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Old 1st September 2010, 11:03 PM   #1
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Default QUAD 99 POW problems

Hi, I have a Quad 99 POW (stereo power amp) with an annoying fault; the right channel has a constant rustling noise which steadilly gets worse as it warms up. It sounds a little like DC leakage through something.

I can't find schematics, Quad won't supply them. Can anyone help?

Cheers, Kevin

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Old 5th September 2010, 02:49 PM   #2
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Its most likely a capacitor thats beginning to die (popping) or a transistor thats broken down (rustling or hissing) (typically the input transistor). I would propose you either send it back to quad for a service which is sensible (as quad service is not so expensive) or open her up if you have the experience and ideally the test kit.

Look at all the electrolytic capacitors in the amplifier and order a new set, (as you might as well replace all of them in both channels. I would also suggest swapping the input transistors if the capacitor upgrade fails to resolve the issue.

Good luck.
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Old 5th September 2010, 03:35 PM   #3
Mooly is offline Mooly  United Kingdom
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Does the problem repond at all to tapping the PCB with an insulated tool with the amp on ?

Faults like this can be very difficult. A real long shot but if you could supply a really detailed photo/s of the internals it might help.

Also judicious use of freezer spray may be the answer as the fault responds to "warm up". The secret is to be able to drip just a couple of drops on each suspect part rather than blast everything in sight.
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Old 7th September 2010, 10:34 AM   #4
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First thing I did was change all the electrolytics, which made no difference. All the transistors except the outputs have been changed by another dealer before it got to me, so they're new. I've changed the analogue switches, since the signal processing on it is quite complex, and it still rustled.

I've switchd it on today with the freezer spray at the ready and sod's law, it's been on test for 2 hours and it's as quiet as a mouse; the first time I've not heard it rustle while in my posession!

It doesnt respond to tapping nor warming it up, maybe today being a cool day has helped.
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Old 12th September 2010, 02:45 AM   #5
JohnW is offline JohnW  Hong Kong
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Can you tell me what Analogue switches you changed and the part numbers? they should not be 74XXXX series... rather standard 4066 CMOS series..
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Old 12th September 2010, 06:47 PM   #6
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Yes I changed like for like, they are motorola MC14066B
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Old 12th September 2010, 09:49 PM   #7
JohnW is offline JohnW  Hong Kong
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Ill ask around for you... see what I can dig up.

Any chance of posting a high Res. picture of the Input section (where all the 4066 etc are located)?

John
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Old 19th September 2010, 01:00 PM   #8
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Hi John, yes will take pics this week

It's been on test all last week and still no sign of the rustling! I think I'll attack it with the hairdryer.
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Old 23rd September 2010, 09:00 PM   #9
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Just a follow-up to this for anyone with a similar fault, it was a 1N4148 in the pre-amp section towards the rear of the board and on the opposite side to the channel that was crackling.
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Old 23rd September 2010, 09:50 PM   #10
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I have the Quad 99 pre that I modded by upgrading the typical parts (caps, soft recovery diodes and upgraded volatge regulators), but it died. Seems to be a problem in the - power leg I can't find. Am almost about to say the trafo is dead. Have been trying to get a schematic for that one. If anyone has any suggestions, that would be greatly appreciated.
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