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Old 3rd December 2009, 02:15 PM   #1
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Join Date: Oct 2009
Default Help: problem whit my Perreaux power amp

Helloguys,
here is Alberto from Italy.

Great forum, I've been (only) reading it for a time, but now I need your help...

My system is the following:
- digital source: Sony cdp-x555es
- power amp: Perreaux 3000b (no preamp -the x555es has variable outputs-)
- speakers: Jbl L100 Century

I bought the Perreaux only a few weeks ago, it's a great power amp, but since the first time I connected it to the source (no preamp) it manifested a nasty "blow" (a continuous "ffffffff") form the speakers when the track starts.

No problem with the player disconnected.

Since the Perreaux has ONLY TRS jack inputs (and the player has unbalanced rca variable outputs) I use a diy cable between cd player and power amp, as explained here:

http://www.vandenhul.com/userfiles/d...Y_purposes.pdf

male rca to male balanced jack (TRS).

This is power amp's spec sheet

http://www.perreaux.com/assets/file/.../049-3000B.pdf

as you notice, input impedance is indicated only for "balanced". Does it mean that tha amp accepts only balanced sources??

Is there something wrong in my setup? I'm going mad whit this "fffff"
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Old 3rd December 2009, 02:46 PM   #2
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I read on the spec sheet:

"Hum and Noise: 80dB below rated output 20Hz-20kHz"

Maye ts this the problem and I can't do nothing??
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Old 3rd December 2009, 04:15 PM   #3
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Join Date: Jul 2004
Location: Italy
Quote:
Originally Posted by albamaiuscola View Post
Helloguys,
here is Alberto from Italy.

Great forum, I've been (only) reading it for a time, but now I need your help...

My system is the following:
- digital source: Sony cdp-x555es
- power amp: Perreaux 3000b (no preamp -the x555es has variable outputs-)
- speakers: Jbl L100 Century

I bought the Perreaux only a few weeks ago, it's a great power amp, but since the first time I connected it to the source (no preamp) it manifested a nasty "blow" (a continuous "ffffffff") form the speakers when the track starts.
No problem with the player disconnected.
I understand the "blow" as "soffio" i.e a white/pink noise not a hum (line frequency noise)
As for your description we have (at least) 3 cases:

1) Cable disconnected from the player: OK
2) Cable connected to the player AND Track starts: "blow"
3) Cable connected to the player AND player ON AND Track starts: OK ? (I suppose yes)

In this case it seems the noise is coming out from the player when it is not muted i.e the track stsrts.

Quote:
Originally Posted by albamaiuscola View Post


Since the Perreaux has ONLY TRS jack inputs (and the player has unbalanced rca variable outputs) I use a diy cable between cd player and power amp, as explained here:

http://www.vandenhul.com/userfiles/d...Y_purposes.pdf

male rca to male balanced jack (TRS).
Despite what I have written above you can try the following:

1) connect the blu wire (ground wire on the RCA side) to ground on the jack TRS side
2) connect (on the jack side) the pin left free by the blu wire to ground by 50 - 1kOHM resistor.
3) leave (just for the sake of thiis test) the shield unconnected or connect it to ground on one side

P.S note that the S/N ratio of the amplifier (80 dB as for the mfc specs) is lower than the CD S/N ratio (96 dB)

[Edit]
P.P.S I've read your second post after having post this message. I think you have to check in the direction of the S/N ratio although this figure (80dB) seems very low for a power amplifier

Last edited by diy_audio_fo; 3rd December 2009 at 04:21 PM.
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Old 3rd December 2009, 05:37 PM   #4
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Join Date: Oct 2009
Thank you for your reply.
Yes, the problem is a "soffio", nt a hum.

Quote:
Originally Posted by diy_audio_fo View Post
In this case it seems the noise is coming out from the player when it is not muted i.e the track starts.
Right. Player on, and track stopped, zero noise. All is ok.

Quote:
Originally Posted by diy_audio_fo View Post
P.P.S I've read your second post after having post this message. I think you have to check in the direction of the S/N ratio although this figure (80dB) seems very low for a power amplifier
Well, it seems low value also to me, but now I notice that others amplifier have S/N ratio of 80db... Audiolab 8000se for example. I don't think it is the real focus... Am I wrong?
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Old 4th December 2009, 08:14 AM   #5
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Join Date: Jul 2004
Location: Italy
Quote:
Originally Posted by albamaiuscola View Post
Thank you for your reply.
Yes, the problem is a "soffio", nt a hum.

Right. Player on, and track stopped, zero noise. All is ok.
There are zillion of tests and measurements to perform but IMHO the very first one is to swap the Perreaux with an other amplifier (with approximatively the same gain).

Keep us up to date with your progress (BTW have you tried the cable wiring I suggested? - If I am right it wouldn't have NO positive results)
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Old 4th December 2009, 01:45 PM   #6
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Today I connected my MOBILE PHONE (), a Nokia 5800, with the worst connection possible, direct to the power amp:

-2 male rca/one male 3.5mm jack stereo adapter (to the mobile)
-2 male rca/2 male rca cable (the worst cable you can imagine: the classic white-red)
-2 male rca/male 6.3mm jack mono adapters (to the Perreaux).

The result? Zero blow. The system sound clean, powerful and (reletively) defined.



Tried the same connection on the player, and no problems.

I didn't tried before this configuration because I thought my "reference" cables (diy - very good rca and Tasker c128 ofc microphone cable) in different configurations were the better choice I can made.

And they are well done: no cold slodering, all done with care.
I don't understand
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