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Old 20th January 2012, 11:21 AM   #1
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Join Date: Oct 2007
Location: Leeds
Default PSS Audio 1000 Amp Docs/Help needed

Hi Folks,
just a quick one for starters.

Got my hands on above amp from 2001, which is misbehaving in that it seems to be very quiet (for 300W/8Ohms/channel) and the "Peak"(clip?) light starts flashing on 1 channel when turned up to about half, but there is no audible distortion when fully turned up when music signal around 0db present (neigbours aren't complaining, that's how quiet it is fully turned up!).

This amp is a very strange design in that it uses only npn bjt's and also has some very strange cooling arrangements.

I did try and contact PSS Audio but they haven't responded; however, I have found a thread in this forum dating back to 2002 where these amps were discussed and apparently at that time schematics were available from their website.

So I am hoping, that someone will have copies of these still flying around somewhere, or someone may remember something about these amps?

Otherwise it is up for grabs for cheap, as have too many amps lying around anyway.

I am trying to learn and make my way towards eventually building my own amp but don't as yet know enough about circuits and what they do/look like.

I do know how to check and measure components but please go easy on me, maybe we can all learn a bit from this and subsequent posts/threads, as got some more amps that need looking at but so far have defied me...

Regards
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Old 20th January 2012, 07:08 PM   #2
Tajzmaj is offline Tajzmaj  Slovenia
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Join Date: Mar 2011
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Hi...
So. Once I serviced something similar. I think It was 2000. But all schematics seems to be very similar......if you can post some pictures of opened amp maybe i can find the right one....those amps have one major lethal construction mistake.....bad really bad cooling. I mean really very very bad......The unit which I serviced was badly overheated.......and if I remember correct the outputs were
mounted by some sort of rivets......hard to repair....a lot of work.
Regards, Taj
Attached Files
File Type: pdf SCH%20Ampli%208-C2.pdf (66.2 KB, 93 views)
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Old 20th January 2012, 07:58 PM   #3
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Hi Taj,
thanks for that. I am pretty sure you are absolutely right with the attached schematic and in what you say. Not only are the O/P devices riveted(!) to the pcb, but also the fan to the whole heatsink, so should the fan ever fail you can't even replace it.

You can have a look at some pics on their website. I think the pics of all the innards of the PSS are the same on there, so doesn't really matter which one you look at. By the looks of it the 1000 just has less caps and less O/P transistors than the 2000, although not sure. I'll post some pics in a day or two, just in case.

By the way, if you go on their website, don't raise the cooling thing with the guy who designed them: I tried to contact him about it and got some abuse back but no reply to the request for a schematic. Go figure.

I'll have a look at that drawing you gave me and see what I can come up with.
May need a few pointers and/or explanations of what certain circuits do because i want to learn how to eventually build my own amp(s), or at least confidently tweak some...

regards
Jens
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Old 20th January 2012, 08:17 PM   #4
Tajzmaj is offline Tajzmaj  Slovenia
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Join Date: Mar 2011
Location: Ljubljana
If I'm correct i get all files from PSS website...so I have here something like 20 files. All similar. Uf I remember now that fan is riveted....hehe funny and sad....
I replaced op amp at 2000 by OPA604 but there was a problem with power dissipation at voltage drop resistors in supply rails. But 741 which was in 2000 sounds really like crap...
So if you need anything else pm me or send me an email. I'm in the UK btw.
Best regards, Taj
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Old 20th January 2012, 10:55 PM   #5
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Join Date: Oct 2007
Location: Leeds
Hi mate, thanks again for all the help.

I am beginning to think they were trying to develop this amp as a HiFi, well, home amp which could also be used as a PA amp, hence the soft wishy washy sound and the quiet(ish) fan? Doesn't look very successful but it will do fine for me to learn some fault finding techniques and circuit functions.

That's if you are happy to talk me through it? I'll try and do some Horowitz & Hill reading in the meantime...

This amp uses TIP50 near the inputs and MJE13007/5852 near the outputs. There are also provisions for TIP41c/42c in place of the MJE. Funnily enough, also found a few of those 741 in there.

I looked at the data sheets for those MJE and they are fast switching devices usually used in industrial switchmode applications? What are they doing in here? Are they drivers of some kind?

I need to print the schematic off and sit it next to the pcb. It doesn't really help, that there are no values in the schematic but I hope that channel b is alright and try and just compare.

Re the flashing "peak" LED where would you start looking and, most importantly, why? What would cause this to flash with normal audio signal and only half turned up? Well, the voltage drop is larger here than on the other channel, therefore it can not be a faulty LED on the other channel. So where does it get its' signal from? See, if I understood circuits I would know that instantly.

Maybe you could even talk me through what each section/part of the diagram does?

And also, what would you use instead of those 741's.

I think you may begin to see just how far down the ladder I am starting...

I am just about to dive into that diagram and try and identify the points you mentioned, so wish me luck.
Thanks again
Jens
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Old 21st January 2012, 04:37 AM   #6
Tajzmaj is offline Tajzmaj  Slovenia
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Join Date: Mar 2011
Location: Ljubljana
Hey...I have separate files for part list and for boards as well. At list I think so. Send me an email and I will send you all those pdf files....because of size it is impossible to do it here...
Here we can discuss.....hehe....I will try to remember something else ....
Best regards, Taj
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