PYE Compressor/Limiter Thread *boards shipping* BOM up!

[bieckmusic]

Thanks so much for the info, I do need to get a scope and signal generator.  Plus I don't have an rms voltmeter, which really messes me up sometimes... 

great job!!

Greg

 

[bruno2000]

Got just one channel up and running, and have a couple of observations.
1.  My osc signal is pretty nasty looking, not like the traces you published.  I need to have a look at it out of circuit.  No problem adjusting to 250kHz,
2.  No matter what I adjust, I cannot get a signal with less than 3% distortion through the system, even with the osc pulled.
More testing next weekend.
Best,
Bruno2000

 

[Biasrocks]

Wondering if we have a definitive version of this build at this time.

It seems like it's still up in the air and I would like to start this project with
at least a reasonable expectation of success.

Mark

 

[mdainsd]

Mark, I think you will be OK. There has been a little fooling around with it since the support never materialized from the maker of the boards.

But, it works. There are a couple of working ones, and a couple coming to life but going through some teething problems. The more that come on line the easier it will be to identify pitfalls and avoid them.

 

[bruno2000]

Progress!
Both boards pass audio, and I get about 30dB of gain with both pots full up and the sc xf disconnected.  Side chains are not matched at all, so something is wrong.  No time this weekend to check components, but back at in a couple of weeks.
Best,
Bruno2000

 

[bruno2000]

Also, beware Edcor transformers!  I ordered 4 of their 600:10k for the sidechain.  One was terminated incorrectly (CT and End reversed).  Now they track together in "compress / off", but there is still something wrong in "limit / on"
I am constantly amazed by you folks with limited test gear that get these projects done........
Best,
Bruno2000

edit, spelling error.

 

[mdainsd]

Check the seven conductors that hook the main board to the switch board carefully. It would be easy to make  mistake there.

 

[bruno2000]

Thanks for the thought, but I'm using ribbon cable.  Less chance for error.
Probably bad solder/
Best,
Bruno2000

 

[bruno2000]

I have 2 channels up and running, tracking really well, but have a couple of questions to those of you that have built. 

What Voltage are you running on the rail?  The manual calls for 16V, but I have seen 20-21V mentioned. 

What output transformer are you using?  Mine are really sensitive to loading on the output.  Seems to me that there would be a beefier output section to drive a transformer.

More thoughts:

I have a drawing #84575/00 that shows a completely different output section with an output transformer that has a feedback winding.  The scan is not so good.  Anyone have a better one?

I question the 175 ohm choke in the power supply section.  Makes the output rail pretty soft.  Thinking about winding my own choke with a MUCH lower DCR.

I made some in/out graphs, and will post later today.

Thanks for the help!

Best,
Bruno2000

 

[mdainsd]

Hi Bruno

I run my rails at -22V

I use the edcor 600:10K XSM (I think) for the output as well as the side chain. Ive fooled with them both, running them forwards and backwards, also all the way across the windings or just center tap to one side, trying to find just the right balance.

I have that schematic you are talking about with the output transformer with feedback and a full PP output. Ill see if I can get it scanned, no promises though.

As far as that 30dB gain...These things are originally designed for unity gain. The two attenuators are physically linked in the originals. This is where I am with that. They should be in lockstep with each other, if you increase the threshold one step, a corresponding decrease of one step on the gain attenuator should still be giving unity gain throughout (in 1:1 ratio). Mine does not yet do this and I believe that the problem is the willy-nilly choice of the output transformer.

 

[bruno2000]

Thanks for the info!  When I ran the output up, and connected a 600r load to the output, some strange things began to happen.  The circuit is just not stable.  All it has are those 560s running on 16V (22V).  That's not much swing.  Now I know in the "Pye book" the circuit shows an output transformer, but I wonder if this wasn't meant to be an interstage transformer rather than an output(?).  That's why this "new" (to me) circuit is of interest.

Here is my input vs. output graph showing the curves.  Looks like the 1:2 setting might be really nice!

Best,
Bruno2000

Edit:  The curves are 1:2, 1:3, 1:5, and Limit

 

[mdainsd]

Wow! Those curves look about right on. Was the red top line the limit trace? If it is ist should be 8 dB above the knee of the red trace below it. You're close!

I was trying to do the same by photographing the Oscope with a modulated burst, what a pain in the ass, LOL.

Does that graph represent the full range of threshold?

 

[bruno2000]

I should have mentioned that these are stereo sweeps, but the two cards are not "linked".

The input and output controls did not change for any of these sweeps, just the "ratio" and "limit" switches.  I did run the same sort of tests at different input/output settings, and as expected, the knees just moved up and down.

More output tests this weekend.

Best,
Bruno2000

oo812green

 

[mdainsd]

Hmmm. Puzzling. You say no adjustment were made to the threshold or gain controls, but the different sweeps are displaying different threshold levels. The knees should all be at the same place, except for limit which should be 8dB above the threshold obtained from the compression ratios.

 

[bruno2000]

Hmmm. Puzzling. You say no adjustment were made to the threshold or gain controls, but the different sweeps are displaying different threshold levels. The knees should all be at the same place, except for limit which should be 8dB above the threshold obtained from the compression ratios.

Could that be because I have made no effort to adjust R52?  All of the other "trimmers" on my boards except the Voltage adjust are the suggested resistor values.
Best,
Bruno2000

 

[bruno2000]

So I'm going to ASSume that I need to make a 2 section pot or switch that is 10k log for the input section coupled with a 10k r/log for the output section.  Might take some tweaking to get it right.........
Best,
Bruno2000

 

[mdainsd]

No, you dont have to do that. As long as you remember that the two controls work in tandem (if you turn one up, turn the other one down), all is good.

If you turn them both up, you will run into distortion pretty quick.

I am working at replacing mine with stepped attenuators, the originals state in the manual "40dB attenuators 2/dB/step reverse coupled"

 

[bruno2000]

No, you dont have to do that. As long as you remember that the two controls work in tandem (if you turn one up, turn the other one down), all is good.

If you turn them both up, you will run into distortion pretty quick.

I am working at replacing mine with stepped attenuators, the originals state in the manual "40dB attenuators 2/dB/step reverse coupled"

That sounds like a great idea!  I should do that too.
This weekend I'll try adjusting R52 to see if I can line up all of the knees.  Any other tests you'd like?
Best,
Bruno2000

 

[bruno2000]

Question: So when the attenuator is in the "middle", the input pot is 20dB down, and the output pot is 20dB down as well?
Thanks!
Best,
Bruno2000

 

[mdainsd]

Basically, yes. that is the cross over point were both attenuators are at the same value.