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Project Specific Discussions => Dynamic Processors => Topic started by: Gustav on May 16, 2014, 04:07:03 AM

Title: Retired:Symmetrical FET
Post by: Gustav on May 16, 2014, 04:07:03 AM
PCB for an 1178/stereo 1176 circuit, designed with the help of the great people on this forum.

Left for archiving.


 Schematic  (https://pcbgrinder.com/download/Symmetrical-Fet/Sym_FET_Schem.pdf) -  (errata - 30K should be 30R1)

 BOM  (https://pcbgrinder.com/download/Symmetrical-Fet/Sym-Fet-BOM.pdf) In addition to the list, I have been using NOS NPD5566 dual JFETs.

 Board Layout  (https://pcbgrinder.com/download/Symmetrical-Fet/Symmetrical-Fet-board.pdf)

(https://pcbgrinder.com/image/cache/data/Finished/Symmetrical-FET-500x500.gif)

(https://pcbgrinder.com/image/cache/data/Stuffed_Boards/1178-stuffed-500x500.gif)


Hope you enjoy!

Gustav

Title: Re: Symmetrical FET
Post by: Greg S. on June 30, 2014, 05:12:49 PM
Does someone have a Backside Pic showing the connection of the Com ports between the main pcb and the gr/meter board?

thx
Title: Re: Symmetrical FET
Post by: Greg S. on July 01, 2014, 09:58:43 AM
I belive, i got it..

I prefer 3 IDC 8-pin connectors


Layout Com2!

https://pcbgrinder.com/download/Symmetrical-Fet/Symmetrical-Fet-board.pdf

There is a single pin at the Main-Board's right side upper line which should be wired to the GR-Board's right side down line

This is the key!

 ::)

Title: Re: Symmetrical FET
Post by: Gustav on July 01, 2014, 02:41:20 PM
Greg, if you check the board drawing, they are "lined up", but I had this connecting in mind, which should make it obvious.

- Will be adding some more documentation to this project, when I get the correct size pots :)

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on July 01, 2014, 03:10:29 PM
Hi G!

Check both rightsided Pins!
Title: Re: Symmetrical FET
Post by: Gustav on July 01, 2014, 03:18:16 PM
Hi G!

Check both rightsided Pins!

Sure, but it could be a trap!

Its still easier to just "think like the connector" I posted. Not much wizardry to it, really.  :)

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on July 01, 2014, 03:39:50 PM
...
Always Funny... Sunny   ;D ;D

Title: Re: Symmetrical FET
Post by: Greg S. on July 02, 2014, 02:02:49 AM
I got the last missing parts today, so I can complete the 1178.. We will see G.


Suggestions for the next Revision:
   
   2 Meter light circuits at the PSU
   Com1-3 Pin inscription

Would be great G!

In the End it's DIY and I simply love building those boxes
Title: Re: Symmetrical FET
Post by: Gustav on July 02, 2014, 07:58:47 AM
...
Always Funny... Sunny   ;D ;D

Its hard to foresee what people do to ones design - This was designed for the angled connector to avoid wiring completely :)

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on July 02, 2014, 10:28:24 AM
Almost there,,

Some features are still not done.. (holes at the front) ..

But as far as the Com-Port-Problem/Discussion isn't solved, I wont start it up!

But it's already quite good looking..

 ;)
Title: Re: Symmetrical FET
Post by: Gustav on July 02, 2014, 12:20:51 PM
as far as the Com-Port-Problem/Discussion isn't solved, I wont start it up!


Sorry, I thought you already worked it out from the picture I posted.

Heres a different angle showing how the connector hooks up from the main board to the control board. Since you're not using the intended connector, just lay out how your chosen connectors/wires would follow the same path...

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on July 03, 2014, 03:56:59 AM
It's working.
my Com's were right!  8)

My NPD5566 seem to work too..
(Have to calibrate. 'em)

I will match some BF245a's just for fun and try 'em too..
Which Fet's did you tried?

No Hum, thats fine.

Is there a reason, why you changed the Input Pot to 1K (original get's 10K)
I got a 22k lin at the Attack, 25k are hard to find

Changing the ratios didn't have so much effect..

I got a bit white noise at the outs,.
The noise is always there, it's not effected by some pots!
HMMM, thinking about that!
Will rewire by using shielded Cables

Next up:
The both Elcos at the outs are free to choose from 2200uF-4700uF
The G-1176 got 470uF, might you comment on that G?
Title: Re: Symmetrical FET
Post by: Gustav on July 03, 2014, 06:36:16 AM
It's working.
my Com's were right!  8)

My NPD5566 seem to work too..
(Have to calibrate. 'em)

The pictures you sent me by mail were fakes, but I will be checking some of those too

I will match some BF245a's just for fun and try 'em too..
Which Fet's did you tried?


Only original NPD5566 so far. I have a stack of different types, I Will be doing experiments with before offering a kit.

No Hum, thats fine.

Is there a reason, why you changed the Input Pot to 1K (original get's 10K)
I got a 22k lin at the Attack, 25k are hard to find

The original is 1K, so I can't comment on a reason to change it from 10K.

22K/25K - Different series land on different values (Alpha pots land on 25K, OMEG on 22K), but I consider those identical.

Changing the ratios didn't have so much effect..

Maybe the transistor you used isn't a good choice, or maybe your lack of calibration plays a part. Worked perfectly here.

I got a bit white noise at the outs,.
The noise is always there, it's not effected by some pots!
HMMM, thinking about that!
Will rewire by using shielded Cables

Since you're using alternative wiring, you may experience alternative results from my prototypes. Measurements were fine here.

Next up:
The both Elcos at the outs are free to choose from 2200uF-4700uF
The G-1176 got 470uF, might you comment on that G?

Its what I had laying around/tested it with, so the note stayed on the silk screen. You could probably ask the same for a few other values in the build. You may not even need it, and if you run transformerless, bigger can't hurt in case your signal should see some ginormeous impedance..

Gustav
Title: Re: Symmetrical FET
Post by: gyraf on July 03, 2014, 09:58:22 AM

Changing the ratios didn't have so much effect..

Maybe the transistor you used isn't a good choice, or maybe your lack of calibration plays a part. Worked perfectly here.

Remember that this circuit lowers the threshold when you select lower ratio - trying to keep average GR the same. This means that you can't expect levels to change significantly with ratio - measure real ratio by comparing input level increase (initially over-threshold) of say 10dB to output increase dB.

Jakob E.
Title: Re: Symmetrical FET
Post by: Greg S. on July 19, 2014, 05:01:41 AM

Changing the ratios didn't have so much effect..

Maybe the transistor you used isn't a good choice, or maybe your lack of calibration plays a part. Worked perfectly here.

Remember that this circuit lowers the threshold when you select lower ratio - trying to keep average GR the same. This means that you can't expect levels to change significantly with ratio - measure real ratio by comparing input level increase (initially over-threshold) of say 10dB to output increase dB.

Jakob E.

Dear Jakob,,

I finally found yesterday a really good pair of BF245a's, Mason's Site was very helpfull.. thx Mason..

The effect of compression is not as good a pair of Gustav's 1176ers.(Rev V/K, sold out meanwhile)

Do you have any suggestions for other Fet's?
BF245B? 2N5457?

Or what did you used?



Title: Re: Symmetrical FET
Post by: Gustav on July 19, 2014, 12:27:15 PM

Changing the ratios didn't have so much effect..

Maybe the transistor you used isn't a good choice, or maybe your lack of calibration plays a part. Worked perfectly here.

Remember that this circuit lowers the threshold when you select lower ratio - trying to keep average GR the same. This means that you can't expect levels to change significantly with ratio - measure real ratio by comparing input level increase (initially over-threshold) of say 10dB to output increase dB.

Jakob E.

Dear Jakob,,

I finally found yesterday a really good pair of BF245a's, Mason's Site was very helpfull.. thx Mason..

The effect of compression is not as good a pair of Gustav's 1176ers.(Rev V/K, sold out meanwhile)

Do you have any suggestions for other Fet's?
BF245B? 2N5457?

Or what did you used?

Jakob didn't build this unit, so he would have no way of answering this.

As mentioned, I only built it with the original NPD5566 thus far, but I will be trying out some different FETs, after I get an order of pots in.

Did the fake you tried out not work?

Gustav

(And a side note, Phat Phet=my final 1176 board revision, so not sold out but updated)
Title: Re: Symmetrical FET
Post by: Greg S. on July 20, 2014, 08:02:13 AM
I meant your early 1176er that are close to Mnats layout G.
I don't have any others 76ers PCB's..

This is what I got for my three NPD5566 B0923 from eBay - 5bugs each..
They seem to work, Both Channels are pretty close-up, but the all div to each other..




Title: Re: Symmetrical FET
Post by: Greg S. on July 20, 2014, 08:04:17 AM
as jpg
Title: Re: Symmetrical FET
Post by: Greg S. on July 20, 2014, 11:01:18 AM
working now!!!  NPD5566 is doing what it should.

by the way, 3 different Ratios, right?

I will hard-wire anything,
hope, my tiny white noise is affected by the molex I used..
but in the end, it's all right..

THX for all that were part of this Project.

It's been a great Pleasure and a Privileg for me!


Special THX to Gustav..

=)
Title: Re: Symmetrical FET
Post by: Greg S. on August 13, 2014, 06:50:46 PM
I reworked the Frontpanel and the Wirings, no more Molex and I added a MU-Shield for the Transformer!

Noise got less..  :)

But there is still some at one channel, but I will get this!


Title: Re: Symmetrical FET
Post by: Greg S. on August 13, 2014, 06:51:21 PM
pic 2
Title: Re: Symmetrical FET
Post by: G-Sun on August 29, 2014, 03:39:25 AM
Is the symmetrical fet a cleaner version than the usual v.D?
How well is the stereo-link behaving? Good enough for mastering?

