volume/balance troubles Quad 33/303

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28-Mar-2018 12:36 PM

jlintl

jlintl

Posts: 10

Hey gang,

first post here, and trying to get the best out of my Quad 33/303 ESL57 combo - I have bought is three years ago, and everything sounds to my satisfaction, except for the balance control which has been funky from the beginning, but worsened lately.

the plastic parts are structurally fine, and I tried to readjust that two-screw collar on the balance pot. That didn't change the outcome. Even if I crank the balance pot by hand I can't get the speakers to equal volume...

That said: I kind of realized that the balance pot works, because it changes the volume levels...the problem is that the left channel is much louder than the right one in general.

I also changed speakers to opposite channels, and they're just fine.

I am sure you guys can point me into the right direction here.

I was about to order a revision kit for both amp/preamp, but if the problem is much simpler than that I will probably hold off with a complete overhaul, since I am otherwise happy sound-wise. That is, unless you tell me that it's totally worth it ;)

Thanks,


Joe



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04-Apr-2018 02:45 PM

Frank

Frank

Posts: 34

Hi Joe,

on my Quad33 I took a very simple approach. I bypassed the balance pot all together. I do not care much about balance anyway ;-)

Frank

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05-Apr-2018 01:59 AM

EJP

EJP

Posts: 1503

Change the two 100uF capacitors that lead to the balance control. They are located on the motherboard in the top right corner as you look from the front. Polarity: +ve is to the rear.
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09-Apr-2018 12:58 PM

jlintl

jlintl

Posts: 10

Thanks for your tip - I did the 33/303 revision, but the problem persists - left channel is much louder than the right one. Any other ideas?

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10-Apr-2018 12:39 AM

EJP

EJP

Posts: 1503

Maybe the balance control itself is faulty. Measure its resistance from centre to each side with the balance slider in centre position. Should be about 1k each.
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10-Apr-2018 09:05 AM

jlintl

jlintl

Posts: 10

Thanks for the explanation - I know how to solder pretty ok, but have otherwise very little understanding of electrics.

This helped a lot to rule that out - the pot is good.

 I flushed all the switches, which I noticed helped a lot, but I also found out that one of my amplifier boards is causing problems (simply by switching them/and inserting just one of them at a time). At higher volume one board distorts noticeably.

 I also realized that they look almost the same, but not quite - do you think it is weird that on position C400 of the amplifier boards there are two very different capacitors? Would you advise switching them to equal parts. If so which ones will I need for that?




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10-Apr-2018 09:49 AM

EJP

EJP

Posts: 1503

Unless you have frequency response anomalies I would leave C400. As long as it is .068uF (68nF) it doesn't matter what it looks like. But I would check the polarity of all three electrolytic capacitors (C401/5/6) on the offending board, and also measure the 15K and 270K and 100K resistors and replace if necessary.

Dada Electronics Australia
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10-Apr-2018 10:30 AM

jlintl

jlintl

Posts: 10

C401/405 has been replaced, but C406 has not yet, as they were not in the revision kit - I contacted Stefaan already, and will replace them as soon as I have them.

So maybe it's as simple as that one C406 is in a worse condition than the other...Allthough I didn't have the distortion before I started the revision, just the balance problem.

The resistors measure fine.

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11-Apr-2018 02:41 AM

EJP

EJP

Posts: 1503

Did you renovate R411/412? And if so did you get them the right way round?
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11-Apr-2018 06:51 AM

jlintl

jlintl

Posts: 10

yes I did - right way round means on the right position? Not polarity I guess, as I assume they don't have any?

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11-Apr-2018 07:21 AM

EJP

EJP

Posts: 1503

Yes that's what I mean, and also correct values. I think you're going to have to check everything on the offending amplifier board: just compare it to the other one, component by component, and note the differences here.
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12-Apr-2018 11:13 PM

jlintl

jlintl

Posts: 10

Found it!

the amp boards are in less than optimal condition - some of the tracks are broken, and have partially been repaired with wire. It wasn't until I shaked the faulty board and heard a slight rattling noise. So now I just reconnected with some solder, and voila, volume is back up again. I can't run a full test right now as the kid sleeps, but I think there's still some distortion. 

I feel like it would be worth it to find better boards and swap them out for the ones I have. Are they hard to get, or are there maybe even redesigned ones available at all?

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13-Apr-2018 01:09 AM

EJP

EJP

Posts: 1503

Very good.

Broken PCBs don't cause distortion. You still have a component fault somewhere.

We don't remanufacture these boards but if you contact me off list (see Contacts above) I may be able to help. But you shouldn't need it.

Dada Electronics Australia
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13-Apr-2018 09:42 AM

jlintl

jlintl

Posts: 10

the parts I can get a result from with my multimeter are all measuring the same. Some I can't get any results with, but I think that has to do with some parts needing to be separated from the board to be measured, which I am hesitant to do.

Can you maybe point me to a spec list of parts needed for the amp boards, so I can order them all together and kind of start from scratch?

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13-Apr-2018 10:34 AM

EJP

EJP

Posts: 1503

It's in the service manual, in the Downloads section here. But there's no point in replacing components that are the same in the working channel. I would have a good look, again, at the solder work, and particularly around the terminals of the three large capacitors, which are relatively common failure points. Maybe then if still no joy replace all three transistors, wth BC549 or BC550.
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13-Apr-2018 10:50 AM

jlintl

jlintl

Posts: 10

Oh nice... are those parts available through DADA?

I will be looking into doing the three main capacitors and transistors including the C406's, which I had not done yet.

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13-Apr-2018 09:28 PM

jlintl

jlintl

Posts: 10

pfffffff....finally.

big thanks for your help - you kept me motivated trying and searching - I was close to giving up...in the end it was a bad solder with one of the resistors I replaced. 

 Next time I do this I will hold the board against a light source to see through holes that were not filled up with solder right away.

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14-Apr-2018 02:27 AM

EJP

EJP

Posts: 1503

Very good. It's not really about filling the holes, just ensuring a good joint. I always eyeball them twice: once when cutting the leads, and again, under magnification and strong light, afterwards. You want a nice pointy mountain, no crater around the lead, and not a blob or a complete miss.
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