QUAD 606 Mk2 Power amp PROBLEMS

[arupg]

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 speaker’s 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?

 

[big jim]

Go to quad405.com
its part of Grace Audio and you will find the 606 circuit



all the best jim

 

[arupg]

Thank you. That was a good lead....

 

[audiomatic]

Hi;

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

regards, audiomatic

 

[arupg]

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......

 

[johnm]

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.

 

[johnm]

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/public/606schematic[2167].pdf

 

[MLoc]

Hey John,
Have you had any luck resolving this issue?
I'm having a similar problem with a Quad 306 I just picked up.

 

[johnm]

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.

 

[audiofan]

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 ...

 

[johnm]

Thanks for your help Audiofan. That might well be the cause, I'll check this week. It would be wonderful if it's something so simple. This area of R40 & C14 is earthed to the chassis via a screw & copper washer, so I'll check the components and clean the earth connection. I have already checked the phono sockets and internal cabling and they are fine, and have also used phono shorting plugs too. The problem is restricted to the right channel pcb only. Nothing is over-heating, and otherwise it sounds fantastic, so fingers crossed it's something minor. It's fortunately not a loud hum.

If the R40/C14 area doesn't solve the problem I may just replace T15 & T16 as they're so cheap & easy to source, and I believe create the virtual earth.

Here's the R40/C14 area:

 

[johnm]

Update: Have checked the earthing of R40/C14. Fine. Also desoldered one end of each & checked R36/R37, R38/R49, R33, R12 and R3. All fine.

I have yet to check the virtual earth components T15 & T16, but I have bought spares just incase.

Has anybody any further ideas, or has come across this before?

Thanks,

John.

 

[jolugodi]

Hello.
My English is very poor but I hope you can understand me.

I´d like open my 606 but I can't do it. What kind of screw use? What type of crosstip screwdriver I need?

Thanks

José Luis

 

[ejp]

You need a Posidrive screwdriver. Turn it upside down and remove all four screws from the bottom and also the four feet. Then remove the four screws from the inset panel. Then gently remove the bottom, which is now on top of course.

 

[as_audio]

.. may be sticky due to thermal compound and hard to get the bottom cover off.

 

[jolugodi]

Thanks, ejp and as_audio, but I think a pozidrive screwdriver don´t fit in the four screws on the bottom.
They are more like cross or double-slot screws but with very little deepness. With a normal Slot screw drive I don´t get to turn the screws because the slot is little deep and the screwdrive go out when I try.

 

[as_audio]

Are you sure it is nesserary to open it so you should have adequate tools.

 

[jolugodi]

I don´t know if I understand your answer, as_audio.
I need open the 606 amp because the input right is failing: I have opened the band which recovers the lateral and I have seen the interior cable is loose and I need solder it.

 

[Ian Finch]

The specified screws are indeed Pozidrive. Pozidrive screws look similar but are not the same as standard Phillips, cross point screw heads. The hole is shallower and identified with four extra lines, showing between the slots on the screw head. The pozidriver itself looks like it is blunt or is a short version of a Phillips type driver. Because the socket is shallow and cannot accept the long, tapered point of the Phillips driver, it just spins around and damages the socket. Use the right tool.

This link to an advertisement that happens to show the difference, so I hope I have understood your problem and that this helps: Pozidriv vs Phillips: What's the Difference? - Shop4Fasteners

 

[ejp]

Thanks, ejp and as_audio, but I think a pozidrive screwdriver don´t fit in the four screws on the bottom.
They are more like cross or double-slot screws but with very little deepness. With a normal Slot screw drive I don´t get to turn the screws because the slot is little deep and the screwdrive go out when I try.

In other words you don't know what Posidrive means.