The official G9 help thread

[haima]

DING!  ;D

another success story 

 

[ruckus328]

Today I modded my G9 with an "outsourced" HV-PSU. 100Hz hum completely disappeared. It makes no difference in noise, if the G9 is connected or not; it is dead-quite.  

One question - what's the little black box behind the regulator?  Bridge?


Seperate question to anyone that may know - any issue with using 25VA transformers?  Not sure what that's going to do to my voltages, as lower I go in VA, more my voltages will droop under load and not sure what that's going to do as far as the second step up transformer, if it will be enough to matter or not.

Also, anyone have any recomendations for a pilot light?  All the lamps I can find seem to be 100mA.  Thought about just running an LED with appropriate dropping resistor, but again, because of the transformer schemes, will lighten up the load an potentially increase the output voltage on the secondary xfmr (again though, don't know if the difference will be enough to matter)

 

[haima]

One question - what's the little black box behind the regulator?  Bridge?

Looks like it to me!

Also, anyone have any recomendations for a pilot light?  All the lamps I can find seem to be 100mA.  Thought about just running an LED with appropriate dropping resistor, but again, because of the transformer schemes, will lighten up the load an potentially increase the output voltage on the secondary xfmr (again though, don't know if the difference will be enough to matter)

I've done that before- just pull the guts out of a incandescent pilot light, and hot glue a led in there (with appropriate dropping resistor). Works well.

 

[ruckus328]

I wasn't even thinking of going that route, just planned on using a panel mount LED from the get go.

Any idea if 25VA power xfmr's is ok?  I have them on hand.  I guess if noone knows I can just give it a try, worst case my rails dip and I have my answer.

 

[Dr-Mbogo]

One question - what's the little black box behind the regulator?  Bridge?

Yes! It is a bridge rectifier, I had lying around. Much easier for the connection on a vero board.

 

[marvelouzone]

ok, here's another long question...

I plan on using ecc88 on output stage. So far this is what I know:
Heaters: 6.3 volt 365ma.
My question on this is can I parallel off the output of d13-16(before 7812s)  to run an lm317 to adjust for 6.3v. Will the current from first transformer(secondaries 2*15 50va) be enough to power both regulators? If this is yes, can d13-d16 handle the current draw from both regulators? I believe they are 1 amp.

With using the ecc88, I believe the plate voltage needs to be below 130v if i'm not mistaken.
I seen somewhere in the forum that a resistor needed to be used, but cant seem to find the post now. My question is what value resistor would I need to drop to proper voltage, and were would I put it? Is there somewhere I could just drop it in on the board, or would I have to do something custom to make it work? A small explanation would be appreciated.

question about a tube.. .
1976 Mullard/Amperex A-Frame 6DJ8 ECC88

Anybody familiar with these? I have to admit I wasnt born in 76(I'm a younger DIY'er) ;D The tubes dont say mullard, but the seller says it has been confirmed by date codes GAO over B6I4 GA? over B6I1 they in-disputably were made in Great Briatain by the Blackburn Mullard. I can pick up a matched pair for 75usd Worth it? Whats the big deal with the A-frame if any? I have to admit, I have really little knowledge on tubes and some of there circuits..

last question.. Does 320v on c14 an 310v on c15 seem out of spec? Only reason i'm asking is because I built power supply offboard. I know the voltage regulator will start working once there is a load, but does that voltage seem high to start with? If it matters I used 2 of the triode dual capacitors 100+100 uf caps. So 200uf for c14 and 200uf for c15? good or bad?

 

[marvelouzone]

ok, here's another long question...

I plan on using ecc88 on output stage. So far this is what I know:
Heaters: 6.3 volt 365ma.
My question on this is can I parallel off the output of d13-16(before 7812s)  to run an lm317 to adjust for 6.3v. Will the current from first transformer(secondaries 2*15 50va) be enough to power both regulators? If this is yes, can d13-d16 handle the current draw from both regulators? I believe they are 1 amp.

