QUAD 33 BALANCE

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01-Sep-2019 09:42 PM

LOWTHERMAN62

LOWTHERMAN62

Posts: 61

Another quad 33 balance problem. I have completed a revision per you guidelines and unit is performing very well, hovever i have a problem with balance. I can acheive perfect balance only when the balance is almost to the stop on one side( this is controlling the pot direct with the slider mechanism disconnected. When I centre the balance control and meter 500 r on each side the balance is way off, When I reverse the amp boards the problem shifts to the other side. Balance pot reads 1k and seems to work perfectly. 2x100uf caps have been changed, volume control reads good. Amp boards have been compared and all components such as caps resistors and transistors read perfectly. Help please.

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02-Sep-2019 09:58 AM

EJP

EJP

Posts: 1644

If you've modified the gain, check that you got the two gain control resistors the right way around, i.e. not interchanged in one channel.
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02-Sep-2019 12:11 PM

LOWTHERMAN62

LOWTHERMAN62

Posts: 61

I checked these and ok, however noticed an open circuit between some components when metering point to point to check  any differences between the two boards. remade soldering joints and checked with meter, all ok. balance now spot on with the balance pot dead centre. success. Thank you so much for your help. Regards Stewart.

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02-Sep-2019 12:58 PM

Stefaan

Stefaan

Posts: 613


This means that there is a different gain in the 2 channels.

Was the problem there before you did the revision?

If not I would re-check all the soldering joints you made during the revision with a magnifying glass and / or a multimeter.

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02-Sep-2019 03:51 PM

LOWTHERMAN62

LOWTHERMAN62

Posts: 61

Stephaan, I found a track near one of the transistors open circuit so remade all joints along the track and checked under a magnifying glass , metered again and checked the nearby new bc550. It was not reading correctly so i replaced it. The balance is now working properly and i had a slight fsssh noise on one channel which has now dissapered, All is good. Thanks again for you assistance as always. Regards Stewart

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