On 11/10/2020 8:48 PM, Phil Allison wrote:
David Farber wrote:

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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.
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** 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

Hi Phil,

My experience with commercial(?), high powered audio gear with switching
power supplies is almost nil. I'll check out class H on Wiki and while
I'm there, I'll check out any other classes that I haven't come across.

Yesterday, I installed the PC board into the chassis and connected the
front panel connectors. The result was the earth ground became tied to
the power supply ground which should have made voltage testing much
easier except for the fact that I could no longer access the bottom of
the PC board. It's next to impossible to accurately put a probe on
anything from the component side. Many parts are covered in epoxy(?) or
hot glue(?) and the power transistors are totally obscured by the heat
sinks that surround them.

Thanks for your reply.
--
David Farber
Los Osos, CA