transformer, but I don't know what it could be because I took a separate one of the same transformer and drove it loaded and unloaded and while it doesn't handle much level, it doesn't do that.

Both builds pass signal, the one with the big transformer passes signal down to 20HZ at really high output levels (it distorts at around 18 dBu 6V rms 17V peak to peak approx).  I ordered a couple of LL5402's and LL1538's last night.  Maybe they will work better.

I am going to swap an OEP Trafo into that build and see what happens, I used a 11uF output cap on the EOP build, don't know if that could effect anything.

Using the larger C25 did not help anything (but it did take a long time to discharge), I still see variations in voltage in time with the sine wave.  Looks like the first stage is using 0.5mA because the voltage drop across R31 is 5 volts.

There is always noise but the thing is what is "normal" noise for this HV supply.

I did hook it up to an amp on the bench and listened a bit and it didn't sound too noisy, i couldnt hear the B+ noise
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on January 26, 2013, 10:32:10 PM
I just got my 2 yesterday, quite nice indeed Rodney!, I gotta say thanx to bruce0 also for working through some of the pains, if this was left to my newb arse, the project would be finished in the shipping box :o! I will be watching the progress with bated breath.

Rodney, I noticed your comment on what the G9 was best for, i'm new to the G9, if you dont mind me asking, on what sources does it shine?

thanx fellas
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 27, 2013, 12:47:00 PM
Ok, so I spent a bit of time trying to get the HV supply working.  Here are things that I found that make it better:  1) Put more load on it (3 150ohm resistors to ground), I thought this might be because the on-time or off-time of the chip was limited, looked at the data sheet, but the way this PSU runs it is on for most of time and off for only 1 usec which is shorter than the minimum off time.  So maybe more load fixes that.

Then I began reading the data sheet. They do mention shielding and radiation. They say if you are going to make an adjustable supply to make it with R1 (or on our schematic R503+R504) from 10K ohms up.  Ours is below that.

Further they suggest a cap across R2 (R502 on our schematic) rather than across R1 which is what we did.  And the values of that cap are much lower 47pf to 220pf the smaller the better.

So I pulled all my power supplies apart, and built them as follows:

1) I used 2 resistors not 3, because the three resistors make a sort of coil for the radiation to excite, and a smaller coil is better.
2) I used 2.2M for R502, and 13.7K for the combined R503+R504. (This produced 4 units between 244V and 245V but I DVM matched the resistors so the units would be comparable)

3) I put 47PF across R502, which fit now that there are only two resistors.  There is 243  volts across there so a high voltage cap is called for.
4) I experimented with various shields.  I found that the best arrangement was a shield of .006" thick AD-MU-80 high permeability Mu Metal.  Shielding the inductor didn't help much.  It is easy to measure the field, it is HUGE and can be measured with a bare oscilloscope probe all the way over at the input transformer.   I will send pictures of the shield.

With the above I get a stable, oscillation free supply.  I built 4 of them, and on 2 I get 7mv noise, and on 2 I get 12mv noise, and I can't for the life of me tell why those two are different.  Any ideas are welcome.

With the stable supply the OEP's behave much better, but still cant produce a sine wave at 0dB 20Hz, although they can produce something that vaguely resembles a sine wave now. I may chop the boards up to fit my salvaged traffo's after all because they run down to 20 Hz no problem.

The power supply on both sides of the R31 resistor varies in time with the sine waves to a pretty large degree, which is disturbing. 

Shield - AD-MU-80 .006" thick, I think it works.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Easiestwaytonotchcuttwoslitsandfold_zpsdcda45bc.jpg)

Notch to clear the sense resistor so you don't short it.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/ShieldDetail-Notchtoclearsenseresistor_zps52b692c6.jpg)

Installed it is pretty nifty, tacked to the sense resistor at the ground end, and one of the ground pins.  But watch clearances there are a lot of things at 250 Volts on the board the FET in particular

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Shield-3_zpsb7d4a7d9.jpg)

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Sheild-2_zps08889e31.jpg)

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Sheild_zpsd9af72b5.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 27, 2013, 04:31:50 PM
Hey bruce...

first off, just wanted to say thanks for your help on this...

I've been messing with this for a while as well... My first thoughts were that adding the cap from the feedback pin to ground ruined the output regulation, making the feedback sense too 'slow' to see the output ripple. I see that you've removed it, so that disproves my theory.

One thing I should note, you mention the datasheet calls for a feed forward cap across R502. We have that, it's C509, 10nF. The reason it's so big is because when I tried using smaller caps (in the past) it would become unstable and oscillate at low frequency. So, take out C509 if you've put a parallel cap in place. See what the effects are.

Also note that the fet is a big source of radiation. That big to 220 tab will radiate amost as much as the fet.

I think you're right to increase the feedback network impedance. My original thought was to lower to combat the HF interference but that is probably not solving anything.

Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 27, 2013, 05:49:16 PM
Ok, I did not see that.  I feel like a bit of a dope.

So c509 is already doing what i am trying to do.

I think the impedance change or the shield must explain the improvement I got, because my added caps weren't changing C509 by more than 3%.

I go back to the data sheet and look at the FB-Ground resistor (r1) contemplated therein.  They spec it to be 10K to 500K, so if they use the device to double triple or do 10x voltage they must assume the R2 (output to fb) resistor is going to be 20K  to 5M ohms.  So they are contemplating corner frequency of the R2/feed forward cap at between 36000Hz and 677Hz.    The notion being that it won't regulate in response to changes above that frequency because they are damped out.

But with a 10,000pf cap in there (C509) we are putting a corner frequency of 15.9 hz as (from the schematic 1M ohms) and when you lowered that to 270,000 ohms then the corner frequency moved to  59hz (I used 330,000 so I had 48Hz.  So those are far from what the data sheet contemplates, and basically damp out voltage regulation for changes faster than that.  That could explain why the voltage varies in time with the audio sine wave... ( I think that means it It reduces regulation 6db per octave above 50hz! )   For an audio B+ circuit I think we need regulation to respond to changes as fast as 2000 hz minimum because I think below that B+ sag due to load in response to signal will exceed the noise level of 7 mV.  And apologies but I am not doing math here I am doing this by the seat of my pants from what I saw on the scope.

So I think I need to lower C509 to fix that problem.  At 2.2M for R502 that means I need 47PF or less, I am going to rebuild the 4 HV boards I have with 47pf, 250pf, 1000pf and something bigger and I will report back if any of those are stable.  I am wondering if I further increase the impedance will I have a problem? Even if the feedback circuit is 10M ohms I still have 25000 nA flowing through there with 250 volts, and at 24 volts 2500nA so it should be fine right? (the data sheet says the FB pin needs 20 nA max).
 
Sounds like you have been down this same path and got LFO (low frequency oscillation) so if you can tell me it wont work, go ahead and save me the work.

And while I am thinking about it I really want to thank you for spec'ing this HV board with sockets and headers, I could never have tried these variations if it was soldered! and would have given up long ago!  As it is I have been pretty busy with my Hakko 808 desoldering gun (favorite tool) and the boards are well made and are holding up well.

As for the MOSFET tab is it drain source or gate (data sheet didn't say)?  Even if it is drain it is just a switch right, I mean can it be creating the kind of magnetic flux that the inductors do?

The inductor is radiating magnetically like a son of a gun.  I set my oscilloscope probe to 5 mV sensitivity and I get a signal with the probe waving in the air an inch or two away from the inductor!  It is 20 - 30 mV signal when I get within a half inch.  You figure the resistors and caps have big conductive rings formed by their leads (and a coil in the case of the metal film resistors which are like a foil slinky inside).  I will try to measure the field inside the shield, and see what the tab is radiating on the bottom.

I don't know what our B+ noise target should be, do you?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on January 27, 2013, 06:14:58 PM
One other thing.  When the Datasheet says "maximum switch on time", and "maximum switch off time" I don't know which thing "on" is and which thing "off is".  Does "on" mean the MOSFET is conducting?

The reason I ask is that currently if you look at the Drain pin on the scope it is "240" Volts ish for 1 u-sec, the "0" volts ish for 9 u-secs.  So that is "Off" for 1 u-sec, and "On" for 9 u-secs.  The minimum switch off time is 2.3 u-sec, so either we need a smaller inductor or more load (or I have swapped what On and Off mean) or maybe C509 is interfering somehow.

In any case I thought I would let you know it is "not conducting" for only 1 or 1.1 u-Sec which is half the datasheet minimum.  This is my first foray into switching PSU's and while I am fascinated, I am also befuddled.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 27, 2013, 06:31:33 PM
The switch is normally off, on when at least 10V is applied to the gate.

I had previously tried 470pF with no luck, but that was the old layout and I don't remember what the feedback network was. Still probably worth trying.

In some areas the datasheet if very vague. They're assuming that we're using it for probably a max of 24V out. We're kindof in uncharted territory with this chip. The max668 chip, however, is used as a 48V phantom power converter on their website, and their tech support engineer was steering me in that direction (he seemed to not want to help me with making this part work.)

You may be onto something with the inductor being over spec'd. I hadn't thought of that as a problem. I got that value from tech support, but the datasheet says:

"inductor values range from 10μH to 300μH.
22μH is a good choice for most applications. In applications
with large input/output differentials, the IC’s
output current capability will be much less when the
inductance value is too low, because the IC will always
operate in discontinuous mode. If the inductor value
is too low, the current will ramp up to a high level before
the current-limit comparator can turn off the switch.
The minimum on-time for the switch (tON(min)) is
approximately 2μs; select an inductor that allows the current
to ramp up to ILIM.
The standard operating circuits use a 22μH inductor.
If a different inductance value is desired, select L such
that:
      VIN(max) x 2μs
L ≥ -------------------
              ILIM
Larger inductance values tend to increase the start-up
time slightly, while smaller inductance values allow the
coil current to ramp up to higher levels before the
switch turns off, increasing the ripple at light loads."

My math is not so great. So I don't know how to calculate L. I do know that 100uH was too little, and caused the controller to just lock the switch on and suck current through it. I wonder what backing off to around 200uH would do.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 03, 2013, 10:03:36 PM
Some notes from my build:
Update:  More incorrect info.  I have now measured noise and there is no discernable difference with the screening can I built, except if you use the Cinemag input Trafo, which is very close to the HV psu, for the Lundahl and OEP (with screening can) input trafo's the noise is the same with or without my screen on the PSU


Update:  I had a lot of bad information in this post, I have updated it to correct that information.  The supply does regulate fine, the problems I think now are in filtering and in induced currents in the ground strap of my oscilloscope probe from the radiation of the power inductor.  See my more recent posts for what parts I ended up using
The G9 is a tried and true, this GIX works, but the B+ supply  on this design needs some fiddling. 

In the end the fiddling I did was to improve the filtering.  That is specified in a more recent post.

When the HV comes on it comes on faster than the heaters, and the voltage exceeds 250 Volts.

You can fit 350V 10uF on the HV card (there are 10mm diameter ones, anything up to 19mm high fits). The voltage surge above 250 Volts at the tubes until the heaters come one and if you build it with a resistor instead of a HV jumper you get a voltage drop. Update: I put the values I ended up using in a more recent post.

A startup delay would be cool, I will look at that. 

If you want to run "In Phase" and Line (not mic) the relay cois are both powered all the time. R33 and R34 spec'd at 100 putting the relays exactly at the OMRON maximum rated current, can be 120 to 140 ohms and is better.   A lower current relay is also available.

I used right angle SIL square pins to mount the tube board, they are stiffer that way, which is nice because the tube holder gets stressed upon insertion, but you have to pull the black plastic part off the off the SIL header after mounting them on the tube board, which is easy enough if you go slow, or you warm it with a heat gun.

The total current draw on POWER ON is 0.5 amps between +16 and +24 combined, so I am not sure how many you could turn on at once in one rack, it depends upon your PSU.  Again a startup delay might help.

I shielded the HV card, not because I think it will quiet the power, but because I am worried about the magnetic radiation from the inductor. The input transformer in particular is susceptible to such stuff. Here is a link to a video that shows the amp noise varying in response the nearby objects (first my finger, but only within an inch of 270Volts!) then the oscilloscope probe.

http://s1221.beta.photobucket.com/user/Bruce0/media/G1X%2051X/IMG_1542_zps9f9d1029.mp4.html (http://s1221.beta.photobucket.com/user/Bruce0/media/G1X%2051X/IMG_1542_zps9f9d1029.mp4.html)

It turns out that the shield improved my performance because it prevents the oscilloscope from picking up the radiation, so it really wasn't improving the power supply.  However I plan on using the shield because I don't want it effecting other components or other 51x modules.

Here is the shield I put in place, it is designed to fit the HV PSU exactly, and it is NOT SQUARE.  It tack solders onto two of the pins which are grounded.  I later modified it to bend it away from the HV Out pin, because it is really close to that 262 V and it is grounded.

I can provide a template, for cutting your own shield.  It folds up from one piece and then is tacked in two places with solder.  I made mine out of mumetal.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1548_zps451c6bf5.jpg)

I hot glued the output cap to the top of the relays, which seems pretty secure, and was the only way to fit the polyprop caps well. It also leaves room for a 22uf cap there.  The tube rubs against it when sliding in or out, but then sits clear of it.  The input Lundahls seems upside down but i think that is right.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1547_zps5c695dcc.jpg)

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 07, 2013, 12:55:33 AM
Thanks again bruce for all the help. You seem to be able to wrap your head around switching circuits better than I.

That shield you've made is awesome. Any measurable improvement over unshielded? I've yet to find noise contamination on the output of my build, so I haven't invested much time into improving shielding for the converter. Future designs will definitely feature a fully shielded converter, in case it's ever an issue.

I'll be updating the BOM and schematic to reflect the converter parts changes.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 07, 2013, 09:08:19 AM
Updated table with more data

The build as designed and specified works fine!
I got a personal message from one builder concerned that he was biting off more than he could chew, and I realized that my obsession with PSU noise might be disruptive.  So by all means build this lovely project, it is really a nice bit of work. The "Stock Build" works fine.

Most of us with GDIY 51X racks have gone to the trouble of building big linear supplies and keeping switching noise out of the system, and this HV supply is necessarily a switching supply, so what I am trying to do is to mitigate any effects of putting this in my GDIY 51X rack, but I admit most of the noise I have detected so far has been on the bench and NOT on a set of speakers.

The relatively high noise levels in the B+ power supply is mostly not audible.  There are four noise sources I am working on:

I don't have enough experience with the G9 to have an expectation with respect to noise level.  In fact I have a rack mount G9 I am building to try to find this out, but i have been delayed by the Par-Metal puzzle.

I bought an assortment of inductors and Sense resistors, and I have fried a couple of MAX1771's (ouch) and here is a summary of my testing, and some test data:

I have a longer writeup of this, but in general it is a balancing act. Smaller inductors generally lead to higher frequencies but if they are too small the regulation feedback pin never gets near enough to 1.5V to trigger, and if it gets too far out of whack it defaults to the maximum (16.5usec - 46K Hz) or sometimes to non-oscillating continuous mode ("Amplifiers do, Oscillators don't"). Larger Sense resistors generally increase frequency but to a point, but interfere with regulation, and tend to produce consistent frequencies.  I am searching for a balance of high frequencies (100kHz to 300kHz) that vary like white noise.

Update: Note that the ripple current increases as the inductor size decreases, and can get to be a very large current.  It is better to use larger inductors if you can maintain the voltage and frequency.

All of these measurements are taken with the HV jumper configured as a 750 Ohm resistor, and the regulator set for 255V.  All tests from J onward had the Rodney cap installed (.1uf 50V MLCC)
IDInductorSensefrequencyComments
A100uH.06226kHz to 35kHzMaintains 255V, not warm
B100uH.06234kHzMaintains 255V, not warm, don't know why A and B are different
C68uH.06246kHzSometimes goes to continuous mode 23V sometimes produces 140V, MOSFET and Inductor get hot
D22uH.040Unrecorded62V, Hot MOSFET and Inductor
E33uH.062Unrecorded75V, sometimes 23V
F56uH.062Unrecorded110V
G22uH.120>300kHz234V unstable output ( Rodney cap might fix but voltage is low, and the chip is not designed for above 300kHz)
H47uH.120250kHzMaintains 255V,  Hot MOSFET and Inductor
I56uH.160 UnrecordedMaintains 233V, Stable but low, Warm but not hot
J68uH.120130kHzMaintains 255V,  Not really warm (acceptable), RC (Rodney cap)
K47uH.160287kHz230V,  Warm inductor and MOSFET
L100uH.160148kHzMaintains 255V,  (No notes on temperature, but not hot) RC
M100uH.12096kHzMaintains 255V,  (No notes on temperature, but not hot) RC
O330uH.250101kHzMaintains 255V,  (not hot) RC (stock)
P1000uH.250Reads 43kHz must be 46kHzMaintains 255V,  No notes on temperature RC
Q680uH.25058kHzMaintains 255V,  (No notes on temperature, but not hot) RC
R180uH.250>200kkHz248V (low) RC
S180uH.160141kHzMaintains 255V,  (No notes on temperature, but not hot) RC

Update: see my later post, I believe the smaller inductors are a bad idea.  There are significant differences in audible noise and measured PSU noise,  but my test environment is not controlled enough yet to sort that out, and some of it has to do with shielding, transformers and individual tubes. I will report back after racking one and measuring noise and a listen.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on February 08, 2013, 08:07:56 PM

 Bruce O , can you update your bom  ?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 08, 2013, 09:04:06 PM
I will I am still changing values. 

The BOM as specified works fine, but I am still testing. and will update values as soon as I am done.  We have a blizzard here now, and I will have a bit of time while we are snowed in.

One thing I have discovered is that for this high frequency switching PSU work I need to use a different tip on my oscilloscope probe, otherwise the ground wire makes a loop that picks up more signal than the signal that is there.


Title: Re: [BUILD] GIX-51X tube preamp
Post by: EmRR on February 09, 2013, 01:39:57 AM
It'd be nice if we had a Rolls Tubule (or similar) to study.  These sorts of supplies are an area of total ignorance for me.  Thanks to bruce0 for all the data observations. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: shabtek on February 09, 2013, 06:48:15 AM
+1 thanks Bruce for generously contributing feedback to this project--nice to see an old guru learning new things.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on February 09, 2013, 10:45:25 AM

 The roll  500 pre uses a 12dw7  , so I presume one tube only ,  going for about a grand
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 10, 2013, 02:17:57 AM
It'd be nice if we had a Rolls Tubule (or similar) to study.  These sorts of supplies are an area of total ignorance for me.  Thanks to bruce0 for all the data observations.

I did reach out ot maxim IC for some help, but a lot of my layout choices were made by studying other gear, including the Sound Skulptor mp66. They have documents for it on their site.


 The roll  500 pre uses a 12dw7  , so I presume one tube only ,  going for about a grand


The roll unit has to function within the VPR power specs, so they can't use the current that two tubes need without burning two rack spaces. I also imagine they outsourced the design of the switching supply and had to buy up a couple thousand units to have them produced, which jacks up the price a lot.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: EmRR on February 10, 2013, 12:12:34 PM
The pictures of the Rolls don't look like they have any custom modules, but it's hard to say. 

I hadn't looked at the MP66, interesting piece.   I notice there's no apparent spec given for one of the PSU inductors, and they have a fitted shield around the whole thing. 

I'm gonna talk out my ass for a second and bring up the parallel film caps in the PSU.  Are they creating an inherently good condition, or is it possible they might be lowering ESR at a given high frequency to a point that destabilizes?  Disregard as needed! 

