Re: Effect of Variac on Monoblocks

A glorious response. Curious in light of previous helpful and cordial
ones, free of your compulsive cruelty.

I'm not an objectivist Arny. I've tried to be, the scientist within
compels it; but amps sound different, quite different frequently.

ICs and cables: I've been a maximum skeptic for decades, using
generics and zip cord. But recent experiments have shown that these
items do indeed sound different, frequently meaningfully. It is
distressing, looking for the physics, and the yet the conclusion is
inescapable.

I'm convinced that, though objectivists do not necessarily have
inferior ears, they may have ears which are insensitive to things the
subjectivists detect. Like my wife who can distinguish colors that
look utterly the same to me.

AB, ABX testing is useless. Sometimes amp problems/ strengths take
weeks to emerge. The instantaneous nature of the AB test does not
allow enough time for the ear-brain to acquire the target. This is not
true of speakers generally because of the massive differences between
designs. Sufficient differential for near instant target acquisition.

Anyway, keep the responses coming. I need smattering of high quality,
gratuitous immaturity in my day, and yours is of the highest quality.

I'm not running 800 bucks worth of 63 V lytics at 63 Volts. Not
necessary.
Dave


On Mon, 24 Mar 2008 09:27:16 -0400, "Arny Krueger" <arnyk@xxxxxxxxxx>
wrote:

"Wink" <x@xxxxx> wrote in message
news:2c2du3529iu69fpq2np7cmfr61405lvb68@xxxxxxx

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]

Running 63 volt rated caps at 63 volts will probably not cause explosions,
but it will shorten their useful life to spec, given other operating
conditions are spec. Since you probably aren't running them as warm as spec,
they will probably still live longer than spec. Furthermore, its not like
electrolytics explode if run 1 volt over spec. They can probably take 20% or
more overvoltage, with no undesireably results other than a somewhat
shortened life.

Bottom line, you could experiment for a few minutes or a few hours with
rated power line voltage being appled, and nothing bad would happen.

The mystery is the sound, which is sort of peculiar.

And of course, being an unwashed amateur, you have no proper listening tests
to back this up. With all due respect, which ain't much, why would anybody
with a brain even comment on your random perceptions?

You probably are scrunching up your ears every time you listen to these amps
because you *know* about the *violence* that is going on inside. Come back
when you've got evidence of something more electronic and technical than the
state of your mind. :-(

Hard to explain, but what is the source?

Your state of mental stress due to your under-rated caps, which aren't all
that under-rated?

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.

Not to mention your obvious state of guilt and self-deinal.

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.

Well, the Variac probably adds a little ESR, and may shift the harmonic
content of the powerline measurably. But on balance, those are the sorts of
thing that a well-designed power amp is supposed to take in stride.

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

If the origional caps were OK, then the added/replaced caps were acts of
either futility or obsessive behavior. If they weren't OK, why didn't you
get proper caps instead of inflicting this marginally-rated crap on your
psyche?

Seriously!

As far as the bias-shift theory goes, the fact is that a well-designed power
amp can't be allowed to suddenly fall apart because the rail voltages are
20% or whatever low.

IME a lot of power amp output stages will do a credible job of amplifying
when the rail voltage is 20% of spec. Not 20% low, but 20% of. Of course the
power output will be only about 10% of spec, but what do you expect, power
from no where? ;-)



.

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