Quad 33 left speaker dies when filters on

[ecodan]

Hi all, having an issue with my Quad 33 preamp losing its left channel with a pop sporadically when filters are turned on (right speaker never makes popping sound and does not stop ever). Interestingly when any of the filter buttons are pushed in, all buttons create a pop in the left speaker when engaged, and for no reason it just dies. However if filters are cancelled, everything returns to normal, no popping no speaker loss. What's going on ???

[Binkman]

13oots2 put up a post about capacitors..
viewtopic.php?f=85&t=44492

Popping is an almost dead sure sign of capacitor leaking or just going south. being on one channel with your system is probably in the second link showing the buffer boards. Look at the caps on those in your box and see if the tops are bulging. They should be flat. I added some links to get high quality audio caps for audio made by Elna. Should be an easy fix.

pics of your system plus the schematics.
https://www.google.com/search?q=Quad+33 ... 16&bih=488

Binky

http://www.hembrow.eu/personal/quad33-303.html Shows the buffer boards.. I suspect the caps are going and the author notes same.

[ecodan]

Thank you, that's the sort of info I need!

Have already tried switching the left and right card (which made no difference), but now will look closely at the caps -which makes a lot of sense. Those links look to be very handy... I will do some reading tonight!

[davidsrsb]

The 33 is a single power supply design, so it is easy to compare dc voltages between the channels to spot a leaking capacitor. The 33 had a reputation for contact problems with the plug in modules

[ecodan]

Just had a look at the revision kit dada electronics sell, seems it might be the simplest way of finding the culprit... replace them all! Its certainly the right price at 22 euros, but is it any good?

http://www.dadaelectronics.eu/shop/quad ... vision-kit

[LPspinner]

Hi guys: just caught up with this thread, I am a big fan of the little QUAD 33 for its looks and historic value, I love mine to bits….

I have experienced similar issues to the ones you describe when I restored one of my QUAD 33 control units. You’re symptoms sound like the problem is in the filter switches. These switches are a complicated multi-way setup that was custom made for QUAD. These switch assemblies have a reputation for being noisy when the sliding contacts start to wear out.

The switch internals can sometimes be rejuvenated by disassembly and manually cleaning bending the switch contacts back into shape, but it is fiddly, time consuming and a small jeweller’s toolkit will make the job much easier.

Do a Google search on the noisy QUAD 33 filter switches and you should find several pages on the net which show you how to pull apart the switch assembly. The other alternative is to find an unserviceable QUAD 33 and salvage the filter switch assy from this. QUAD may still have new filter switch assemblies (their service department is actually very good) but I doubt that a highly specialised spare part like this is still available.

Hope this helps and good luck.

[ecodan]

Cheers for everyones input.
Have received my Dada electronics Quad 33 kit, so will do the upgrades on the weekend, plus clean the switches board connectors etc as best I can at the same time.

[ecodan]

Yesterday, my young lad and I put the Dada electronics revision kit through the 33, plus squirted cleaner into the knobs, switches board slots etc. We also checked everything for dry solder joints.

Well the revision definitely improves the sound!!! The stage is big now and really detailed. I know base and treble have improved, but its the mid range that i'm particularly chuffed with, so much more detail now off vinyl and cd.
So far no more problems with speaker channels. However since I tightened the card slots last time it hasn't happened either, that said I have been careful not to change the filter settings (the other suspected cause) ... time will now tell if its fixed!

On other matters, I'm going to put a Dada kit through the 303 now, its hard to resist!

P.s LPspinner, thank you for alerting me, i'll pull the switches apart if all else fails...

[davidsrsb]

Those card slots were always the Quads weak link.

[ecodan]

Final verdict:

33 problem were fixed with dada kit and cleaning / crimping of card slots.
This made the midrange noticibly clearer and added base. Speaker popping and stopping has gone.

Dada kit through 303 uncovered a problem with two out put transistors (couldnt set the psu voltage to 67v) once replaced the sound just leapt out of the speakers, with hugh improvement to treble mid and base!

The moral, if you buy one these: get a dada or similar quality cap replacement and basic revision through it and re-awaken the beast!!! Cost me peanuts was easy to do with my basic soldering skills and the dada support was fast and efficient - even on a sunday with 8hr time difference!