If I want some color, what would I consider then?
Title: Re: Symmetrical FET
Post by: gyraf on August 29, 2014, 05:10:06 AM
This is basically a 1178. It will give VERY good stereo tracking compared to any 1176-setup you can make.

And yes, it's somewhat cleaner than the standard rev. F - but most perceived "sound" still comes from the FET gain-reduction, which is the same as 1176 through all revisions (excluding early non-LN-version 1176's)

Jakob E.
Title: Re: Symmetrical FET
Post by: rob_gould on August 29, 2014, 08:37:23 AM

Any reason why this won't fit into 1RU if small meters are used Gustav?

Thanks,

Rob
Title: Re: Symmetrical FET
Post by: Gustav on August 29, 2014, 10:19:12 AM

Any reason why this won't fit into 1RU if small meters are used Gustav?

Thanks,

Rob

I havent checked it, but no - no reason. The front panel board is not too tall for 1RU, so you should be able to mount it as is.

I was planning on building both a 1 and 2RU this month, when my pots for the kits arrived, but I currently have a suspicion they missed my order, and I will be waiting another 3 months :)

They have dual gang 4M7 pots at Reichelt, which will work with a little leg bending for the PCB.

Gustav.
Title: Re: Symmetrical FET
Post by: rob_gould on August 29, 2014, 10:30:04 AM

Any reason why this won't fit into 1RU if small meters are used Gustav?

Thanks,

Rob

I havent checked it, but no - no reason. The front panel board is not too tall for 1RU, so you should be able to mount it as is.

I was planning on building both a 1 and 2RU this month, when my pots for the kits arrived, but I currently have a suspicion they missed my order, and I will be waiting another 3 months :)

They have dual gang 4M7 pots at Reichelt, which will work with a little leg bending for the PCB.

Gustav.

Tak!  Seems like a straightforward and fairly cheap project so I think I'll give it a go when I've cleared a bit of backlog...
Title: Re: Symmetrical FET
Post by: G-Sun on September 03, 2014, 11:28:57 AM
This project is just what I'm looking for,
except for maybe one one thing: Sidechain hi-pass-filter
Isn't that important for mastering and 2bus duties?
Title: Re: Symmetrical FET
Post by: G-Sun on September 04, 2014, 07:17:09 AM
So, I guess drumbus and masterbus is not the typical application for the Symmetrical FET.
I just need to rethink my setup a little.
Title: Re: Symmetrical FET
Post by: Gustav on September 04, 2014, 03:23:06 PM
So, I guess drumbus and masterbus is not the typical application for the Symmetrical FET.
I just need to rethink my setup a little.


I feel the addition of a side chain high pass is a symptom of a problem using the gear in 99 out of 100 times, but opinions will vary on that.

I would not use the symmetrical FET in a mastering type set-up, but who knows - someone might love it in that application.

I think these kinds of questions would be better suited for "Studio A"!?

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on September 04, 2014, 03:53:57 PM
DEFO G!
Title: Re: Symmetrical FET
Post by: gyraf on September 05, 2014, 04:01:12 AM
I feel the addition of a side chain high pass is a symptom of a problem using the gear in 99 out of 100 times

+1
Title: Re: Symmetrical FET
Post by: G-Sun on September 05, 2014, 04:52:08 AM
I feel the addition of a side chain high pass is a symptom of a problem using the gear in 99 out of 100 times, but opinions will vary on that.
..
I think these kinds of questions would be better suited for "Studio A"!?
Ok, thanks!
So, instead of thinking bus-gluing with low ratio, I could think more bus limiting with higher ratio? Like 8:1 on drumbus or masterbus?
(Sorry for wrong subforum, but I am talking about how to use the gear in question)
Title: Re: Symmetrical FET
Post by: Deepdark on September 05, 2014, 06:33:07 AM
I think you could give it a try whatever the situation and see if it met your needs. You could use it acs guitar buss or vox buss, too. Why not using it on your master chan to glue everything together :) i always put a Compressor on my master chan with low ratio to glue and lower the residual peaks :)
Title: Re: Symmetrical FET
Post by: Gustav on September 05, 2014, 09:01:17 AM
I think you could give it a try

This!

Its an 1178 clone, and the transformers are different - you can google some opinions on the original unit, or you might be able to rent one, but no matter how many posts you construct on the subject of gear selection, you will not be able to get a Gearslutz type of answer to the questions you are posting.

If you are skilled enough to venture into mastering, you could apply your skills to make a qualified guess about what will work for you, but if you are really unsure, the best route might be to audition and buy a commercial unit.

Hope that helps :)

Gustav
Title: Re: Symmetrical FET
Post by: Deepdark on September 05, 2014, 09:24:13 AM
it's always a matter of tastes, too. I saw a lot of time people using this kind of gear in the mastering process with indredible result. I'm sure the design is pretty good here and and could works on a lot of sources. Just my 0.02 :)

by the way, good job Gustav and Jakob!?
Title: Re: Symmetrical FET
Post by: G-Sun on September 07, 2014, 05:41:44 AM
Thanks folks!
(I'm not that skilled that I qualify for mastering, but I am stupid enough. So, it may happen anyway :) )

Ratio: I'm a little confused. Is 2:1 supported? I see 4, 8, 12, 20 (as original) on Gustavs frontpanel pdf (https://pcbgrinder.com/download/PanelPDF/SYMFET2RU.pdf) )

I rarely use anything above 8:1 ..
Title: Re: Symmetrical FET
Post by: Gustav on September 07, 2014, 06:29:51 AM
Is 2:1 supported?

Nope.

Gustav
Title: Re: Symmetrical FET
Post by: G-Sun on September 07, 2014, 07:44:27 AM
Is it a problem modding it according to this schemo (http://groupdiy.com/index.php?action=dlattach;topic=47168.0;attach=11207;image) ?
I believe I'd prefer 2:1 4:1 8:1 and 12:1

I should look up Igors F76 shcemo. Anybody who has it?
Title: Re: Symmetrical FET
Post by: Gustav on September 07, 2014, 08:22:47 AM
Is it a problem modding it according to...

You could compare the schematics as a start (at least the part you have to the 1178)

Also, I generally recommend that people build something, make sure they have it working as intended and make observations (with their ears) about the stock circuit before doing modifications.

Hope that helps.

Gustav
Title: Re: Symmetrical FET
Post by: G-Sun on September 07, 2014, 09:51:44 AM
You could compare the schematics as a start (at least the part you have to the 1178)

Also, I generally recommend that people build something, make sure they have it working as intended and make observations (with their ears) about the stock circuit before doing modifications.
Thanks for the tips!
I need to decide on what projects to go for and what frontplates to order (with what text).
I demoed IK Multimedias versions of different compressors, to give me a better clue about which direction to go. Now I'm just more confused.
I'll not clutter this build-thread with more of my confusion.
I'll start a post in Studio A :)

Edit: http://www.gearslutz.com/board/so-much-gear-so-little-time/953064-one-man-production-workflow-gear.html#post10396593
Title: Re: Symmetrical FET
Post by: G-Sun on September 29, 2014, 11:55:25 AM
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?
Title: Re: Symmetrical FET
Post by: Gustav on September 29, 2014, 12:13:46 PM
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.

Alpha seems to have lost my original order for pots, so I have to wait another 3 months, which is why I took it down.

Gustav
Title: Re: Symmetrical FET
Post by: G-Sun on September 29, 2014, 03:13:27 PM
Gustav: I see the kit is removed from you shop.
Is it still coming, or has there been some change of plans?

I haven't looked through the BOM closely. Many hard-to-find items/ many vendors if buying just a pcb?

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.

Alpha seems to have lost my original order for pots, so I have to wait another 3 months, which is why I took it down.

Gustav
Ok, thanks for the info!
Title: Re: Symmetrical FET
Post by: djfatum on October 14, 2014, 12:01:40 PM
potentiometer 4M7 anyone knows where it can be purchased ?? :-[
Title: Re: Symmetrical FET
Post by: G-Sun on October 14, 2014, 12:09:37 PM

Just one "hard-to-find" part - 4M7 dual gang pot, which can be found at Reichelt.
Gustav
Title: Re: Symmetrical FET
Post by: djfatum on October 14, 2014, 01:23:18 PM
I found only the mono version   :-[
Title: Re: Symmetrical FET
Post by: Gustav on October 14, 2014, 01:36:27 PM
I found only the mono version   :-[

PO4S-LIN 4,7M

Gustav
Title: Re: Symmetrical FET
Post by: djfatum on October 14, 2014, 03:40:27 PM
Thank you for your help   8)

Andrzej
Title: Re: Symmetrical FET
Post by: Wayne on October 15, 2014, 11:46:46 AM
Hi All

Total Noob question, Im still learning but im getting there... slowly! Ive been putting one of these boards together, I'm just putting in the last parts and was wondering about the values for the program regulator resistors - is there a formula to working these out that i am missing?

Many thanks


Title: Re: Symmetrical FET
Post by: gyraf on October 15, 2014, 12:37:45 PM
Quote
" program regulator resistors"

What do you mean?

Jakob E.
Title: Re: Symmetrical FET
Post by: Wayne on October 15, 2014, 12:43:35 PM
ahh i think i might have worked it out, on this board in the PSU section there is 4 resistors marked K and R with no values, but having looked a touch harder, from what i understand they are the resistors for setting the output voltage for the 317 and 377.... (first time I've done this part my self)

So for what i understand the out put voltage of these needs to be +18v and -18

would a value for R be 240ohm and K be 3k3...?

