Meat Plow wrote in message ...
On Wed, 14 Apr 2010 17:42:57 +0100, "Arfa Daily"
wrote:

Anyone got knowledge of this power amp ? Particularly looking for bias
setup
procedure.

TIA

Arfa


Never did one but if you hadn't a print for it here's some.

:http://akdatabase.org/AKview/display...album=18&pos=7

It's #8 of 24

VR404 is idle current trim on right ch, 403 on left. VR402 is DC
balance on right ch, 401 on left. I suppose the balance is pretty
simple, just zero out. Don't know where the test points are for idle
current. But with a quad of silicone planars on each side wouldn't it
be around 30ma?

I was guessing at around 20 to 25mA, but I now have a copy of the service
manual, courtesy of Trevor over on uk.r.a. It's actually a bit of an 'odd'
setup procedure in that they give you four pairs of test points, but then
you have to glue 4 x 100 ohm R's around each two pairs, and then adjust for
32mV between the junction points of these R's ...

The DC balance adjustment is also a little 'odd'. First you set the O/P
impedance selector to 4 ohms, then check the offset at the speaker
terminals, and adjust, if necessary, for 0V. Fair enough, and exactly what
you might expect. But then you reset the O/P impedance for 8 ohms, and check
that the DC offset is " +/- 60mV " ...

I'm sure that something has got lost in the translation there, and what they
actually mean is that first you set for 0mV on 4 ohms, and then check that
on 8 ohms, you do not get more than a maximum 60mV offset. Would you agree ?

Arfa