With using the ecc88, I believe the plate voltage needs to be below 130v if i'm not mistaken.
I seen somewhere in the forum that a resistor needed to be used, but cant seem to find the post now. My question is what value resistor would I need to drop to proper voltage, and were would I put it? Is there somewhere I could just drop it in on the board, or would I have to do something custom to make it work? A small explanation would be appreciated.

question about a tube.. .
1976 Mullard/Amperex A-Frame 6DJ8 ECC88

Anybody familiar with these? I have to admit I wasnt born in 76(I'm a younger DIY'er) ;D The tubes dont say mullard, but the seller says it has been confirmed by date codes GAO over B6I4 GA? over B6I1 they in-disputably were made in Great Briatain by the Blackburn Mullard. I can pick up a matched pair for 75usd Worth it? Whats the big deal with the A-frame if any? I have to admit, I have really little knowledge on tubes and some of there circuits..

last question.. Does 320v on c14 an 310v on c15 seem out of spec? Only reason i'm asking is because I built power supply offboard. I know the voltage regulator will start working once there is a load, but does that voltage seem high to start with? If it matters I used 2 of the triode dual capacitors 100+100 uf caps. So 200uf for c14 and 200uf for c15? good or bad?

Can anyone help???

 

[jackies]

Why do you want to use ECC88? Maybe you should just build it with 12AU7?
I built mine with 12AU7, it works just fine.
You don't need any kind of expensive vintage tubes, regular kind of tubes will be good enough. Neither do you need a matched pair. Tube rolling is of course, fun, so once your preamp is working you can buy a few more different tubes and try and see for yourself if there would be any difference in sound and if you could find something you like/dislike.
310v without load is where it should be. (220*1.4=308)

 

[marvelouzone]

Why do you want to use ECC88? Maybe you should just build it with 12AU7?
I built mine with 12AU7, it works just fine.

I could be wrong, but my reasoning Is that I read other members say that ec88 gives 6 more db when used on the output stage. I plan on using 12au7 on input stage, just wanted to try something different on output stage.

So anybody have any recommendations on how to do this?

 

[audiophreak]

Hi,
  Here is a link to a thread you may want to read, - http://www.groupdiy.com/index.php?topic=9813.200  -  I have done the ECC88 mod as well as tried a different out put transformer and it all sounds good,
                         HOWEVER....
                                             I now have three G-9s and find for my taste I like the stock G-9 with 12AU7s in all positions

 Just my 2 cents   ;D

  EDIT :  with Lundahls in input and output

 

[ruckus328]

Guys, can anyone give me any insight as to the best method of grounding this thing?  Seems the way Jakob indicates to ground it on his page contradicts how I would normally do things.  Is there some reason to run Pin 1 on the xlr's to the board as opposed to chassis/star ground?  And which point on the main board should I pick up ground, the HV supply section I presume?  Any help would be appreciated.

 

[gyraf]

I star the ground on the PCB, at the ground-connection of inputs. And at the XLR's, I chassis-ground pin1 of the first input XLRf, and power-ground to the same point.

So yes, it isn't a "standard" star ground, but needs to be done this way to help grounding integrety on the PCB audio path, where it's most needed.

This scheme works like a charm on current-generation G9 pcb's.

Jakob E.

 

[ruckus328]

OK, so I'll try it the way you've indicated.  So Pin 1 of the first fem xlr goes to the main board (to the ground connection of the 3 pin connector on the main board).  Power ground from IEC goes to this same pin one on the xlr (basically Pin 1 on the first xlr is the star point).

But 3 questions - where should pin 1 on the other fem xlr go?  Not to the main board, correct?  Jump that over to pin one on the first xlr?

And what about the outputs?  Leave pin 1 floating on them?

Where should I pick up chassis ground to connect to pin 1?

Thanks

 

[marvelouzone]

I'm no guru here, So correct me if I'm wrong, but pin 1 from the chnl 1 input xlr should go to chassis ground. The easiest way for me to do chassis grnd is to get a bolt,2 washers,locking washer, and 2 nuts. Drill a hole through back of case. You want the hole to be same size as bolt, a little bigger wont hurt, but the snugger the better. scrape around the hole with a razor, or something to take paint off, you want bolt/washers to touch bare metal. Put washer on the bolt, and slide the bolt through the hole so that the head is on the outside of case. put locking washer on the shaft of the bolt on the inside of the case and put first nut on. tighten it down. get some ring terminals appropriate for your bolt and wire size. you can use one terminal if you like that you crimp all 3 ground wires in or you can use separate terminals. your choice. you want to attach your IEC(mains) ground, pin1 of input 1(female)xlr. and pcb ground to this bolt. put a washer and nut on the end and tighten down. I dont know if its frowned upon or not, but I usually put a glob of solder on the whole assembly(bolt, nuts, washers..) after everything is working and verified, to prevent any type of vibrations or movement from working bolts/nuts loose. Its also a good idea to tin your wire before you put it in the terminal to crimp, that way you can add a little solder and heat to it once its crimped to add a little mechanical and electrical reinforcement to the durability of the crimp/connection. Some of my techniques are probably overkill, but its nothing like finishing a build and then having to trace down a ground loop, so make sure all grounds are exceptional tight. If I missed something, or made a mistake feel free to correct me....

