Help needed to diagnose preamp channel unbalance.


Hello all. The preamp is a new dual mono linestage with both balanced and single-ended connections. The volume control is an Alps motorized pot. There is no balance control, just a single stereo volume control.

The problem is that at low volumes, there is a channel mismatch resulting in the right channel being noticeably louder than the left. The problem was confirmed to be with the preamp through cable/channel swapping and listening with matched channel test CD's. Correct phase was also confirmed. When the volume is increased to moderate levels, the left channel seems to come fully on-line so that proper balance is restored. This is obviously an unacceptable situation for low level listening.

Has anyone had a similar problem? Is this likely a tracking problem with the volume pot? Is it possible this will improve as the electrical components and volume pot break in, since the preamp is new with only about 15 hours on it? - Thanks
mitch2
It's a very common problem that potentiometers don't track well at the lower end of the range.

In what position do you have that problem (8 o'clock)? what is the loudest position you can crank it up to?
The control goes from about 7:30-8 o'clock (lowest) to about 4:30-5 o'clock (highest). The problem begins to go away at about 9 o'clock, so it occurs at the lower settings, during low level (everyone else in bed) listening levels. I had some balanced Endlers laying around (-10 dB) as well as some balanced DIY in-line attenuators (using Vishay's) that I had used with a preamp years ago. Using these gain reducing devices in-line pushes the volume control up into the range where it tracks well, even at lower volumes. Of course, as Elizabeth suggests, my solution will be to work this out with the seller. In response to 6550c, it is a SS pre. Thanks all.
If the volume control is discrete resistor based, then its one of the following possible scenarios:

Cathode and plate resistor mismatch between the channels.
(no, tube mismatch wont affect gain unless the cathode is grounded and you are using a biased grid)

negative feedback resistor mismatch or broken

B+ completely off (I mean it has to be off by some 20%) on one channel vs the other.

But if its just a cheapie "alps" or more likely Chinese counterfeit alps, then its the volume pot.