Cheers
Title: Re: Symmetrical FET
Post by: djfatum on October 15, 2014, 04:11:02 PM
calculator  :)

http://www.a-ling.net/alweb/hifi/lm317_lm337_reg_calc/lm317_lm337_reg.htm (http://www.a-ling.net/alweb/hifi/lm317_lm337_reg_calc/lm317_lm337_reg.htm)
Title: Re: Symmetrical FET
Post by: Wayne on November 04, 2014, 12:36:39 PM
cool so just powered up my build seems to be working :)

Anyone go any tips on how I calibrate the VU's on this?

Cheers

Wayne


Title: Re: Symmetrical FET
Post by: Gustav on November 05, 2014, 11:12:55 AM
cool so just powered up my build seems to be working :)

Anyone go any tips on how I calibrate the VU's on this?

Cheers

Wayne

I just did some work on the assembly guide, and Ill do a small calibration guide.

You should be able to use the 1178 manual for stringent calibration, but to get you moving..

In the section of the PCB marked "meter circuit", you should see 4 trimmers.

The ones marked "ZERO (R/L respectively)" at coordinates S2 and S8 will adjust the 0dB point on your VU.

The ones marked "TRACK (R/L respectively) at coordinates S4 and S7 will adjust the meter throw/tracking.

The two remaining trimmers marked "Q-BIAS (R/L respectively) at coordinates A5 and D5 set the FET bias.

Gustav

Title: Re: Symmetrical FET
Post by: Greg S. on December 13, 2014, 09:05:32 AM
Hi Guys,
finally I wanted to denoise my early built Sym Fet.

Does someone know,
Are there some wrong printed parts?

1  At The Pre Amp e.g. are 3 30K for each Channel,
Gustav told me to use 30R, same at his built guide.
2  Why are there 2200-4700uF at the Lundahls?
I mean, the 1176LN got there 470uF
The original didn't got one!
I mean, never ever use a C direct into the Signalpath,
If you want to block DC, use something like this



3  Did some checked why there are Labeled 4 Ratios and at the Lorlins got 3 Connctions?
Title: Re: Symmetrical FET
Post by: Gustav on December 13, 2014, 12:33:09 PM
Hi Guys,
finally I wanted to denoise my early built Sym Fet.

Pots differ from my set-up, may be a wiring issue, and it may be worth looking at the grounding done, toroid set-up, heavier connection for ground from XLR, see if you can tap into the board on any problem area and draw a clean ground to chassis, etc. I have no discernible noise in my builds, so it should be possible with the board you used and implementation of similar wiring and mounting.

Does someone know,
Are there some wrong printed parts?

1  At The Pre Amp e.g. are 3 30K for each Channel,
Gustav told me to use 30R, same at his built guide.

Because its printed wrong on the silk screen, it was corrected in the info, yes.

2  Why are there 2200-4700uF at the Lundahls?
I mean, the 1176LN got there 470uF
The original didn't got one!

You can probably use a lower value, but its just to make sure we block any DC, and avoid creating an audible filter at the same time. Its what I had when I tried it out.

I mean, never ever use a C direct into the Signalpath,

C = electrolytic capacitor?

Never, like the output of 1176 you mentioned? :)

I also added electrolytic capacitors in front of the pots to avoid scratchy pots (google it, seems to be a common problem on the original). You may leave those out too for a more pure path, if you wish. Make sure to check for DC on the output.

3  Did some checked why there are Labeled 4 Ratios and at the Lorlins got 3 Connctions?

Sounds like you referred to the original schematic for the output cap, you could easily do the same for this.

Hope that helps!

Gustav
Title: Re: Symmetrical FET
Post by: just.sounds on February 02, 2015, 09:18:05 AM
I almost completed one of these puppys. Nice sound !! on one channel....

One problem one channel seems to POP the output cap (before the trafo) one output cap was making acousitical sound and another one started to leak fluid....

Any guess what could cause this? The input/gain reduction on this channel is looking fine. Opamp is fine output transistors are checked and replaced so there must be a short somewhere. but i can not find it yet.

Title: Re: Symmetrical FET
Post by: mike76 on March 25, 2015, 03:59:02 AM
Hi,

I was wondering how much current is necessary for the device? Would approx. 300mA be enough? How would I get to know how much is enough (from theory or calculating)?

Thanks guys and girls.
Title: Re: Symmetrical FET
Post by: Gustav on March 25, 2015, 05:09:33 AM
I almost completed one of these puppys. Nice sound !! on one channel....

One problem one channel seems to POP the output cap (before the trafo) one output cap was making acousitical sound and another one started to leak fluid....

Any guess what could cause this? The input/gain reduction on this channel is looking fine. Opamp is fine output transistors are checked and replaced so there must be a short somewhere. but i can not find it yet.

Are the transformers mounted? And did you measure DC at the output on the channel with a problem ? (before the blocking cap).

Gustav
Title: Re: Symmetrical FET
Post by: Gustav on March 25, 2015, 05:12:05 AM
Hi,

I was wondering how much current is necessary for the device? Would approx. 300mA be enough? How would I get to know how much is enough (from theory or calculating)?

Thanks guys and girls.

You could measure the current draw on the circuit. I can't remember it to be honest, and it doesnt seem like I made a note of it.

Any reason why you need the exact draw?

Gustav
Title: Re: Symmetrical FET
Post by: mike76 on March 25, 2015, 06:01:52 AM
HI Gustav,

I'm planning the built, I have an 2x0,3A toroid at home and I'm not sure, if that would be enough.
Title: Re: Symmetrical FET
Post by: Greg S. on March 25, 2015, 05:54:57 PM
I use this one here
http://www.conrad.de/ce/de/product/605767/Ringkern-Transformator-230-V-2-x-15-V-2-x-100-A-30-VA-Sedlbauer
Remember to change the LM317, lm337 resistors for getting +-15V
Title: Re: Symmetrical FET
Post by: mike76 on March 26, 2015, 02:26:11 AM
Thanks for your reply.  I will try the transformer I already habe. Since it is2x18, no calculation neccesary :)


If there is a demand, I could post a complete BOM from Reichelt
Title: Re: Symmetrical FET
Post by: XAXAU on March 27, 2015, 05:18:53 PM
Is 2:1 supported?

Nope.

Gustav
So it's not possible to change out resistors to get different ratios? The 2:1 would be a very useful one!  8)
Title: Re: Symmetrical FET
Post by: Gustav on March 28, 2015, 04:00:50 AM
Is 2:1 supported?

Nope.

Gustav
So it's not possible to change out resistors to get different ratios? The 2:1 would be a very useful one!  8)

Its probably possible, but you would have to figure it out for yourself.

Gustav
Title: Re: Symmetrical FET
Post by: mike76 on April 13, 2015, 10:25:42 AM
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike
Title: Re: Symmetrical FET
Post by: Gustav on April 13, 2015, 11:10:03 AM
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike

200/220pF, makes no difference here.  If it says 200 on the PCB, I must have made a mistake on the silk screen.

Hope that helps :)

Gustav
Title: Re: Symmetrical FET
Post by: mike76 on April 13, 2015, 11:46:20 AM
Hi,

there a two different values in the BOM and on the PCB for the Input-Amps. The BOM contains 220pF ceramic capacitors, on the PCB is 200pF printed. What are the right values?

By the way, it is a solid PCB, very easy to work with and feels like high quality.

Thank,

Mike

200/220pF, makes no difference here.  If it says 200 on the PCB, I must have made a mistake on the silk screen.

Hope that helps :)

Gustav

It did, thanks :)
Title: Re: Symmetrical FET
Post by: mike76 on April 19, 2015, 09:58:49 AM
Is there any explanation, why the test points are different in voltage although using the same resistors? I've got -18,5V and 17,8V on the other side.

I suppose, as I am a newbie, the values should be as equal as possible? Maybe because of tolerances?
Title: Re: Symmetrical FET
Post by: Greg S. on April 19, 2015, 10:41:27 AM
no, should be quite closer to +-18V or as I prefer +-15,
eg: +18V > 220R and 2,95k(3k)
        +15V > 220R and 2k42(2k4)
check the Ac's coming from the Transformer, if they are the same, check the resistors at the ladder Filter.
Otherwise check the LM317 and LM337
Title: Re: Symmetrical FET
Post by: mike76 on April 19, 2015, 11:16:16 AM
I'm confused. The transformer's ac is 2x20v, the resistors in the filter are the same. The difference ist about 0,5V, coming from the LM337. I used this one https://www.reichelt.de/ICs-LM-10-LM-999/LM-337-220/3/index.html?&ACTION=3&LA=5000&GROUP=A2151&GROUPID=5464&ARTICLE=10473&START=0&SORT=artnr&OFFSET=16 (https://www.reichelt.de/ICs-LM-10-LM-999/LM-337-220/3/index.html?&ACTION=3&LA=5000&GROUP=A2151&GROUPID=5464&ARTICLE=10473&START=0&SORT=artnr&OFFSET=16)

Maybe the LM337 is broken!?
Title: Re: Symmetrical FET
Post by: Greg S. on April 19, 2015, 03:47:27 PM
You might change it as well but you may also use a voltage devider to be more confident.
Or a trimpot, I would recomend  a 5k Bourns.
Title: Re: Symmetrical FET
Post by: mike76 on April 20, 2015, 12:22:10 AM
Thanks, Greg, I will report my progress.
Title: Re: Symmetrical FET
Post by: Greg S. on April 20, 2015, 01:05:38 AM
I forgot to write, a Primpot for the K- Resistor!
http://www.circuitstoday.com/wp-content/uploads/2011/04/LM317-typical-adjustable-regulator-ckt.png (http://www.circuitstoday.com/wp-content/uploads/2011/04/LM317-typical-adjustable-regulator-ckt.png)
 :D
Title: Re: Symmetrical FET
Post by: Harpo on April 20, 2015, 06:19:45 AM
I forgot to write, a Primpot for the K- Resistor!
http://www.circuitstoday.com/wp-content/uploads/2011/04/LM317-typical-adjustable-regulator-ckt.png (http://www.circuitstoday.com/wp-content/uploads/2011/04/LM317-typical-adjustable-regulator-ckt.png)
:D
:o Better don't refer to this amount of errors/mixups/nonsense in the shown vreg. schematic and formula.
The only correct information seems to be the pic on the right hand side, copypasted from a voltage regulators datasheet.
(make sure to look at the correct parts parameters, because the vregs datasheet most often shows both LM117 and LM317 and parameters are not all the same, IE the current setting 240R resistor is ment for a LM117 that would better be 120R for a LM317 part to ensure draw of minimum load current in order to maintain regulation.)
Title: Re: Symmetrical FET
Post by: mike76 on April 20, 2015, 07:06:41 AM
Okay, thanks, I have to work this out. For the beginning, I've ordered a second LM317. I have used several resistor combinations  but ended always in a difference at about 0.5v.

