Hello,
I bought the kit from one of your French distributors to have a quick reading of the RMS power of guitar amps that I repair, build or modify in my workshop.
I successfully assembled it and it is “functional”, but the reading of RMS power is optimistic by 30% : by example, 13W are displayed when all my other instruments read 10W. I can triple check with :
- a Fluke table top multimeter model 45 (vintage !), that has been calibrated yearly until 2010, which has a RMS power function,
- by calculating from readings of other multimeters,
- and by checking on my scope.
I have a signal generator, a dummy load (resistive) to simulate speakers (these are tube amps that request a load), and a choice of amps to make tests.
I could check that the 30% excess reading is consistent over frequencies from 50 to a few thousand hertz, as well as from 10W to 150W.
I thought I could trim the reading by adjusting what for me is the input divider stage consisting of R4 (220k) and R5 (33k). My assumption was that if I can lower R5 to 24k I would correct the reading from 130% to 100% .
Does this approach make sense to you ?
Best regards
Chris