I see Mouser has a few 12V:200V/300V DC-DC converters now, at $123 apiece(!). 

Watching with interest....
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 10, 2013, 01:32:29 PM
Well, there's a HF noise on the line that should be removed, and there needs to be at least one ultra low ESR cap on the output to deal with that.

I think the number one problem we were having before was a wrong inductor size. It seems the 330uH was too big, and was causing a condition where the controller was pulsing at a very low pulse width. A 100uH inductor allows the pulses to widen out and get the fb pin doing all the regulating work. Bruce has done a great job documenting what works and why. The current sense resistor and the inductor are two component that must work together.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 10, 2013, 06:39:51 PM
Parts
I did my final build with the following:

L501            330uH (as originally specified) (Updated)
Rsense          0.250ohms (as originally specified)
L503            1200 uH Bourns 652-RLB9012-122KL
NEW CAP         Tack a .1uf ceramic capacitor (350V) between the end of that inductor and the HV out on the boost converter on the back of the board.
HV Jumper       200ohms ( I used a 1/2 watt, I don't know why Gyraf specs the R31 at 2 watts, it sees 5-7 mA and has a 5 volt drop. What am I missing tube guys?) (update)
C507            22uf I used EKXJ351ELL220MJ20S, it fits fine.
C25             350V 22uf also fits EKXJ351ELL220MJ20S (update)
C25             350V 10uf 350V 10uf, if you want to be true to Gyraf design 647-UVY2V100MPD (HV card exceeds 250V on startup)
C503            350V 10uF 647-UVY2V100MPD (HV card exceeds 250V on startup)
C508            450V 1uF version RDED72W105MUE1C3A (HV card exceeds 250V on startup)
R502            300,000 ohms
R504 + R503     A single 1800 ohm resistor (measure these with a DVM, a small difference on this part makes a big difference in voltage)
R33 and R34     120 to 140 ohm to reduce current use
C509            I built mine with this omitted.  I found it makes no difference. (Update)
Shield          I put a shield on my HV boards, if you want I can upload a pdf template of it.


You can use a bigger resistor for the JV jumper and get better filtering, but I find it is fine for the noise frequencies present and it keeps the supply impedance low.

The smaller inductor was my bad idea.
I have been reading up on boost converters, and it turns out the ripple current produced by the power inductor is related to it's size as well, and on some of the inductors I was suggesting was getting as high as a few amps! (actually limited by saturating the inductor)  That's why they were getting hot.  We want to keep that number lower so that the ripple voltage is low and so that we don't get above the rating of the filter inductor (L503).
 
Last night I modeled our boost converter using the cooper and bussman guidelines document, and this table is a summary of that:

Inductor   Vin   Vout   Iripple
 330        24   245     0.410
  68        24   255     1.998
 180        24   255     0.755
 330        24   255     0.412
 680        24   255     0.200
 820        24   255     0.166
1000        24   255     0.136

Note that the ripple current on my smaller inductors is much higher than the rating on the L503 inductor which is around 370mA.  Furthermore the ripple current makes ripple voltage in the B+ voltage (we don't want that). That voltage is related to the ESR of the CAPs used to store and filter the pulses.

So really we want a larger inductor, but I tried them today, but I couldn't maintain high frequency, and 255V except with the 330 inductor.  (The current ramp up on the larger inductors is slower, and the result is more efficient, but not enough energy get's stored if we run them at high frequency).

Actually you get a really quiet supply that works with a 0.120Ohm sense resistor and a 1000uH inductor, and it uses less amps from the GDIY 51x power supply, but it runs at 56Khz.  It has lower ripple by half, and it sounded quiet. 

The 330uH Inductor with the .250 sense resistor is good.  It may be we can use a larger inductor, I am going to try out the next size larger and see if it works, but 680uH is too big.

The improvement that can be made is in the filtering.  All the "design tips" documents on boost converters say you need to put an LC filter after the boost converter.  In the schematic, that LC filter is formed by L503 with C507/C507.  The general recommendation is to have the LC filter frequency at 1/10th the boost converter frequency, and this is where we have diverged from the recommended design. Our boost is running at around 15K, and our boost is running at around 100-120K.

Here are Spice models of the frequency responses at the Driver and Gain stage anode for the original schematic and one using the filter changes specified above. Red is the Driver Stage, Green the Gain Stage.
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/HVPSUFilterperschematic_zps0b6b0448.jpg)(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/HVPSUFilterperthispost_zps12536817.jpg)

Note: There are other LC filter arrangements that work, but this one fits best.  You can use much smaller inductor like a 22uf axial cap which fits pretty well across the top of the relay, but you still have to bypass it with a low ESR ceramic and that fits on the back,  so I chose this approach.  If anyone wants I can provide the various options.


Mea Culpa section:

#1) The LFO oscillation I noted in earlier posts DOES NOT EXIST! it was an artifact of using an oscilloscope probe with a ground wire and clip.  When I shorten the ground wire and clip as shown here, the problem goes away.  This is just a bit of bare wire wound around the tip replacing the ground clip:(http://i.cmpnet.com/powermanagementdesignline/2008/12/TI_pwrtip6/Figure_2.jpg)

#2) The shield is not strictly necessary.  What the shield was doing was preventing my scope from picking up the false signals that I was interpreting as LFO oscillation.  But the field is strong and I am going to use a shield out of an abundance of caution.

(There should be a sheepish grin icon!) ;D  Sorry.

Bruce
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 10, 2013, 10:53:25 PM
Bruce, I'm a bit fuzzy on where this new inductor goes?

NEW CAP         Tack a .1uf ceramic capacitor (350V) between the end of that inductor and the HV out on the boost converter on the back of the board.

Are you just hanging another .1uF on the output or is this after L503?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 11, 2013, 09:17:43 AM
Bruce, I'm a bit fuzzy on where this new inductor goes?

NEW CAP         Tack a .1uf ceramic capacitor (350V) between the end of that inductor and the HV out on the boost converter on the back of the board.

Are you just hanging another .1uF on the output or is this after L503?

Well the inductor replaces L503.  I updated the post where I said L502, sorry for the confusion.
Note: In the picture and only for test, L503, and L501 and the HV jumper resistor are mounted on long lead's, tacked on. This is so I didn't have to keep soldering and unsoldering the boards which would surely have ruined them by now. For a build you should mount these properly although you can see that the inductor is a close fit and may need to be angled depending upon your choice of part.  (Also note C28, the 48Volt filter cap, is a 63V 100uF panasonic which I squeezed in). You can also see the Blue 450V C508, and the 350V C503, and the tacked on Rodney Cap.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/PositionofL503_zpse67517a3.jpg)


The new cap goes on the back of the board. 

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1762_zpsc66096ba.jpg)

As far as the part selection for that inductor see the note at the bottom.

All this L503/NewCap filter does is lower the filter corner down to about 1K, and puts it 40dB down at 13K where before there was a 10dB peak.  See the compared Spice model plots in previous post. The 8ohm HV jumper (I used 8.3 ohm that I had lying around from discrete opamp builds) makes an RC filter with C507 that smooths out the peak on the LC filter.  You can put more RC filter there, see my note at the bottom.

So instead of Boost Converter->LC Filter->Anode. you now have Boost Converter->LC Filter->RC filter->Anode.

In the MP 66 Schematic there is a 10uH/22uF LC filter (L3/C31) filter that does the same thing followed by a 2.2K/22uF RC filter  (R30/C17) (which is easier to fit without API format space constraints) which is down 60db at 10K Hz, and has large voltage drops and current limits.  By omitting and equivalent to C31 and R30 on that schematic the GIX-51X essentially runs no RC filter to the driver stage and has a 16.2K resonant peak (as seen in earlier posts).  All the boost converter guides say you have to run an LC filter after the converter, you can use big F small H, or big H small F.  The latter fits better as a retrofit to the GIX-51X.




LC filter part selection: You could find an axial inductor that can handle the .41mA ripple, but probably not that short.  You could take a long axial and mount it vertically (like the resistors on the HV board) and it would fit but a lot of the axials seem to be low current.  The one I tested with is a rewound version of an extra L502 part I had ordered (the 47uH one).  I rewound it with about 7 feet of 32 gauge magnet wire to replace the 22 gauge that was there,  pulled off wire till it measured 995uH, then soldered on leads and mounted it (see picture).  I had to lean it away from the HV board so it would not contact. 

One thing you may need to be concerned with is Q factor, which i frankly don't really understand.  Some of the Boost Converter notes mention the following fact.  This filter will filter the same frequencies that are "seen" by the FB voltage divider, so a "High Q" filter (I think this means a steep filter) may interfere with regulation or cause some problem.  I did not have a problem with that, but I don't really know the Q of my Inductor (I am thinking it is about 50).

More RC filtering: I put an 8.3 ohm resistor in the HV jumper. A larger resistor in there fits easily and dramatically improves the RC filter, but causes a bigger voltage drop. I saw 5 volts drop from a 750 Ohm resistor so there is about so it must be around 8mA or so.  If you do that you need to run the HV card above 250V, which works fine (R502,504,503 of 300K, 1500R, and 282R worked perfectly with a 750 Ohm HV jumper).  Do that and you must run 350V caps for C503, C508, C509 and for that matter C507 and C25 which I recommend anyway because the boost converter as originally spec'd always exceeds 250V on startup until the heaters warm up.  Those parts are available and do fit, C508 is RDED72W105MUE1C3A where you have to bend the leads because it is a 5mm LS part).  I put the smaller filter there because I couldn't measure an improvement with more, and it would allow folks to run at 250V if they already bought all the parts (albeit exceeding ratings briefly on startup).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 11, 2013, 09:19:20 AM
No LFO!  That's great news.

Yes unless you are the Bozo (me) that measured the non-existant LFO in the first place!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 11, 2013, 09:48:44 AM
bruce0,

Thanks for sharing your findings.  Are there any other limits on the inductor we should be aware of when sourcing?  Max DC.current etc?

Thanks,
Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 11, 2013, 11:39:43 AM
Thanks for sharing your findings.  Are there any other limits on the inductor we should be aware of when sourcing?  Max DC.current etc?

Thanks,
Ian

Ian:

I am out of my depth when sourcing the part, but here is what I have pieced together.  Someone with knowledge of magnetic components might provide much better advice:

1) Q Factor: No idea.  But based upon your question I read up and I think a higher Q factor is the combination of high uH and low DCR making the filter more "specific" to a frequency and raising the amplitude of the response peak at the corner frequency ( And the peak could trigger the feedback in the MAX1771 that regulates voltage, so if you have trouble maintaining voltage a high Q factor in the filter could be the problem).

2) Current: The Ripple Current using the 330uH inductor models out at 410mA, but I have not measured it.  I think that is what the part is exposed to.  The load current is in the order of 8mA, so 418mA.

3) DC Resistance: I think lower raises the Q factor, but in general I think lower is better but you will find you don't have much choice, the size, core material, turns and wire size are all pretty much connected mathematically. My test part would spec 1700uOhms (milliohms) or 1.7 ohms max but measured at 1.3 Ohms. 

4) Size: It needs to fit where L503 fit. Lead spacing is an issue, Fitting next to the HV card is an issue, If it is too tall it will stand up next to the Power Inductor (L501) and that is radiating like crazy even though it is a shielded inductor and I don't know what kind of mutual inductance issues you might get there.  In my test setup, as you can see in the picture, both of those inductors are raised up off the card, and I didn't have any problem with interaction that I could detect.

5) Henrys:  I chose 1000uH.  A smaller inductor will raise frequency where the steep part of the curve starts, but might be fine.  My corner models around 1kHz corner, if you use a 470uH inductor that moves up to 1.6kHz, it would probably be fine too.  My choice of 1000uH was because it is hard to get a higher value inductor that will handle the current and fit, but any value 300uH and up would probably be fine.

6) Tolerance doesn't matter obviously

7) SRF: Self resonant frequency is also a limiting factor, not sure but I certainly think you want this in the mhz range and up.  I am not sure of my measurement tools at high frequency so take this with a grain of salt, but I see noise at just about 1mHz range so you want SRF to be above and far from that.  I think the part I made had SRF around 1.6mHz but again this is a guess.

8 - General: Not sure if it matters but what this is I think is called a choke but also seems to be called a fixed inductor.  Chokes and Power inductors seem to be a special case of fixed inductors.  I don't think you want a power inductor although I think they might work fine (I don't know how they differ).  I don't know if shielding would hurt or help, I think it couldn't hurt but I chose unshielded because most fixed inductors were.

Thus exhausting my "knowledge and conjecture" on the topic.



Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 11, 2013, 06:41:00 PM

 Bruce O , can you update your bom  ?

Here is an updated BOM as I currently have built it.  Doesn't spec L503 or the New Cap, I ordered some choices from mouser and will try them out tomorrow, and post what I use.

File is a tab delimited spreadsheet file, can be imported as tab delimited
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 14, 2013, 06:56:29 PM
Success. I am happy with the now undetectable (to me) noise levels in the HV power supply now, and I am in the process of putting all the modules together the same way.

I am using the 330uH power inductor (L501) with the .250 sense resistor as originally spec'd.  ( See note below on Inductor tests I ran if interested), replacing L503 with a bourns 1200uH inductor and a .1uF cap on the back of the board to ground. I am using 200 Ohms as a HV Jumper, and I am putting shields on the HV board, because I think I heard the difference, but I am no longer sure and I am venting them because the get mildly warm and there is an electrolytic in there. I have updated the previous post with my final changes.

The preamp is quiet, and as I have been doing testing and the differences I hear are from individual noisy tubes, and I have replaced a couple and all 4 modules are quiet now.

I have attached an updated BOM to this post with the parts I used.

bb

Note:  Leaning inductor L503

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1763_zps10e58e8c.jpg)

Note: Tack solder .1uF on back

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_1765_zps76c6a505.jpg)

here are more details, if you are interested, in my testing results.

Inductor Tests
I have now tested 470uH and 390uH inductors with the HV Board as L501 (the power inductor).  They both work using 0.200 ohm sense resistors.  However they run at 99khz, and 70kHz respectively and I think that is too low, and I think the 330uH is the one I am going with.  I think I want the switching to be further from the audible frequency range, and easier to filter.

I did some stress tests by putting a 47K resistor to ground at the driver stage plate, as a way to test these HV power supplies with higher current.  (The 470uH works with 0.250 resistor, but add 5ma through that 47k resistor, and it starts to sink to lower voltages. They do work with the higher current with the 0.200 ohm resistors).

I like the 330uH inductors best, with the 0.250 ohm sense resistor.  I have test it audibly, and with a dummy mic, and gain and output all the way up, it seems quieter, but I can't really tell.

I did some tests on the filtration for noise getting back on the 24V input power line, and the noise that gets through that filter is below my ability to measure.  So I am not worried about the switcher dirtying up the power for the other modules. 

Filter Inductors
As to filter inductor L503, I have tried filter inductors with a Q factor of 20 and of 90, and they all work the same as far as I can tell, they all will fit but they need to lean away from the HV board especially if you fit a shield on it. I have tried the Murata and the Bourne 1000uH inductors.   I have the others, but I am happy with the Murata (I am getting the noise on the HV after filtering at -80dB (about .007V rms noise on 252V, .005V pk-pk).  I can measure the noise in the drive stage (but it's not audible) so I am upping my resistor to 200 Ohms in the HV jumper.

I think any of the following will work for the L503:

Manufacturer             Mouser

(I tested) Bourns       652-RLB9012-102KL       RLB9012-102KL     Q>20
(I tested) Murata       580-18R105C             18R105C           Q>92
(I tested) Bourns       652-RLB9012-122KL       RLB9012-122KL     Q>15 - a bit bigger

I inspected an example of the following also, they fit, I think they would work fine.
           Abracon      815-AIUR-02H-102K       AIUR-02H-102K
           Fastron      434-01-102J             434-01-102J   

The cap to ground on the back of the board with this inductor is:
Murata       81-RDER72J104K8M1C1A    RDER72J104K8M1C11A   Multilayer Ceramic Capacitors MLCC - Leaded .1UF 630Volts 10%
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 15, 2013, 05:29:49 AM
bruce0,

That's great news, thanks again for your perseverance.  I'm placing a mouser order for a couple other projects today so this is great timing.

If you don't mind a daft question and brief summary:-

L501  - same as BOM
.250 sense resistor - same as BOM
L503 - now 1mH
additional 0.1uF cap to rear of board as per your photos

When you say HV jumper what do you mean?  Sorry for the dumbness.


Thanks,
Ian


Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 15, 2013, 08:12:38 AM
HV jumper is a wire jumper that Rodney included in case the G9 needed more HV psu filtering.  I thought it did.  It can be seen below.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/47ufpolypropmademenudgetheothercaps-Version2_zps9fff1209.jpg)

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/Cardduringassemblynotefillimentpower_zpsc4fd99e0.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 15, 2013, 08:45:46 AM
Ah, great thanks for that.  Will any ol' 200ohm resistor do or do we need >.5w?

In a glorious turn of events I've just received my parcel of GIX boards!

Thanks Rodney, these are GREAT!


Thanks,
Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 15, 2013, 09:35:33 AM
i used a 1/2 W resistor.  But the voltage drop across the resistor in the idle state is less than 3 of volts 249V on one side, 252V on the other.  Jacob specifies a 2W resistor for R31, which has a 5V drop across it (250V/245V).

I would have thought that 2W was way overkill ( 3V over 200 ohms is 15mA *3 is .045W! And R31 5V over 1000 ohms is 5mA *5 or .025W)  but maybe there is a vacuum tube notion I am not familiar with.  Or maybe i should crank out a huge signal into 600 ohms and remeasure. 

So the answer is, you got me!

Maybe some Valve guy would chime in.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 15, 2013, 03:09:05 PM
There's really no other trick here. The resistor just needs to hold up under max current draw. I have yet to measure what that is, but once i get around to adding the filtering to my unit, I'll report back.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 15, 2013, 05:26:38 PM
Correct.  But the cap on the back really matters, if forms an LC filter with the 1000uH cap that causes a steep cutoff (with no peak because of the resistor) at about 1k and makes the biggest difference.

I added large caps and such as listed in the other post, but that was just to try to replicate the caps on the g9.


If you want i will send you (gemini86) a little shield and you can see what you think.  I will PM.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on February 19, 2013, 12:32:26 AM
Bruce, thanx again for your work on this, i will be ordering up some mousakey, and getting started as soon as i get a minute.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: vineyardgray on February 19, 2013, 02:46:56 PM
Am I the only one who gets very bizzare formatting (i.e. no formatting) with Bruce's Rev. 6 bom?   :o  If not too much trouble, could someone who's local copy isn't all mangled by Notepad post a pdf?

Thanks Bruce for your hard work and Rodney for the great project!   :)

Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on February 19, 2013, 05:11:14 PM
+1
It's Better than nothing but will take a lot of time to unscramble.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 20, 2013, 11:14:39 AM
I will post a pdf, sorry.  GROUPDIY did not allow excel uploads (maybe it is not a open format?)

Attached is as PDF for your viewing pleasure.

Cheers

BB

(PS:  If you "FILE->IMPORT" that the original into almost any spreadsheet and choose tab delimited file and you will have a readable and editable spreadsheet).
Note the BOM is not complete, stuff is missing mostly if i had it
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 21, 2013, 12:19:58 PM
Hi Bruce,

Just for clarity:

"R504 + R503     A single 1800 ohm resistor (measure these with a DVM, a small difference on
this part makes a big difference in voltage)"

Does this mean that you used a single 1800ohm resistor to bridge where R504 & R503 would have been?  I think the word 'these' has thrown me.

