On my quest to get a better handle on tone volume leveling I measured the sound pressure levels of different DT-25 amp configurations when used with HD500 preamps. I used the HD looper to generate a sequence of medium fast 8th notes of some pitch and then setup the sound pressure meter to use an A weighted frequency sensitivity (emulating human ear) and an averaging measurement method [Leq], which gives you an 'Equivalent Continuous Sound Level'  to factor out sound level changes due to playing multiple notes with slightly different force. Based on several measurement runs through the amps and using different preamp settings and guitar models I suspect that there will be some variance of +/- 1 dB or even more. Maybe some of you have or want to do similar things and can report back with your experience.

I found the Class A, Pentode, Type III configuration to be the loudest and the table below lists how far off the other amp configurations ended up in my measurements. Interrestingly there is a spread of about 13.5 dB, which most people will probably judge as 1.5 times volume difference. My average level when measuring was about 90 dB Leq.

I would expect that one has to compensate by the delta dB on the mixer to balance tone volume if the only thing one does is switching to a different amp configuration, e.g., if you started with A, P, III and want to go to A, D, III you'd have to raise the mixer gain by about 8 dB to remain at the same outputvolume level. It would be interesting to know how this works (if at all) for other players and whether there are not some other factors that need to be considered to make this a useful table.

Martin

Message was edited by: Martin Dorr (added clarification that I used HD500 preamps to drive the DT-25)