The positive side works as expected, at the moment with gregs recommendation at about 15.04 V.

If the replacement does not work,  I have to dig deeper ;)

Btw, does the elektrocaps need to have 63v? I put 30v in it.

Thanks and sunny greetings from cologne :)
Title: Re: Symmetrical FET
Post by: Harpo on April 20, 2015, 09:03:41 AM
'a second LM317' would be for another/different positive supply rail. You want a LM337 for your negative supply rail.
You want to meet the min.load requirement for your neg.rail. Depending on manufacturer of your 337 vreg, this will be in range 5mA ... 14mA. Assuming 10mA for the more common suspects, the current setting R96 (R- resistor) will need a parts value of 1.25V/0.010A=125R. Pick a 120R part for a 1.25V/120R=10.4mA min.current draw. The voltage setting R93 (K- resistor) will have a parts value of (15V-1.25V)/0.0104A=1322R. Picking a 1K3 should be close enough, and ignoring the additional typ.65uA Iadj * 1K3=about 0.09V that would vanish in parts tolerances.
A temporary connected maybe 1K5 between -15V and 0V reference voltage would have a similar -meeting the min.load current- effect before you connect the rest of your circuit, so you might try this first.
Parts come with tolerances, so for usual you design  for worst case conditions in order to not damage or blow up connected parts. (The -from Gustavs schematic- TL072 and TL074s have an absolute max.rating of +/-18VDC=36V between supply pins that you don't want to exceed).
'Btw, does the elektrocaps need to have 63v? I put 30v in it.'
Your 35V (not 30V, be more exact with your numbers) rated electrolytic caps will be sufficient, except for the 1000uF caps C37, C38, C39, C40 that might get close to the edge when you assume +10% high mains voltage and an unloaded or barely loaded mains transformer (typ.+15%) with your -from previous post- dual 22VAC secondaries in front. ((22VAC+22VAC)*1.1*1.15*sqrt(2)-2*0.6V)/2=38.75V raw DC per rail in front of the regulators. The differential between voltage in front of the regulators and voltage at regulator output (from previous numbers worst case 38.75V-15V=23.75V -dropout too much) times current drawn from your circuit will be transfered to heat, so the vregs might require a heatsink attached, further leading to the conclusion that a dual 22VAC secondary probably wasn't the best bet for your wanted +/-15VDC rails.
Title: Re: Symmetrical FET
Post by: mike76 on April 20, 2015, 10:28:41 AM
Dear Harpo,

thank you for your extensive explanation. I appreciate that.

I will consider this in my further progress. I'll print this, cause I suppose, I need to read this several times regarding the content :)

Anyway, I ordered 337 not 317 yesterday and 63V caps, too. The transformer was rated to 2x18V and supplies 2x20.05V.

Thanks again, as I can imagine and understand, that questions and requests like mine can be annoying to read and answer for somebody, who might is a professional.

Mike
Title: Re: Symmetrical FET
Post by: mike76 on April 21, 2015, 06:57:44 AM
Here we go again  ;D

I changed the LM337 (because I already desoldered it) and changed the resistors as you suggested. It looks much better now: 15.05V at the positive and 15.1V at the negative (15.26 before changing resistors).

I assume, as you wrote, that a difference of 0,05V shouldn't make any headache, does it?

Now if I calculated correct, there are about 28V of raw voltage, minus the 15V equals 13V. Would that be too much for the vreg to handle without cooling or would it be better to go higher with voltage?

Thanks for this important lesson :-)

Mike



Title: Re: Symmetrical FET
Post by: Nick Franklin on April 22, 2015, 06:50:40 AM
Hi all,

Does anyone have the physical dimensions of the main PCB?

Thanks,

Nick.
Title: Re: Symmetrical FET
Post by: mike76 on April 22, 2015, 09:59:07 AM
Hi Nick,

about 300x170 mm.

Mike
Title: Re: Symmetrical FET
Post by: Nick Franklin on April 23, 2015, 02:05:30 AM
Thanks Mike, you're a legend!  8)


Hi Nick,

about 300x170 mm.

Mike
Title: Re: Symmetrical FET
Post by: Nick Franklin on May 12, 2015, 07:27:43 AM
Gustav,

Boards and transformers arrived this morning and I populated this afternoon. Beautiful boards as always, a pleasure to work on. Well done.

I'll post pics when I finish it off in the next week or so.

NF.
Title: Re: Symmetrical FET
Post by: mike76 on May 12, 2015, 08:27:12 AM
Hi there,

I just build my second unit after totally killed the first after connecting the front PCB the wrong way. After trying to remove the angled connection, I damaged the PCB. So I ordered a second one, which I got ready to go.

It doesn't work as expected, one channel does not give any sound, although the meter is corresponding.

I have got 2 pcs of NPD5566, which I got from China. What would an appropriate replacement for that? I can't get no answer, beside the bf245 in this thread. I'm not really sure, if they are working.

I think, something in the output section seems not to work. May the output transformer is not giving the signal, cause I built adapter-pcb for edcor xs 1100.  On the IC, the current seems to be fine, I'm not getting through the schematic where to look else or how to measure, if the transformer is working. Should I get an audoi signal at the outputs, when the transformers are removed?

Thanks, it is getting frustrating.

Title: Re: Symmetrical FET
Post by: Gustav on May 12, 2015, 08:41:22 AM
Hi there,

I just build my second unit after totally killed the first after connecting the front PCB the wrong way. After trying to remove the angled connection, I damaged the PCB. So I ordered a second one, which I got ready to go.

It doesn't work as expected, one channel does not give any sound, although the meter is corresponding.

I have got 2 pcs of NPD5566, which I got from China. What would an appropriate replacement for that? I can't get no answer, beside the bf245 in this thread. I'm not really sure, if they are working.

I think, something in the output section seems not to work. May the output transformer is not giving the signal, cause I built adapter-pcb for edcor xs 1100.  On the IC, the current seems to be fine, I'm not getting through the schematic where to look else or how to measure, if the transformer is working. Should I get an audoi signal at the outputs, when the transformers are removed?

Thanks, it is getting frustrating.

For trouble shooting, try to isolate some of the issues you are asking about to things that can be checked or solved by comparing with the working channel.

- Should I get audio signal at the output when the transformers are removed?
- Is your adaptor working?

After that, you should be able to check voltages on the ICs and transistors on the working channel and compare to the non-working.

I would agree, your problem is in the output. If the NPD5566 you have were not working (pretty unlikely both would be bad, and on the same channel), you would not be getting any action on the meter.

Also - did you check the build guide/notice one set of pads on the dual gang pots need to be jumped if you use those?

Hope thats a start.

Gustav
Title: Re: Symmetrical FET
Post by: Greg S. on May 12, 2015, 03:48:00 PM

Also - did you check the build guide/notice one set of pads on the dual gang pots need to be jumped if you use those?

Might you please explain your Post Gustav?
Title: Re: Symmetrical FET
Post by: gt_jumper on May 12, 2015, 10:43:43 PM
Hi guys, Im starting this project soon, my board is on the way . Thankyou Gustav for all this effort  :)

Will a single 3.6Kohm  VU meter work on this project ok? 
Title: Re: Symmetrical FET
Post by: mike76 on May 12, 2015, 11:41:28 PM

Also - did you check the build guide/notice one set of pads on the dual gang pots need to be jumped if you use those?

Might you please explain your Post Gustav?

Greg, I think, Gustav means that the middle row of  the pot pads has no function and doesn't have to be connected.

I did not do this, but I used wires with connectors, which I want to remove to See, if something is wrong here. Unfortunately, my soldering Station is not working anymore, the new  one should arrive soon. Thanks for your suggestions, Gustav. I will try it soon.
Title: Re: Symmetrical FET
Post by: mike76 on May 13, 2015, 01:59:59 AM
After checking the transistors and IC, they seem to have the same values. But I have noticed a difference at the Transformers: without connected audioinput and pots, I have about 12 kOhm between pin 3 and 4 and between pin 3 and 5 in the left channel, but not in the right channel. That leads me to the conclusion, that I may should check the Transformers adapter of the channel that doesnt work.

Edit: After sending an audiosignal through the device, again without pots and frontpcb, I've got a signal (very weak) on both channels, one of them are about 6-8 dbfs louder than the other one. As soon as I got the new soldering station, I will remove and check the transformers.
Title: Re: Symmetrical FET
Post by: mike76 on May 14, 2015, 10:26:12 AM
So, this is getting really weird  :o

I switched the + and - outputs at the xlr/jack combo. I used an mono jack to my patchbay. Suddenly I could here both channels. The strange thing is, that I could here both channels even I didn't switched the device on! That was heavily distorted and quieter. If I switched it on, the signal was getting louder. But lacking of something, I would say bass (was a drumtrack). But I didn't have any pots, the frontpcb, etc. connected. Just the pure device.