I've attached a .png showing the location of the 1k8 in RED.  R504 and R503 should be left out. 

If you could also repost the picture of the cap on the underside of the board that'd be really helpful.

Thanks again,
Ian

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 21, 2013, 12:36:57 PM
That is correct. the cap goes between the output of l503 and ground.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 21, 2013, 02:26:14 PM
(Corrected resistor numbers) R503-R504-R502 form a voltage divider between the output of the boost converter and ground.  The feedback pin (FB ) on the Max1771 wants to see 1.5V for regulation coming from between R502 and R504.  It is set up so you can combine two resistors to get there (R504 and R503). You can use whatever resistors you want to get to that value.

I just happened to have 300K and so I needed 1800R to get to 252V  and I had one, so i jumped over two resistors with one.  But if you have a 270K resistor you would use a different value which you might make up from two resistors.

The factor of output voltage seen at the R502 R504 Junction is (R504+R503)/(R502+R503+R504)
In my case:
1800÷301800 = 0.005964215

The regulation target voltage is when the FB pin is at 1.5V so:
My regulation target is:
1.5 / 0.005964215 =251.49 (Volts)

But if you happened to have a 270K resistor and a 1K resistor you can "cross multiply" (sheesh) 1800 X 270000 /300000 =1620 so you would need about 620 ohms.

1620÷271620 =  0.00596421471
(1.5 volts) / 0.00596421471 = 251.5 volts

The most sensitive parts are the small resistors a small difference in value makes a big difference in output voltage, so it is nice that the card has a spot for two resistors. 
Overall you want the total resistance of the three resistors to be large (they are across 250 volts or so)

Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 21, 2013, 03:01:54 PM
Now I see!  Thanks.

So the originally spec'd R503 and R504 are used when in combination with the originally spec'd R502 (270K).  I'll measure and calculate before install and aim for 250v.

Thanks again,
Ian


Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 21, 2013, 06:03:53 PM
Exactly, and you got the correct resistor numbers (I corrected my post).  When the unit is running it drops about 2 or 3 volts across the HV jumper if you use a 200 ohm resistor there.  I used 350V caps because the voltage goes a bit high till the tubes get hot.

( if you are using 250V caps shooting for 250 will exceed the rating for 20 seconds every time you power up)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 22, 2013, 12:18:59 AM
Note:
I am getting Pops when changing Gain.  The G9 BOM recommends MBB (make before break) switches, also known as shorting switches.  The switch in the BOM is non-shorting.  I plan on trying to replace mine, will report the results.  I am hoping that the backplane of the switch is the same so I can just unsnap the front rather than unsoldering.

The pop's are not bad, I thought they were tube microphonics when they sat on the bench because the unit moved with each click, but in the rack they are audible.  Because of the clever gain structure that shifts from first stage to second stage I am not sure a cap across the anywhere works to minimize this, I will try to look into it.

In any case I recommend choosing but NOT 105-2454 which is non-shorting.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 22, 2013, 09:34:44 AM
Thanks,

I'm having a crack at getting this near completion tonight.

When selecting R503 and R504 are there any value limits I should avoid.  I've populated the board with 120R and 1k5 1/4w resistors as this seemed the simplest solution to getting the 1620ohm (with 270K - R502) - when supping my coffee at work it dawned on me that I hadn't thought about the possibility of a too low value at 1/4w.

Hope that makes sense?

Thanks,
Ian

Current state of things:

(http://media.tumblr.com/4c2d2ba32589e0b1eb69c6678586dc56/tumblr_inline_mimflev37H1qz4rgp.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 22, 2013, 11:40:41 AM
Ian:

At 250V a 250K resistor will run 1 mA, so 1ma times 250V is 1/4 watt.  Don't go below 250K total resistance.  But the real issue is not too low a value because of resistor rating, the feedback pin (FB) needs like 20 nano-amps (I.E irrelevantly small), the problem is that the resistor divider is also a LOAD on the output (since it is from the output to ground). 

The 2 valves use about 12.5 of B+ (I can't calculate this, but this is just by measuring the voltage drop across the filter resistors I put in).  This means that if the voltage divider is in the order of 50K or less you are adding 50%! to the load on the power.  SO you want a large value resistance here.  I wouldn't go below 250K total resistance just because the load might effect the heat etc, and I have tried values up to 2.2M and they all power the unit (though at the time I was not measuring results properly, see earlier posts).  Earlier we thought a higher resistance might have interfered with the regulation but I am of the opinion that anywhere between 250K and 12.5M is ok (at 12.5M there are 20,000 nano amps running through the network).  So look around the resistors you have and find a combination that gives you the voltage you want.

bb
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 22, 2013, 11:47:10 AM
Bruce,

Thanks.  Currently I have installed:

R502 - 270k
R503 - 1k5
R504 - 120R

All 1/4w...

(http://media.tumblr.com/5ab7a388217459ed046f6e805034caaf/tumblr_inline_mimghy1Hv21qz4rgp.bmp)

Thanks again.
Ian

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 22, 2013, 12:12:00 PM
Sorry about the bom errors, guys. Bruce, do you have a good part number for the rotary switch? The part i put on the bom is not the one i used, since i accidentally ordered a solder lug version (it was mbb though).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 22, 2013, 01:01:45 PM
I was looking for stock in MBB/Shorting, and I think I am going to order a Lorlin CK1054 from mouser.  It has a 38mm long flatted shaft so I guess I need to cut it and I am hoping that my knobs will fit, I haven't checked where the flat is.  They also have a MBB 6mm round shaft I think. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 22, 2013, 01:43:00 PM
I do know that some of mousers part descriptions are off when it comes to lorlin. Check the part numbers against the data sheet. I kindof like the alpha switches better.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 22, 2013, 11:41:07 PM
I had another project with a MBB switch, so I opened up one of the switches, and the way they make them BBM is they have little "risers" between the contacts.

This is the BBM
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/image_zps5f18fab5.jpeg)

This is the MBB version, no bumps, the contact rides down and makes before breaking.
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/image-1_zps3bc5db75.jpeg)

If I only had a little chisel... To remove the bumps. So I hammered on an old worn out soldering iron point, and clipped the end.
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/image-2_zps4b7c61de.jpeg)

At about 600 degrees F the plastic is very soft, but not liquid.  Cooler may be better.  God only knows what fumes I breathed when doing this, I was careful to leave no little pieces in there.  And I didn't know what type of grease was in there (speak up if you do) so I use a little de-oxit.
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/image-3_zpsa60eccee.jpeg)

It doesn't look pretty, and it took 20 minutes for one switch (after making the tool, which needs to be sharp and narrow, if I had a narrow chisel it would be better, they would pop off clean and pretty).

The switch works like a MBB now, and when changing the gain the changes are better.  Still not super clean.  Stop 4 is always a pop because of the electrical architecture  ( I wonder if a high value drain or leak resistor somewhere would fix that) it pops the first time you turn past it.  Anyway after that test I am sure that MBB would be better, and I ordered the MBB parts from mouser, I can always change the switch shafts and use the ones I have.

If you do pop one of these apart, keep the shaft pulled tight into the front section or you might lose the little ball and spring, which is small, and can be hard to get back in.  You will almost always dislodge the contact spring which is loose.  There is no problem with that but you will wonder where to put it back so I thought this picture would help, you put it back right next to the number like this.

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/image-4_zps9061db55.jpeg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 22, 2013, 11:44:34 PM
breathe it in, fellas. This is what diy smells like. (burning plastic)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 26, 2013, 07:17:32 AM
Right,

So I'm getting ready to test this beauty out. 8)

For my own purposes, and for anyone else wanting to do so, can you recommend a test measurement procedure?

Can I simply plug in the unit without valves/tubes installed and measure the voltages to the relevant pins or do I need a dummy load of some kind?

Thanks,
Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 26, 2013, 10:47:14 AM
I would have tubes in. They tough a nails and can take a lot of abuse if something isn't right. They're the best kind of dummy load.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on February 26, 2013, 08:05:30 PM
a.f.a.[we]k.  what / where is the most accurate up to date mouser bom ?
is it post one or Bruce's  ? tia
ouch my mouser order is going to be big ..................
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on February 27, 2013, 08:41:14 PM
Hey guys,
I can't find RV16AF-41-15R1-A50K on mouser... do you have any other ref n°?
Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 28, 2013, 01:49:26 AM
Check your BOM and don't buy 105-2454 which is BBM you need to choose a MBB gain switch, otherwise the most recent BOM I posted is partial mouser version 7 which has that BBM switch (incorrectly)..  As far as the pot is concerned I got it at  mamouth electronics.http://www.mammothelectronics.com/RV16AF-41-15R1-A-p/210-100-a.htm (http://www.mammothelectronics.com/RV16AF-41-15R1-A-p/210-100-a.htm) i think it is just log with longish pins for vertical mounting
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 28, 2013, 09:18:22 AM
jandoste,

I'm just about to test my first one (valves arrived today).

I had the same with my mouser BOM, so for the Pot I just used a 'normal' A50K pot with solder lugs and used spare wire (trimmed resistor legs) instead of the specified long pins.

Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on February 28, 2013, 11:09:07 AM
Hey fellas,

I'm going to be ordering stuff monday, Please pardon me if i missed it, but is there one solid and correct BOM available? or maybe a shopping cart? If not, when i'm done my orders, and finished my builds, i will post every piece in my BOMS, and try to make a single(or a few) shopping cart out of them. The least i can do after Rodney and Bruce did so much work on this!

thanx
guys
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on February 28, 2013, 01:02:01 PM
Hey guys,
thanks for the update!
so Tonycamp please share your BOM with us :)
Cheers
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on February 28, 2013, 03:48:05 PM
Evening.

A quick note to say it fired up OK!

(http://media.tumblr.com/b2db898b2ecc4f9fb912e6d0afaa4adc/tumblr_inline_miy6tjqXfY1qz4rgp.jpg)

It sat there for 15mins with no flames or smoke so it's not dangerous at least.

I do have a slight issue with LF thumping, flicking the HPF to 50/120hz helps get rid of it.  I had not included the RodneyCap(TM) on the hv board, is that needed in conjunction with Bruce0s mods?

Thanks
Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on February 28, 2013, 04:08:23 PM
I found this one... what do you think that can I go with this Alpha:) ?
http://fr.mouser.com/ProductDetail/Bourns/51AAA-B28-D18L/?qs=sGAEpiMZZMtC25l1F4XBU7rZyhV5cpJRbFi75AXK5JU%3d

Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 28, 2013, 10:02:12 PM
hey guys!

thanks for hanging in there...

The BOM will be edited as soon as I find a suitable switch. Mouser doesn't seem to have a MBB(shorting) switch with round shaft AND pcb pins. Everything is D shaft. So if you're using regular set screw type knobs, tD shaft will work fine, not so sure about collet knobs, though... anyone have experience with that?

Mouser MBB(shorting) with D shaft: 10WA344
Mouser MBB(shorting) with roudn shaft (this has solder tabs, so you'll need to snip them off to use on the pcb) 105-13571

Both are lorlin. Alpha witches are also good as an alternative.

Ian, the "rodney" cap is required to stabilize the low frequency oscillation. The other added filtering components noted by bruce are for filtering out any residual high frequency noise.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on March 01, 2013, 04:40:04 PM
 ;D ;D ;D ;D ;D ;D ;D ;D

AWESOME.  This thing sounds GREAT! 

Thanks so much to Gemini86 for the adaptation and for sharing it, and to Bruce0 for the additional work/share on the PSU mods.


In case anyone was wondering what the LF thumping sounds like - I've uploaded a before and after Cap sample:

https://soundcloud.com/minoian/gix-thump (https://soundcloud.com/minoian/gix-thump)


Thanks again - this is ace!

Ian.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on March 01, 2013, 05:10:08 PM
anyone have a complete mouser cart for this thing?    Gemini, are you gonna do another run of PCBs and metalwork?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 01, 2013, 07:35:33 PM
If i get enough interest for 25 pieces, I'll order more brackets and face plates. I still have plenty of pcb kits. I had (incorrectly, maybe) assumed that most people would want to diy the face plates.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on March 02, 2013, 04:22:05 PM
;D ;D ;D ;D ;D ;D ;D ;D

AWESOME.  This thing sounds GREAT! 

Thanks so much to Gemini86 for the adaptation and for sharing it, and to Bruce0 for the additional work/share on the PSU mods.


In case anyone was wondering what the LF thumping sounds like - I've uploaded a before and after Cap sample:

https://soundcloud.com/minoian/gix-thump (https://soundcloud.com/minoian/gix-thump)


Thanks again - this is ace!

Ian.

cool news, how bout some samples hitting it hard with a kick drum or bass guitar? :)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on March 03, 2013, 09:35:46 AM
Ask and ye shall receive:

http://www.groupdiy.com/index.php?topic=51639.0 (http://www.groupdiy.com/index.php?topic=51639.0)

Hope it is useful.

Ian.
 ;D :o
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on March 05, 2013, 10:09:43 PM
cool samples, sounds great!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on March 19, 2013, 10:25:53 AM
Just for maddness , Radial now has a tube 500 series pre

Radial Powertube Tube Preamplifier
Retail Price: $800.00

High voltage 12AX7 tube drive with 60dB of gain
Smooth sounding Jensen Transformer input
Hand inserted 100% discrete class-A electronics
Single wide module fits all 500 series rack formats

The Radial PowerTube is an 'old school' 100% discrete class-A vacuum tube microphone amplifier intended to capture the essence of the voice or instrument while adding the rich harmonics, warmth, and character of a transformer coupled tube circuit.
Designed to fit inside the Radial Workhorse and other 500 series racks, the 'single-wide' PowerTube begins with an ultra low-noise Jensen input transformer. This exhibits near perfect frequency response while producing the warm Bessel curve Jensen is legendary for. The signal is then amplified via a select 12AX7 tube using an innovative non-radiating charge pump that supplies 140 volts to the tube to deliver the excitement and character of a high-voltage vintage tube amplifier. This feeds a class-A balanced output stage that together, can produce as much as 60dB of gain. This makes the PowerTube ideal for use with all microphones.
Features include an easy-access front panel XLR input with a safely recessed 48V phantom power switch. To optimize signal-to-noise the Powertube is equipped with fully variable trim and gain controls. A 10 segment LED bar graph provides visual feedback and driving the PowerTube into the red is encouraged. This increases the grit, harmonic content and distortion. For even more character, activating the Air adds a slight edge to a male vocal or sparkle on an acoustic guitar. Low frequency resonance is easily tamed using the high-pass filter. For added pleasure, the PowerTube comes factory-loaded with a select 12AX7 tube along with a second Tonebone distortion pedal tube for more grit and madness.
The Radial PowerTube... the true character of a world class vintage tube preamp without the noise!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 19, 2013, 11:54:02 AM
Sounds pretty cool, maybe I should smack together a one bottle pre and peddle it for 600 bucks a pop and rake in tons of profit.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: okgb on March 20, 2013, 11:36:17 AM
You've done allot of the work already  .............
more curious how they implemented their charge pump , filiment current
and how they get the gain out of one tube [ 40 db from the tube some more from the input xfmr ]
roll music uses the 12dw7 which has a high gain section but the radial doesn't mention an output xfmr
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 21, 2013, 09:50:17 PM
"This feeds a class-A balanced output stage that together, can produce as much as 60dB of gain"

Notice the missing over-hype about an output transformer... I'm going to guess a solid state output, like you would find in maybe an ART pro tube piece. They don't want to loose the gain in an output transformer.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on March 21, 2013, 11:09:34 PM
So, a bunch of people built this.   but no one has soundbytes of it on drum overheads or vocals or horns or anything?   
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 21, 2013, 11:15:15 PM
I'll probably have some vocals recorded this weekend... probably.

Once I get a little road case built I'm going to loan it out to a local recording studio to put it through it's paces.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on March 22, 2013, 01:44:55 AM
 Has anybody successfully built one yet? I've been holding off till project was worked out.
 Looks like build guide is getting better. Can't print out complete BOM, can't to do a Mouser Cart.
 Any help.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on March 22, 2013, 07:16:46 AM
Definitely!

And it sounds GREAT!   :)

I'll be using one in anger this weekend so will hopefully have a better feel for it, but so far I'm very happy.

For reference - I built mine with OEPs.


Ian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 22, 2013, 11:40:00 AM
Winetree, I'm trying to make the time this weekend to try to iron out the bom and build guide. This is no commercial product and I am making assumptions on peoples troubleshooting skills. There's also the official g9 thread for general circuit troubleshooting. But yeah, I'll definitely try to get all the needed info in one place.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: canidoit on March 22, 2013, 10:09:43 PM
Will this be available as a normal 500 series 16 volts version??
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 22, 2013, 10:32:10 PM
I hadn't planned on it. Two tubes take up way more power than is available in standard 500 format. I wanted this to be a 1U preamp, because rack space isn't plentiful in most studios. It is possible to run it off +-16 though, with modifications.

run the boost converter on +16V, it will suck up a lot of current, probably over 200mA. The tube heaters can run on the -16V rail, but need to be rewired from series to parallel and then they'll need either a voltage dropping resistor (a big one) or a regulator to bring -16 volts up to -12.6V. This will draw 300mA on the -16 rail, so more than 2U worth of power. If you're not running everything in your rack at full power all the time, this will work fine. It's just not VPR compliant.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on March 23, 2013, 09:43:12 PM
Have you tried it? With 16v you may want an inductor smaller than 330uH. Duty cycle would be higher and frequency would drop ( probably to 76k hz which is based on the 16usec max on time)but it should work.

If you want to keep it above 100k hz you may need a smaller inductor than330uH I have a spreadsheet calculation and if anyone cares I all take a shot at an initial value.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on March 26, 2013, 06:08:55 AM
Hey Guys,
Which tube did you use?   ::)
Thanks

 
I found this one... can I go with this tube?
EDIT: http://www.banzaimusic.com/ECC82-12AU7-JJ-Matched-and-Balanced.html

EDIT2: My bad :( I received all parts! but bad news :-[ this Lorlin switches is the bad one!  Do you think that also will work?
http://fi.mouser.com/ProductDetail/Lorlin/CK2368/?qs=%2fha2pyFadugzyIKxLH3BYupOnqRNmej1oo6IfF6M0Mg%3d
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 27, 2013, 01:16:33 AM
I just used a nice quiet used RCA for V1, V2 didn't seem to make any noise, no matter what tube I used.

Right now I'm messing around with a JJ 12ax7 in V1. Sounds...kinda thin and crunchy. Kinda nice for guitar DI though.

I'm trying to figure out a good switch number. The one I'm using right now is the CK 1458. This is a NON-shorting switch. People are saying that we need a shorting switch, but I'm not convinced. I'm still not hearing any bad pops when gain switching. Maybe a little tick at best. After all, we're only switching AC signals with the switch. there should be no change in DC charge of the cap.

Please somebody correct me if I'm wrong.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: EmRR on March 27, 2013, 01:50:46 AM
Gain is always a shorting switch, otherwise there are jumps at best, speaker cone launching pops at worst.  You don't want to change a non-shorting on a low frequency source with a loud sub or bass bin powered, or a 500W amp on your precious NS-10's.  Shorting gets smooth transitions with no breaks in continuity; think about a pot, continuous resistance. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 27, 2013, 02:10:57 AM
No, I agree with that. In this specific case, though, is it not a bust? The switch it already bypassed by a 1M resistor, as well as the fact that a momentary open condition between switch positions would result in low gain, not high gain or loud pop.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on March 27, 2013, 02:52:32 AM
... a momentary open condition between switch positions would result in low gain, not high gain or loud pop.

