Quad 33 Balance Control Issue

HI - I have a recently purchased Quad 33 pre which is feeding into my 303 power amp, of course. I notice that the balance control needs to be far over to the right in order for the sound to be central between my speakers. It sounds great, but I'm wondering if anyone can shed light on this control and what might be causing this?
 
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Welcome to diyAudio :)

I believe one issue can be that the volume control can suffer poor tracking at low levels so you need to rule that out first. This is made worse with high output modern signal sources which mean the volume has to be kept low.

I'm guessing (maybe incorrectly) that you haven't a scope and signal generator as that is the sure fire way to prove conclusively what is happening.
 
Thanks, no I don't have such equipment and really wouldn't want to go there! I just bought my friend's 70s LP12 fitted with a Goldring cartridge and playing through recently acquired Monitor Audio floor-standing speakers, listening to Springsteen's Tunnel of Love album and it sounds just fantastic! So, maybe it doesn't matter where the balance slider is at? No issue with the volume knob that I can hear.
 
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No issue with the volume knob that I can hear.

Mis tracking or channel matching of the volume control would show in the centre image shifting as you change the volume setting. Typically the more the pot is turned up and the more accurate the matching becomes.

Do the line inputs also need the balance control shifting to one end to centre the image, or is it just the phono input affected?
 
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@ejp suggestion is a good one:

Check that the pot is electrically centered at the centre position of the slider.

Put your meter on ohms and connect the black meter lead to ground (chassis) and measure in turn to each arrowed point (which is the negative end of the two capacitors). With the control centred you should see approximately 500 ohms to each arrowed point. The 1k pot could have a 20% tolerance but you are looking for approx equal readings to both points.

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