… is it possible to translate mV output to increase in db?

[microstrip]

(...) As for the imbalance, doesn’t Audio Note get it right with the two completely separated volume controls for the left and right channel?

Even for the same brand it will probably depend on the price of the equipment - we can expect that better equipment has better quality potentiometers with more accurate channel matching.

You have to measure it if you don't trust the manufacturer ... It is extremely easy to measure - you just need a track test , an AC voltmeter and a RCA / test lead adapter. I had a poor surprise with a manufacturer of very expensive high-end equipment ...

 

[DonH50]

Even for the same brand it will probably depend on the price of the equipment - we can expect that better equipment has better quality potentiometers with more accurate channel matching.

You have to measure it if you don't trust the manufacturer ... It is extremely easy to measure - you just need a track test , an AC voltmeter and a RCA / test lead adapter. I had a poor surprise with a manufacturer of very expensive high-end equipment ...

My experience matches @microstrip ; some very expensive components had very bad low-level channel imbalance. And so did some very cheap stuff, though there were stellar examples at both price ends as well.

If you measure, I strongly suggest doing it with the power amp (speakers) off (which would probably be the case anyway since you need to measure the preamp's output), and check that the test tone is within the meter's bandwidth (some meters are designed only for power lines so only have ~100 Hz bandwidth). I usually use 1 kHz if the meter supports it, and 50 or 100 Hz otherwise. Should not matter, and you just need a relative reading showing the difference in voltage between the two sides. It is usually a bigger issue at the lower end of the control (minimal volume) but not always.

 

[mtemur]

Japanese TKD offers linear potentiometers for 50K and 100K. I used it and it’s notorious for not matching channels at very low levels. BTW it sounds extremely fluid. Others are all logarithmic AFAIK.

 

[DasguteOhr]

TKD sounds pretty damn good.
You need a true rms millivoltmeter , they work over a wideband e.g 10hz- 30khz.
Exsample hp 400e ~ 120€ used

 

[Balle Clorin]

… in the end, for a technical dumbass like myself, 0.4 mV should be louder than 0.2 mV at same volume level, right?

As for the imbalance, doesn’t Audio Note get it right with the two completely separated volume controls for the left and right channel?

Two volume pots is a very crude balance control , how do you know they are equal or set equal ? And stay equal at different position , setting volume equal by ear will get you in the 1-3db range of difference . Set them visually equal is maybe the best you can do. I measured the output Voltage of my tube amp with maaany different tubes in and notices the balance was off mostly yo one side regardless of tube, it turned out to be an balance error in the blue Apls volume pot meter and not so much tube deviation the imbalance varied with setting . Without a balance control it could not be corrected, so I matched tubes to fit the error at my typical listening level

Measuring 1khz or 400hz tone at typical listening volume a comparing voltage at output terminals ( RCA or speaker) and converted to db relative difference it a check worth to do, then you can tune the L and R volume perfectly.but are your speakers within 1db ? Probably not…

No need for a fancy measuring device as above. A simple digital multimeter can interpret 400 or 1000 Hz good enough. Or get a secondhandFluke True RMS multimeter if you want