My opinion... on the first 3 clicks (steps 2,3 and 4) the momentary open causes a decrease in attenuation so an increase in gain (perhaps 9db or 12db not too much because the attenuation is not much), and clicks 5 through 10 I agree with you completely the momentary open results in lower gain, which is still be audible, but not loud.

But the thing that is odd, is the 4th click.. where the attenuation goes away, and the gain stage steps begin.  That step is where I got a pop when I used non-shorting switches.  The other steps were audible clicks, but not big pops.  But step 4 is a pop.  Oddly the first time I pass step 4 it is a big pop, and after that, if I turn the gain down and back up again, step 4 is no longer a big pop.

The non-shorting switch is usable, but if I change gain levels while tracking I record a click.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 27, 2013, 10:23:21 AM
I see. I'll have to take measurements from mine while switching, because I'm not getting the same pop.

As far as I can figure out, mouser only carries a shorting switch with a D shaft (with PC pins). That will work with set screw knobs, but I'm not sure about collet knobs. Or you can get a round shaft shorting switch, but with solder lugs instead of PC pins and just snip the lugs off.

Sorry I don't have the time to research exact part numbers at the moment. Will get to that after work today.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: EmRR on March 27, 2013, 11:30:10 AM
I recall Mouser carries several different brands that all fit the Lorlin footprint. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on March 27, 2013, 08:40:29 PM
Alpha, lorlin, and I think there's a C&K switch also. At least in their catalog, none of them come in a shorting round shaft with PC pins. It's just as easy to clip the solder lugs off though. (I had to do this for one of my channels.)

EDIT:

The part number for the MBB (shorting) switch, with PC pins and a flated D shaft should be CK1054.

again, if you're using standard set screw knobs, this will work fine. Collet knobs, I have no clue.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on April 08, 2013, 11:08:04 PM
couple quick questions....

Will this work in an API 500 series lunchbox type of unit or strictly -/+ 24 VDC only?

Has the BOM been finaized and corrected with all the proper parts?

Can someone who has already built the unit give me an estimate of what the BOM will cost? I'm trying to figure out how much this Pre will cost with all the materials?


Thanks
G
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 09, 2013, 12:17:32 AM
I suppose I should get around to getting the BOM situated... sorry, life has a way of keeping me busy doing stupid stuff lately.

I'm gonna start sorting it all out so all the info is in one place on the first post.

But to answer your question, this preamp was designed to run on +/-24V. There was a brief discussion earlier in this thread about converting it to 16V operation. It's definitely possible, but has not been tried yet.

Build cost is pretty straight forward for your small passive components, then there's your choice of tubes with is a big variable, then there's the iron. I myself like the OPE input, but I'm having second thoughts about the OEP output. I think this preamp would sound much better, bigger low end, less muddy mids if it had something with a larger core. Many like the Lundahl transformers, but they're too spendy for me. I'm going to put some edcor xs1100 transformers in mine soon, which edcor  advertises as being an LL5402 substitute. I doubt they're in the same league, but for the money, you can't go wrong.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on April 09, 2013, 12:55:04 AM
I'd be interested in this build but I know there are 2 things that would deter that interest a bit. For one, I have already decided on a radial engineering six pack power rack which I believe is only 16 VDC 500 series but the feature set is second to none for the price and what you get even the cube power rack. SO that is why 16VDC is important to me.

Second, I'm new to DIY but I have a few builds under my belt. With that said, when I run across post that have many changes or testing in progress or updates I get confused easily.

In this instance it seems many test and updates were discovered along the way so I only want to order once when it is time to build the BOM.

Any time frame on when the BOM might be updated?

Thanks G
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 09, 2013, 01:06:14 AM
Bruce0 did a great job of testing the DC boost converter, basically dissecting it. He wanted to see what made it tick. After trying a few other variants, the original design was kept it works great. The one addition was a 100n cap on the converter controller's feedback pin to filter noise and stabilize the HV output.

Now, given that you're using 16V rails, you'll have two major problems to overcome. First being that the tube filaments are wired in series for 24V rails. Even when you wire them in parallel for 12V operation, they will consume 12V @ 300mA. The max spec per 500 slot is 130mA, I believe. So you're going to use up more than 2 rack spaces on one preamp (in the way of power supply). Secondly, the HV boost converter is designed to run on 24V. It uses about 120mA on the +24V rail, and would use even more when run on 16V rails.

So your 6 pack will quickly fill up if you try to adapt these to 500 series spec. OR, you can upgrade your power supply to handle the extra load.

These would also go nicely into a 1U 19" rack enclosure.

I hope that gives some sort of insight. I'll try to have the BOM straightened out by the end of the week maybe.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on April 09, 2013, 02:31:48 AM
Toure14, you'll just waste slots if you try to run it in a 16V box, and cuz you'll have to cut traces and whatnot as well.  it's PHYSICALLY designed to fit into the 18slot connector of 51x.  Every lunchbox clone out there is 16V and uses the 15-pin slot connector.   GroupDIY 51x is the only thing that uses 18pin connectors and a pair of 24V rails in addition to everything else that is built in to the VPR (500-series) spec.   Don't waste your time with the Radial box if you are serious about this particular project.   just hit up Jeff/Sahib/Volker for the 11slot 51x chassis and PSU and be done with it.  it's like 700USD for everything. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on April 09, 2013, 07:53:02 AM
Thanks for the clarification guys.....decisions decisions... :-\
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on April 12, 2013, 08:14:36 PM
I've decided to go with the 51x rack but I'll still look for an alternative to a 1 slot or maybe 2 slot power supply. Something like what chunger built in the build thread for the first generation PSU for ths rack. Then I'll still have to figure out some cosmetic stuff to make it mobile. too bad I can't just swap out the board inside the Radial Engineering workhorse six-pack. That would be so perfect plus I get all the built in features.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 12, 2013, 08:49:56 PM
Welcome to diy, you can implement those features you need into your own rack, with a bit of creativity and some hand wiring.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on April 12, 2013, 08:59:30 PM
yeah the DIY part is cool for those who have the hand tools and workstations but for someone like me who is generally good at building from an already tested design, DIY can tend to be expensive and challenging...frustrating.

It's like knowing what you want in your head but not having he resources to build it. I'll give it a shot though.

Now if only someone had a Radial Engineering Cube I could disassemble... ::)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 13, 2013, 03:45:04 PM
Updated first post:

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 18, 2013, 11:48:32 PM
So, anyone else have some show and tell? Who's building these? Or are you all hoarders, like me?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on April 20, 2013, 03:12:38 AM
I had a slight detour to build a test signal driver that could drive RightMark tests through these both in Mic and Line mode, but I now have four units in test.

2 with Lundahl input and output
1 with OEP input and Output
1 with Cinemag Input and OEP output

Here are the 4 racked up for testing (Show and tell)
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2023_zps450b382b.jpg)

I wanted to verify my ears for the additional HT PSU filtering I thought was necessary, and I was able to measure a 8dB improvement in RMS noise measured with the additional filtering. 

In most of my testing I found that the little Metal Shields I built for the power supplies make no detectable difference (they ranged from 0.6dB better to 0.2dB worse!) or at least not a difference that was repeatable in my test environment.  That was until I tried the Cinemag input transformer.

As you can see from this picture, the Cinemag sits closer to the power supply than the other transformers.  When testing with the Cinemag (using RightMark RMAA through a USB sound interface and my test interface) I see 3dB lower noise on with the shield in place.  But I can ONLY measure this on the Cinemag (I think because it so close to the HT power supply).

(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2025_zpse76da698.jpg)


Other testing conforms to what folks see on the Gyraf G9. I was seeing a pretty substantial low end rolloff on all the units until I tried one with an old Altec input transformer, and then I got a Cinemag input transformer and again it had less rolloff (at 20Hz I was seeing it down 10db, with the OEP and Lundahl input transformers,  with the Cinemag it is about 3dB down). 

Sure enough if I drive the test interface through the Guitar/DI input on the front I don't get the big rolloff either, so I am pretty sure the input transformers are involved.

There are posts about this on the Gyraf board, and my measurements match the ones there pretty close, but they speak of different OUTPUT transformers.  What I am seeing is that the input transformer can effect the low end (I assume because in Line mode the input transformer is still in the path).

I also see a bit of a high end response peak on the OEP. 

In any case Jacob warns on the G9 board that it is important to test with your ears, so I think it is time I get these into use and hear what they can do.  They test out quiet enough.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on April 20, 2013, 09:13:57 AM
it's nice to finally see some racked up finished units!   

I'm curious to know what this guy sounds like on different sources. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 20, 2013, 05:49:35 PM
Great stuff, Bruce. I had heard of the typical frequency response roll-off associated with the G9. For me, it kindof adds to the charm of the preamp.

It's great to get some testing done with the cinemag input. That noise issue was a concern for me when doing the layout. I tried to fit it in there a million ways to try to get it further away from the converter. The end result was the best I could do at the time. I wonder what an additional aluminum sheet would do to shield the RF, since it's a great RF shield. Maybe insulate the inner shield with some tape and then wrap it with aluminum foil and ground it at one point.

Although, I've always been a minimalist, if it's not a problem, why try to fix it.

Great work!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on April 20, 2013, 09:34:04 PM
I just have a thin folded MuMetal shield, but I think the field is Magnetic, and really any Steel sheet would do it, like a cut up tin can.  I can try that if you like.  I think you want something that is permeable.

I am just using mumetal foil (cuts with scissors, very thin) much thinner than a tin can.

As I said, no measureable effect except for the Cinemag... and I think that is because of the position.  Perhaps it is possible to order triple shields on the Cinemag... you can on Jensens... That would surely eliminate any issue.

I just don't get the rolloff differences related to the input trafo though.   I think the OEP needs a zobel too. Want me to post some measured sweeps?

Currently I have 3 flavors, all of them are quiet.  Here they are, and my test gear in the background.
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2028_zps5c295a25.jpg)


Lundahl In - Lundahl Out
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2030_zps003b746d.jpg)


OEP in OEP out
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2029_zpsd91b6c50.jpg)


Cinemag In, OEP Out
(http://i1221.photobucket.com/albums/dd463/Bruce0/G1X%2051X/IMG_2032_zps274d44c7.jpg)

b
Title: Re: [BUILD] GIX-51X tube preamp
Post by: JamesW on April 20, 2013, 10:13:04 PM
You my find the noise comes from the orientation of the Cinemag transformer rather than the proximity 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on April 20, 2013, 10:16:05 PM
I can't hear the noise.  It is -88.7db noise level vs -85.6 noise level (this test gear does not measure below -96dB or so, so the absolute numbers should be ignored, but the relative numbers show it is a minor issue.)   If it was loud a human can't hear less than a 3dB difference, at -80 plus db... it is way in the noise.

The orientation of the trafo is tough.  The circuit board has a place for pin 1... and there you go.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on April 20, 2013, 11:49:02 PM
All this testing, and not a single person has actually used these preamps for recording since they finished their builds?    COME ON PEOPLE!!!  FOCUS ON WHAT MATTERS!!!!    :P   ;D
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 21, 2013, 12:49:21 AM
If I spent more time recording and less DIY, this preamp would never have happened.

:)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on April 21, 2013, 12:35:48 PM
There is a fantastic set of talks by Rupert Neve from 2007 AES at <http://rupertneve.com/company/notes/>.  A real pleasure to listen to all of them, very interesting and lots of nice anecdotes and he talks about lashing together sound systems from scrap for Winston Churchill after the war.

Relevant to this post, this audio track <http://rupertneve.com/wp-content/i/2007-rupertneve-aes-1.mp3> (at minute 3:44 seconds) he speaks directly to the issue of this post, Mr. Neve saying  "the question of measuring something or using your ears to listen to it has always been one of the great problems, we all know that you can measure as deeply as you like and it often doesn't co-relate to what you actually hear, we've all got our theories I am sure as to why that should be, but you see...." and he goes on some and he quotes Lord Rayleigh from his book The Theory of Sound "directly or indirectly all questions connected with this subject must come for decision to the ear, as the organ of hearing and from it there can be no appeal."  and he also quotes Lord Kelvin "in physical science the first essential step in the direction of learning any subject is to find principals of numerical reckoning and practicable methods for measuring some quality connected with it, I often say that when you can measure what you are speaking about and express it in numbers you know something about it but when you cannot measure it, when you cannot express it in numbers, your knowledge is a meager and unsatisfactory kind it may be the beginning of knowledge but you have scarcely in your thoughts advanced to the state of science".  And then Rupert goes on with his thoughts on the matter.

They are fun, there are several hours of them.

b

All this testing, and not a single person has actually used these preamps for recording since they finished their builds?    COME ON PEOPLE!!!  FOCUS ON WHAT MATTERS!!!!    :P   ;D
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 22, 2013, 03:01:28 AM
Okay mulletchuck, you asked for it...

it aint pretty, but it's something. Recorded last weekend, here's a rough mixed clip of vocals and electric guitar through the DI jack.

Not my best vocals, I could have done a few dozen more takes...

https://soundcloud.com/gemini86-1/g9-51x-vocal-and-guitar-test (https://soundcloud.com/gemini86-1/g9-51x-vocal-and-guitar-test)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on April 28, 2013, 08:15:25 PM
Hey guys,
I am not sure about "C26, C27, C29" I got some 100uF but 35V or 100V... can I use 35...100V or I need to get more voltage :)?
Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on April 28, 2013, 08:19:09 PM
C26, 27 are both filtering the +-24V rails, C29 the 16V rail, so 35V is fine on all those.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on May 01, 2013, 10:13:51 AM
Hello everyone,
I have ordered some kits and now have questions concerning different transformer options and their impact on the sound. I already read about the different low frequency rolloffs pointed out by bruce0, but can someone comment further on the sound of some of the combinations? (difference between prices are huge) Anybody used the ea2622 on input? I will be shopping at classicapi soon, so I could buy them there.

input is much aprreciated and thank´s a lot for this awesome project!

 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on May 01, 2013, 08:32:31 PM
I would really love to build a pair of these, but no one has posted clips of what they sound like on a bunch of sources (drums, guitars, pianos, horns, vox, etc).    Who's actually used these guys in the studio, what did you use them on, and how were the results?   I'm only bringing this up because my 2 51x chassis are full, so if i were to put these guys into regular use, i'd need to get a 3rd chassis and that opens a completely new can of worms lol
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 02, 2013, 05:54:45 PM
Once I build a road lunch box, I'll be handing mine over to a local studio owner. That will take a while though.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on May 02, 2013, 06:41:35 PM
Thanks Rodney!

C26, 27 are both filtering the +-24V rails, C29 the 16V rail, so 35V is fine on all those.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 02, 2013, 06:44:36 PM
so are there any sound clips. yes? no?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 02, 2013, 06:51:41 PM
Okay mulletchuck, you asked for it...

it aint pretty, but it's something. Recorded last weekend, here's a rough mixed clip of vocals and electric guitar through the DI jack.

Not my best vocals, I could have done a few dozen more takes...

https://soundcloud.com/gemini86-1/g9-51x-vocal-and-guitar-test (https://soundcloud.com/gemini86-1/g9-51x-vocal-and-guitar-test)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on May 02, 2013, 07:09:57 PM
that sounds pretty good.   What's it sound like without the reverb/compression?   

Let's talk about that DIY U47!!!   who's build is that and what capsule?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on May 02, 2013, 07:25:03 PM
My bad!  :'(
How I get it I don't remember but I received mouser package this morning...
http://fr.mouser.com/Search/ProductDetail.aspx?R=CK2368virtualkey12200000virtualkey105-2454
and this one is non shorting  :o :o :o So I'm not sure if it will work?
Any advice?
Thanks


hey guys!

thanks for hanging in there...

The BOM will be edited as soon as I find a suitable switch. Mouser doesn't seem to have a MBB(shorting) switch with round shaft AND pcb pins. Everything is D shaft. So if you're using regular set screw type knobs, tD shaft will work fine, not so sure about collet knobs, though... anyone have experience with that?

Mouser MBB(shorting) with D shaft: 10WA344
Mouser MBB(shorting) with roudn shaft (this has solder tabs, so you'll need to snip them off to use on the pcb) 105-13571

Both are lorlin. Alpha witches are also good as an alternative.

Ian, the "rodney" cap is required to stabilize the low frequency oscillation. The other added filtering components noted by bruce are for filtering out any residual high frequency noise.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 02, 2013, 07:49:11 PM
Bruce was having clicking issues with his using non shorting switches. I haven't experienced issues. I haven't looked into it a ton to see for sure but it seems that clicks should only happen on the first four settings. In those positions the switch is attenuating v1b's output, after that it's attenuating the feedback signal to increase gain. There's no DC present on the switch.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on May 02, 2013, 10:38:12 PM
Bruce was having clicking issues with his using non shorting switches. I haven't experienced issues. I haven't looked into it a ton to see for sure but it seems that clicks should only happen on the first four settings. In those positions the switch is attenuating v1b's output, after that it's attenuating the feedback signal to increase gain. There's no DC present on the switch.
Funny you should mention this, I just posted on the G9 thread that this problem was because of microphonic tubes (in 2 out of 4 preamps), and now that those tubes are swapped out, and the preamps are bolted down in the rack, the clicks and pops are gone.

So I am using BBM switches on 3 of the preamps and leaving them that way, they are not noticeably different from each other.  Changing gain sounds the same on both, and it reasonably quiet (no pops).

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 02, 2013, 10:48:50 PM
Good to know I'm not just crazy! haha...

Seriously that had me stumped.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on May 02, 2013, 10:55:56 PM
Really sorry, I originally stuffed all 4 preamps during test with handfuls of 12AU7's from a drawer... And it just didn't occur to me.  So that's uh.. 2 strikes.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 02, 2013, 10:58:44 PM
It's all good.

I'm currently using some old GE tubes from a Hammond organ. Took a while to find a good quiet one for V1.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 11, 2013, 03:09:38 PM
Was putting a cart together last night from mouser and I ran into some questions with the B.O.M. so here we go...

I need a lil bit more clarification on which capacitors to select especially the ones that don't specify WIMA. Many choices pop up so I use the filter to filter the choices and then I'm still left with many to choose from and for someone like me that is too confusing.

Example: the first CAP says "1000uF/35V 5mm LS Aluminum Electrolytic. Since there is no brand specified here I go to passive components, capacitors, electrolytic, then I select the capacitance filter and the noted value, the voltage filter and the noted value, then the Lead Spacing noted value. But i'm still left with 91 possibles after that. I try to shoot for 5-6 possibles

Again I'm having this issue with ALL the caps that are not specified WIMA or just has a value by it and nothing else, so if I could get some assistance on this issue it would help a great deal.
For the CAPS labeled WIMA I noticed that there are options for the LS. Is there any importance to this at all other than price from what I see?

