Quad 33 Balance Control

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06-Feb-2011 03:11 AM

Fuzzface

Fuzzface

Posts: 62

Hi Guys,

I did a Dada revision on my Quad 33 last year and it sounds much better but i've just noticed a problem with my unit.

I usually just leave the balance control dead centre but when I tried it just, I found that the balance control only seems to bias towards the right channel and adjusting it to the left doesn't increase the output to that channel. Also, not sure if it's my ears deceiving me but the left channel doesn't seem as loud as the right.

I've tried it with another pair of known working driver boards and it still happens.

Both electrolytic caps on the filter board were replaced as per the Dada upgrade.

Do you think it may be a faulty balance pot?

Regards
Richard
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06-Feb-2011 10:58 AM

norman

norman

Posts: 73


hi, what worked for me is I measured the resistance either side of the variable resistor ( blance pot) until I got an equal value then set up the link to the adjuster so it was middle positon: if you adjust the pot either way off centre - and don,t get common readings per degree movment - then yip the pot is crapped
norman
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06-Feb-2011 01:54 PM

Stefaan

Stefaan

Posts: 593

Hi,

Although the balance-pot is rarely used in daily life I have known some cases where it was working badly because the internal contacts were oxydated.

It attenuates the sound connecting one of the channels to mass through the 100µF capacitors. So you can disconnect both sides from the pot (by desoldering the wires on top). Now both channels should work with the same volume. If this is not the case the problem is somewhere else, like on the Tape-boards, in the switches or in the volume-pot.

A replacement for the balance-pot can be found here:
http://www.dadaelectronics.eu/shop/components/potentiometers/carbon-potentiometers/1k-mono-lin-carbon-potentiometer

Stefaan
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07-Feb-2011 04:23 AM

Fuzzface

Fuzzface

Posts: 62

Cheers for the advice guys.

I've had the unit apart and checked the balance pot on a meter and it's fine. I've also tried it with a known good tape adapter board and the balance is still not working properly.

I recently had to put a replacement switchboard in so I probably need to re-check my wiring on that when I get some more time. I don't know if the problem was there before I changed it though.

Regards
Richard
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08-Feb-2011 07:12 PM

Fuzzface

Fuzzface

Posts: 62

Well, I've managed to sort it now - very easy to fix - doh!

Should have checked before really but I found a bad solder joint where the left channel lead from the balance pot connects to the filter board.

There still seems to be a slight difference in output when the balance slider is dead centre but I guess I can adjust that by altering the position of the connecting rod to the the pot.

Regards
Richard
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08-Feb-2011 11:36 PM

EJP

EJP

Posts: 1589

Before you do that I would check the values of R411/412. These determine the gain and there could be enough variation in them to cause channel imbalance. Replace them with 1% metal film of the correct value. Also check the tracking of the volume pot.

Dada Electronics Australia
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09-Feb-2011 05:10 AM

Fuzzface

Fuzzface

Posts: 62

Ok,

Thanks Esmond. I'll check those resistors. A lot of the ones in my Quad 33 are the old carbon type and i've found a lot of them in the past to be way out of tolerance so that could be the problem.

Regards
Richard
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09-Feb-2011 08:50 AM

norman

norman

Posts: 73

glad to hear that, i,m new to this stuff, but also found that quite a few of the original R do not match the spec, didn,t know if it was me or the kit - as a mechanic I find it difficult to consaider how a solid state - no moving part electronic thing like a resistor can wear out

norman
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09-Feb-2011 09:07 AM

EJP

EJP

Posts: 1589

Electrons are moving parts. Carbon resistors tend to go high in value, and the higher the initial value the more this is observed. Also the higher the voltage across the resistor the more this is observed. In the limit they fail open-circuit.

Dada Electronics Australia
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10-Feb-2011 04:14 AM

Fuzzface

Fuzzface

Posts: 62

Yes, Esmond's right....

I've got a very early Quad 33 (Serial no. 787). The majority of the resistors were the old carbon type ones (as you'd expect from a 40+ year old unit).

I checked them all and ended up replacing all of them for 1% film type as they were so far out of tolerance.

