BTW my amp failed the same way again. DC offset at the output. Just no way to service it with 4 square inches of the circuit boards delaminating. Nearly impossible to take any measurements! Unless I wanted to blow the whole darn thing.
retro, what changes have you thought about when you rebuild yours?
DonS
retro, what changes have you thought about when you rebuild yours?
DonS
Well, to start of with, it appears my amp may be incomplete then, perhaps lacking some boards. I'd have to sit down with the circuit too tracing it out to see if it was maimed or anything, but eyeballing it, it appears to be ok.
From the schematic I can guess why DC drift is a pain w/o the servos: it's feedback network consists of a resistor divider and that's it. There is no cap (usually electrolytic) in the shunt. I have no idea what it is in reality on my unit. One of the features I liked about the unit was the capacitorless feedback network supported by the servo. To me that's a strong point. I also notice there is no parallel cap with the feedback resistor which to me would make for a more stable circuit, but perhaps there is something I don't know and a good reason why PS Audio never included it. Like I said, the schematic is the farthest I have ever gotten with my amp. If my amp doesn't have all this stuff I thought it did, I just may lose interest, but we'll see. It might open the door to other possibilities.
The 100C schematic looks pretty much like the 200c topology wise. The 100C I have worked on briefly, but just to undo some bad wiring. One day I'd like to redo it as well, and it does have a servo. But, if yours has a servo, I'm still not sure then why you have DC drift problems. Perhaps all is not what it seems on your amp. The 100c differs quite a bit in construction from the 200c.
I probably would have started off with modding the power supply for the front end, but would just have to sit down with it to see what would fit. I also had planned to work on the VAS section cause I'm not so sure I'm really satisfied with it. It burns hot and looks to swing a lot of current for the voltage gain, not to mention supplying the output stage. It's a low-gain, low feedback amp, or at least advertised to be. I'd have to sit down for some calculations. Anyway, I was planning on messing with that part and pulling out my spectrum analyzer to perhaps capture some gain phase plots in open loop. It's still a pipe dream at this point and still wouldn't represent the amp I'd build if I designed from scratch, but it would have elements. I've just been busy redoing other gear is all. There's a lot of fun stuff out there to work on.
From the schematic I can guess why DC drift is a pain w/o the servos: it's feedback network consists of a resistor divider and that's it. There is no cap (usually electrolytic) in the shunt. I have no idea what it is in reality on my unit. One of the features I liked about the unit was the capacitorless feedback network supported by the servo. To me that's a strong point. I also notice there is no parallel cap with the feedback resistor which to me would make for a more stable circuit, but perhaps there is something I don't know and a good reason why PS Audio never included it. Like I said, the schematic is the farthest I have ever gotten with my amp. If my amp doesn't have all this stuff I thought it did, I just may lose interest, but we'll see. It might open the door to other possibilities.
The 100C schematic looks pretty much like the 200c topology wise. The 100C I have worked on briefly, but just to undo some bad wiring. One day I'd like to redo it as well, and it does have a servo. But, if yours has a servo, I'm still not sure then why you have DC drift problems. Perhaps all is not what it seems on your amp. The 100c differs quite a bit in construction from the 200c.
I probably would have started off with modding the power supply for the front end, but would just have to sit down with it to see what would fit. I also had planned to work on the VAS section cause I'm not so sure I'm really satisfied with it. It burns hot and looks to swing a lot of current for the voltage gain, not to mention supplying the output stage. It's a low-gain, low feedback amp, or at least advertised to be. I'd have to sit down for some calculations. Anyway, I was planning on messing with that part and pulling out my spectrum analyzer to perhaps capture some gain phase plots in open loop. It's still a pipe dream at this point and still wouldn't represent the amp I'd build if I designed from scratch, but it would have elements. I've just been busy redoing other gear is all. There's a lot of fun stuff out there to work on.
retro, I am still interested to see the 100 schematic. Can you post or email please. The feedback is completely DC coupled so that there is no DC roll off, no shunt cap little DC feedback. Add the cap and you don't have an amp that is flat to DC. Stable no, sounds good yes. However I am not sure this is because it is flat to DC.
BTW if your amp does not have the added servo board, it's just a very early amp that never got serviced by the factory.
Like I said before, let me know if you would like the updates that the factory provided. I highly recommend them. My amp was the oldest amp in the field that still worked at all without the servo. (4 years)
DonS
BTW if your amp does not have the added servo board, it's just a very early amp that never got serviced by the factory.
Like I said before, let me know if you would like the updates that the factory provided. I highly recommend them. My amp was the oldest amp in the field that still worked at all without the servo. (4 years)
DonS
I'm interested, but I don't have a 200C. I have two old PS-IIc+ amps that are in need of refurbishing. I have been collecting some of the needed parts to replace all the power semiconductors. I want to add a DC offset servo to them, but first I want to get them working again.
