2. amps-preamps
  3. 1291501029

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
elizabeth
6,726 posts
 
It is almost certain to be the volume control has a problem.
As 'new', I would expect it to not have that problem. Either return it for another one, or get the volume control replaced. (sending it back and they tell you thier is no problem is going to be another problem.)
Waiting is not going to fix the problem. (It may become less noticable, but will never go away.
My two cents.
6550c
393 posts
 
Is it a tube preamp? I have had this happen when tubes are way missmatched. Just like you said, at low volumes the sound was allot louder in one channel. At higher volume the sound tended to even out.
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restock
826 posts
 
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?
mitch2 OP
1,911 posts
 
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.
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