• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Quad 303 Left Channel Output Issue

DaveFloyd40

DaveFloyd40

New Member
Hi there,

I've just reinstated my old Quad 303 after a few weeks of replacing components, etc. This comes after years of no use. It is coupled up with the 33 pre-amp and now sounds incredible!

The only issue I seem to be facing now is a noticeable difference in volume between the left and right channels with left having a lower output. The only way they sound perfectly balanced is when the balance slider on the pre-amp is all the way to the left. Could this be switch related on the 33 pre-amp or would it have something to do with one of the components on the driver board?

Any suggestions and advice would be greatly appreciated!
 
Register to hide this ad
Is the output switch on the 33 set to Stereo? It may be these need a little contact cleaner,also try pressing the various filter buttons a few times,ive had similar problem in the past,give the switches and pots a clean,make sure the boards are seated correctly inside the 33,theyre little champs!Dont usually cause any problems
 
Wilburchubs said:
Is the output switch on the 33 set to Stereo? It may be these need a little contact cleaner,also try pressing the various filter buttons a few times,ive had similar problem in the past,give the switches and pots a clean,make sure the boards are seated correctly inside the 33,theyre little champs!Dont usually cause any problems
Click to expand...

Hi there,

Thank you for your suggestions! Yes, it's currently set on stereo. I've tried pressing the switches but will have to wait until my order of switch cleaner arrives before doing a thorough job on them. Other than this little issue I am really enjoying having the Quad system up and running again.

Thank you again for your advice!

P.S These Quads were known for their "hum", weren't they? I'm noticing a very slight hum between music tracks.
 
Its probably the main caps in the 303-theyre a doddle to work on if you're a bit "handy"
Had all sorts of stuff over the years,but a 33/303 combo is a joy to have
 
Hi Wilburchubs,

Thanks again for your reply. Hm, I wonder because I replaced the main caps in the 303 so surely it won't be that? Anyway, I'm going to go through everything with a fine-tooth comb AGAIN... Perhaps I'm missing something!

It would appear that the hum is emanating from the 33 control unit and interestingly enough when I press the "cancel" switch the hum disappears. Any ideas?
 
Last edited:
Move the 33 away from anything else,one of mine was very sensitive to being near other equipment
Is the hum present on all inputs?
 
I will give that a go in the morning.
Yes, it's definitely present on all inputs. I've always battled with this little issue yet I've not been able to remedy it.
 
Alright, an update:

I've sorted out the channel issue [i.e one channel being softer than the other] so it's sounding even better than before but I am still struggling with the hum.
I'm supposing I would do well to replace capacitors and transistors in the 33 control unit and see if that solves the issue?
 
Further update:
Amplifier was running perfectly. Well, almost... I had 67V and 33.5V on left channel but the right channel drifted between 33.5V - 31V during the course of a day's worth of playback.
Next morning, I switched on the amplifier at which time R120 burned out and then R114 and R126 followed suit... Uhm, I've decided I'm going to replace all components on the boards and then try again. After 45+ years I believe a complete makeover might just do the trick. I'd already replaced the main caps and bridge rectifier and when the amp ran for the few days it did I sort of imagined my problems were solved... Sadly, not.
 
Hi, My problem is in the right channel has low output, plus measuring the 1&5 Pins leaves no 33.5volts only 2.7volts
I think I'm going to start replacing the large main caps as well they look pretty old. If anyone has any info it would be
great to hear from you.
 
You are better off trying to find the problem before mass replacing all parts - if the problem persists - where do you look?

The original failure was either dirty controls or, more than likely, a failing transistor.

For a burning resistor, theres likely a transistor associated with that that has failed.

I'd pull & test your outputs and work back from there, ie: the pre-drivers too.

When I rebuilt a 303, I found that I couldnt really get it sounding half-decent until the pre-drivers had been replaced. So those could be a weak point.
 
Hi there,

Thanks for the advice. I appreciate it.
Fortunately I didn't end up replacing everything as it did in fact turn out to be those transistors you mentioned. Once I replaced those and the resistors which had been burned she was back up and running and I've been enjoying the music ever since.
 
You must log in or register to reply here.
Back
Top Bottom