Slight channel imbalance after installing the upgrade

[heavycowboy]

Hello,

Just finished installing the upgrade. Sounds wonderful! More of everything and smoother to boot. However, I now have a slight imbalance between channels with the left being quieter than the right. I've swapped tubes, cables and changed sources to no avail. All of my voltage checks were in range except for a slightly high B+ Reg value.

Here are my results:

6U = 130.4V
16U = 135.1V
B+ Reg = 188V
4U = 8.02V
14U = 8.05V

How would I go about measuring if there actually is an imbalance? And where should I focus my attention when looking for the problem?

Thanks in advance,

Todd

[Paul Birkeland]

To measure for imbalance, you'll need a source that can play a 60Hz signal into your Moreplay.  The most convenient sources for this are things like phones/tablets with 1/8" headphone jacks, then you can use a signal generator app and an 1/8" to RCA adapter cable to shoot the signal in.

You'll also need an multimeter that can measure small AC voltages.  For a meter that's not autoranging, this will mean seeing something like a 2V AC scale.  For an auto meter, just pop into the manual to be sure that it can measure fractions of an AC volt. 

With the 60Hz playing into the Moreplay inputs and your meter in hand, you can start (with the Moreplay off) by measuring the AC voltage between ground and each lug on the input selector.

[heavycowboy]

Hi Paul,

I had a chance to take the measurements you recommended and found no significant difference in voltage between the input selector lugs going to L-IN and R-IN on the balance pot.

I went ahead and turned the amp on and measured the voltage between L-IN and R-IN on the volume pot, and I did find some variance (1.102 vs 1.070). Could this difference in voltage be causing the imbalance I'm hearing?

Thanks again for your help.

[Paul Joppa]

... and I did find some variance (1.102 vs 1.070). Could this difference in voltage be causing the imbalance I'm hearing? ...

That's only a quarter of a decibel - barely audible.

[Paul Birkeland]

You'd want to turn the volume pot all the way up and see what appears at the output jacks of the preamp while it's playing.