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

Yes that is correct if youre not using in line trimmers (which im not) i have little bridges on the wipers of all of them except the voltage adjust.

OK, this is where I'm at.  I have one channel passing a signal.  If you see attached pic.  The yellow trace is the input signal & the Blue trace is the very noisy output signal.  It seems to have some oscillator artifacts.

I could post some transistor voltages, but I'm not convinced they're all correct as the compressor doesn't seem to be doing much apart from passing a noisy signal.
Would be very useful at this time if someone who has a working unit could post the transistor V's & give us a hint as to how to calibrate the presets.  Anybody know of someone who could do this ?

Off to France on a job tomorrow so, won't get to work on my unit for a few days but should be able to get on line.

Cant help you (yet), still waiting on input transformers. The only poster that has indicated he has a working unit is SR1200.

Does that HF stuff go away as you lower the input? Not familiar with computer scopes, but is the output set on 5V per division? 10:1 probe or something?

I have left the chopping transistor(s) off of my boards until I get clean audio in and out...

The HF stuff is there regardless of input level.   

You can test the amps without an input transformer, just hookyour testsignal  to the input pot.  The first transistor is decoupled with a cap.

The scope might have been set to 1:10.  I'm not sure I only just got it, because my ancient analog scope died the first day I was trying to test this unit.

I now have meter action, but no actual compression ......  However I'm using some old GR meters that look they they have come from original Pye's, so they may not be the same F.S.D as the ones you guys are using.

Still could do with some info on how to set these presets.  SR1200 do you have any info since you seem to be the only person with a working unit ?

Any resolution to that HF hash you had all over the place?

My transformers arrived this morning, so hopefully this weekend I can wade into mine......

Seems if you are getting meter deflection that the side chain is working to a point. Did you triple check the pin-out on the chopping transistor? Thats about all thats left between the meter drive and the audio path.

No, I still have HF all over the place after the chopping circuit.

I have checked the chopping transistor pinout.  I wish I had more info about the presets.  I read the original PYE manual, but most of the presets are factory set fixed resistors so there's really no info on how they should be set. 

LOL. Yeah Ive got several original PYE manuals now, not much use really. I thought I had it made with the transformer specs in one of them. Only value listed: "DC resistance very low" wow, that sure helped. Can you disable your oscillator easily? I think I would approach trying to get clean audio through it at roughly unity gain, then start in on the SC et al.

Yes, it's easy to disable the oscillator, I just unplug it ...... However there is some real weirdness going on & I still can't seem to get a clean signal.

Sounds like you are dealing with some sort of oscillation. Its funny I recall one of the first replies in this thread and it was yours asking about the trickyness of designing RF circuits.

I havent powered mine. But when I was talking to Cinemag about transformers the very helpful gentleman asked if I had a schematic, which I provided to him. He suggesting removing C3, 4 and 5. Possible issue here?

Don't think the caps are the issue I get a clean signal until the junction of R16 R17.  the other side of R17 is where it becomes full of RF.  I tried installing 49mH inductors that I had instead of R1 & R68, but it makes little or no difference.

If you dont calibrate the "chopper" you're going to have a bad time.  Are you sure you have the clock set to the correct (or thereabouts) rate?  When i first powered mine up all i got was noise and a headache, after i calibrated that chip, all was well.

That was the first thing I did ....

I found a mistake I made.....   

I incorrectly hooked up the s/c transformer, so the primary was open circuit.  Sorted that out & had one channel sort of working, but I think the calibration was all over the place. 

I also had the meter working, but not properly.  I couldn't get it to sit at zero with no GR happening, & when it did operate it was a bit "on/off".  However that could be down to the calibration.

Anyway something happened & it's not good anymore.  Will have to investigate further tomorrow.

Some observations about the trimmers

R42

If you hook a scope up to junction R17/R18 & play with trimmer R42 it enables you to make an injected sine wave symetrical.  Note that at this point you will see the side chain signal superimposed onto the audio signal, so it will appear a bit ....fuzzy ...  See the yellow trace in the attached pic

R23

If you scope the output R23 makes an injected sine wave appear on the output socket more symetrical.  Although on my unit it won't make it completely symetrical (more investigation required).  See blue trace in attached pic.

R44

This appears to change how much the sidechain affects the audio signal.

I know the 2 oscilloscope traces are out of phase. That's to do with where I connected the scope probes. The overall signal is in phase.

I'm still getting a superimposed sawtooth wave on my output signal.  I'm not entirely sure where this is coming from at the moment.  I don't think it's anything to do with the sidechain because the frequency is much lower, unless it's a sum & difference type artifact.

I now have one channel working quite well now.  Still a little bit of RF, but it's compressing properly.

The meter circuit also is working, although I can't get it to zero when there is no GR happening.  This could well be because I am not using the specified meters.    So, I will probably need to play with some resistors to get it working.

One thing worth noting is that if turning the output pot up a lot, the a sine wave seems to distort quite badly, which made me think that the unit had an issue.  So it seems quite level dependent.  This may not be an issue with an original unit where these controls are ganged together.  However it could be a transistor biasing issue, where some of the resistors have been changed from the original values.

SR1200 do you have a way to check these observations ?  I would be interested to know whether it's just me getting these issues, so I know whether I need to carry on tweaking the circuit.

thats good news Rob! Was it a matter of fooling with the trimmers? Or fooling with the input output level controls? Or a combination of the two?

A bit of both.  I was prodding the pcb a bit, & found some areas that affected the response, so I reflowed the solder..

I'm using a garderners 10k:10k on the input, an OEP on the sidechain, & a Jensen JE123p in a 1:3 configuration on the output.

How did you organize the output transformer? As a 3:1 step down (seems like this cant produce diddly for output) or the other way 1:3 step up?

1:3 step up.  They are quadrifiler wound so they have 4 identical windings.