Then I prepared two symmetrical jacks and connected them correctly (tip =hot, blue=cold) to the pcb. There again barely something to hear and heavily distorted.

I'm a bit confused and don't get the clue behind this. Is it possbile, that a not properly output transfomer can cause such a behaviour? But then both of them has to be wrong connected, which I can't  imagine.

Very confused, very very.
Title: Re: Symmetrical FET
Post by: mike76 on May 22, 2015, 11:50:29 AM
After days of reading, checking and measuring, I finally brought this unit to life :-)

After accidently made one 4R3 glow like a lamp because of the  wrong direction of an IC after changng. Some parts had to be changed after that and I learned my lesson well :-)

I think there were two errors: on the one output transformer was one wire disconnected from the pins, don't know why. And I traced a lack of voltage on the input stage to the npd5566, I think it was cold soldering thing on one of the resistors.

However, it is working, everything seems fine. Now I need to calibrate this and although I know where to calibrate, I would appreciate some advice. I read the 1178 manual, but I am not able to measure in dbm, so if there is an other solution, that would be fine.

I just did some work on the assembly guide, and Ill do a small calibration guide.
...
Gustav

Didn't find that anywhere, may in the assembly guide, but it is not linked anymore on your website?

Thanks for your help and patience ;)
Title: Re: Symmetrical FET
Post by: Nick Franklin on May 24, 2015, 02:49:38 AM
Fired mine up last night. All the voltages check out. Just waiting for my release pot to arrive then I'll calibrate and see how this sucker sounds :)
Title: Re: Symmetrical FET
Post by: Gustav on May 26, 2015, 02:47:45 AM
Fired mine up last night. All the voltages check out. Just waiting for my release pot to arrive then I'll calibrate and see how this sucker sounds :)

You could set a fixed release to get you going :)

Hope it works out.

Gustav
Title: Re: Symmetrical FET
Post by: Nick Franklin on May 26, 2015, 04:07:38 AM
I thought about it,  but I'm happy to wait :)

I'll post some pics when I'm done.

Fired mine up last night. All the voltages check out. Just waiting for my release pot to arrive then I'll calibrate and see how this sucker sounds :)

You could set a fixed release to get you going :)

Hope it works out.

Gustav
Title: Re: Symmetrical FET
Post by: gt_jumper on May 26, 2015, 09:31:34 AM


I'll post some pics when I'm done.





Very keen to se your pics!
Title: Re: Symmetrical FET
Post by: gt_jumper on May 28, 2015, 11:17:10 PM
i think i have bought the wrong power transformer, i need one with 2x18v ,  not the single 18v one i have here?

(http://i36.photobucket.com/albums/e27/gt_jumper/20150529_125642_zps6c8hq6me.jpg)
Title: Re: Symmetrical FET
Post by: gyraf on May 29, 2015, 01:26:13 AM
Yes, that transformer is wrong for this project.

Jakob E.
Title: Re: Symmetrical FET
Post by: Gustav on May 29, 2015, 01:37:12 AM
Also, I would run it on 15V (2 x 15V), based on the feedback from builders.

Gustav
Title: Re: Symmetrical FET
Post by: gt_jumper on May 29, 2015, 02:02:54 AM
Thankyou very much gentlemen :)

would this be far more suited? It's got great dimensions too!

http://au.rs-online.com/web/p/toroidal-transformers/6718943/
Title: Re: Symmetrical FET
Post by: gt_jumper on May 29, 2015, 10:19:20 PM
Also, I would run it on 15V (2 x 15V), based on the feedback from builders.

Gustav

Anything else need to change on the board to use an input voltage of +15/-15vdc?
Title: Re: Symmetrical FET
Post by: Greg S. on May 30, 2015, 03:26:55 PM
the LM317, LM337 Resistors   ;)
Title: Re: Symmetrical FET
Post by: gt_jumper on May 31, 2015, 12:46:29 AM
the LM317, LM337 Resistors   ;)

Sweet, I'll grab a 2x15v toroid then!!
Title: Re: Symmetrical FET
Post by: gt_jumper on June 01, 2015, 09:34:23 PM
Can i use n4007 in the place of Z10? I have a large bag of N4007s.
Title: Re: Symmetrical FET
Post by: Gustav on June 02, 2015, 11:01:38 AM
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav
Title: Re: Symmetrical FET
Post by: gt_jumper on June 02, 2015, 08:25:31 PM
Thanks for the answer.

This should do the trick yes?
http://au.rs-online.com/web/p/zener-diodes/0812465/
Title: Re: Symmetrical FET
Post by: Gustav on June 03, 2015, 12:36:03 AM
Thanks for the answer.

This should do the trick yes?
http://au.rs-online.com/web/p/zener-diodes/0812465/

Yep.

Gustav
Title: Re: Symmetrical FET
Post by: Nick Franklin on June 04, 2015, 12:25:05 AM
Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:

(http://s2.postimg.org/w66yp7c8p/1_BIG.jpg)

(http://s30.postimg.org/k7oee0bup/2_BIG.jpg)

(http://s18.postimg.org/ufjm6ul61/3_BIG.jpg)


Title: Re: Symmetrical FET
Post by: Gustav on June 04, 2015, 01:05:35 AM
Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:

(http://s2.postimg.org/w66yp7c8p/1_BIG.jpg)

(http://s30.postimg.org/k7oee0bup/2_BIG.jpg)

(http://s18.postimg.org/ufjm6ul61/3_BIG.jpg)

That build is insanely good looking...

What did you use for the FET?

Gustav
Title: Re: Symmetrical FET
Post by: Nick Franklin on June 04, 2015, 01:09:33 AM
Thanks G!

I used an NE5566!

Nick.



Just finished mine up. No dramas at all. Pleasure to build, thanks Gustav! Sounds excellent. I've owned a number of 1178's in my life and this is definitely made of the same stuff :)

Here's a couple of pics:


That build is insanely good looking...

What did you use for the FET?

Gustav
Title: Re: Symmetrical FET
Post by: mike76 on June 06, 2015, 01:56:32 PM
Even mine was finished today, and after days and weeks of Amateur mistakes, torture as well as half a dozen flashing 4R3, I finally did it. Thanks again for all your support   8)

I really learned a lot with this project.

(http://s29.postimg.org/3kjrx48f7/IMG_20150606_165601.jpg) (http://postimg.org/image/3kjrx48f7/)
Title: Re: Symmetrical FET
Post by: mike76 on June 07, 2015, 09:56:48 AM
Today with further calibration I realised a strange behavior. The balance even of the uncompressed signal changes, when I move the output knob and especially the release knob.

Lets say I have a kick and a snare. When turning the release knob from slow to fast (CW) the balance changes as if the slightly right panned snare walks to the left. And even worse, if I put the release knob to its maximum, the output volume is increasing about 8dbfs and the unbalance changes completely to the other side. Should that be in bypass?

Any ideas?
Title: Re: Symmetrical FET
Post by: mike76 on June 08, 2015, 01:45:40 PM
So, now changed ic's, incl npd5566.

The imbalance still there, but no shifting from left to right. The meters shows the balance difference   as well as the bars in the daw.

The difference changes by changung input/output volume, which indicates that the npd5566 should work as  expected.

Could this be a calibration problem? May I should rewire the pots, cause I used Molex for the connections.

May there is always an imbalance?

Beside that, the compressor seems to work fine and can make a bass track really growl if pushed into the red.
Title: Re: Symmetrical FET
Post by: gyraf on June 09, 2015, 10:31:05 AM
It's impossible to achieve 100% complete tracking  - but something like 1dB tracking up to 15dB GR should be within reach.

What are your differences, at what settings?

Jakob E.
Title: Re: Symmetrical FET
Post by: mike76 on June 09, 2015, 12:12:08 PM
Hello Jakob,

it doesn't matter at which settings. After calibration as Gustav describes it on the Website for the 1176, I have a really good stereo tracking. As soon as I change the threshhold via input, the imbalance appears.

I recently realized, that I used 20% tolerance trimmer for the qbias. May this could be the source of evil?  Thanks!
Title: Re: Symmetrical FET
Post by: gyraf on June 10, 2015, 07:27:35 AM
how much un-balance, at what GR?

Maybe trim your threshold (=the input to sidechain from output level pot) down a bit in one side?

Jakob E.
Title: Re: Symmetrical FET
Post by: Gustav on June 10, 2015, 10:52:08 AM
Hello Jakob,

it doesn't matter at which settings. After calibration as Gustav describes it on the Website for the 1176, I have a really good stereo tracking. As soon as I change the threshhold via input, the imbalance appears.

I recently realized, that I used 20% tolerance trimmer for the qbias. May this could be the source of evil?  Thanks!

Mike - remember that the "calibration" I have in 4 steps without metering on my site for the Phat FET is not at all accurate. I feel its not overly critical on he 1176, but for this fellow┬┤, digging out the manual and doing the calibration properly will yield much better results.

I also have a feeling some things could be improved with this design, based on feedback, but I am sort of sidestepping upgrading this project with a different take on a new unit I am working on with much more control and a basic DIY circuit that has been proven to be accurate. (I took the 1178 direct from schematic, not proven or tested in DIY).

Gustav
Title: Re: Symmetrical FET
Post by: Harpo on June 10, 2015, 11:09:52 AM
(I took the 1178 direct from schematic, ...
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
Title: Re: Symmetrical FET
Post by: mike76 on June 10, 2015, 11:43:07 AM
Okay, thanks for your words,

I read the 1178 manual several times, got confused with dbm, dbu, Vrms, etc.

I send an testtone from cubase -18dbfs (my converters should be at this level) and set the meters to +1. Then GR mode, bypass off, Ratio 20:1, Release full cw. Then set the Qbias to 0db on the meters.

