[BUILD] STA LEVEL PCB OFFICIAL BUILD & HELP THREAD

[fallout]

There's any trick I can try without having that stuff nor a great experience tube wise?

You could try buying different tubes and swapping them around. haha

Although I'm not sure how far that would get you. I guess I'm not seeing how the 6BA6's are contributing to the problem but admittedly, I'm not familiar with this circuit whatsoever.

You're saying that with the side chain tube (6AL5?) pulled, you're not getting any distortion on the output whatsoever? I would think that would rule out the amplifier section, again I'm not very familiar with how this circuit works. It looks like the side chain is connected to the plates of the EL90's.

I suppose a cheap test would be to try different 6AL5's and see if you notice any difference in behavior.

Also, I'm not sure if the amount of DC offset on the grids of your EL90's is contributing to your issue. Everyone else's builds seem to be in the mV range which is what I'd expect. Yours is almost .5V or thereabout. You can check and make sure your coupling caps and resistors connected to the grids of the EL90's are correct, just to be sure.

Hopefully someone who is familiar with this circuit could offer better advice but I'd think something is wonky in the sidechain circuit if you're not getting distortion in the amp section.

 

[1wildthing]

I restarted from the beginning measuring PSU voltages and I discovered that my F+ originally settled on 6.3V now pushes 8.81V. So I checked the LM338 and I noticed that the input voltage is 9.35V and the output stays on 8.81V don't matter how I set the F+ Trim. Am I wrong or this means that the regulator passed away?

 

[TLRT]

I restarted from the beginning measuring PSU voltages and I discovered that my F+ originally settled on 6.3V now pushes 8.81V. So I checked the LM338 and I noticed that the input voltage is 9.35V and the output stays on 8.81V don't matter how I set the F+ Trim. Am I wrong or this means that the regulator passed away?

Is it genuine lm338 from trusted seller? Make sure you use the silicone and plastics separators however if the IC has short to gnd it is going shutdown mode. 8.8 v can ruin your tubes also check them.

 

[TLRT]

You could try buying different tubes and swapping them around. haha

Although I'm not sure how far that would get you. I guess I'm not seeing how the 6BA6's are contributing to the problem but admittedly, I'm not familiar with this circuit whatsoever.

You're saying that with the side chain tube (6AL5?) pulled, you're not getting any distortion on the output whatsoever? I would think that would rule out the amplifier section, again I'm not very familiar with how this circuit works. It looks like the side chain is connected to the plates of the EL90's.

I suppose a cheap test would be to try different 6AL5's and see if you notice any difference in behavior.

Also, I'm not sure if the amount of DC offset on the grids of your EL90's is contributing to your issue. Everyone else's builds seem to be in the mV range which is what I'd expect. Yours is almost .5V or thereabout. You can check and make sure your coupling caps and resistors connected to the grids of the EL90's are correct, just to be sure.

Hopefully someone who is familiar with this circuit could offer better advice but I'd think something is wonky in the sidechain circuit if you're not getting distortion in the amp section.

This is a tricky feedback System where the el90 sends AC signals to 6al5 which create the DC control signal to 6ba6's,the the poweramp cancelling the DC. If you use fast release and double Mode you need super balanced tubes and circuit otherwise the poweramp cannot cancel out the DC and you get the "thump"

 

[1wildthing]

Is it genuine lm338 from trusted seller? Make sure you use the silicone and plastics separators however if the IC has short to gnd it is going shutdown mode. 8.8 v can ruin your tubes also check them.

I bought it on eBay because Mouser and Banzai Music were out of stock. It seemed to be solid. I’ll look for shorts or I’ll substitute it.
Thanks!

 

[TLRT]

I bought it on eBay because Mouser and Banzai Music were out of stock. It seemed to be solid. I’ll look for shorts or I’ll substitute it.
Thanks!

Then sorry it will be fake. Check farnell they have in stock and 100% genuine. Same happens now with tl783,nobody has stock Till 2024 spring

 

[fallout]

This is a tricky feedback System where the el90 sends AC signals to 6al5 which create the DC control signal to 6ba6's,the the poweramp cancelling the DC. If you use fast release and double Mode you need super balanced tubes and circuit otherwise the poweramp cannot cancel out the DC and you get the "thump"

Interesting, thanks. I'll keep this in mind when I finally start putting mine together. I never really looked into how a vari-mu compressor works. They certainly look different than what I'm used to.

What's confusing to me is listening to 1wildthing's sample, it sounds extremely distorted and not a 'thump'.

 

[TDJ]

hey all! about to start my build, can i completely bypass the relay board and connect audio in/audio out directly to the XLRS or are there other alterations that need to be made?

 

[fallout]

hey all! about to start my build, can i completely bypass the relay board and connect audio in/audio out directly to the XLRS or are there other alterations that need to be made?

I don't see any reason why you couldn't.

 

[MHProd]

I'd like to build a pair of these. Is there a consensus on the most authentic output transformer to use? I built a couple of HiFi amps and wasn't a fan of the Edcor OTs or Hammond. Never tried the Sowter. Aren't the current transformers used by Retro made by Triad?

 

[TDJ]

curious if anyone ran into or discovered how to fix. my sta works perfectly. all voltages are spot on. i’ve noticed over the last several days i get the slightest fizz (distortion) when the threshold is met and the compression kicks in. i thought it was maybe gain staging, but i’m believing that less and less because it seems to do it no matter what i try. once compressing, if the needle doesn’t reach zero, it doesn’t happen again. it will only happen when compression has reached zero and then the threshold is met again. i have new tubes on the way, but thought i could pick everyone else’s brain first. thanks!

 

[wrentema]

- when the mode switch is on triple mode the unit seems to produce some kind of distortion glitches even when I reduce the input gain. The glitches are audible even in dual mode but in a smoother way. They are more audible with faster attack. They disappear when I push down the input gain but at that point the gear is not compressing anymore

I had the same. Ordered two balanced 6BA6 tubes (the rest is already matched..) from TLRT (here on GDIY) and it really solved my problem. I can use Double/Triple mode now without problems. I still have to do some more testing. But so far it has improved a lot!!

Thanks TLRT!

 

[Forcemusicgroup]

Where can I buy the PCB's for these if still available ?

 

[TLRT]

Where can I buy the PCB's for these if still available ?

Check white market thread

 

[EugeneKei]

Do you know guys if there any cheaper replacement for sowter 9062 and EDCOR CXPP10-600-8K? maybe someone used OEP and vigortronix and can suggest appropriate model to use as input and output transformers?
Thanks in advance

 

[TLRT]

Do you know guys if there any cheaper replacement for sowter 9062 and EDCOR CXPP10-600-8K? maybe someone used OEP and vigortronix and can suggest appropriate model to use as input and output transformers?
Thanks in advance

Edcor is the cheapest output transformer I think. There is a Hammond version but that isn't really cheaper too.