David Farber wrote:

==================


Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


I hadn't realized that the ramp up occurred within 1 second. I powered
it on without the Variac and sure enough, the waveform made a gradual
change within that 1 second timeframe. Everything seems to powering up
OK. Checking the audio will be next.

** So far - so good.


I'm still curious about the power supply question I asked in my previous
post (see below) regarding how the two bridge diode circuits seem to be
adding voltage in a series circuit.
============================================


** Yep- it sure is complicated !!.

The DC supply is *series stacked* with a low an high voltage components.

Then a pair of IGBTs for each channel is used to *regulate* the voltage to the main BJT amplifiers so it TRACKS the incoming audio. Maybe not perfectly but reasonably close to demand and just a lite more volts than needed by the load at any moment. The low voltage DC supply sets a fixed lower limit.

Look up "class H" on Wiki.

I only know of one other amp maker doing this, Lab Gruppen.

Crazy complicated - why not go Class D an keep it simple ??


...... Phil