 

[audiophreak]

Hi ruckus328,

      On page 27 of this thread I posted a link to pix of my first G-9, you can see the green star ground wire I have on the inside of the rear panel.
    The Shield on pin 1 on the INPUT XLRs still goes to the designated pad on the PCB, AND is also wired to the Star Ground point along with the IEC Safety Ground.
 
  Thats what I did anyway, and it works for me  ;D

 

[ruckus328]

Hey guys, I got my unit up and running, however I'm having terrible noise/oscillation problems.  Noise floor is at about -50dbu with no signal.  Audiophreak - turns out I grounded my unit almost like you have yours, except I don't have the jumper wire between pin 1 of the input xlr's like you do (which creates a ground loop btw if you also have both of these pin 1's going to the main board) 

I have:
Mains ground to star ground bolt.
Pin 1 of each input xlr going to the main board
Pin 1 from only one of the input xlr's going to star ground bolt

It looks like you guys don't have pin 1 of the output xlr's grounded - is this correct?  Leave the outputs floating?

Dr-Mbogo - I tried figuring out how you have your main board/xlr's grounded, but I can't see any wires in the pic you posted going from either of those to the chassis/mains ground?

I'm going to go try the wire mod for the instrument jacks and report back.  I already have the 245V power supply off board so I don't know what else it could be.

Any ideas/suggestions are welcomed.  Thanks.

 

[Kingston]

Now that you already have the external B+ supply fix you can forget all the various voodoo ground tricks. Don't even try to follow the myriad of weird grounding instructions given for G9 as they will only confuse. one applies: the same one that applies for every single balanced audio unit you are already familiar with from other projects. Directly from rane instructions.

1. XLR pin1 all of them, whether that's input or output goes to your star ground, and nowhere else. Doesn't matter if you group them or take them all individually, as long as they all end up in that same point.

2. IEC safety ground goes to that point also.

3. B+ PSU output filter cap "ground" goes to star ground. This is where your whole unit references ground. Some people might tell you to take the first PSU filter cap to star instead, but there's rectifier crud still present past that point. That's why the PSU output filter cap is the better reference.

That's it. Nothing from the PCB touches star ground directly. None of the XLR pin1 touches the PCB.

Now you can start troubleshooting the real source of noise.

 

[ruckus328]

Kingston, check, check, and check on the pin 1's and IEC ground - it's how I have it now and how I would normally do it.  I have the output xlr's daisy chained and then to star ground, same with the inputs. 

Here's where I get fuzzy though - on the cap banks I have both the input filter cap's and output filter cap's grounds tied together and THEN going to my offboard power supply.  From there a ground wire runs back to my main board.  So I'm confused what to do here or how I should be doing it.  Ultimately though from what your saying I should be running a wire from the offboard power supply to my IEC ground, correct?  This is again how I would normally reference the unit to star ground (same way it's done in my sb4k layout for example).  Thanks.

 

[Kingston]

Here's where I get fuzzy though - on the cap banks I have both the input filter cap's and output filter cap's grounds tied together and THEN going to my offboard power supply.  From there a ground wire runs back to my main board.

From here (your PSU main out) goes one wire to star. Leave the filter caps be.

wait, do you really have an actual external B+ regulator, or are you just talking about having the filter caps off board, but the rest of the B+ circuit still on the main board? a picture says more th...

 

[ruckus328]

The whole B+ Supply is offboard.  The filter caps are the big JJ chassis mount type so they are right next door and wire to it.

http://dl.dropbox.com/u/4740474/G9/G9_PS.JPG