"Jim Lesurf" wrote in message
...
In article , Dave Plowman (News)
wrote:
Common way to stop the thump you can tend to get with a MOSFET amp
at
switch on was a relay on the speaker output.

It occurred to me that in these days of cheap high power triacs it
might
be better to ramp up the AC into the amp - even if it uses a
conventional power supply?

Some amp designs might 'thump' anyway as the bias points passed
magic
values that caused various parts of the circuit to 'wake up'.

Comments welcome. ;-)

Personally, such thumps have never bothered me. The only change I
made to
my Armstrong 700s was to eventually bypass their output relays.
After a
decade or more they did as I'd predicted originally and started to
give
unreliable connections. So I shorted across them.

Provided the thump doesn't bother the speakers or blow you across
the room
I simply regard it as an audible 'switched on' indicator.


Surely the risk is d.c. offset as almost all modern amps and certainly
a MOSFET amp would have split supplies.

I built one based on the Ambit PCB but then built the JLH regulated
supply which has relay protection for the L/S. One channel on that
decided to sit at about 120mV and there was no way I could get it
down. The supply rails were almost identical so I can only assume that
something has slipped in the amp design.

Without a doubt though the best power amp I have ever heard. Does 112W
into 8R and 224W into 4R - and that takes some doing!


--
Woody

harrogate3 at ntlworld dot com