--CAPS--
     1000uF/35V     1   "C504"   5mm LS Aluminum Electrolytic
          100nF     6   "C12, C30, C31, C32, C33,  C505,    5mm LS 63V WIMA 
          100nF     3   "C501, C502","RODNEY CAP"   2.5mm LS 63V WIMA
          100nF     2   "C506","FILTER MOD"   7.5/10mm LS 250V Ceramic
           100u     3   "C26, C27, C29"
            10n        2   "C8, C9"   5mm LS WIMA 63V
            10u   /63V     1   "C7"   22.5/27.5mm LS FILM
        10uF/250V     3   "C25, C503, C507"    5mm LS Aluminum Electrolytic
            1u5        1   "C4"   (mouser)505-MKS41.5/250/10
           220n     2   "C2, C10"   5/7.5/10mm LS WIMA 250V
           470n/250V     1   "C3"   10/15mm LS WIMA 250V
           470n     1   "C5"   5/7.5/10mm LS WIMA 250V
           470u     1   "C11"
            47u        1   "C28"   
            4u7        1   "C13"   22.5/27.5mm LS WIMA 250V
            68p     1   "C6"

Below are the rest of the parts that I could not find on mouser:

50K-log     1   "RV1"   Alpha  RV16AF-41-15R1-A50K
1.2mH     1   "L503"   (mouser)562-RL187-122J-RC OR EQUIVALENT
1N4004     3   "D2, D7, D502" (this part had options that I wasn't sure to about)

Once I get the needed assistance I will submit my BOM for review here in the thread and make my Mouser cart available to everyone so for those like me, there is a simple few clicks and off to checkout.

Thanks in advance
G
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 11, 2013, 03:59:01 PM
the electrolytics are pulling a really light duty here... the voltage they're receiving is already low ripple, they're just there to reduce cross-talk between modules and add some local stabilization. I use either panasonic or nichicon. After you've filtered down to the specifics noted on the BOM, just choose an inexpensive one.

The pot isn't available at mouser. I got mine from mammoth electronics: http://www.mammothelectronics.com/RV16AF-41-15R1-A-p/210-100-a.htm (http://www.mammothelectronics.com/RV16AF-41-15R1-A-p/210-100-a.htm). You don't HAVE to use that pot, any 16-24mm pot with solder lugs will fit in the space, but you'll need to hand-wire it to the board with short leads.

The inductor is a typo... my bad, I'll fix it. This is the correct part: http://www.mouser.com/ProductDetail/Bourns/RL187-122J-RC/?qs=%2fha2pyFadujgImkQujR83nj3U1cRlrXUQG8gC2LJipSQenDdgLZDWg%3d%3d (http://www.mouser.com/ProductDetail/Bourns/RL187-122J-RC/?qs=%2fha2pyFadujgImkQujR83nj3U1cRlrXUQG8gC2LJipSQenDdgLZDWg%3d%3d)

The 1n4004 is easy, just make sure it's a through hole part. This one is in stock, it's cheap and there are 228 thousand available. (http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/1N4004/?qs=sGAEpiMZZMuQUXCJI7Y4lnwnhMohE%2fNv)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 11, 2013, 04:11:02 PM
what about the LS for some of the WIMA caps is that just for pricing options as well? what is the size that was originally spec'd? so it is safe to assume all CAPS are electrolytic if not stated as something else?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 11, 2013, 06:40:42 PM
what about the LS for some of the WIMA caps is that just for pricing options as well? what is the size that was originally spec'd? so it is safe to assume all CAPS are electrolytic if not stated as something else?

The options listed are just options. Some are more available than others so I added pads for multiple LS options. I generally go by price there as well.

Anything that's not marked as a film cap is an electrolytic. The lead spacing for them should be 5mm, but anything close will work. Unless you use snap-ins, the leads will be plenty long enough to fit whatever lead spacing needed.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 12, 2013, 02:44:03 AM
Almost done with the Mouser cart few more questions:

on these caps there is no specified voltage so is 35V okay to use?
  100u     3   "C26, C27, C29"
  470u     1   "C11"
  47u     1   "C28"

on this cap the specified LS isn't an option. Only 15mm. Can I use another 15mm instead which is the exact same as "C3"?
  470n     1   "C5"   5/7.5/10mm LS WIMA 250V

These part numbers aren't readily available (backordered). Are there any subs?
   ES3G     1   "D501"   (mouser)625-ES3G-E3
   330uH     1   "L501"   (mouser)652-SRR1210-331M


   
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on May 12, 2013, 09:55:35 AM
Hey Rodney,
I allready solder L503 but maybe i must change it no?
thanks
(http://i1236.photobucket.com/albums/ff442/jandoste/photo-9_zps37ed21ba.jpg) (http://s1236.photobucket.com/user/jandoste/media/photo-9_zps37ed21ba.jpg.html)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 12, 2013, 12:45:13 PM
Almost done with the Mouser cart few more questions:

on these caps there is no specified voltage so is 35V okay to use?
  100u     3   "C26, C27, C29"
  470u     1   "C11"
  47u     1   "C28"

on this cap the specified LS isn't an option. Only 15mm. Can I use another 15mm instead which is the exact same as "C3"?
  470n     1   "C5"   5/7.5/10mm LS WIMA 250V

These part numbers aren't readily available (backordered). Are there any subs?
   ES3G     1   "D501"   (mouser)625-ES3G-E3
   330uH     1   "L501"   (mouser)652-SRR1210-331M

 100u     3   "C26, C27, C29" should all be 35V

  47u     1   "C28" should be 63V

  470u     1   "C11" is for V2's cathode, which is very low voltage so it can be as low as 6.3V.

This inductor for L501 may fit...  (http://www.mouser.com/ProductDetail/Coiltronics-Cooper-Bussmann/DR127-331-R/?qs=sGAEpiMZZMsg%252by3WlYCkU%2f747tLNB7Mqyi3J9aRSFzE%3d)it's slightly larger, (by .5mm) so you'll have to try your luck, or keep sifting through the mouser catalog for something closer. Or digikey has them in stock.

This diode for D501 will work perfectly. (http://www.mouser.com/ProductDetail/Vishay/ES3F-E3-57T/?qs=rfh7uIuiIO01g1HzZKLhUA%3d%3d) It's the same diode but with a 300V reverse breakdown instead of 400V, which is still a safe margin above the 250V output of the converter.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 12, 2013, 12:46:16 PM
Hey Rodney,
I allready solder L503 but maybe i must change it no?
thanks
(http://i1236.photobucket.com/albums/ff442/jandoste/photo-9_zps37ed21ba.jpg) (http://s1236.photobucket.com/user/jandoste/media/photo-9_zps37ed21ba.jpg.html)

Yeah the originally spec'd L503 is not correct. Change it out for a 1.2mH part (part # in BOM)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on May 12, 2013, 01:03:58 PM
Thanks Rodney!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 12, 2013, 02:27:22 PM
Last question and my cart should be completed today and Rodney and I can send it to you for review.

"C5" and "C3" have the same capacitance rating the only difference being the Lead Spacing requirements. I read on page 2 of the thread that the leads had to be bent for "C3" at 15mm LS and currently when I search WIMA caps as according to the BOM for "C3" and "C5" at the given values .47u and 250V, only 15mm LS is available.

When I drop the voltage to 100V I get 5/7.5/10 mm LS options which would probably work much better for the CAPS spacing requirements, however the voltage drop is significant.

My question is can I use 100 volt WIMA CAPS for "C3" and "C5" instead of 250V?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 12, 2013, 02:37:10 PM
The difference between c3 and c5 is that c3 must be 250V, where c5 can be 100V, since it is only block the DC from v1A's cathode when at low gain settings, which will be around 80V max. I'll change the bom to reflect that.

RE: c3 touching the tube pins... thepins will get warm as the tube heats up. But it's my experience that these low power tubes only get warm, not HOT. I can pull a hot tube out bare handed without discomfort. The cap's plastic housing will be rated for much higher operating temperatures. It's not exactly pretty, but it's fine.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 12, 2013, 02:45:58 PM
The difference between c3 and c5 is that c3 must be 250V, where c5 can be 100V, since it is only block the DC from v1A's cathode when at low gain settings, which will be around 80V max. I'll change the bom to reflect that.

RE: c3 touching the tube pins... thepins will get warm as the tube heats up. But it's my experience that these low power tubes only get warm, not HOT. I can pull a hot tube out bare handed without discomfort. The cap's plastic housing will be rated for much higher operating temperatures. It's not exactly pretty, but it's fine.

Thanks Rodney...I'm going to go over my cart and then share it with you and then hopefully before the day is out this build can have an official Mouser cart minus the 50k Log which is from mammoth audio.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 12, 2013, 03:23:17 PM
Okay this is just out of pure curiosity Rodney, but would 100v work for c7 instead of 63v keeping the same capacitance?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 12, 2013, 04:43:46 PM
Higher voltage rating is always ok. If it fits, it's good.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 12, 2013, 05:31:35 PM
Higher voltage rating is always ok. If it fits, it's good.

Okay thanks. I sent you an email with a link to the mouser cart I put together. If you verify everything then you can post it to the beginning of this thread for everyone to use. I followed the order of the BOM so a person can literally go right down the line item by item.

Only thing missing is the 50'k log from mammoth but i'm sure you can post a link for that right under the cart if you approve it.

I don't know how to measure the knobs or which ones to recommend to folks so i guess you can post that info in the BOM as well.

Thanks for the assistance
G
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 12, 2013, 07:14:23 PM
Looks pretty good to me. Thanks for doing that, Toure. Updated first post with the mouser cart.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on May 13, 2013, 11:48:08 AM
Looked at first post.
Where's the Mouser Cart?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 13, 2013, 11:56:20 AM
Looked at first post.
Where's the Mouser Cart?

I don't know how to do the whole hyper link thing where I can attach it to the words "Mouser Cart"
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 13, 2013, 01:19:39 PM
Ummm. Sorry, it was there last night but I'm not seeing my changes. I'll try again at lunch. Maybe the edit didn't go through.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 13, 2013, 01:41:03 PM
there.. fixed it.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: maq3396 on May 13, 2013, 10:35:38 PM
Thanks for this build everyone!

Looking forward to building a pair of these.

Mine will be for male and female vocals.

Can anyone comment on tube selection or optimal input/output transformer for this application?

Thanks in advance

Cheers
Mac
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 14, 2013, 05:34:45 PM
I really like JJ tubes for new glass. Old stuff? Right now I have some used 50s rca in there. V2 doesn't seem to care about being a noisy tube. V1 might need to be selected for low noise.

Lots of people seem to prefer lundahl for the transformers.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: maq3396 on May 15, 2013, 04:46:47 PM
Thanks Rodney!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 20, 2013, 10:59:47 PM
where are people sourcing their lundahl trafos and tubes?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on May 21, 2013, 07:41:43 AM
Hi Toure,

You can get both the Lundahls at: http://www.canford.co.uk/

silent:arts also sells Haufe input transformers (Haufe ST8456), just 30€+vat each.

For tubes I highly recommend these Teslas 802S (White print around 60´s yellow print around 70´s) if you want to go for Telefunken quality.

http://www.ebay.de/itm/THE-ULTIMATE-NOS-Matched-Pair-of-Tesla-ECC802S-12au7-ECC82-tubes-Ships-from-US-/181030421911?pt=Vintage_Electronics_R2&hash=item2a26410597

one guy also has these black plates with white print, but I don´t know much about them.

http://www.ebay.de/itm/1-Paar-original-TESLA-ECC802S-Rohren-tubes-ribbed-plate-neuwertiger-Zustand-/171039824397?pt=DE_TV_Video_Audio_Elektronenr%C3%B6hren_Valves&
hash=item27d2c49a0d

regards, Kvothe
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on May 21, 2013, 10:48:29 PM
Yeah I didn't see the LL1578 trafo which is 1:10 which I want the most I can get out of this pre. plus Tube wise I'm looking for warmth, presence, and color. will I get that with the Telefunken tubes? i though maybe RCA, Mullard, or Apmrex might give me that sound. I hear the telefunken sound is very clen and stresses the high end a bit more.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on May 24, 2013, 06:49:15 AM
Nice NOS RCA, Amperex or Mullard are a good way to go for character and colour,  though they sound quite different from each other. My second pair will have NOS RCA, or Amperex Bugle Boys, if I can afford those.

A question concerning resistors: Is a 250V rating for metal film resistors ok, or should I use the 300V or higher rated?

thank´s for the cart by the way, Toure!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on June 10, 2013, 10:37:29 AM
Hi!
I want to design my own frontpanel... can anybody share a ftp-file or a doc with the dimensions for the GIX-51X-Front with me?
Thanks!
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on June 10, 2013, 12:16:06 PM
Wanna place an order for parts.
 Is the Mouser Cart up-to-date?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 11, 2013, 01:49:40 AM
Here's a front panel dimensional drawing I (hastily) drew up. It's in metric, so google is your friend for conversion.

Faceplate Layout (https://docs.google.com/file/d/0B6s_klsk9wMDNklvMmhSZnZZUmM/edit?usp=sharing)

Winetree: You'll have to check with Toure14 about his mouser cart.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on June 11, 2013, 04:34:04 AM
Thanks Rodney!
metric is cool, i live in germany :)
i made a template for FrontDesign.

It´s based on Rodneys dimensions but it is not verified!!!
Maybe someone can compare it to a real faceplate, just to make sure i made no mistake!

You have to rename the file to "fpd" (it is not allowed to upload an fpd-file).
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on June 11, 2013, 10:08:03 AM
Thanks Rodney!
metric is cool, i live in germany :)
i made a template for FrontDesign.

It´s based on Rodneys dimensions but it is not verified!!!
Maybe someone can compare it to a real faceplate, just to make sure i made no mistake!

You have to rename the file to "fpd" (it is not allowed to upload an fpd-file).
Chris

How do you view it? Your link opens up all weird for me. Do you have a better upload or different picture?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on June 11, 2013, 10:35:57 AM
rename the file from whatever.txt to whatever.fpd, then open it with whatever app opens a fpd file. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on June 11, 2013, 10:46:45 AM
Its a template for the app FrontDesign from schaeffer:
You have to download their FrontDesign-Software.
Than replace .txt with .fpd and you can design your own faceplate and let scheaffer or someone else with a CNC-machine make the frontplate.

http://www.schaeffer-ag.de/index.php?id=3&L=1 (http://www.schaeffer-ag.de/index.php?id=3&L=1)

Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on June 11, 2013, 11:05:47 AM
got it
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 11, 2013, 12:29:00 PM
I actually have an fpd file, I think I posted it in the original thread, let's see if I can find it.

Okay I found it, but I'm not sure it's up to date. I'll post the last revised file I have while at lunch.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on June 19, 2013, 05:05:40 AM
Hi!
First Version of my faceplate  :)
(http://www.chrisreiss.de/GIX51X-faceplateV05.jpg)
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on June 19, 2013, 12:00:19 PM
Nice.   here's mine.   I did it so it matches all of the other modules i have done.   The switch holes are bored in the back so that the mounting nuts will go on underneath.   Added 2 small screw holes so i can use small black screw to mount the plate to the bracket,  instead of the switch nuts doing this job.  I noticed i have my phase markings reversed though from the one above.  ill need to double check that.

(http://gunpointrecording.com/gdiy/qmp-GIX.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on June 19, 2013, 12:38:52 PM
Nice.   here's mine.   I did it so it matches all of the other modules i have done.   The switch holes are bored in the back so that the mounting nuts will go on underneath.   Added 2 small screw holes so i can use small black screw to mount the plate to the bracket,  instead of the switch nuts doing this job.  I noticed i have my phase markings reversed though from the one above.  ill need to double check that.

(http://gunpointrecording.com/gdiy/qmp-GIX.jpg)

Regarding those bolts... Can I assume they travel all the way back to the tube board?  If so, please take a look at how close those are to high voltages.  Perhaps you would consider a pair of nuts, with the part that hits the tube board being nylon or something.  Otherwise you are putting a conductor in that lets a person get his finger with in few mm of a tube base.

Alternatively (and very carefully) you could ground the bolts, but on the stock faceplate they would be insulated by the PCB material and only grounded if they were connected to the back, and the back to the case.

Also be aware, if you intend to have the switches have nuts installed on them then silkscreen "Mic" and "150 Hz" might be partially obscured.  This happened to me on the default plates, but I think I was supposed to omit those nuts.

I eventually omitted the nuts.

Sorry if you guys have all this figured.  The design is really tight, and well thought out, and changes to it should be just as well thought out.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on June 19, 2013, 12:43:17 PM
Nice.   here's mine.   I did it so it matches all of the other modules i have done.   The switch holes are bored in the back so that the mounting nuts will go on underneath.   Added 2 small screw holes so i can use small black screw to mount the plate to the bracket,  instead of the switch nuts doing this job.  I noticed i have my phase markings reversed though from the one above.  ill need to double check that.

(http://gunpointrecording.com/gdiy/qmp-GIX.jpg)


would you mind sharing your version of the faceplate or sending me the file... ;D
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on June 19, 2013, 05:00:20 PM
In regards to these faceplates. Is there a way to get the center holes to line up all the way. I think the Hi-Z hole is off center from the rest of the holes (a bit farther to the left)  in the mid section? would adding some spacers be simple or no?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on June 19, 2013, 05:18:05 PM
Very nice gunpoint :-)
i´m was not sure about the phase switch, i guess gunpoint version is right.
I guess you can raise the DI-Input or mount it on the plate and connect it with short wires, but better let Rodney confirm this...
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on June 19, 2013, 05:23:37 PM
Very nice Toure :-)
i´m was not sure about the phase switch, i guess toures version is right.
I guess you can raise the DI-Input or mount it on the plate and connect it with short wires, but better let Rodney confirm this...
Chris

I don't have a version up at least not yet but gunpoint version which is all black is sort of the direction I'm heading in. I was hoping he/she would be willing to share the faceplate
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on June 19, 2013, 05:39:20 PM
I don't have a version up at least not yet but gunpoint version which is all black is sort of the direction I'm heading in. I was hoping he/she would be willing to share the faceplate

Sure thing.   Not really finished yet... still need to make sure my added mounting screws line up.   Also haven't finalized knob choices yet so i may move the markings around once i find out the final knob diameters.    The holes for the 2 mounting screws are for http://www.amazon.com/gp/product/B000FN1EJS/ref=oh_details_o00_s00_i01?ie=UTF8&psc=1 (http://www.amazon.com/gp/product/B000FN1EJS/ref=oh_details_o00_s00_i01?ie=UTF8&psc=1)

zipped the fpd file here:
http://gunpointrecording.com/gdiy/qmp-GIX.fpd.zip (http://gunpointrecording.com/gdiy/qmp-GIX.fpd.zip)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 19, 2013, 09:21:36 PM
Just to jump in here and offer my two bits;

The 3 toggle switches were never meant to be mounted to the faceplate. I built mine so they are just about flush with the front. The faceplate is bolted to the bracket via the gain switch, output pot and instrument jack. It's quite solid.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on June 19, 2013, 10:21:21 PM
Just to jump in here and offer my two bits;

The 3 toggle switches were never meant to be mounted to the faceplate. I built mine so they are just about flush with the front. The faceplate is bolted to the bracket via the gain switch, output pot and instrument jack. It's quite solid.

My plan is to mount faceplate with 2 added mounting screws ( they're visible in the design I posted ) and instrument jack.   I have 2mm counter bored on the back for the gain and output.   This is so I can use a knob style that sits flush w the faceplate.   Since those nuts will be behind the faceplate and not securing it... I decided to add the 2 holes for small mounting screws.   
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 20, 2013, 01:33:03 AM
ah, okay I understand now... I misread your earlier post and thought you said you added blind pockets on the backside to allow for a nut behind the toggles, when there's no need for that.

Carry on.

PS, here's a pic of the oxblood chicken heads on my second unit. The chicken heads are too big for this design, but I think they're fun and retro.

http://i.imgur.com/qEyZspH.jpg (http://i.imgur.com/qEyZspH.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Brolik on June 23, 2013, 05:12:16 PM
Hey guys, C6 68pf ceramic is spec'd 250v or greater in the BOM, but the one in Toure14's Mouser cart is 50v. Was this a revision that I missed or just a mistake in cart?

Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 23, 2013, 05:18:52 PM
It's not actually blocking any DC, just passing bypassing HF signal around R10 (47K), so the voltage is not important. I spec'd at 250V to ensure it could handle a large signal swing. 50V should be fine.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on June 26, 2013, 03:26:08 PM
PS, here's a pic of the oxblood chicken heads on my second unit. The chicken heads are too big for this design, but I think they're fun and retro.

http://i.imgur.com/qEyZspH.jpg (http://i.imgur.com/qEyZspH.jpg)

The smaller chicken heads work fine, and they are available in oxblood from CE, etc. I only have black ones handy:

--mark
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on June 26, 2013, 07:15:34 PM
Link to those?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: irfrench on June 27, 2013, 05:56:37 AM
Link to those?

+1


I'm looking at getting my second built up - can anyone recommend a mouser alternative to the 330uH (652-SRR1210-331M)?  I'm not entirely sure what the specs of the inductor need to be (Max. current, Max. DC resistance etc.)  :-[

Thanks,
Ian

 8)


Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on June 27, 2013, 03:09:46 PM
I guess I misspoke. :-[ They don't seem to have maroon/oxblood:

http://www.tubesandmore.com/products/P-K900
http://www.smallbearelec.com/servlet/Detail?no=1190

--mark

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 27, 2013, 04:36:25 PM
Yeah I was looking around last night. If you really had to have that color, it would be hard to paint them. I'm not sure if I'm keeping them or not. I might grab some rca knock offs.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Makofoed on July 11, 2013, 04:56:01 PM
Received my kits, thanks Rodney!

Stuffed the pcbs tonight, just waiting for the transformers now.
Of course I ordered too thick caps for 100nf and 10nf so it looks a little clumsy.
Also I had to bend C3 slightly in order to make room for the tubepcb. 
Tested them both with the DI input, and directly out from the 4.7uf cap and they both work great.

Went for Lundahls all the way and the ll1538 is currently out of stock, should ship 16 july, cant wait!
Also, Mouser has gotten the Inductor back in stock.

Magnus
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on July 17, 2013, 08:55:27 PM
I have 4 unbuilt kits. Not enough time.
Would you mind sharing the Parts Cart?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on July 17, 2013, 10:38:00 PM
I have 4 unbuilt kits. Not enough time.
Would you mind sharing the Parts Cart?

 http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=be0cfb162d (http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=be0cfb162d)

Here's mine.   I haven't built yet so i can't verify all the parts. You may want to double check.  I'm still waiting on the rectifiers which should come within the next week or two.  I have everything else though.   Using lundahls and aux7's, which i've already acquired.  I'm Looking forward to starting the build.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on July 23, 2013, 03:42:58 PM
Heu Rodney quick question.

In regards to the Lundahl transformers would the 38XL or the 78Xl fit with the added 3.5 mm in height each add? I want to really max out this pre and I haven't ordered my Transformers yet. Also wouldn't I get more out of the 1578 since its 1:10 or 1:5 in this case better?

Thanx
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on July 23, 2013, 04:12:31 PM
I think the XL has a much larger core and wider pin spacing. Regarding the step up, you could use whatever you wanted but the higher the step up, the more you could overload v1. A lot of legacy valve preamps use a 1:10.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on July 23, 2013, 04:26:32 PM
pin spacing is the same its just a smidgen taller by 3.5mm than the regulare which is 17mm. And yes the core is 45% larger...so would the added height of the XL transformer be too much or would I still clearance? also can V1 be changed to safe guard overloading?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on July 23, 2013, 05:16:45 PM
Well if the pin spacing and pinout is the same and the core will fit in the space, no problem. No need to change v1, but you might be using the input pad a bit more. (Except that you can't use the pad and phantom power at the same time, so either use external power if needed it external pad, if needed.) Nothing wrong with a little tube overdrive, it comes on pretty soft.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on July 24, 2013, 12:16:16 AM
Now that I'm finally home from work, looks like the XL should fit just fine. The bracket is .75mm thick, then 5mm spacer, then 1.5mm pcb, then 20.5mm for the 1538xl puts everything at 27.75mm or 1.1 inches about. That's actually a lot shorter than the OEP transformers I have in mine right now.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on July 24, 2013, 12:33:52 AM
cool... i really want to get the most out of this pre so i was looking at the XL38 and XL78...thanks for clarification Rodney
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Brolik on July 31, 2013, 02:19:50 PM
Hey guys, this might be a stupid question, but I noticed that the Gyraf G9 design calls for a LL1528 input transformer, while this 51X version calls for a LL1538. Just wondering what the deal is there...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on July 31, 2013, 07:20:36 PM
I changed it. The 1528 had split windings that aren't needed for this application and by switching to the 1538, we could use other lundahls with the same pin out, so we have more options.

Just a heads up:
I may be a little hard to get ahold of for a bit. My wife and I just had our first child on Monday and I've taken on a second job to make ends meet. I'll still be around but my free time is super limited.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: shabtek on July 31, 2013, 08:04:09 PM
Congrats!

it was nice knowing you buddy. :P
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on July 31, 2013, 10:41:03 PM

Congratulations Rodney!

And don't worry... kids love to have a 1:00AM feeding while you are posting to GroupDIY! 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on August 01, 2013, 12:42:31 AM
haha! Yeah it's already been a rough few days. I'm working graveyard shift a few night a week (weekends mostly) at a coffee stand, which has actually been really fun so far. My day job is starting to really wear on me, and it's getting to the point where I don't know how much longer I'll be there. Once I'm more stable financially, I might make a plunge and quit my day job so I can focus on my family and my next career move.

I'll for sure be around, since it doesn't take much time to respond to posts, but my current projects are on hold for now. I have a couple more 51x projects coming, and you know me, they won't be simple or straight forward to build. So, prototyping will take a long time with so much on my plate.

So, back to the 1538 VS 1528:

The 1528 (http://www.lundahl.se/pdf/1528.pdf) has dual secondaries, which could be wired for 1:5 or 1:2.5 step up. We don't want or need 1:2.5 for this application, so there's no need to have the option.

The 1538 and 1538XL (http://www.lundahl.se/pdf/1538_8xl.pdf) have a different pinout, and only a single secondary winding. It can still be wired for 1:2.5 operation, but only by wiring the primaries in series instead of parallel. This is still not needed, but here's where the bonus comes in; the 1538 has the same pinout as the 1576, 1577 and 1578/1578xl which are 1:7, 1:14 and 1:10 respectively. So, now you really have some options to play with the build. Sometime soon I'll be pulling out my oep iron and putting in a 1:10 input, into a 12ax7 for V1, reducing the overall feedback to increase gain and then hand winding a 4:1 output. I predict this will take the preamp from a very mild, clean warm sound to a dark, brash, grungy sound when really smacked hard.

So, that's just some insight into why I chose the input transformer options that I did.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Brolik on August 01, 2013, 12:26:38 PM
Awesome, thanks. Congratulations on the new family member!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on August 01, 2013, 01:19:28 PM
is the BOM finalized yet?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on August 05, 2013, 12:45:52 AM
Chuck,

The BOM is current and accurate. The mouser carts that people are posting are, however, not verified yet. (I don't think)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on August 05, 2013, 01:36:06 AM
Bey Rodney quick question. How much would a faceplate cost in all black with white lettering? pretty much a color reverse of what u have now?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on August 05, 2013, 01:22:20 PM
Well, the cost per unit would be the same, but I think the tooling fee would be around 80 bucks, then another 30 or so for air shipping. You really only get a good deal in large quantities. I'd suggest using Schaeffer or contact Dan with collective cases in the white market.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on August 05, 2013, 02:58:16 PM
Hey Toure, I had the same idea for my number 5&6  ;)

I am ordering some faceplates from Frank at NRG in Germany. If you want in I could order more and send some your way.
fpd file: http://uploaded.net/file/1htg2hj2 (http://uploaded.net/file/1htg2hj2)
I will also order some SSL9k 500 frontplates with culteousness1´s design as seen here: http://www.groupdiy.com/index.php?topic=42552.160 (http://www.groupdiy.com/index.php?topic=42552.160)

Prices will be about 20-25€ excluding taxes and shipping.

regards, Kvothe
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on August 05, 2013, 03:08:35 PM
Hey Toure, I had the same idea for my number 5&6  ;)

I am ordering some faceplates from Frank at NRG in Germany. If you want in I could order more and send some your way.
fpd file: http://uploaded.net/file/1htg2hj2 (http://uploaded.net/file/1htg2hj2)
I will also order some SSL9k 500 frontplates with culteousness1´s design as seen here: http://www.groupdiy.com/index.php?topic=42552.160 (http://www.groupdiy.com/index.php?topic=42552.160)

Prices will be about 20-25€ excluding taxes and shipping.

regards, Kvothe

Funny You should say lol. I'm currently e-mailing Frank back and forth Now. I am also about to purchase SSL 9K5 and 4K5 face plates. I posted a pic of the Black Faceplate for my 9K5
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on August 05, 2013, 03:09:33 PM
Here is a pic of the other face plate frank is doing for me
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on August 05, 2013, 03:10:55 PM
I cant get your FPD file to open up but I assume if its Rodney's original design but just black with white lettering I may be interested. Where do you live Kvothe?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on August 05, 2013, 03:17:12 PM
Great timing! You need the latest front panel designer software to view it. I live in Germany, but if you are already in contact with Frank just order some.
Frank is a great guy :)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on August 05, 2013, 03:21:52 PM
Yeah I just got it to open thanks. I am going to send Frank your all black FPD file so he can add 1 to my order for the GI 51X. thanks Kvothe
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on August 05, 2013, 03:26:11 PM
You are welcome Toure!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on August 09, 2013, 05:45:01 AM
Hey guys,

I just tested my preamp and everything seems good so far. No smoke, tubes light and heat up as they should and the unit is passing signal. But I have to crank up gain and output all the way to get a 'usable' signal level. I just built the unit following the latest BOM and the actual schematic. First thing I'm gonna do is measure the HV. Can I just check the voltage at the output of the HV board or is there a better point?
After the first powerup I also realized that I had put the additional 100n cap on the HV board across the lower two resistors (R503+R504 see attached pic) instead of the outer two resistors R503+R502).
I corrected it now but still have the weird behaviour. Is it possible that this damaged something, leading to that lack in gain I have?

Cheers
Benjamin
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on August 10, 2013, 06:26:05 AM
I checked the HV on the output of the HV board and it's 242V when I power the unit up and then decreases to about 233V after half a minute. The voltage should be around 245V I guess.
Should I change the resistors on the voltage-divider to get closer to the 245 Volts?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on August 10, 2013, 02:22:36 PM
I checked the HV on the output of the HV board and it's 242V when I power the unit up and then decreases to about 233V after half a minute. The voltage should be around 245V I guess.
Should I change the resistors on the voltage-divider to get closer to the 245 Volts?


242V is fine, and if you have heater voltage (which you do) then you are heating an powering the tube correctly.

Your brief error with the cap should not have made a difference, that is just the voltage reference and you stabilized it incorrectly (although you did put 230 plus volts across the 50 volt cap for a bit, it is a ceramic and probably can take it, and if that was the problem then it would be short or open, and both of those would manifest as a stability problem so that is not the problem.)

Photo's would help but here are some thoughts:

There is a jumper labeled on the board HV jumper.  It needs to be connected somehow with a wire or resistor (I used a resistor but it works with wire too).  if not, then your lovely 242 volts are no where near the tubes!

So some test methods:

A thought on HV probing (this is what I do)
Plug the unit into a test power supply turned off. Select a good set of probes for your DVM (no loose wires, cracked insulation or funkyness allowed) ground the COM leg of your DVM with a clip to a good ground on the card and then tape with electrical tape over the entire end of the RED dvm probe exposing only the tip.  Set the DVM for 2000 volts and then turn on the PSU, don't connect any speakers or headphones (so you don't blow them or your ears), wear rubber shoes, no loose cloths, and with your left hand in your pocket and NOT leaning over the unit you use your right hand to carefully probe the HV source. (this avoids making you a ground, and avoids having as much current through your heart if you become one, you could screw up and get blown across the room but you have a better chance of not dying this way.)

What to test:

I would probe the bottom plate of the tube board and look for HV to the tube itself.  There should be.

There should be I think around 70 to 100 volts running to one side of the output cap, and pretty much nothing on the other side.

if you have that, then you have 1) a heated tube (because you saw it) 2) B+ to the tube (because you measured it) and 3) connectivity to the output cap (which is working fine).

If you have all that, then you have to kind of wonder about RV1 the output pot or the filter network (high pass filter on the switch) turn the switch off and that eliminates those filter caps (if you forgot to install them.. on the little daughter board. like I did the first time).

I suppose you could have a bad or incorrect output pot, you could check that (should be 50K ish across it and the center should vary resistance )



After that it is a bad tube but I am not willing to suggest that without some more data.  Here is the data that would help:

What does it "sound" like or what signal are you seeing? is it a clean signal? Noisy? Tell us more.

What is the input signal?  Are you using a mic or a test generator?  What is the impedance of the test generator and where is it connected?

Suggestion:  You can connect a test generator  or signal to the High impedance plug on the front of the unit... thus bypassing some circuitry (good for debugging). You should turn OFF the phantom power (good for protecting test generators) and turn mic line to LINE (though it doen't matter if you are using HiZ input plug).  The output POT should be adjusted to the middle position (just in case you have a reverse log pot in there or something, at least some signal will get through).

Show us a picture of the card.  It is worth 1000 words.  A nice big picture clear is good.  A good place to put them is Photobucket it is free, and then link them here which they make easy.

Inspect the back of all the cards for solder bridges and cold solder joints.  Do this with a strong magnifier (my eyes are bad I use a Loupe) slowly, left to right and right to left creeping across the face of the card, stopping at each joint.  have a sharpie with you to mark questionable joints.  If it doesn't take 20 minutes at least, you didn't do it.

Inspect the front of the card for missing components.  Really... it is quite common.  Any open holes in the card should make sense (like you know why nothing is in it).

Let us know more details of sounds, measurements, etc.

Good luck

Bruce



Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on August 10, 2013, 06:33:03 PM
Hi Bruce.

Thanks for the detailed information. I'll post a photo of the board tomorrow and try to check the rest you've mentioned.

Benjamin
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on August 10, 2013, 08:35:57 PM
Hi Benny,

Looks like bruce is on top of helping get you started. He's right about being cautious around tube voltages, your natural instinct is to brace yourself when trying to poke around, but make sure you don't. No part of your body should be touching any part of the preamp or the table you're working on.

First thing I do when I fire up a new piece of gear is check all running voltages. Print out a copy of the schematic, then start checking voltages and write them down next to the corresponding points in the circuit. This will make it easy to spot problems. Then if everything looks right, you can move on.

You can post your voltages here for us to help troubleshoot, just check at each pin on each tube. Looking at the tube pins from the bottom, pin one is the counter clockwise most, and then 2, 3, etc... they are also labeled V1 and V2, v1 being on top and V2 on bottom (it's weird I know, but the layout just worked better that way.)

Let's do that first, then we can move on to signal flow testing.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mylesgm on August 10, 2013, 10:05:04 PM
pulling parts together.  Would the Lundahl 1530s currently for sale in the BM suit this build?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on August 13, 2013, 03:32:32 PM
Hey guys.

Today I found out that somehow my 51X psu puts out -34V on the -24V pin. Last time I checked the voltages was about half a year ago where all voltages were perfectly set. Misterious. I'm gonna fix that first before I investige further on the GIX problems. The -24V are used for the heater voltages, I think. So can a too high heater voltage result in a lack of gain in my preamp? I just turned power on for about a minute or so on every test. So not longer than 3 minutes with too high heater voltage.
Time for further testing...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on August 14, 2013, 07:47:33 AM
Hi!
I´m finishing my frontplate with frontdesign and i wanted to be sure about the Phase-Switch:
Which position is (up or down) the reverse-Psoition or 180°? i can´t really tell from the schematic and the fotos?
thanks
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on August 14, 2013, 11:33:46 AM
Hi.

The original frontplate says IN(in phase) in the upper switch position and OUT (out of phase) in the lower.
But I haven't checked if it's actually right.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Marc Duchesne on August 16, 2013, 11:32:18 PM
Here is my new addition of those pre's, sounds sweet.


Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on August 17, 2013, 11:42:49 PM
Where'd you get the knobs?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Marc Duchesne on August 18, 2013, 06:59:05 PM
Here...

http://www.tubesandmore.com/products/P-K900

regards,
-marc
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Marc Duchesne on September 02, 2013, 08:03:47 PM
Hi people, is this normal to get some induced noise when touching the switches. Ground or something... I am also getting some random really small buzzing noise on the output signal.

Thanks for any help !
-marc
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on September 02, 2013, 08:40:05 PM
Like what happens when you touch the strings on a stratocaster and how it mutes the buzz?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Marc Duchesne on September 03, 2013, 12:45:54 PM
Yes exactly... If I lower and raise volume it goes away. It is pretty small signal but annoying.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 04, 2013, 03:04:53 PM
Rodney I'm placing my order for tubes today and had a quick question. This is my first time working with tubes so is there anything I need to know? Or is it as simple as ordering 2 identical tubes? or do they need to be for input or output? certain size and style?

Again sorry for the newbish question but I want to make sure I get what I need thanks.
G
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 06, 2013, 01:20:37 AM
Hi people, is this normal to get some induced noise when touching the switches. Ground or something... I am also getting some random really small buzzing noise on the output signal.

Thanks for any help !
-marc

Hey Marc,

No that's not normal. Check to make sure your chassis/L bracket has good continuity to ground. Place an ohm meter between one of the toggles and a good known ground point. If you're not in a chassis yet, this could go away when you get it all buttoned up.

Rodney I'm placing my order for tubes today and had a quick question. This is my first time working with tubes so is there anything I need to know? Or is it as simple as ordering 2 identical tubes? or do they need to be for input or output? certain size and style?

Again sorry for the newbish question but I want to make sure I get what I need thanks.
G

I recommend new tubes for this preamp, unless you want to hand select a couple really quiet ones. I've V1 is the only real concern here, since it handles most of the voltage gain. V2 always seems to be silent for me, no matter what crusty old tube I jam in there.

ECC82, E82CC, 12AU7, doesn't matter. I have some old GE's in mine now. Pulled out of an old Hammond B3.

Just don't be a fool and spend money on the gold pins.  ::)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on September 11, 2013, 09:29:56 AM
Hello everyone,

it has been some time since I built these, but I did join to learn and contribute. So here are some pictures.
(http://www.groupdiy.com/gallery/0/51388-110913080950-1661729.jpeg)
(http://www.groupdiy.com/gallery/0/51388-110913080950-1651402.jpeg)
The first pair I built with both Lundahl input and output transformers and a some very nice matched 60´s Tesla 802S tubes. Very clear, 3dimensional, a lot of gain. I have used these live for leadvocals and love them.

(http://www.groupdiy.com/gallery/0/51388-110913081304-1721935.jpeg)
(http://www.groupdiy.com/gallery/0/51388-110913081304-171682.jpeg)
The second pair has Ed Anderson´s input transformer and matched 60´s RCA blackplates tubes. They have a little less gain, a more "up front" sound, better bass response, but occasionally I hear a frequency changing "whine". I think maybe it is a shielding issue, but mu-metal is on its way ;) (I will copy what bruce0 did)

So far this project is great. Needs some time to fit everything, but greatly rewarding when they are up an running.
I have additional pairs of GE triple Mica, Lorenz and Amperex "Bugle Boys" and I will test those with the different transformer options when my microphone split is done.

