Retired:Symmetrical FET

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ChrioN said:
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
 
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..





 
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!

Greg S. said:
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..
 
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.
 
Nick Franklin said:
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
 
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.

Gustav said:
Nick Franklin said:
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
 
Nick Franklin said:
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
 
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.

Gustav said:
Nick Franklin said:
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
 
Nick Franklin said:
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
 
:)

All good Gustav.

Take care.

NF.

Gustav said:
Nick Franklin said:
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
 
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.
 
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)
 
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




 
Not sure sorry!

rock soderstrom said:
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)
 
Nick Franklin said:
Not sure sorry!

rock soderstrom said:
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)
 
rock soderstrom said:
@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
 
Gustav said:
rock soderstrom said:
@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!  :)
 
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