Ded Moroz (aka Santa Claus) brought me the new equipment, so my lab contains following items now:

• soldering station
• Rigol DS1102E scope
• Victor VC2002 functional signal generator
• Mastech HY3003-3 DC power supply
• HP Compaq nc6000 laptop
• mountains of electronic components
• several convolutions of the brain, somewhat straighten arms and other physiological equipment

Lab setup

Electronic details will likely do not match my next scheme (frequent reader will obviously notice this essentially a rule), even although I have really lots of passive and (noticebly smaller amount) active components now. I got several rectifying bridges at least, so will not use part of the transistor as a diode, and couple of the stabiliers.

But we will see, and now let's return to my first LM3886 amplifier with differential PSU, which did not really work like expected. I've attached differential signal from the lab PSU and volia, 20+ amplified output signal. That's how it looked.

Medium frequency sine signal looks good. Well, it almost always looks good.

Low frequency square signal

It shows some problems, but apparently it is the generator, which is not able to produce correct square signal on the small frequencies. If you could see how it tries to do it at 1Hz and smaller frequencies. Looks like it does not use comparator at the output chain for the square signal and just relies on differential and integrating circuits of the operation amplifier, but I may be very wrong of course.

High frequency square signal

High frequency (about 15 kHz, not really high, but high enough for the sound amplifier) amplification produces some delay and stabilizing pike, but it is expected when working with interpolation active filters, which are likely used in LM3886.

Found interesting problems with my LM3886 amplifier and chip behaviour in general during my tests:

• Amplifier differently drains input voltage, when it is turned on, I get -10V and +20V on the terminals. This may be related to the fact, that ground point in the PSU is not really a ground, since it is not 'connected' to the input voltage source, i.e. looks like current does not flow between ground and positive or negative terminals (when connecting voltmeter for example).
• after some short enough time (about several minutes) amplifier stops producing output signal, I checked input voltage, and found that negative voltage dropped from -10V down to -8.5V. Experimenting with the input voltage I found that when negative input voltage drops below (in absolute numbers, i.e. -10 is 'below' than -20 here) -9V, LM3886 is closed and no output signal is produced.

I think input voltage flows likely because of some problems with bypass capacitors connection or wrong ground potential. That analysis I will keep for the next experiments.

Some new scheme will be implemented soon and likely be tested with the loudspeakers during the New Year vacations and celebrations. Stay tuned for the news (operation amplfiers, comparators, timers, stabilizers, bipolar (including Darlington pairs) and mosfet transistors, they all will be used for something I do not yet know exactly what :)!