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Old 25th April 2007, 02:24 AM   #1
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Default Perreaux 9000B schematic?

Hi Guys,

A friend of mine has this Perreaux 9000B amp and one channel is not working properly. I checked the low voltage leg of the power outputs and all are the same except for the -side of the left channel. The good channel and positive side of the left all read .499v. The -side of the bad channel read .348v. I need a schematic to maybe see what component might be causing this unless one of you happen to know.

Thanks, Terry
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Old 25th April 2007, 08:50 PM   #2
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Bttt,

I could really use some help with this. This is a great sounding amp when it is working properly.

Thanks, Terry
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Old 26th April 2007, 03:11 PM   #3
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Hi Terry,
I haven't got a schematic I'm afraid, but you might try contacting the company for a copy (www.perreaux.com). The amp is over 20 years old now, so there are probably no trade secrets hidden in there.

There's a schematic for the 3000B model on this forum somewhere, that you should be able to search and find. It looks like a fairly generic version of Hitachi's original app. notes, and I suspect the the 9000B is very similar, but with a few more mosfets on the output.

Good luck, but be careful inside the amp. They have high voltage rails that can give you quite a belt. I suggest that you keep one hand in your pocket when it's powered up.

Andy
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Old 26th April 2007, 06:22 PM   #4
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Hi Andy,

Thanks for that. I found the 3000B schematic here .

Now I just have to figure out what is causing the low voltage at the outputs.

I'm going to do some voltage checks and maybe post them here if I can't figure it out first.

Thanks so much, Terry
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Old 30th April 2007, 11:35 AM   #5
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I just wanted to say thanks again to Andy for the suggestion. I received the schematic from Perreaux in an email yesterday. It even has some reference voltages on it.

Blessings, Terry
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Old 2nd May 2007, 09:26 AM   #6
ztan is offline ztan  Australia
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Default 8000c

Just opened up my blown 8000c:

One 2SK176 FET blown with Gate to Source short reading 500 ohms. I see these are quite difficult to get.

How critical is matching the output devices: can I replace just one of the five FETS with a good used 2SK176 or Exicon/Semelab new one; or do I need five new matched FETs?

Alternately, can I just take out 1 FET from each group and run with a RMS power of 400W rather than 500W? I probably never come close to using even 50W on account of neighbors and wife.

Does anyone have a bias adjust procedure for these amps?

Thanks,
Ezekiel
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Old 28th July 2012, 05:51 AM   #7
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Hi Guys,

Long tome no see. Sorry for resurrecting such an old thread but I am finally getting around to trying to fix this amp. I did get the Schematic from Perreaux and have attached it here in PDF.

The voltages shown I will list here.

Assuming the rail voltages are within spec (+/- 110 volts) then this is what you should have:

Q5:

base = 107 V
Emitter = 107.5 V

Q3:

Base = -108.5 V
Collector = -54 V
Emitter = -109 V

Q4:

Base = -108.5 V
Emitter = -109 V

Q1 & Q2:

Emitters = 0.7 V


Quiescent current from the power supply under no load should be 170 mA.


There should be 0.6V across RV1 (the bias adjust preset) from one end of the pot to the other (ignoring the wiper)


OK, so here is what I have so far;

First of all, I have +/-120v on the rails instead of 110. I'm not sure why. the Schem shows 84vac on the transformer and mine is showing 77v under load.

Anyway, here are the voltages I am reading on the bad board;

Q5:

base = 115.3 V
Emitter = 115.8 V

Q3:

Base = -116.6 V
Collector = -35 V
Emitter = -117.2 V

Q4:

Base = -116.4 V
Emitter = -117.2 V

Q1 & Q2:

Emitters = 0.744 V


I have 0.874 V across RV1.


Truth is, the good board measures almost exactly the same on all these measurement points.

Where they differ is in the outputs. the gates of the good board read +/- 0.490 V, however the gates on the outputs of the bad board read + .489 V and on the - side they read 308 mv.

Any help will be greatly appreciated.

Blessings, Terry
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Last edited by still4given; 28th July 2012 at 06:05 AM.
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Old 28th July 2012, 06:27 AM   #8
Nrik is offline Nrik  Denmark
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Quote:
Originally Posted by still4given View Post
First of all, I have +/-120v on the rails instead of 110. I'm not sure why. the Schem shows 84vac on the transformer and mine is showing 77v under load.
When you load it ofcourse the voltage will drop a bit - should not be alarming.
About the differnece in rail voltage: A couple of years ago, in some parts of Europe they adjusted the supply voltage so that all countries have the same voltage. So before some EU countries had 220V and other 240V. In Denmark we had 220V and it is now 230V. This means that old amplifiers suddaently have 5% higher secondary rail voltage.
Could it be a similar scenario in your case?


Quote:
Originally Posted by still4given View Post
There should be 0.6V across RV1 (the bias adjust preset) from one end of the pot to the other (ignoring the wiper)I have 0.874 V across RV1.
Where they differ is in the outputs. the gates of the good board read +/- 0.490 V, however the gates on the outputs of the bad board read + .489 V and on the - side they read 308 mv.

Blessings, Terry
It could be the DC-blocking capacitor in the feedback loop (C4) that has failed and is now shorted.
Replace that to start with.
Best thing to do is actually to replace with a bipolar capacitor, which it should have been from the beginning.
You could use two 1000uF polarized caps with the two + leads connected between them, and the two - leads as the new terminals.

It could also be a case of one MOSFET has given up, or is not open. I had similar case recently on an Accuphase P260 (year 1979) with almost the same MOSFETs. Some of them had given up ( open connection) leaving only half the current towards one of the rails because only MOSFET was conductíng, and two conducting towards the other rail.
Makes sense?

So you should check that all the sourceresistors have current running through them, preferebly and equal value +-20%
If anyone of them has an voltagedrop wich is zero or much more than the other ones, it could mean that this MOSFET needs replacement.

If all thing are good, then you could try - carefully - to adjust VR1.
Adjust for a little more bias to make sure all the MOSFETs are safely in an open state. It could just be a small turn and everything could fall into place.
This should however be taken car of by the DC-blocking capacitor in the feedback loop, so start with that.

Regards Henrik
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Last edited by Nrik; 28th July 2012 at 06:36 AM.
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Old 28th July 2012, 09:20 AM   #9
Nrik is offline Nrik  Denmark
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Quote:
Originally Posted by Nrik View Post
This should however be taken car of by the DC-blocking capacitor in the feedback loop, so start with that.
...Reading your messages a bit deeper I see now that you mean the bases of the MOSFETs that have these 0.4-0.5v voltages. ( I read it as the DC offset of the whole stage!)
Well...these voltages doesn't seem to far off ... so what is the real problem?
How is the channel not working? Distorted sound or no sound?
Is the offset of the channel below 30mV?

Is the Idle current around 170mA after 30 minutes without load?
(Measure voltage over the source resistors, divide by value, add all results together)
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Old 28th July 2012, 09:24 AM   #10
Nrik is offline Nrik  Denmark
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... and now I see there are no source resistors

Sorry for all the posting.

How to measure Idle current: Replace one of the fuses with a 0.1 ohm - 0,2 ohm resistor and measure the voltage over it.
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