Mismatched UA LA-610s

[CroyTone Audio]

Hello, I have a couple of LA-610s (first version) in from a customer. the two units work great, but one unit is about 10db quieter than the other at the same settings. I checked voltages on the tubes and they were all pretty well matched in both units and I even swapped tubes between the units to see if it switched but it did not. The units are visually identical on the inside with no replaced parts or modding done to either. Any clue as to what may be causing the volume mismatch?

thanks!

 

[Script]

You could measure and compare btw units systematically at different points from input to output.

 

[pucho812]

Compare both units. Quick check would be if they both are the same at full volume. Might be a wrong pot taper or value

 

[andYz00m]

You could also ship them to UA to have them serviced. I’ve had mine serviced by them in the past. I live next to their office so it’s very easy for me.

Best of luck

 

[CroyTone Audio]

I can trace them a little bit, but without a schematic with part numbers its very difficult. in order to get to the bottom of the board to see those traces I have to remove all the wiring clips. I know they're similar to the the 610 and LA-2A circuits but its hard to trace with this particular board. When I ran them both at full volume there was about a 2V output discrepancy between the two units. I'm fairly sure the problem is on the compressor side since I was able to take measurements at the output of the preamp and the signals matched up. This gain discrepancy is when the compressor itself is bypassed so its got something to do with the output gain.

 

[pucho812]

If you think it’s in the compressor section, try swapping opto cells or can you not do that on these units?