The last pair I will do with OEPs and an all black frontplates I got from Frank at NRG.
(http://www.groupdiy.com/gallery/0/51388-110913082019-1771630.jpeg)

You can find more pictures in my galleries.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on September 11, 2013, 03:58:02 PM
As I posted earlier, I measured the effect of the Mu-Metal shield and it is pretty darn small, 3dB in noise at most.  This is unlikely to be your whine.

When I had a whine it was a noisy tube.  If you don't have a spare tube then try swapping the two for each other.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: kvothe on September 11, 2013, 04:29:57 PM
I will check for noisy tubes, but this "whine" occurs periodically, that is why I did not recognise in the initial test. Could it be something else?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on September 11, 2013, 04:38:01 PM
I had the intermittent whine, seemed to go away at some times (gain levels maybe) or maybe it was just the vibration of changing gain levels.  I would say the whine I heard was maybe 3k-8K hz never could measure it successfully but it was a high whine, and would sort of fade/flop in and out.  That sound familiar?

I fixed it by replacing the tube, but I don't remember whether it was the gain or buffer tube (probably gain).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: EmRR on September 11, 2013, 04:44:44 PM
sounds like a tube noise.  leave them on a few weeks and it may go away. 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 12, 2013, 10:34:54 PM
Very very cool, kvothe!

bruce0, I'm wondering if there's any benefit in trying to measure distortion (due to RF noise clipping at high gain) in a shielded VS unshielded DC converter. That would be the only audible symptom of converter switching interference on the input transformer.

Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on September 13, 2013, 11:47:09 AM
I'm wondering if there's any benefit in trying to measure distortion (due to RF noise clipping at high gain) in a shielded VS unshielded DC converter. That would be the only audible symptom of converter switching interference on the input transformer.

The converter radiates EMI noise at about 110khz (using the inductor size specified) and I don't know what you mean by about RF noise clipping.  That 110K Hz signal can be detected in a transformer near the source, and has low order harmonics in the audio band.  The Cinemag (and the Andersen) are round and thus pretty far from the source (and shielded well) and I think very well protected from that signal. The lundahl not so much, it is closer to the inductor.

I imagine that the noise difference I detected (which is less than 3dB) is some low order harmonic of the 110K because my testing is only from 20 - 20000.  The difference in noise level is apparent in the summaries, but finding a 3db peak is pretty impossible it is lost in the noise of the other self noise of the preamp.

What I heard without the little foil shield was a low frequency hiss at very high gains (A sort of hiss with a rumbly sound).  This reduced when I put on the shield.  I could measure it, but I could not see it on a frequency distribution.

In summary I don't think shielding is worth much (except possibly with the Lundahl input trafo which is 3 times closer to the PSU inductor).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 13, 2013, 11:12:07 PM
I think what I meant was (sorry, a bit sleep deprived) that the input headroom may be decreased because of the switching noise bleeding into the first stage and being amplified, kindof like a parasitic oscillaiton. The feedback network should remove this though, so I guess it's probably not a problem. Leave it to me to start a wild goose chase. I also guess I didn't realize (or had forgotten, more likely) that you had detected some sub harmonics from the switching supply in the audible range. My future designs are going to feature an EMI/RF shield on the main board to protect against these problems.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on September 15, 2013, 09:22:37 AM
I don't think it is a problem.  My test procedure was wrong and when I fixed it the noise was minimal.

My GIX51X are just as quiet as my G9 channels with the external PSU (actually quieter at the moment <grin>).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 17, 2013, 12:39:10 PM
Hey guys,
I still have the problem that my GIX-51X pre does not amplify as it should. I did some listening test with dynamic mics and condensor mics through XLR input and bass or keys through the DI input and I still have very low gain. I can hear the signal, there's no lack of bass or treble and the sound seems o.k. The gain switch is working (it increses gain in steps when turning it cw) and the output pot is working, too. The problem is that I have to really crank up gain to get a half-decent output level. Other members wrote that the preamp has lots of gain.

First thing I checked was the HV board. It puts out 242V so that is o.k. I think.
Heater voltages are o.k. and tubes are glowing nicely. So today I finally had a little time to check the HV directly on the tube sockets.

With my lab-psu on +/-24V connected to the pcb my measurements directly at the tube sockets were:

V1 - pin 1: 82,7V
V1 - pin 6: 158,4V
V2 - pin 1: 5,35V
V2 - pin 6: 235,2V

Measurements taken with a DMM between psu ground and the respective tube pin.
Are those voltages o.k. I was a little surprised about the deviations.
But I'm not that familiar with tube circuits.

Any ideas?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 17, 2013, 01:02:12 PM
Need to see cathode voltages as well.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 17, 2013, 02:05:02 PM
Here were go:

V1 pin 1 - 82.7V
V1 pin 3 - 2.16V
V1 pin 6 - 158.4V
V1 pin 8 - 74.5V

V2 pin 1 - 5.351V
V2 pin 3 - 2.78V
V2 pin 6 - 235.2V
V2 pin 8 - 14.24V
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 17, 2013, 04:45:13 PM
Sorry benny, let me clarify.

We need anode, grid and cathode for all 4 triode sections.

V1:
1 -
2 -
3 -
/
6 -
7 -
8 -

V2:
"etc."

I'll try to help later tonight after work.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 17, 2013, 11:28:12 PM
Okay...

Right off the bat, V2, pin1 is a problem. Check that you didn't stuff the wrong resistor in R30. Should be a 1.5K, but maybe you accidentally used 150K? Although, if that were the case, you the cathode voltage on that section would be much lower. hmmm...

(http://i.imgur.com/J12EZp5.gif)

Have you swapped tubes yet?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 18, 2013, 11:06:14 AM
Hi Rodney

I have already swapped tubes and tried differend brands, too. but that changed nothing. Gotta check the cathode and grid voltages later that evening.

Cheers
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 18, 2013, 11:38:39 AM
The main concern right now, without knowing anything else, is pin 6 1 of V2, which should be closer to 70-90V, not 5V.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 18, 2013, 02:43:32 PM
Here are the voltages after 5 minutes warm-up.

V1 pin 1- 82.7V
     pin 2- 0V (actually a few mV)
     pin 3- 2.16V
     pin 6- 158.4V
     pin 7- 35.8V
     pin 8- 74.5V

V2 pin 1- 5.35V
     pin 2- 5.36V
     pin 3- 2.78V
     pin 6- 235.2V
     pin 7- 5.36V
     pin 8- 14.24V

I'll check for wrong resistors tomorrow.

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 18, 2013, 03:52:27 PM
Are these static, everything at zero voltages?

Here are the voltages after 5 minutes warm-up.

V1 pin 1- 82.7V <--This seems low
     pin 2- 0V (actually a few mV)
     pin 3- 2.16V
     pin 6- 158.4V
     pin 7- 35.8V
     pin 8- 74.5V <--The grid is 38 volts lower than the cathode...this triode is just about in cut-off mode, which greatly reduces gain

V2 pin 1- 5.35V <--Should be around half to 1/3 of supply voltage, I think. Can't remember exactly right now.
     pin 2- 5.36V <--Should be zero
     pin 3- 2.78V
     pin 6- 235.2V
     pin 7- 5.36V <--Should be same as pin 1
     pin 8- 14.24V <--This indicates a drop of almost 9 volts across R30, which is much too high. R30 may be too large, or the current going through it is very high.

I'll check for wrong resistors tomorrow.

I would check for wrong resistors, but also look VERY closely for solder bridges between the pin sockets, as it's very easy to have happen. The fact that voltage on pin 1 and pin 2 of V2 are the same tells me that this may be happening.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on September 18, 2013, 04:29:59 PM
Folks, is the BOM finalized yet?   I still haven't built mine cuz it seems like you guys are still flushing everything out for it.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 18, 2013, 05:34:54 PM
I haven't received any indication since the last bom update that there is any problem with it. It's the mouser carts that are unverified as of yet.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 18, 2013, 10:54:21 PM
Is D502 Between C30 and C32? If it is what orientation do I install it?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 18, 2013, 11:33:42 PM
Yes.

Cathode (marked end) up. It's keeping voltage spikes from going back into your +24V supply.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 18, 2013, 11:57:35 PM
Yes.

Cathode (marked end) up. It's keeping voltage spikes from going back into your +24V supply.

So the side with the gray stripe pointing up correct?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 19, 2013, 01:10:29 AM
yes.

Sorry that it's not more clearly marked on the PCB... limited space and such.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 19, 2013, 10:37:36 AM
I would check for wrong resistors, but also look VERY closely for solder bridges between the pin sockets, as it's very easy to have happen. The fact that voltage on pin 1 and pin 2 of V2 are the same tells me that this may be happening.

I checked R31 and R30 and their values are correct. But I found out that, while soldering test wires to the tube sockets, I must have accidentally shorted pin 1 and 2 on V2. So I cleaned it up and checked the voltages again:

V1 pin1 - 83.2V
     pin2 - 0V
     pin3 - 2.24V
     /
     pin6 - 161.4V
     pin7 - 38.18V
     pin8 - 77.5V

V2 pin1 - 78.1V
     pin2 - 0V
     pin3 - 1.84V
     /
     pin6 - 241.3V
     pin7 - 78.1V
     pin8 - 84V
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 19, 2013, 11:53:27 AM
V2 is looking much better,

V1 still is a concern.

Check R6,7,8,9. Voltage across R6 should not be 39 volts. Try to measure the voltage across R6 directly.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 19, 2013, 01:47:17 PM
I checked R6,7,8,9. Their values are o.k. Voltage across R6 is 0.9mV.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 19, 2013, 01:58:45 PM
Hmmm... not sure what is happening. Power off, pull the tube and measure continuity between pin 7 and 8.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 19, 2013, 02:58:49 PM
Continuity between pin 7 and 8 with both tubes taken out:

V1 - 0.996MOhms
V2 - 1.498kOhms
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 19, 2013, 08:42:38 PM
Well... that seems okay.

Your input stage biasing is off, but without good pics of the board and related components, I can't tell why.

If you've double checked resistors, checked for solder bridges/shorts between pins or other pads, then try injecting a signal and measure the level at the different stages. Start with a 100mV sine, 1KHz, right into the instrument jack. Turn the gain all the way down, output pot all the way up. Check AC signal voltage at each stage.

Also, post pics if possible.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 21, 2013, 12:22:46 PM
Hey Rodney I have a quick question. My C506 Capacitor is small so it fit right in the small lead spacing but looking at it I see neither leg toches the trace is this a problem?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 21, 2013, 12:24:32 PM
Again the cap I used doesn't touch the trace. A pic from the bottom view of C506
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 21, 2013, 03:30:45 PM
Hey Rodney I have a quick question. My C506 Capacitor is small so it fit right in the small lead spacing but looking at it I see neither leg toches the trace is this a problem?

Hi,

you should put C506 in the two holes with the wider lead spacing. There are different lead spacings for different sizes/brands of caps. The way you've put it in, both pins are connected together.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 21, 2013, 06:41:26 PM
Benny, you're correct. The you have it now, toure, the cap is just soldered to both ground pads.

Are you sure that cap is a 100nF/250V? It looks ceramic, which is fine, but just looks a little small.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 21, 2013, 08:21:23 PM
Yes it is polyester film but I already cut the leads so off to radio shack I go
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 21, 2013, 11:21:42 PM
Rodney is it ok to clean the boards with alcohol after everything is soldered on?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 22, 2013, 12:04:12 AM
That's what I usually do. I prefer to use 99% alcohol, rather than the 70% that some stores carry for medical use. It's probably very clean but the water content may cause some residue/noise in high impedance areas.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Benny on September 22, 2013, 05:49:07 AM
Well... that seems okay.

Your input stage biasing is off, but without good pics of the board and related components, I can't tell why.

If you've double checked resistors, checked for solder bridges/shorts between pins or other pads, then try injecting a signal and measure the level at the different stages. Start with a 100mV sine, 1KHz, right into the instrument jack. Turn the gain all the way down, output pot all the way up. Check AC signal voltage at each stage.

Also, post pics if possible.

I checked all resistors twice, today and they all seem o.k. I'll post some pics later today.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 26, 2013, 05:34:44 PM
Almost Done with my Black face and my White face I have a question. In the instructions it left out the "FIL" pads do I just solder some wire to those pads? or I do not need them?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 26, 2013, 06:01:13 PM
Yes, connect the filament pads. Any two conductor wire will work, I used a pair of solid 18ga twisted together.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 26, 2013, 10:46:08 PM
Who sells the OEP transformers in USA?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 27, 2013, 01:35:39 AM
Newark.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 27, 2013, 01:54:58 AM
Rodney I'm gonna shoot you a pm...but for now I'll ask another question. Seeing as how this pre has no lighting indication is there a test procedure to make sure everything is working upon initial startup?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tonycamp on September 27, 2013, 02:50:21 AM
Hi Rodney, i've been mia on this thread for a bit, been cutting my teeth on a lot of projects possessing lower voltages ;D love the way everyones been contributing to smoothing the bumps out of this unique 500 tube pre project! I should be starting my pair soon, but mostly wanted to chime in to say congrats on being a new Dad!

T
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 27, 2013, 11:50:05 AM
Haha, thanks tony!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 27, 2013, 11:57:13 AM
Toure, some people are lucky enough/brave enough to just plug it in and start running signal through it. I recommend powering the 24v rail alone and measuring the hv output to make sure it's working properly.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on September 28, 2013, 02:10:48 PM
are there any wattage specs for the resitors?  i have all 1/4w resisters.   r31 on the pcb is bigger... is 1/4w ok here?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on September 28, 2013, 06:11:09 PM
R31 was specced at 2W for the original G9, but I haven't the slightest clue why. It really only needs to be 1/4W.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on September 29, 2013, 03:40:06 PM
 I had the same question , a short in the tube or the ht psu would stress that resistor while it drained the reservoir and smoothing caps but i don't know how to calculate what is appropriate
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 30, 2013, 02:08:35 AM
had my fingers crossed but i got the low whining/hum some have also experienced
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on September 30, 2013, 12:08:36 PM
Yeah so I tried again this morning and there is noticeable hum seems to die out a little bit with the filter set to 150Hz but it's still there. So do I need that rodney cap or is it the tubes? I ordered my tubes brand new as a matched pair with noise check. So the only thing they couldn't do was burn in. I don't know what burn in noise would sound like so I'm left to assume something is off.

Looking at the schematic am I correct to assume I check the HV Out at the molex connector closest to the tube?

My tubes heat up and nothing is smoking or burnt so kinda drifting at this point... :-\
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 01, 2013, 12:46:09 AM
Yes, the 'Rodney' cap is required to make the converter run smoothly.

Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 01:15:17 AM
so is that the source of my noise problem? and where do i get the Rodney Cap?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 07:18:05 PM
Just thought Id post pictures of my build so I can get some help with this annoying low but present hum. Don't know how to put all the pictures in 1 post so I will take up a few post
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 07:19:09 PM
Top View
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 07:22:18 PM
HV board with Cap installed across R503 and R504
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 07:23:52 PM
I added small spacers so my board wouldn't be grounded to the metal plate
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 01, 2013, 07:28:03 PM
I also can verify that the cart that is accurate although I added WIMA caps where ever I could so Mouser may not have all the WIMAs but TAW Electronics does
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 02, 2013, 01:17:56 PM
Quote
HV board with Cap installed across R503 and R504

put the cap across R503 and R502 as shown in pictures by bruce on side 3 of this thread, reply 45.
Might solve your hum-problem.

Cheers
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 03, 2013, 10:44:21 PM
Quote
HV board with Cap installed across R503 and R504

put the cap across R503 and R502 as shown in pictures by bruce on side 3 of this thread, reply 45.
Might solve your hum-problem.

Cheers
Chris

This solved it...I think I miss read the instructions...Both Pre's are working now..The Lundahls sound amazing with the RCA tubes I have installed in them. While the OeP sounds good with the Raytheon tubes there is simply not enough gain compared to my other pre's but it has a bunch of character to it. I think I am going to swap the OEP input for an EA2622 from CAPI. should get better results

My WHITE Face and My BLACK Face
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 03, 2013, 10:50:27 PM
I love seeing these finished pics... I like to think that someday, maybe one of these preamps will be used to record a hit in a small independent studio and launch some musician or band into stardom and in some why I will have played a small part in all that.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on October 04, 2013, 01:26:52 AM
K&K Audio, LL1538XL is $300.00 WOW
Doesn't list 5402
Can I find a better deal?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on October 04, 2013, 01:34:57 AM
http://www.kandkaudio.com/prices.html (http://www.kandkaudio.com/prices.html)

$94?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 04, 2013, 08:35:32 AM
another one  :) still waiting for some tubes.
but even with old tubes i had at hand the pre sounds fantastic!!
(http://www.chrisreiss.de/DIY/GIX_1.jpg)
(http://www.chrisreiss.de/DIY/GIX_2.jpg)
frequency-plot with old tubes i had lying around (made with fuzzmeasure).
I was surprised to see a clear bass rolloff, even with filters off

(http://www.chrisreiss.de/DIY/GIX_plot.png)

Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 04, 2013, 11:35:40 AM
another one  :) still waiting for some tubes.
but even with old tubes i had at hand the pre sounds fantastic!!
(http://www.chrisreiss.de/DIY/GIX_1.jpg)
(http://www.chrisreiss.de/DIY/GIX_2.jpg)
frequency-plot with old tubes i had lying around (made with fuzzmeasure).
I was surprised to see a clear bass rolloff, even with filters off

(http://www.chrisreiss.de/DIY/GIX_plot.png)

How are you able to attach multiple pictures in one post?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 04, 2013, 12:09:23 PM
You have to have the images hosted elsewhere like Imgur.com then add them in as image tags.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on October 04, 2013, 06:51:48 PM
BruceO,
Thanks, I have 4 kits to build,
It was late and I was looking in the wrong column.
Much better.

Toure14
The bass roll-off seems to be the standard complant of the G9.
IMHO, I don't think tubes will change the roll-off, If that's what your looking for.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 04, 2013, 07:16:26 PM
@Winetree: it was me who measured the bass roll off and i was not complaining. i was just surprised to see this special frequency response... i fact i really love the sound of the GIX :-)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Winetree on October 04, 2013, 08:44:34 PM
Great to hear and thanks for the graphs and pictures.
Looking forward to the build.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on October 06, 2013, 12:38:14 AM

(http://www.chrisreiss.de/DIY/GIX_2.jpg)
frequency-plot with old tubes i had lying around (made with fuzzmeasure).


Tubes so old, they're invisible!   :P ;D
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 06, 2013, 06:21:56 AM
Quote
Tubes so old, they're invisible!
That´s because i aimed for a truly transparent sounding unit  8)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on October 06, 2013, 08:12:13 AM
womp womp!!  lol
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tzman on October 06, 2013, 06:47:07 PM
Quote
HV board with Cap installed across R503 and R504

put the cap across R503 and R502 as shown in pictures by bruce on side 3 of this thread, reply 45.
Might solve your hum-problem.

Cheers
Chris

I just read the thread in preparation to my built and I think there's some confusing information about how to do the Rodney Cap Mod.
Reading the info in the thread I assume you have to put the cap across R503, R504. So looking at the schematic, this would mean to solder one end to R503 and the other end to R502. Just a Chris explained in my quote.
The picture at the start of this thread however has a red bar from R503 to R504. It's actually a picture from post 258 where Benny is describing how NOT to solder the cap.
Am I right in thinking that the picture in the first thread is bit confusing and that the right way to do the Rodney Cap is how Chris describes it in my quote?
I'm really looking forward to building this unit!

