Re: Effect of Variac on Monoblocks

Interesting answers guys. That pa-3d driver card is designed to
operate over a wide voltage range. It is used in the DH-500 which has
90 volt rails. I'll have to talk John Hillig at Musical Concepts about
this. The waveform is fully integrated at something like 17 V rails
and 70 ma. idle bias.

The card uses a single ended front end and I believe Cascoded current
follower output device drivers.

These blocks sound pretty good with Chemi-cons (not old stock
Sangamos) at the 63 V design rail voltage Frankly though, I bought
Clayton S-40, 50 W class A per channel, and it is verging on magical.

I have doubts about whether my blocks will ever compete. Not the
result I was seeking.
Dave




On Sun, 23 Mar 2008 12:35:17 -0500, Wink <x@xxxxx> wrote:

I happened to snag a set of 63V/10,000ufd FK BG caps for my monoblock
PSUs. The rail voltage with stock Hafler xmfr is ~ 63 Volts so to
avoid exploding my $$ BGs, I'm using a Variac to reduce the AC mains
input for a rail Voltage of ~ 53 volts until I replace the Hafler
trafos with lower sec V Toroidals. [Refer to "Hafler Monoblock
Project..." thread]

The mystery is the sound, which is sort of peculiar. Hard to explain,
but what is the source? Of course there are 3 variables that have been
changed: PSU caps from Chemicons to BGs, lower rail voltage (well
within the operating range of the PA-3D driver board), and inclusion
of the Variac twixt house mains and both amps.

Should I expect some odd interaction between the Variac and existing
Hafler power xfmr? Nothing obvious comes to mind. Running stone cold,
the 1500VA, Powerstat Variac has plenty of capacity.

Not much to go on here, but thought I would throw this one out to you
guys. Thanks again...
Dave

.

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