Pye Compressor

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CJ

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ok, this version of the Pye compressor with two output transformers is causing problems,

a new xfmr DIY style was wound and wired into the OPT slot which requires an FB wind, so we went with a 2.2K:600 with a 110 turn FB which works out to about 8.8 to 1 or something,

but the darn thing oscillates, so we are thinking either the FB ratio is two low or there is a problem with the schemo,

a real xfmr was measured with a much higher DCR than we wound, but we thought that this was an error, so maybe the orig xfmr has a lot of turns on the FB wind which does not make sense,


any thoughts? thanks!

 

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> ...an FB wind ..... but the darn thing oscillates

Well.... reverse the FB polarity? Try running it without the NFB connection?
 
Well, if you feel like needing more negative feedback could try lowering the value of the 330Ω resistors...

JS
 
good ideas, thanks!

here is the output section on jpg, gonna see if we can get some voltage readings,

if we fix it, our acoustic guitars will sound just like Cat Stevens with all that plectrum sound and stuff,  :D
 

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To add to the confusion, the manual I have says the DCR of the primary is 2.16 and 2.12 on each side of the CT.  2.16 ohms?  Could that be a misprint?  Secondary is listed as 10.3 DCR and the feedback is 26.2 and 28.0 DCR on each side of the CT.  The CT on the feedback is not used.
Thanks for your wisdom!
Best,
Bruno2000
 
So I pulled out C12 & C13 and attached the balanced floating output of the AP where they had been.  40r source impedance.
Here's a 400 Hz tone through the output circuit.  Input was -10dBm, output was +18dBm.
 

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Back to 40r source, but upped the caps to 15nF rather than 1n5F.  Looking better.
 

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bruno2000 said:
To add to the confusion, the manual I have says the DCR of the primary is 2.16 and 2.12 on each side of the CT.  2.16 ohms?  Could that be a misprint?  Secondary is listed as 10.3 DCR and the feedback is 26.2 and 28.0 DCR on each side of the CT.  The CT on the feedback is not used.
Thanks for your wisdom!
Best,
Bruno2000

Actually, it's the secondary that is center tapped and has the resistance of 26.2+28R, and feedback is 10.3R. At least according to the manual you refer to.
Still fb winding is around 1:1.5 which looks like way too high.  And no phase info.
 
I have a Pye on the bench.
OP tranny 772246 measures almost exactly what the manual says.

Primary is on pins 1 and 3 centre tap on pin 2.
Pins 1 and 2 = 40 micro H. 2.1 ohms.
Pins 2 and 3 = 38.8 micro H. 2.2 ohms

Secondary is pins 7 and 8. 11.08 mH. 10.6 ohms

Feedback winding is pins 5 and 6 (centre tap on pin 9 but not connected).
6.442 mH. 56 ohms.

Can't check the turns ratios or phasing at the moment but will try when I get it powered up.

Hope this helps.
 
DE said:
I have a Pye on the bench.
OP tranny 772246 measures almost exactly what the manual says.

Primary is on pins 1 and 3 centre tap on pin 2.
Pins 1 and 2 = 40 micro H. 2.1 ohms.
Pins 2 and 3 = 38.8 micro H. 2.2 ohms

Secondary is pins 7 and 8. 11.08 mH. 10.6 ohms

Feedback winding is pins 5 and 6 (centre tap on pin 9 but not connected).
6.442 mH. 56 ohms.

Can't check the turns ratios or phasing at the moment but will try when I get it powered up.

Hope this helps.

Cool!
5-6 is secondary, 7-8 is feedback - check with the schematic. Actual measurement with signal generator and a scope will be very helpful indeed.

While it's on the bench could you please check the input and interstage transformers as well?
 
No Ilya, I disagree, the pin outs of the output transformer are as I posted, and are as shown on full schematic of compressor.
The transformer pin outs are marked on the transformer very clearly and pins 7 and 8 have the Zobel network soldered across them.  All my Measurements were taken with reference to the actual numbering on the transformer.
The transformer diagram in the full manual has the output and feedback windings upside down compared to the full schematic but the pinouts are correctly numbered.