Thanks!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Toure14 on October 06, 2013, 07:16:43 PM
Quote
HV board with Cap installed across R503 and R504

put the cap across R503 and R502 as shown in pictures by bruce on side 3 of this thread, reply 45.
Might solve your hum-problem.

Cheers
Chris

I just read the thread in preparation to my built and I think there's some confusing information about how to do the Rodney Cap Mod.
Reading the info in the thread I assume you have to put the cap across R503, R504. So looking at the schematic, this would mean to solder one end to R503 and the other end to R502. Just a Chris explained in my quote.
The picture at the start of this thread however has a red bar from R503 to R504. It's actually a picture from post 258 where Benny is describing how NOT to solder the cap.
Am I right in thinking that the picture in the first thread is bit confusing and that the right way to do the Rodney Cap is how Chris describes it in my quote?
I'm really looking forward to building this unit!

Thanks!

That is exactly why mine was off at first because i got confused on that drawing
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 07, 2013, 06:05:01 AM
Quote
Am I right in thinking that the picture in the first thread is bit confusing and that the right way to do the Rodney Cap is how Chris describes it in my quote?

It is confusing. I think the graphic in the first post is not correct... or at least my units also didn´t work properly, until i changed the position of this cap as shown by bruce in reply#45 (page 3). maybe rodney can confirm the position and change the picture?

by the way: don´t get confused by the bass roll off! Its a 3.5 dB roll off from 100Hz to 30Hz. That´s something you´ll probably do during mixing anymway. I think i like this pre, because they take off some work from me ;)

kind regards
Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on October 07, 2013, 12:22:16 PM
So this cap is one of the last few remaining steps for me.  To clarify,  the instruction in step 9 of the first post is incorrect.   Instead,  the cap needs to connected between r502 and r503,  NOT r503 and r504.  correct?

also,  I can confirm the mouser cart i posted in post 234 seems correct,  except my electrolytic at c11 was too big.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 08, 2013, 09:21:57 PM
Okay, what you're trying to do with the cap mod is to bypass the feedback pin to ground. Here's the pic from the 1st post:
(http://i.imgur.com/3poOPeJ.png)
This picture is illustrating what pads to connect the cap across. If you put a resistor into R504's position the way the silk screen shows, then it's going to be hard to solder the cap to that point, so that's why some have made the mistake of essentially soldering the cap across R503 only. The next best place is to solder to the leg of R502, which is up in the air. That leg is connected to the pad you want to be connected to.

Here's a look at the copper layer, looking from top down:
(http://i.imgur.com/v9RTqUQ.png)

Hope that makes more sense.

***by the way, I received a PM from a fellow DIYer who has mentioned, and I thought it was clear, but again maybe it's not, that this is a bandaid to fix the instability problem with the converter. The feedback network is not an ideal layout and is picking up current noise from the ground, likely because there's a huge ground plane right under it on the bottom of the pcb. If I were a more experienced man, I wouldn't have designed it this way. Live and learn***
Title: Re: [BUILD] GIX-51X tube preamp
Post by: 100WChris on October 09, 2013, 05:17:01 AM
Hi Rodney!
Thanks for clarifying! Now i understand... when you are young and impatient, you don´t read precise, you just look at pictures and than you solder the cap "on top" of R504 and after that you wonder why you have a hum-problem  :D

Quote
is a bandaid to fix the instability problem
we have great sounding preamps! when it takes a bandaid to work... give me a bandaid :)

Chris
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 09, 2013, 12:21:00 PM
we have great sounding preamps! when it takes a bandaid to work... give me a bandaid :)

I agree! But I just wanted to make sure everyone understood that this is not the correct approach to fix this kind of problem. A better layout would be the way to handle it, but the boards were already produced and the masses were hungry. R&D on a poor mans budget is not an easy thing to do.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on October 09, 2013, 04:49:09 PM
Hope that makes more sense.

Perfect sense.  Thanks for clarifying.   Final stretch! just need to find a few spare minutes  :o
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on October 09, 2013, 05:16:33 PM
I thought I'd mention that on my builds I have those resistors on the underside of the board, with the cap on top. It's a bit cleaner looking.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: tzman on October 13, 2013, 08:07:28 AM
Okay, what you're trying to do with the cap mod is to bypass the feedback pin to ground. Here's the pic from the 1st post:
(http://i.imgur.com/3poOPeJ.png)
This picture is illustrating what pads to connect the cap across. If you put a resistor into R504's position the way the silk screen shows, then it's going to be hard to solder the cap to that point, so that's why some have made the mistake of essentially soldering the cap across R503 only. The next best place is to solder to the leg of R502, which is up in the air. That leg is connected to the pad you want to be connected to.

Here's a look at the copper layer, looking from top down:
(http://i.imgur.com/v9RTqUQ.png)

Hope that makes more sense.

***by the way, I received a PM from a fellow DIYer who has mentioned, and I thought it was clear, but again maybe it's not, that this is a bandaid to fix the instability problem with the converter. The feedback network is not an ideal layout and is picking up current noise from the ground, likely because there's a huge ground plane right under it on the bottom of the pcb. If I were a more experienced man, I wouldn't have designed it this way. Live and learn***

Thanks! Glad to know I wasn't going crazy :).
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on January 07, 2014, 01:06:23 AM
Is there a verified Mouser Cart for this project yet?   
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on January 07, 2014, 07:25:04 PM
http://groupdiy.com/index.php?topic=51020.msg686929;topicseen#msg686929
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mulletchuck on January 15, 2014, 03:33:18 AM
also,  I can confirm the mouser cart i posted in post 234 seems correct,  except my electrolytic at c11 was too big.

Can you elaborate on how C11 was too big?  pin spacing?  too large a diameter?  too tall?   

I copied your cart and updated it with parts that were in stock and also filled in the Customer Part Number fields for everything.  Other than selecting transformers and tubes, i'm ready to build this guy! 

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=A43D9472B6

I found this for C11: 

https://www.mouser.com/Search/ProductDetail.aspx?R=EEU-FR0J471Bvirtualkey66720000virtualkey667-EEU-FR0J471B
the case diameter & length was 6mm x 11mm, respectively, compared to the one in your cart, which was 12.5mm x 20mm. 

Can anyone explain the different transformer options and their relative color?    Also, where did you guys get tubes and which tubes, and why that particular tube?

also, in case anyone was curious about transformer prices and where to buy:
Code: [Select]
Input xfmr options

A262A2E $17.64 http://www.newark.com/oep-oxford-electrical-products/a262a2e/audio-frequency-transformer/dp/02M8356
CM-75101APC
LL1538 $82 each http://www.kandkaudio.com/prices.html
EA2622 $45 each http://classicapi.com/catalog/product_info.php?products_id=80
JT-110K-HPC $78.51ea http://www.jensen-transformers.com/prices.html
LL1576 $82 each http://www.kandkaudio.com/prices.html
LL1578 $82 each http://www.kandkaudio.com/prices.html

Output:
A262A3E $17.64 http://www.newark.com/oep-oxford-electrical-products/a262a3e/audio-frequency-transformer/dp/24M0686
LL5402 $65 each http://www.kandkaudio.com/prices.html
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on January 15, 2014, 01:34:41 PM
Can you elaborate on how C11 was too big?  pin spacing?  too large a diameter?  too tall?   

Diameter.   Just a little tight in that area of the pcb to fit that one in there.  You're replacement should fit fine.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on February 14, 2014, 12:33:01 PM
Hey Guys,

I powered up my GIX Tube preamps today but they're not cool :( no smoke no war but I really don't know exactly what's happening here...  I'm measuring that all values are 24V! I do not have any other value than 24V... The tubes values are the same too 24V pin 1 and the latest pin is -23V :(

Do you have any idea?

Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on February 14, 2014, 11:20:32 PM
It sound like the booster isn't operating. It runs off 24V so, it if there's a problem there, it will just be 24V. The two tube's heaters are in series and run off -24V. If everything in the tube circuit looks good, double check your boost converter. Likely failures are soldering of the surface mount components. Reflow them, make sure nothing is shorted or open. Make sure the controller IC is getting proper voltage from the regulator.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: jandoste on February 16, 2014, 07:59:50 AM
Thanks Rodney,

I'm checking everything but I can't see the problem  :-[ I just didn't solder yet the 0,1uf but I don't think that it is the problem...there is nothing shorting or open! maybe I solder some bad component for the booster?

(http://i1236.photobucket.com/albums/ff442/jandoste/photo_zps034e6617.jpg) (http://s1236.photobucket.com/user/jandoste/media/photo_zps034e6617.jpg.html)

cheers,

It sound like the booster isn't operating. It runs off 24V so, it if there's a problem there, it will just be 24V. The two tube's heaters are in series and run off -24V. If everything in the tube circuit looks good, double check your boost converter. Likely failures are soldering of the surface mount components. Reflow them, make sure nothing is shorted or open. Make sure the controller IC is getting proper voltage from the regulator.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 16, 2014, 10:54:46 PM
I would be interested in what is under that huge grey cap (which by the way you can use a 50V cap, it goes across only a couple of volts, you don't need high voltage film there, a little 50V mlcc cap works fine). 

However the output voltage is established by that voltage divider (under the huge grey cap), and if that is set up wrong you could basically turn off the psu (and get about 24V). 

So pay special attention to the R502,R503,R504.  As you can see on the schematic, R502 should be a very high value, and R503 in series with R504 should be a relatively low value.  That voltage divider produces the reference feedback voltage (at the junction of R504 and R502, 1.5 Volts as I recall) for the FB pin on the maxim chip which will keep pumping up the voltage until the FB is 1.5V.  If you have shorted that voltage divider, or mis-ordered the resistors that could explain your problem.

It is possible to fry the maxim chip if you have done something sparky or smokey (once I got a big spark while testing my 250V (probe slipped, fried the end of the probe too) and after that my Maxim Chip was fried and needed replacement).  I think I got about the symptoms you are describing when I did that so if that sounds familiar that is also a possibility.


Also, once you get it going, tell us how it works out without screening cans on the OEP's.  I think I read on the G9 that it can be a problem.  (Little mu-metal cans are available for those for a few bucks apiece.)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on February 16, 2014, 11:15:13 PM
It is possible for the TO-220 case on the bottom of the PSU to touch the pins, and short.  you need to avoid that.

Drain the caps (so you don't kill yourself) and remove the PSU, and measure the resistance from point A to Point B (it should be like 1 meg ish) and from point B to Point C (it should be like 6K ish). 
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on May 05, 2014, 06:06:12 PM
I finally finished up the build!  I have not powered up yet.  Can anyone recommend a good testing procedure?  Want to make sure things look good before i power on,  and i want to make sure the voltages are right before inserting tubes.  Thanks for any suggestions.

(http://i.imgur.com/6Ho9qOC.jpg)
Title: Re: [BUILD] GIX-51X tube preamp
Post by: bruce0 on May 05, 2014, 07:57:02 PM
Great build!

As far as testing... do a visual inspection first, and be careful when testing the B+ 

Make sure the MOSFET under the PSU is not touching the bottom of the PSU (or anything else).
Take a careful look for shorts on the Maxim chip, it is small.
When you measure the B+ voltage it is easy to short the test probe (I fried a Maxim that way).  I found best test points were before and after the jumper resistor under the bottom tube (but you can still short to the ground plane if you nick it so be careful).

My test procedure was to use cheap chinese 12AX7's as guinea pigs, and fire it up.  That was probably not the best way. 

I do have a simple suggestion though. Looking at your nice clean build I would like to point out that the filament power wires run directly under 120KHz power inductor on the PSU, and then touch the input transformer.  (Maybe not a good combination as the top and bottom of that inductor have the least shielding, and the input trafo has the most gain added to it's signal.)

Probably not a big deal.

The PSU is well designed, and does not need additional shielding, but I would re-route and tightly twist the wires.

Better practice (and routing used in Gemini's pictures) would go north then west between the tubes, giving the power inductor a wide berth.  And tightly twist the wires for good measure.

Nice looking front panel and knobs...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 07, 2014, 01:07:33 AM
Great looking build, QMP
Title: Re: [BUILD] GIX-51X tube preamp
Post by: qmp audio on May 22, 2014, 01:43:37 PM
Wow.  So i finally got the chance to test/install and experiment with these.  I'm really liking the sound of them.   excellent.
I haven't run mics through them yet but tried them as inserts on various line sources.  Ended up using them on my overhead stem in a mixing session last night.   I really liked them there.

Also tried running drum bus through them... which i really liked also.   I have some vocal sessions to do so im going to through up a couple mics and try some different combos into these pres for vox.

Thanks.  great project.  So glad I finally got them into service!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: weiss on November 24, 2014, 01:06:05 PM
I finally finished up the build!  I have not powered up yet.  Can anyone recommend a good testing procedure?  Want to make sure things look good before i power on,  and i want to make sure the voltages are right before inserting tubes.  Thanks for any suggestions.

Looking awesome !
Anyone having some pcb's/metalwork left of the gix kit? I'd be very interested.. ;)

greets
weiss
Title: Re: [BUILD] GIX-51X tube preamp
Post by: SKJGProject on May 26, 2015, 09:32:56 AM
anyone wants to sell his pre/ kit? i'm desperately looking for one!
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Mikaeel on July 09, 2015, 02:59:20 PM
Heh, I want to build this preamp too! Will it work with ribbon mic that has 250 ohm impedance?
I wonder, may be author can share drawings, pcb layout (for printing), or the files that he send to the company which had print the pcb?
I will be really grateful for this.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: maq3396 on December 25, 2015, 10:05:22 PM
Merry Christmas all!

Just finishing off my pair.
First one will have Lundahl's  for both in and out.

Wondering what opinions were of a complete OEP build or using the Ed Anderson input?

Cheers and have a great holiday season.
Mac
Title: Re: [BUILD] GIX-51X tube preamp
Post by: Scimitar on January 12, 2016, 03:30:25 PM
Anyone have any PCB's for these, or know where I might source some? I have built the 2U rack version (original Gyraf GIX) and would love to put a couple of these into my new 511 rack.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: shabtek on January 12, 2016, 11:18:06 PM
there are a few finished units in black market
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on May 28, 2016, 05:04:31 PM
I just (finally!)  put together my pair of GIX 51X units. Unfortunately, BOTH HV boosters are not working (only 24V output). I am definitely an SMD noob, but I used a DVM to check all the connections (e.g. pins 1-8 on the MAX1771 to their corresponding components, etc.) I double-checked everything I could -- the diode is working, the MOSFET looks good.

Any suggestions on where to start? I have a 51X 'extender,' but my shop with o-scope, etc. is unfortunately in a different location than my lone 51X rack & PS. Sigh.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on May 29, 2016, 05:51:23 PM
One thing is to check current across the rsense (smd resistor). If your MOSFET isn't grounded, it won't pull the inductor to ground and charge it. When the MOSFET turns off, the charge from the inductor is forced through the diode, into the hv cap.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on June 01, 2016, 12:01:23 AM
Thanks, Rodney.
 I re-flowed the solder joints on the MAX1771s and got both PS working. SMD ... bah!  ::)
They were both producing around 250VDC, so I had to fiddle with the FB resistors to get them down to ~240.

Both units are 'working' now, but output on both seems really weak.

A dynamic mic can only get to about -20db output with a loud 'hello' into the mic and both gains maxed, with slight distortion (as I'd expect on 10/10).

Using a guitar into the DI there is likewise a little distortion on 10/10, and the output signal only gets to about -15db.

The voltages on the 12AU7 tubes seem reasonable (240/84 on V2 plates, 160/81 on V1 plates). The tubes all test good on emission (I haven't tried them on the curve tracer, because that would require a bit of work currently).

I double checked and the both TR1s are A262A3A (1:6.45) and both TR2s are A262A2E (2:1).

Any suggestions what to check next?

Title: Re: [BUILD] GIX-51X tube preamp
Post by: gemini86 on June 01, 2016, 12:35:27 AM
Next I'd check feedback network. Make sure your values are correct. Try swapping tube positions, see what happens.

Also check through the official g9 thread, the circuit is the same, so troubleshooting carries over. The only unique trying about the GIX-51X is the form factor and the hv booster.
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on June 02, 2016, 04:18:49 PM
Thanks again, Rodney.  This would be a lot easier to troubleshoot  if I had my 51x rack & PS in the same room as my workbench.  :-\
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mhuss on June 11, 2016, 12:48:14 AM
I got a 7-pin XLR for my test jig from JS so I could bring my 51x PS down to the workbench and plug it in.  :)

On both units, in MIC mode with both gains maxed, I'm getting about 43 dBv gain (~48mv in / ~6v out) from the first grid of V1 (IN-SEC+) to the plate of V2 (OUT-PRI+) . Is this low or in the ballpark?

Thanks...
Title: Re: [BUILD] GIX-51X tube preamp
Post by: maq3396 on February 17, 2017, 02:30:48 AM
Having been working on this for some time now but am having issues with it.

When powered on it is initially quiet but over 10 seconds or so this buzz begins.

Buzz tends to oscillate a bit....sounds like it is changing gears!

Volume of the buzz does not change with the position of any of the front panel controls.

It passes audio very well

Redone all solder joints and isopropyl ' ed everything.

Any help would be appreciated as I love the sound of this!

https://soundcloud.com/mac-quantz/voice-170217-1mp3

Thanks
Mac
Title: Re: [BUILD] GIX-51X tube preamp
Post by: maq3396 on February 19, 2017, 01:19:09 PM
ok....seems to have resolved by itself!

Left it on overnight and the buzz has completely dissipated

Not the tubes as I tried a different set and they were very quiet as well.

Interesting as it has spent many hours on before!

At any rate I am a happy boy today!

Title: Re: [BUILD] GIX-51X tube preamp
Post by: delaystomper on July 22, 2017, 12:42:43 PM
Hi greetings to everyone ! I know i know im so behind on this project but i just recently joined the 500 series group  just got my rack a few days ago and im looking to build some modules . Im very interested on this gix-51x project , is there any one here that can tell me where to find the pcb's for this unit. I checked the schematic and layout but there is no pcb transfer on it . I know its been here for a while but not all of us were able to jump aboard on it earlier i will  appreciate any help
Thanks
Title: Re: [BUILD] GIX-51X tube preamp
Post by: supersonic on August 03, 2017, 08:07:38 AM
So how about the low frequency response in these ones?  Anyone with OEPs througout?
Title: Re: [BUILD] GIX-51X tube preamp
Post by: iturnknobs on June 29, 2018, 12:23:17 AM
Hello-

Any chance someone has an extra HV converter pcb or the files for it? Fingers crossed.

-Brian
Title: Re: [BUILD] GIX-51X tube preamp
Post by: mtw on December 11, 2018, 05:39:46 PM
I just bought a pair of half finished kits from another DIYer.

The additional bypass cap (the one on the underside of the board) that the seller sent me are too fat to fit between the PCB and the bracket. No problem, I bought some new ones.

I went to Mouser and got 10 of these: Multilayer Ceramic Capacitors MLCC - Leaded RAD 250V 0.1uF X7T 10% LS:5mm (http://"https://www.mouser.com/ProductDetail/810-FG24X7T2E104KNT6")

However, they look nothing like the round caps I've seen in others' builds. The specs are same (0.1ufF/ 100nF and 250V rated) but they look more like little bypass caps than the larger "disc" type.

Will these caps I bought work for this build?