But the problem is: there is even an imbalande in bypass mode, and even without the npd5566 installed,  If I turn the Input volume up, the difference sometimes getting more (about 5db), sometimes less, varying no matter how much I turned the volume up. Two the same settings vary after turning the pot upside down.

I think, that can't have to do anything with the compression circuit, there has to be something in the input. When I turn up the output volume, the differenve stays pretty much the same without the GR activated.

 I think, there should be something else, don't know if it is the pot that I've soldered with wires and molex.

I will check this first, when I got time. But I have to say, that I'm a bit frustrated  >:(  Just want it to get working, it must not  be perfect. The other builders seemed to get it working almost properly. So much time and afford; I do not count the money anymore.

May I have to look for someone who has got more skills and knowledge.
Title: Re: Symmetrical FET
Post by: mike76 on June 10, 2015, 11:53:53 AM
Edit: It is not the input volume, it is the output volume
Title: Re: Symmetrical FET
Post by: mike76 on June 11, 2015, 01:32:55 AM
Okay,

after testing several pots I came to the conclusion, that it is not in the circuit at all.

The pots shows more or less different values in each channel even without beeing connected. When I want to turn the axis, and I am at the point short before turning, differences in the balance appears when connected. slighlty touching the pots is enough to imbalance the sound. So far, so good.

This should be a mechanical problem with the omeg pots. 

But now I got another problem in one chanel. It is "popping" and distorting on higher volume to the rhythm of the bassdrum. I carefully knocked with the back of my skrewdriver on the pcb to see, if anything isnt proper soldered.

May this could be a transisitor or a cap?

getting closer :-)
Title: Re: Symmetrical FET
Post by: mike76 on June 11, 2015, 04:14:34 AM
It might is obvious and well known by far the most of you, it wasn't for me. Found a good article about pot-matching and now I finally understand the Advantages of stepped pots

 8)

Here is an interesting article I found : http://www.practicaldevices.com/techdocs/Pot_Channel_Matching.pdf (http://www.practicaldevices.com/techdocs/Pot_Channel_Matching.pdf)
Title: Re: Symmetrical FET
Post by: gyraf on June 11, 2015, 04:28:40 AM
Aah yes, that makes sense now.

For judging and setting balances, it's often best at full-clockwise settings, as this point is the only not suffering from pot unbalance.

When building my stereo units, I buy 1000 stereo pots and select the 50-75 that is good enough for stereo - and then I use the rest as mono pots or for non-critical functions...

Jakob E.
Title: Re: Symmetrical FET
Post by: mike76 on June 11, 2015, 10:08:09 AM
Hell, this is a neverending story...

Left channels distorts heavily, especially and much mode in gr. Voltage peaks, don't know where they comming from. Input is fine +-15,4 exactly, no peaks.

In gr, left Meter is jumping as crazy with the peaks, changed the 22pf and the 470. no change. Without NPD everythings fine.

Suggestions?
Title: Re: Symmetrical FET
Post by: mike76 on June 12, 2015, 01:26:10 AM
Okay, sorted it out, had something to do with the bias-settings.

I tried to calibrate it with several methods I found, but there is still an unbalance, changing with setting, ie. ratio, attack, release.

My last try will be to match some bf245a and test it, if this doesn't change the stereo image, I will let it be and use it as a mono device :)
Title: Re: Symmetrical FET
Post by: gyraf on June 12, 2015, 04:45:40 AM
It's still unclear how much un-balance you have at what gain reductions...

Jakob E.
Title: Re: Symmetrical FET
Post by: mike76 on June 12, 2015, 09:13:32 AM
Hey Jakob,

thanks for your interest.

I do not think that this has something to do with gain reduction at all.

When I remove the npd, there is still an unbalance. When I move the input, the balance changes from about 1-5 db difference, sometimes at the same level different. Also the outpu knob changes this difference. That should not be an gain reduction problem, I suppose.

This is strange, and again, may the pots are the problem. Do you agree?

Title: Re: Symmetrical FET
Post by: Nick Franklin on June 13, 2015, 10:30:06 PM
I have to say, whilst most dual-gang potentiometers are not perfect, I've never had one 5dB out! I feel like something else is a miss here.

Out of curiosity, the NPD5566 you used, is it a real one, or a slightly more suspicious one from eBay?



Hey Jakob,

thanks for your interest.

I do not think that this has something to do with gain reduction at all.

When I remove the npd, there is still an unbalance. When I move the input, the balance changes from about 1-5 db difference, sometimes at the same level different. Also the outpu knob changes this difference. That should not be an gain reduction problem, I suppose.

This is strange, and again, may the pots are the problem. Do you agree?
Title: Re: Symmetrical FET
Post by: mike76 on June 14, 2015, 01:12:38 AM
Hi Nick,

it is indeed from eBay, China.

But, as I posted above, even if I remove the NPD and turn the input/output knobs, the difference is there and changes. Not always 5db, most 1-2. but this changes, randomly.

I am not sure, if this is caused by the pots or anywhere else my circuit.

I have only basic understanding of the schematics. Therefore I decided to put it back in my rack until this changes or I found someone, who is more experienced than myself :)
Title: Re: Symmetrical FET
Post by: mistahad on June 15, 2015, 10:09:33 AM
Question regarding the 2N5566

How should I install (polarity-wise) a 2N5566 in CAN-6 housing? It has a small notch on one side.
http://www.ebay.com/itm/2N5566-Encapsulation-CAN-6-Matched-N-Channel-JFET-Pairs-/110886784102? (http://www.ebay.com/itm/2N5566-Encapsulation-CAN-6-Matched-N-Channel-JFET-Pairs-/110886784102?)

Thanks
Title: Re: Symmetrical FET
Post by: gt_jumper on June 15, 2015, 11:32:07 PM
Is there any issues with using a pair of single pots instead of the dual gang units? (getting hard to source)
Title: Re: Symmetrical FET
Post by: Gustav on June 16, 2015, 12:41:03 AM
Question regarding the 2N5566

How should I install (polarity-wise) a 2N5566 in CAN-6 housing? It has a small notch on one side.
http://www.ebay.com/itm/2N5566-Encapsulation-CAN-6-Matched-N-Channel-JFET-Pairs-/110886784102? (http://www.ebay.com/itm/2N5566-Encapsulation-CAN-6-Matched-N-Channel-JFET-Pairs-/110886784102?)

Thanks

theres an alternative mounting spot on the board, but you will have to check the datasheets for the parts and compare pin-outs.

Gustav
Title: Re: Symmetrical FET
Post by: Gustav on June 16, 2015, 12:41:49 AM
Is there any issues with using a pair of single pots instead of the dual gang units? (getting hard to source)

Reichelt.de

Gustav
Title: Re: Symmetrical FET
Post by: Gustav on June 17, 2015, 08:10:46 AM
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
Title: Re: Symmetrical FET
Post by: gt_jumper on July 02, 2015, 10:23:30 AM
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.

Thanks Gustav :) I went with the Zener i linked you to.
Title: Re: Symmetrical FET
Post by: gt_jumper on July 02, 2015, 10:27:20 AM
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?
Title: Re: Symmetrical FET
Post by: Gustav on July 03, 2015, 01:04:54 AM
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?

A little off, but close enough to move ahead Id say.

I would probably tweak the negative rail.

Gustav
Title: Re: Symmetrical FET
Post by: gt_jumper on July 09, 2015, 09:55:55 PM
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?

A little off, but close enough to move ahead Id say.

I would probably tweak the negative rail.

Gustav

Thankyou Gastav :)

Here is a progress shot with rainbows!

(http://i36.photobucket.com/albums/e27/gt_jumper/20150710_115302_zpsjwnd5zjg.jpg)
Title: Re: Symmetrical FET
Post by: Paradigm X on August 07, 2015, 08:34:49 AM
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
Quote
Thanks Gustav :) I went with the Zener i linked you to.

Sorry, bit confused, are you now saying install 1418s? BOM on first page says zener. Should this not be updated if so?

Cheers
Title: Re: Symmetrical FET
Post by: Gustav on August 07, 2015, 09:09:43 AM

Sorry, bit confused, are you now saying install 1418s? BOM on first page says zener. Should this not be updated if so?

I will assume you mean the 4148, and if so, yes - install those.

Since I made the MS76, the project is no longer available, so I haven't been updating the documents. Following quote should also clarify how hard you would have to drive it to matter.

Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.

Thanks Gustav :) I went with the Zener i linked you to.
Title: Re: Retired:Symmetrical FET
Post by: ChrioN on December 28, 2015, 07:22:25 AM
So, did anyone have success in building this compressor? Seems like a cool project, even though its discontinued status.
Title: Re: Retired:Symmetrical FET
Post by: Gustav on December 28, 2015, 07:55:55 AM
So, did anyone have success in building this compressor? Seems like a cool project, even though its discontinued status.

Heres an example.

http://groupdiy.com/index.php?topic=56181.msg757286#msg757286

I was informed removing C24 C25 would improve noise performance, but haven't investigated. I consider the MS76 a replacement for this project.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on March 25, 2016, 02:23:20 PM
Finally, I found the answer to the Question, why the Symm-Fet is so noisy

But I had to design a completely new PSU.

As an example:
My PSU delivers at 450mA for Pos- and Neg- Supply Rail, -120dBV (<22kHz) and -105dBV (<100kHz) Ripple and Noise.
The Symm-Fet needs round about 200mA for both Rails, so I'm pretty save with that.

The original PSU-design is a LM317-337 combination which is about -60dBV(<22kHz) Ripple and Noise
The Main Outputstage, a push-pull-amp, (BD139, BD140) is directly powered by the PSU.

et voila..

 



Title: Re: Retired:Symmetrical FET
Post by: mistahad on March 29, 2016, 07:32:04 AM
Greg - very good info! My symfet has been sitting without use because of the very same problem, one channel is very noisy.

