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QUAD 606 Mk2 Power amp PROBLEMS
QUAD 606 Mk2 Power amp PROBLEMS
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Old 1st March 2007, 01:27 PM   #1
arupg is offline arupg  Latvia
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Default QUAD 606 Mk2 Power amp PROBLEMS

Hi

I notice a peculiar thing from my 606-mk2 power amp driving my B&W Matrix 802s. When I turn-on the amp while all rest of the gear is powered-off, I notice a slight buzz on the RIGHT channel speakerís Tweeter while the LEFT channel is totally clean & absent.

What could the source of this noise in the 606-II?

Your guidance will be most helpful. I do want to rectify this ASAP. Can it be one of the small value caps? If so, which one or where to look for in the amp.

Thanks in advance!


P.S. Anyone has a schematic of this amp or the new Quad 909?
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Old 2nd March 2007, 06:49 AM   #2
big jim is offline big jim  England
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Go to quad405.com
its part of Grace Audio and you will find the 606 circuit



all the best jim
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Old 2nd March 2007, 07:29 AM   #3
arupg is offline arupg  Latvia
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Thank you. That was a good lead....
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Old 3rd March 2007, 12:14 PM   #4
audiomatic is offline audiomatic  Germany
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Hi;

check the virtual ground circuit (T15/T16 and resistors).... if faulty, also have a look at C9/C11.

regards, audiomatic
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Old 3rd March 2007, 06:41 PM   #5
arupg is offline arupg  Latvia
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Thanks for the tips. C9/C11 220uF caps can be the cause. I am not sure that around T15/T16 and its associated resistors, if they could be the cause.

Do you think it could be some of the small caps located around the input area like around the opamp. Alternative is whether the opamp itself is wearing off......
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Old 16th February 2017, 12:02 PM   #6
johnm is offline johnm  United Kingdom
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Ressurecting this old thread, I'm having exactly the same problems with my Quad 606. I've detemined it's not the internal wiring, loose phono sockets, or any dry joints, and all the caps were replaced last year. Like your case the left channel is totally silent, with a slight hum on the right side. I guess I need to check the offset +/- psu voltages are correct, R36, 37, 39 & 39, and that the op-amp is getting a stable 6V8 via pins 4 & 7.
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Old 16th February 2017, 01:11 PM   #7
johnm is offline johnm  United Kingdom
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Have measured the DC rail voltages (uneven by design). The values Quad mention in the service manual are 57.8V, and -53.6V.

On the (silent) left channel: 57.6V, and -52.7V.

On the right channel with slight hum: 58.2V and -52.7V.

Don't seem badly out of spec, likely just different tolerances in the secondary windings.

Not sure how to measure the op-amp voltages as the pcbs are screwed into the case that also acts as a heat sink...

Edit: datasheet link - http://www.meridian-audio.info/publi...%5b2167%5d.pdf
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Old 23rd February 2017, 03:33 PM   #8
MLoc is offline MLoc
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Hey John,
Have you had any luck resolving this issue?
I'm having a similar problem with a Quad 306 I just picked up.
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Old 26th February 2017, 12:57 PM   #9
johnm is offline johnm  United Kingdom
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Quote:
Originally Posted by MLoc View Post
Hey John,
Have you had any luck resolving this issue?
I'm having a similar problem with a Quad 306 I just picked up.
Hi there.

No I haven't unfortunately. No responses either to this problem alas.
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Old 26th February 2017, 04:56 PM   #10
audiofan is offline audiofan  Canada
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This amplifier us one transformer with 2 output windings ... then you have 2 indepandant chanels ... and both have their ground linked to chassi with R40 & C14 ... depending houw input sokets are mounted ( and this I dont know) you may have a ground loop ...

First test is using shorted RCA plug in both input and see what you have at output.

Then I would remove one of these 10 ohms resistors ... and see if the noise is gone.

According to me it is safe to do this ... but you may wait fer other comment ...
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