I double checked all the parts and the weldings. Both were OK.
Then I used a signal generator and an oscilloscope to investigate the gain stages. Here is what I found:
- input: 1 x 500 mV sine
- IC1A pin 1: 7 x 500 mV sine
- IC1B pin 5: 5 x 500 mV sine
- IC1B pin 7: 5.5 V square (BIG gain)
- IC2B pin 7: 7 x 500 mV square
- Tone pot, center tap : 2.5 x 500 mV (here is the big output drop)
- Out (max vol.): 2.5 x 500 mV (a little lower that the input)
No matter how high is the input signal the aoutput does no change much.
My conclusion is that the tone control drops the signal a lot and to get a loud output is necessary another gain stage like the transistor BMP or the Rat.
Any comments or suggestions?