Can you please share some additional info about the PSU. Did you build it yourself or can one be purchased with similar specs?
Keen on getting my machine up an running too.

thanks!

Finally, I found the answer to the Question, why the Symm-Fet is so noisy

But I had to design a completely new PSU.

As an example:
My PSU delivers at 450mA for Pos- and Neg- Supply Rail, -120dBV (<22kHz) and -105dBV (<100kHz) Ripple and Noise.
The Symm-Fet needs round about 200mA for both Rails, so I'm pretty save with that.

The original PSU-design is a LM317-337 combination which is about -60dBV(<22kHz) Ripple and Noise
The Main Outputstage, a push-pull-amp, (BD139, BD140) is directly powered by the PSU.

et voila..
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on March 29, 2016, 04:28:35 PM
check PM,
I made it on my own
Title: Re: Retired:Symmetrical FET
Post by: sharpeleven on March 30, 2016, 08:19:28 AM
check PM,
I made it on my own

me, too please!  ::)
same here, one noisy channel...
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on June 06, 2016, 07:54:59 PM
What kind of noise where you guys hearing? The right channel of mine is pretty hissy. I didn't notice it at first but it's pretty annoying now.

NF.
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on June 15, 2016, 05:36:39 AM
Quick bump. Interested to hear if others' units are hissy?

Thanks xoxo

NF.
Title: Re: Retired:Symmetrical FET
Post by: Gustav on June 15, 2016, 06:00:09 AM
Quick bump. Interested to hear if others' units are hissy?

Thanks xoxo

NF.

Hi Nick.

The project was "retired", so you're not likely to find new inputs beyond what was shared in the thread.

I also added a little tidbit a few posts back that should be worth trying.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on June 15, 2016, 06:08:08 AM
Hey Gustav,

Yeah I get that it's retired. Just thought there might be a few people still out there hanging on to theirs. My build is really nice and sounds fantastic aside from the hiss. Would be great to make it a bit more usable.

Thanks for your help,

Nick.

Quick bump. Interested to hear if others' units are hissy?

Thanks xoxo

NF.

Hi Nick.

The project was "retired", so you're not likely to find new inputs beyond what was shared in the thread.

I also added a little tidbit a few posts back that should be worth trying.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Gustav on June 15, 2016, 06:15:51 AM
Hey Gustav,

Yeah I get that it's retired. Just thought there might be a few people still out there hanging on to theirs. My build is really nice and sounds fantastic aside from the hiss. Would be great to make it a bit more usable.


Like I mentioned. I posted a suggestion that answer that adresses your question, and Greg added a post, powering it by a different PSU - so unless I am missing someting, your answers are in the thread.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on June 15, 2016, 06:39:34 AM
Hey brother sorry if I offended you somehow, I didn't mean to. Maybe I'm reading too much into your post but you sounded a little off-put. Again, my apologies if that is the case. I must stress I am NOT sweating about this project. It's fine. I think about it now and then and mean to do something about it at some point. I might also add that I am super appreciative of your work around here. I've been here since the days you were just offering PCB's of others projects, and to watch how your business has grown is fantastic.

I have read the thread. This also isn't my first rodeo. I'm across both your solution and Greg's. I'm just gathering information before I pull the thing apart again.

 I'm curious as the KIND of noise others are experiencing i.e is it hum? Is it hiss? is it buzz? is it somewhere in between. No big deal just curious. If my hiss is different to everyone else's then maybe my problem isn't inherent in the project itself but something I did individually.

Is it so bad to keep the conversation going? What's a few more words on the internet.

Hey Gustav,

Yeah I get that it's retired. Just thought there might be a few people still out there hanging on to theirs. My build is really nice and sounds fantastic aside from the hiss. Would be great to make it a bit more usable.


Like I mentioned. I posted a suggestion that answer that adresses your question, and Greg added a post, powering it by a different PSU - so unless I am missing someting, your answers are in the thread.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Gustav on June 15, 2016, 06:48:12 AM

 I'm curious as the KIND of noise others are experiencing i.e is it hum? Is it hiss? is it buzz?

Sorry, I missed that specific wish.

I was only trying to be helpful. (Not to expect "new input", since project has been replaced a long time again, pointing to solutions posted in the thread), not the slightest off-put. (edit:putting a smiley in here to make this clear, which apparently, I am bad at in writing  :D Sorry about that! )

I had no problems with the units I built, so can't really comment on the type of noise. I may have used very low value resistors for the CRC filters, but other than that, no difference  (I know, thats more solution based than what you're looking for feedback on, but its the best I can offer personally).

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on June 15, 2016, 09:47:35 AM
 :)

All good Gustav.

Take care.

NF.


 I'm curious as the KIND of noise others are experiencing i.e is it hum? Is it hiss? is it buzz?

Sorry, I missed that specific wish.

I was only trying to be helpful. (Not to expect "new input", since project has been replaced a long time again, pointing to solutions posted in the thread), not the slightest off-put. (edit:putting a smiley in here to make this clear, which apparently, I am bad at in writing  :D Sorry about that! )

I had no problems with the units I built, so can't really comment on the type of noise. I may have used very low value resistors for the CRC filters, but other than that, no difference  (I know, thats more solution based than what you're looking for feedback on, but its the best I can offer personally).

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on July 05, 2016, 01:49:10 AM
Gang,

Just for the record,  I too re-built the power supply for this unit and after initial testing this seems to have resolved the noise issue.

I used a basic +/-18V PSU kit from the local electronics hobby store.

NF.
Title: Re: Retired:Symmetrical FET
Post by: rock soderstrom on July 05, 2016, 06:21:56 AM
Hi Nick ,thanks for information!  I am close to build up this project and I ask myself if there is a way to  get rid of the noise problem on the  original pcb without an additional psu pcb.

Whats the problem with the onboard psu? It looks like a standard textbook implementation of a bipolar psu to me...

Any hints?

cheers  8)
Title: Re: Retired:Symmetrical FET
Post by: Paradigm X on July 05, 2016, 11:26:57 AM
hi rock.

i also have a pcb and was looking to build my symmetrical fet soon. i need to order the parts tho. its my first 'pro-audio' build, although i have built a number of synth bits. Hadnt realised it had been discontinued.  hoping some kind people can help out if i get stuck, although ill cross that bridge when i come to it.

edit: does anyone have the fpd file that was on gustavs site? it doesnt appear to be there anymore?

many thanks
Ben




Title: Re: Retired:Symmetrical FET
Post by: Nick Franklin on July 05, 2016, 09:38:37 PM
Not sure sorry!

Hi Nick ,thanks for information!  I am close to build up this project and I ask myself if there is a way to  get rid of the noise problem on the  original pcb without an additional psu pcb.

Whats the problem with the onboard psu? It looks like a standard textbook implementation of a bipolar psu to me...

Any hints?

cheers  8)
Title: Re: Retired:Symmetrical FET
Post by: rock soderstrom on July 06, 2016, 05:39:26 AM
Not sure sorry!

Hi Nick ,thanks for information!  I am close to build up this project and I ask myself if there is a way to  get rid of the noise problem on the  original pcb without an additional psu pcb.

Whats the problem with the onboard psu? It looks like a standard textbook implementation of a bipolar psu to me...

Any hints?

cheers  8)

Ok, thanks! Maybe someone else can enlighten me? Cheers


@Ben: You are not alone! 8)
Title: Re: Retired:Symmetrical FET
Post by: Gustav on July 08, 2016, 08:51:04 AM
@Ben: You are not alone! 8)

1RU panel, not tested!

https://pcbgrinder.com/download/FPD/SYM1RU.fpd

2RU, which I used for my builds.

https://pcbgrinder.com/download/FPD/Sym_FET2RU.fpd

Probably too late, but if its really the PSU making problems, it wold be great if someone would try measuring AC on the DC lines. Could possible be cleaned up with a well placed cap, instead of replacing the PSU.

I do have a unit within arms length at a local studio. The "problem" is, I dont have the noise, but I could try poking around, measuring AC, and see if I can make it go away if I find any.

A question

I used 4R7  resistors in the filter portion of the PSU, so thats less current draw. Could that affect the stability of the regulators? I have had regulator oscillation on some designs (VECA, check the errata), and simply correcting with the standard application note cap for stabilisation works like a charm.

Also, what have you guys been using for the dual FET?


Gustav
Title: Re: Retired:Symmetrical FET
Post by: rock soderstrom on July 08, 2016, 10:19:00 AM
@Ben: You are not alone! 8)

1RU panel, not tested!

https://pcbgrinder.com/download/FPD/SYM1RU.fpd

2RU, which I used for my builds.

https://pcbgrinder.com/download/FPD/Sym_FET2RU.fpd

Probably too late, but if its really the PSU making problems, it wold be great if someone would try measuring AC on the DC lines. Could possible be cleaned up with a well placed cap, instead of replacing the PSU.

I do have a unit within arms length at a local studio. The "problem" is, I dont have the noise, but I could try poking around, measuring AC, and see if I can make it go away if I find any.

A question

I used 4R7  resistors in the filter portion of the PSU, so thats less current draw. Could that affect the stability of the regulators? I have had regulator oscillation on some designs (VECA, check the errata), and simply correcting with the standard application note cap for stabilisation works like a charm.

Also, what have you guys been using for the dual FET?


Gustav

Thanks Gustav for the fpd files and your help!  :)
Title: Re: Retired:Symmetrical FET
Post by: Paradigm X on July 08, 2016, 10:41:23 AM
Brilliant. Many thanks Gustav.

Ill have a look into getting the parts ordered soon, will be a good next project. As soon as i get a vco calibrated...

Cheers, all the best
Ben

 :)
Title: Re: Retired:Symmetrical FET
Post by: Gustav on July 15, 2016, 07:42:38 AM
I checked for AC on the DC rails, and there was nothing. I was really hoping that would the culprit.