Eg, some of the 15k resistors were reading nearly 19k on my meter so they had to be replaced.

Richard
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31-Mar-2011 06:59 PM

brianb

brianb

Posts: 3

Having problem with my Quad 33 driving 303  ( 303 tested ok ) -  Sound output on right channel only when balance slider is moved to left volume is reduced slightly but still no output to left speaker. I have substituted the balance pot with another 1k pot but no difference  -  suggestions as to problem please.  
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31-Mar-2011 11:24 PM

EJP

EJP

Posts: 1589

It won't be the balance pot, probably the left channel. Swap the amplifier boards around: if the problem moves it is one of those boards, otherwise probably the tape board. If it's the amplifier board, check for dry joints on the big capacitors.

Dada Electronics Australia
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01-Apr-2011 11:35 PM

brianb

brianb

Posts: 3

Have already swopped boards -  no change  -  amp checks out ok with another preamp  -  using CD through Radio 1 input  -  CD player checked OK  - considering your upgrade but would prefer all working first so that I can check each stage

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02-Apr-2011 02:57 AM

EJP

EJP

Posts: 1589

I always do it the other way round: do the service first then fix the faults. They disappear 90% of the time because of the service. The service only takes an hour. Much less if you've done it a few times ;-)

Dada Electronics Australia
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04-Apr-2011 06:56 PM

brianb

brianb

Posts: 3


Thank  -  I repect your knowledge and will order the upgrade kit.  -   hope to report success in due course.
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14-May-2013 07:58 AM

beeroclock

beeroclock

Posts: 1

Hi Guys,

I have just replaced the balance pot on my Quad 33 (replacement supplied by DaDa electronics) and it works perfectly - as long as you leave the cover off!  What I mean is that the degree of rotation of the pot required to actually adjust the balance is greater that you can get with the little slider thingummy on the front of the unit!  Unless I am missing something, the pot really needs to achieve full left to right resistance change in about 60degrees of rotation whereas it actually takes about 200degrees. The result is that you can hardly hear the difference in balance right from one end of the slider to the other.

 Richard. 

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04-May-2014 03:05 PM

mini37

mini37

Posts: 1

Hi Steffan, can you confirm if I do not need the balance control I just de-solder the connections, that's it,  or do i have to join them.


regrds

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29-Jul-2014 12:16 AM

paulo

paulo

Posts: 4

Hi. I'm repairing a 33 serial 19672 and I've noticed an annoying noise, like a "frfshsffsshtt" on L ch. It does not increase with volume and no input selected, but the noise mutes when cancel is pressed. I think this is happening after the amps, since I've swapped the amp boards and also tested with another tape adaptor and the noise remains on L. In addition, R ch sounds lower and lacks some bass on radio inputs, but a curious thing is that I have normal reproduction on tape replay input with cancel switch on. I've replaced all green caps on tone circuit and checked the resistors, but problem still goes. Any tips, welcome. Many thanks.
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14-Jan-2017 03:50 PM

paulo

paulo

Posts: 4

I've removed the bad pot and replace it by one fixed 560R 1% resistor per channel in series with C5 and C6 to ground. I got a better channel balance and a noticeable quality improvement as well. A tip for ones who doesn't use the balance control.
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15-Jan-2017 05:38 AM

EJP

EJP

Posts: 1589

I missed your earlier post. If it doesn't happen on tape input it is one of the transistors on the tape board, or one or more of the 220k bias chain resistors if you didn't replace them. Or, as a long shot, another resistor on that board. Almost certainly the transistor.

Instead of doing all that around the balance control you could have just removed C5 and C6, but I don't think that was the real problem.

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28-Apr-2019 01:30 PM

LOWTHERMAN62

LOWTHERMAN62

Posts: 36

Hi there . Reading this topic helped as i have just completed a revision on my 33. I had a channel imbalance and checked all the obvious as outlined, but could not find the problem. balancs control was behaving in a peculiar manner so tested and 1k either side was ok. Rechecked the c5 and c6 on the main board and eureka under the microscope i had lifted a track around c5 thus breaking the contact. May be a point to investigate if you have a large imbalance , and a balance control that does not funcyion properly. Regards

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