watchnerd
Grand Contributor
This question is specific to a headphone amp, but I guess could generally apply to other applications, as well.
All the following description is for the Schiit Mjolnir 2, which uses 2 x 6922 tubes as a gain stage, and then a SS output stage, set to high gain.
Scenario A:
On the belief that volume pots have channel imbalances at low level:
1. Crank volume knob on amp to max, which is about 5 o'clock on the pot
2. Modulate volume via integrated amp pre-out, which uses digital volume control. For this purpose test, the level was held constant at -37 dB
Result:
Grid noise shimmering / microphony is a audible on all tubes during quiet passages, ranging from barely noticeable on the best tubes to very noticeable and annoying on the worst
Scenario B:
After the results of A:
1. Dial the amp volume back to about 3 o'lock
2. Use more gain on the preamp volume, setting it to -31 dB
Result:
Subjective music volume seems about the same between A & B, but the grid noise was dramatically reduced.
=====
So what's going on here?
Are the tubes being driven into overdrive at max pot gain?
All the following description is for the Schiit Mjolnir 2, which uses 2 x 6922 tubes as a gain stage, and then a SS output stage, set to high gain.
Scenario A:
On the belief that volume pots have channel imbalances at low level:
1. Crank volume knob on amp to max, which is about 5 o'clock on the pot
2. Modulate volume via integrated amp pre-out, which uses digital volume control. For this purpose test, the level was held constant at -37 dB
Result:
Grid noise shimmering / microphony is a audible on all tubes during quiet passages, ranging from barely noticeable on the best tubes to very noticeable and annoying on the worst
Scenario B:
After the results of A:
1. Dial the amp volume back to about 3 o'lock
2. Use more gain on the preamp volume, setting it to -31 dB
Result:
Subjective music volume seems about the same between A & B, but the grid noise was dramatically reduced.
=====
So what's going on here?
Are the tubes being driven into overdrive at max pot gain?