I noticed I was drawing the lights for everything from the toroid directly. Thats another possible difference.

If this is some easy fix, I have some time the next few weeks. I could redraw the schem and give  a single sided/self etch version a shot...

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on December 24, 2016, 01:33:12 PM
Hi Nick ,thanks for information!  I am close to build up this project and I ask myself if there is a way to  get rid of the noise problem on the  original pcb without an additional psu pcb.

Whats the problem with the onboard psu? It looks like a standard textbook implementation of a bipolar psu to me...

Any hints?

cheers  8)

Take a look at the paper of an LM317 and LM337.
They got -60dBV ripple and noise at the out.
You may get ca 80dBV by adding an 100uF/25V Elko Cap across the Adjustment Resistors in the PSU!
Try it out

Title: Re: Retired:Symmetrical FET
Post by: Gustav on December 26, 2016, 08:23:36 AM
Take a look at the paper of an LM317 and LM337.
They got -60dBV ripple and noise at the out.
You may get ca 80dBV by adding an 100uF/25V Elko Cap across the Adjustment Resistors in the PSU!
Try it out

I think I tried this with no change on this.

Maybe caps by the BD139/BD140 would solve all!?

Still retired, may see if I can do changes and bring it alive for 2017 if theres any interest and solutions.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on December 26, 2016, 01:45:36 PM
I'm still working at this project!

Perhaps you add a Servo at the Output-Stage?
You should add some Resistors for Biasing the BD139/BD140!
Title: Re: Retired:Symmetrical FET
Post by: frederickalonso on December 28, 2016, 08:32:44 AM
 ;) Go Gustav, like your work.
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on December 30, 2016, 04:49:20 PM
I spend some more hours on that project, here is what you may do for improvements:
First I have to mention, that I got different Schematics and Layouts of these Projects.
I do not know how much Revisions Gustav made, so some Names might be wrong!

Perhaps Gustav might send me the Final Version! THX

0 PSU
Replace the On-Board-PSU and Replace ist by something less noisy, e.g. 7815, 7915 Regulation with some LOW-ESR Caps behind the Regulators

1 Input section:
R1, R2, R3, R4, R5         10k > 1k
less Johnson Noise!

2 Input Section
add 100k to GND at the Input
e.g. Pos-Left, Neg-Left, Pos-Right, Neg-Right

3  Input VOL POT
R40/R66    1k  >  ALPS RK27112 10k log

3 Output Driver
C24, C25, C32, C33  100uF/25V  >  unused

4 GR-Meter-Tracking
TL074 > OPA4131 or MC33079

5 Magnetic Shield
I added a Round MU-Metall Schield to the Power-Torroid and at the Top and Bottom Case too Self-addhesive Mu-Metall!
There should be no space between those Mu-Metal-Shields!

6 Zener
ZD10 > 1N4148

7 Output Driver
D1, D2, D3, D4, D9, D10, D11, D12 > 1N4148

8 Lundahls Output
Add 1k parallel to the Outputs of the Lundahls between Pos and Neg

9 OPA's
NE5532AP seem to be the Best,
I tried OPA2134 and LM4562, Values were worser!
Didn't check MKP's as replacement for the 100u Caps following at the Input stage

10 Pots in General
I simply used ALPS RK27112
Input      POT 10k log
Output POT 100k Log
Attack  POT  20k Log
Release POT 1M Lin

Those ALPS got Differences up to 20%, If you want real StereoKompression, you will have to match 'em out!!!

If you want extended Release times, try to change R52 via Switch or Relay

11 Fet's or NPDXXXX
I used BF245A, matched 'em on my own,
http://www.masonaudio.org/diy/comp1176

Result:
At 0dBu Input and Output, I got -94dBu Noisefloor on both Channels
-3dB: 9Hz, 100kHz

Good Luck

GrG
Title: Re: Retired:Symmetrical FET
Post by: Zebra_PD on April 11, 2018, 05:06:30 AM
Hi!

Im going to attempt to build a 1178 klon in a UREI 353 case. Also got a hold of a NOS  1178 frontplate on ebay for the build.

After some research I believe that this design is the best starting point for my project.

The 353 shares some similarities in design and was hoping to save/use as much as the original UREI components as possible. Will make my own build thread when I have sourced most of the parts needed to start the build.

But I have some questions Im hoping you Gustav or perhaps some one else of guys who have made this build could help me answer.

1. Is it possible with this pcb design to use the original output transformers (12614)  from the 353 for this build as well? Looking at the original schematics the 353 and 1178 seems to share the same output transformer. On a similar issue, is it possible to use the same original power transformer (16-12261) for this build?
 
2. Is it possible to use the same 4 gang inter-locking switch bank as for the 1176?
Like the one from Hairball (http://www.hairballaudio.com/catalog/parts-store/switches/meter-switch-bank-assembly)
or mic and mods (https://www.micandmod.com/hardware-parts/1176-power-ratio-switch-bank-assembly.html#/39-pcb_kit-yes_2_euros)

Or do I need a different one? What was the reason this design uses knobs instead of swiches?

3. Do you happen to have some of the PCBs left and/or planing to print some more?

4. Otherwise is the current MS76 possible to use with the my output transformers (12614) and power transformer (16-12261) to get the same  stereo 1178 sound? I guess since I read in the officiell build thread for the MS76 that is based on the G1176 design but lacking the input transformers similar to the late silverface/1178 design? 

Title: Re: Retired:Symmetrical FET
Post by: Gustav on April 12, 2018, 02:23:19 AM
1. Is it possible with this pcb design to use the original output transformers (12614)  from the 353 for this build as well? Looking at the original schematics the 353 and 1178 seems to share the same output transformer. On a similar issue, is it possible to use the same original power transformer (16-12261) for this build?

You can use the output transformer (do you have two?), and we would need to know whats on the secondaries of the power trafo to know. It won't make any difference, though.

You can also use them for something else - they are not tied to these particular applications.

 
2. Is it possible to use the same 4 gang inter-locking switch bank as for the 1176?
Like the one from Hairball (http://www.hairballaudio.com/catalog/parts-store/switches/meter-switch-bank-assembly)
or mic and mods (https://www.micandmod.com/hardware-parts/1176-power-ratio-switch-bank-assembly.html#/39-pcb_kit-yes_2_euros)

Or do I need a different one? What was the reason this design uses knobs instead of swiches?

It uses switches, just a different type of switch - comes down to simple availability and convenience.

3. Do you happen to have some of the PCBs left and/or planing to print some more?

Sorry, no.

4. Otherwise is the current MS76 possible to use with the my output transformers (12614) and power transformer (16-12261) to get the same  stereo 1178 sound? I guess since I read in the officiell build thread for the MS76 that is based on the G1176 design but lacking the input transformers similar to the late silverface/1178 design?

The best answer I can give is, you can try and report back.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Zebra_PD on April 12, 2018, 06:31:48 AM
You can use the output transformer (do you have two?), and we would need to know whats on the secondaries of the power trafo to know. It won't make any difference, though.

You can also use them for something else - they are not tied to these particular applications.

 

It uses switches, just a different type of switch - comes down to simple availability and convenience.

Sorry, no.

The best answer I can give is, you can try and report back.

Gustav
[/quote]

Thank a million for your reply Gustav!!

The power trafo ( 16-12261) is 2x18v and has the same ID number in both the 535 and the 1178. Someone also suggested me to also keep the volt regulators from the 353? Hence I have read in this tread that some people having problem with the power supply in there build perhaps i might be a good idea to keep as much as possible from the power part of the 535?

Yes I have two original output transformers (12614) since the 353 is a M/S unit with both mono and stereo input and and outputs :)

Well thats to bad that you didnt have any spares or planing to print some more..... Im trying to learn how to use Eagle haven't  been able to import the PDF version of your schematics and/or board design yet. I know it is asking a lot but would it be possible for you to share/sell a copy of your gerber file? If so you can reply to the email I sent you Gustav using the contact form on the PCB Grinder site.



Title: Re: Retired:Symmetrical FET
Post by: Gustav on April 12, 2018, 07:50:33 AM

The power trafo ( 16-12261) is 2x18v and has the same ID number in both the 535 and the 1178. Someone also suggested me to also keep the volt regulators from the 353? Hence I have read in this tread that some people having problem with the power supply in there build perhaps i might be a good idea to keep as much as possible from the power part of the 535?


I think trying to add some decoupling caps around the transistors would have a bigger impact, and I am sorry, but I dont have the gerbers for the project anymore.

Gustav
Title: Re: Retired:Symmetrical FET
Post by: Zebra_PD on April 12, 2018, 03:44:46 PM
I think trying to add some decoupling caps around the transistors would have a bigger impact, and I am sorry, but I dont have the gerbers for the project anymore.

Gustav

Thank you for the advice with the decoupling caps :)

Well that's to bad but writting a schematics Gerber file from scratch will prob be very educating and will have to learn it someday anyway.

Now I will stop flouting this retired post. Will keep posting in my own drowing board post. https://groupdiy.com/index.php?topic=68767.0

Hope it's OK to post any future modified version of your original schematics in that post for feedback and help from the forum? Will of course credit you as original designer in all the files. If not just please let me know Gustav.
Title: Re: Retired:Symmetrical FET
Post by: Greg S. on November 19, 2018, 07:28:26 AM
Hi Gustav, will you ever relaunch this project?
Title: Re: Retired:Symmetrical FET
Post by: Gustav on December 04, 2018, 07:00:57 PM
Hi Gustav, will you ever relaunch this project?

Hey Greg!

I consider it an earlier step towards this, so not likely

https://pcbgrinder.com/index.php?route=product/product&path=59_61&product_id=64

Gustav