Will post turns info when I can power the unit up to fully test it, I need to fix the power supply first.
DE
 
You are correct. I was mislead by the resistance values and somehow managed to mess up the  winding numbers. Apologies.
 
I've returned to working on the Pye after an extended break to deal with more pressing things.
The story so far: Powered it up after checking the psu was the correct voltage.
One of the output transistors was running very hot, the other cold.
Powered down, checked transistors, the cold one had high resistance EB  junction. Both transistors look as though they've been running hot, PCB discoloured  under them.
Replaced both transistors with new 2N3053s.
Checked driver transistors and all resistor values, all good.
Replaced all electrolytics on both boards with nearest values of Vishay BCs. Old ones were a mixture of originals and replacements.
Powered on, BOTH output transistors now run very hot, but most voltages around them are almost correct.
Unit is passing signal, but couldn't test fully due to overheating.
Measurements indicate that power in output transistors is not excessive, but they get VERY hot.
Suspect HF oscillation but don't have a scope at the moment to investigate further.
The original psu is not quite as per the circuit I have but it has two germanium transistors in it, recipe for disaster in the future.
I'm going to replace the whole psu with a modern one.
Not the easiest device to work on, all component leads are bent over before before soldering making removal difficult and PCBs traces lift easily. Also the rats nest of hand wiring under the boards is hard to work round.
Still hoping to get the turns ratio of the output transformer WHEN I get it working! New oscilloscope arriving next week.
 
If this issue isnt yet resolved,

It may be of interest to know that the PYE compressors were based on the BBC design. Checking out some of those diagrams might help...?
 
Cutterwoller said:
If this issue isnt yet resolved,

It may be of interest to know that the PYE compressors were based on the BBC design. Checking out some of those diagrams might help...?

Thanks for the info!  We have  lots of diagrams, but no actual transformer to measure.  That's our present dilemma.
Best
Bruno2000
 
you might have some shorted turns in that OPT if you only get 2.1 ohms,

better send it here for a rewind,  ;D

that nickel core might be playing  havoc with the digital ohm meter, hopefully you can scope all the windings and get some ratios,
 
Found this guy that builds PYE comps and contacted him, but he won't tell anything about his units.  Says he spent a lot of time, spent a lot of money................
http://www.pompye.com/index.html
Any member have one of these?
Best,
Bruno2000
 
At last got the Pye back on the bench. It's the 845751 horizontal version, not the upright version but the electronics are pretty much the same.
The transformers measure as follows:

Input trans  (771273) - DC resistance and inductance as in my earlier post.
Turns ratio 1:1.

Side chain trans ( AL22390) - DC res and inductance as per earlier post.
Turns ratio 1:1+1 (pins 1 and 3 : pins 4, 5 and 6 so it's wired as a 1:2 step up into the bridge rectifier).

Output trans (772246) - all resistances as per my earlier post and as per the service manual (no shorted turns it would seem).
Turns ratio primary to secondary  = 1: 1.08.
Primary to feedback winding = 1: 1.44.
Centre tap of primary ignored, all measurements are taken by putting 100mV across pins 1 and 2 and measuring across pins 5 and 6 or 7 and 8.
All measurements taken with transformers disconnected from electronics.
Output transformer will take +8 dBu without saturating and is almost flat from 10Hz to 20kHz.
I can't easily test at the claimed +24dBu.
Any questions or further info required?
Meanwhile, does anyone else have a Pye to compare? I still have a problem with op transistor temperatures, they should have heat sinks but these seem to have been removed and I also think the standing current is too high. I'm using new 2N3053s but some schematics list BFY56s. Voltages around the output stage are almost correct but not quite right so might need bias tweaks to cure the problem. Total current draw is 170 mA which is about right.
I'm running off a bench psu at the moment as I don't trust the germanium transistors in the original not to fail and destroy the compressor!
Hope this is useful info and any suggestions and observations welcome!
DE
 

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