I am curious about the 200C design. What kind of power supply (V, transformer VA, and capacitance) does it have?
If you are willing and interested, email me and we could trade soft copies of the 200C schematics for IIc+ schematics...
Mirlo
I am curious about the 200C design. What kind of power supply (V, transformer VA, and capacitance) does it have?
If you are willing and interested, email me and we could trade soft copies of the 200C schematics for IIc+ schematics...
Mirlo
Don, i have mail and i want those schematics too.
Please, upload them to me:
panzertoo@yahoo.com
Tell me if you want a simulator, old, small simple and effective...i can send it to you.
regards,
Carlos
Please, upload them to me:
panzertoo@yahoo.com
Tell me if you want a simulator, old, small simple and effective...i can send it to you.
regards,
Carlos
to work in the garage anymore. (95+F)
Me too, please.
Is it possible to (please)get a copy of the schematic and/or manual for the PSaudio 200C? TIA.
-chas
clm811@yahoo.com
Is it possible to (please)get a copy of the schematic and/or manual for the PSaudio 200C? TIA.
-chas
clm811@yahoo.com
DC offset at speaker terminals
I recently purchased a "non-working" PS Audio 200Cx with the intent of using the PS and case as a platform for a Leach amp clone, but I was advised by others to try fixing it first.
I replaced a bad cap & all the fuses and now it seems to "work", tho' I haven't connected my loudspeakers yet, being cautious;
However, there is a DC offset of approximately -0.75V at the speaker terminals of one channel(the other channel is much better, at about 6.5mV offset).
Anyone familiar with what could cause the large negative DC offset, and is there an adjustment/technique to reduce this?
Thanks in advance!
-chas
I recently purchased a "non-working" PS Audio 200Cx with the intent of using the PS and case as a platform for a Leach amp clone, but I was advised by others to try fixing it first.
I replaced a bad cap & all the fuses and now it seems to "work", tho' I haven't connected my loudspeakers yet, being cautious;
However, there is a DC offset of approximately -0.75V at the speaker terminals of one channel(the other channel is much better, at about 6.5mV offset).
Anyone familiar with what could cause the large negative DC offset, and is there an adjustment/technique to reduce this?
Thanks in advance!
-chas
Found it!
Paul at PS Audio was kind enough to respond to my query, and put me in touch with Rick Cullen, who does his warranty service.
Turns out the trimpot near the input jack is for adjusting offset(while the one in the center of the PCB is for bias).
If adjusting the pot doesn't solve it, I'll replace some more caps and check the input FETs, etc.
It's always a pleaure to deal with companies like PS Audio, who care enough to help us , rather than saying "send it in", like some of the bigger companies.
-chas
Paul at PS Audio was kind enough to respond to my query, and put me in touch with Rick Cullen, who does his warranty service.
Turns out the trimpot near the input jack is for adjusting offset(while the one in the center of the PCB is for bias).
If adjusting the pot doesn't solve it, I'll replace some more caps and check the input FETs, etc.
It's always a pleaure to deal with companies like PS Audio, who care enough to help us , rather than saying "send it in", like some of the bigger companies.
-chas
I recently purchased a ps audio 200 CX with one side not working. Can you send me a schematic for the 200 CX to siteon@ymail.com? For now, I would like to repair it as is. Thanks, Jim.
PS Audio 200C/CX lives again, maybe.
First off is the schematic I have. Sorry for the quality but it was hand drawn by me in 85 on graph paper from an even uglier drawing I got from the guy who designed it at PS. Don't recall his name, just that he was nice enough to remember me asking and to actually send it to me when he returned home.
http://i206.photobucket.com/albums/bb50/mikeiver1/200C_CX.jpg
I have 3 of these things, two of the 200C and one 200CX and all are messed up in some way. They sounded great when they were working. We even used one to drive a pair of Apogee Centillas set to 1 Ohm It sounded good but the thing needed serious fans.
So did the guy reworking the 200C to an A40/200C melding ever complete it and get it working?
First off is the schematic I have. Sorry for the quality but it was hand drawn by me in 85 on graph paper from an even uglier drawing I got from the guy who designed it at PS. Don't recall his name, just that he was nice enough to remember me asking and to actually send it to me when he returned home.
http://i206.photobucket.com/albums/bb50/mikeiver1/200C_CX.jpg
I have 3 of these things, two of the 200C and one 200CX and all are messed up in some way. They sounded great when they were working. We even used one to drive a pair of Apogee Centillas set to 1 Ohm It sounded good but the thing needed serious fans.
So did the guy reworking the 200C to an A40/200C melding ever complete it and get it working?
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