I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

**Er, use a smaller value resistor. Alternatively, you could replace the fan
with a new one, which has better bearings and can cope with lower Voltages.
You could also kick the fan into high speed, at switch on, then allow the
resistor to come in, to drop the speed down.


Can I replace this with a computer cooling fan?

**Not usually. Computer fans are generally 12 Volt DC and pretty crappy.
They're also difficult to add speed control to.

What size do I
need?

**Same size as the oringal.

How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

**Papst make some excellent termperature-sensitive fans, which would be
appropriate for your needs.

--
Trevor Wilson
www.rageaudio.com.au

Thanks for the reply. More below.


"Trevor Wilson" wrote in message
...

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with
an
inline resistor. I got the voltage so low that the fan will
not
even spin unless I reach inside and give the blade a spin.
That
is both easy to forget and annoying to do.

**Er, use a smaller value resistor. Alternatively, you could
replace the fan
with a new one, which has better bearings and can cope with
lower Voltages.
You could also kick the fan into high speed, at switch on, then
allow the
resistor to come in, to drop the speed down.

As it stands, the fan has only one speed with the resistor in
place. I do not know how to "allow the resistor to come in"
later. The resistor I used was recommended at the time by the
amps designer, though he sounded very much like he was guessing.
With my luck, if I guess at another value, I will get one that
makes it loud again. I would just as soon start out by completely
replacing the puppy with something quieter, i.e., better
bearinged, as you advise.



Can I replace this with a computer cooling fan?

**Not usually. Computer fans are generally 12 Volt DC and pretty
crappy.
They're also difficult to add speed control to.

The Antec and Zalman fans in my computer are speed controlled, and
mighty quiet, too. More important, I am pretty sure the fan in my
'zilla is 12V DC.

What size do I
need?

**Same size as the oringal.

I guess I deserved that answer. My hope was that someone knew the
size offhand so I would not have to take the puppy apart once to
measure, and another time to put a fan in later when the order
arrives.


How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat
after
a few hours.

**Papst make some excellent termperature-sensitive fans, which
would be
appropriate for your needs.

I've heard all sorts of good things about Papst computer fans, but
it seems like going the temp sensitive route is just a more
complex guessing game than is playing with resistor values. I
have no idea what temps I want. I do know the amp sounds better
when it is quite warm, and that a very slow turning fan seems to
move enough air over the heat sinks that it will never overheat
under the conditions I expose it to.

Which takes me back to wanting some sort of speed control. I can
turn it up just high enough to be sure the fan will spin at turn
on, but remain inaudible. And, on the off chance I decide to
drive it a lot harder than I do now, I can just turn it up further
still. A Papst that is not temp-sensitive might well fit the
bill, if I can just figure out what size to get.

Again, thanks for the reply.

Phil


--
Trevor Wilson
www.rageaudio.com.au

"Phil Anderson" wrote in message
news:uoiZa.74573$Oz4.17482@rwcrnsc54...
I would just as soon start out by completely
replacing the puppy with something quieter, i.e., better
bearinged, as you advise.

Be aware that the bearings are not the only thing that make a noise. The air
flow itself is a major factor. Papst and others make fans with different
CFM ratings (cubic feet per minute) and corresponding SPL levels, for the
common sizes.

Temperature sensitive electronic fan speed control, is usually the best
option though.

TonyP.

"Phil Anderson" wrote in
news:WMgZa.74397$Oz4.17285@rwcrnsc54:

I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil




Do like McIntosh does and put a thermoswitch on the output heatsinks and wire
it to the fans. The fans will then only come on when needed.

r

--
"Any sufficiently advanced technology is indistinguishable from
magic."

Arthur C. Clarke (1917 - ), "Technology and the Future"

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54

I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.


Can I replace this with a computer cooling fan?

Yes.

What size do I need?

Start out with a fan the same size as the existing fan.

How about a speed control?

Computer cooling fans typically are rated for use with 12 volt DC power at
something like 0.1 amp.

Therefore you need to arrange for an appropriate voltage source in your
ampzilla. There's plenty of power DC there, but you'll need to drop the
voltage. An ideal way to accomplish this would be to build a variable
voltage DC regulator whose output voltage is controlled by a simple
potentiometer. Then adjust this potentiometer for the desired fan speed.
Most PC-style fans operate pretty stably down to 7 or 8 volts. Much below
that, stalling at power up can be a problem.

My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

If a fan the size of the existing fan is too noisy and pushes too much air,
replace it with a smaller fan mounted in a baffle plate. Your goal is to use
a larger fan spinning at the slowest speed that moves enough air and avoids
stalling at power up.

One way to avoid stalling at start-up is to drive the fan through a resistor
with a fairly large electrolytic cap in parallel. The cap will provide a
kick to get the fan rolling, and the resistor will run it at a slow steady
speed.

Which version of this GAS unit do you have? I owned the original (model with
crazy lettering logo). The fan was very noisy, and I reduced it by elevating
it up from the shelf. I put 4 of my kid's building blocks beneath the feet
and most of the noise was gone, as if it were in large part caused by the
rush of air upon the shelf surface. My Ampzilla IIi, never remained in
repair long enough for me to be bothered the fan noise (which was far less).
I think you are extremely fortunate in having a working unit. (None of the
GAS amps generated the current required to drive speakers of 4 ohm
impedance, so mine ended up driving a pair of Stax headphones.) My GAS unit
is really idling since is too big to use as a doorstop and not owning a
boat, I'm not in any need of an anchor.

"Phil Anderson" wrote in message
news:WMgZa.74397$Oz4.17285@rwcrnsc54...
I need advice on replacing the cooling fan on my GAS Ampzilla.
The current fan was too loud, so I tried slowing it down with an
inline resistor. I got the voltage so low that the fan will not
even spin unless I reach inside and give the blade a spin. That
is both easy to forget and annoying to do.

Can I replace this with a computer cooling fan? What size do I
need? How about a speed control? My Ampzilla needs very little
cooling, but if the fan is all the way off it will overheat after
a few hours.

Advice please.

Thanks,
Phil

"Norman M. Schwartz" wrote in message
...
Which version of this GAS unit do you have? I owned the original
(model with
crazy lettering logo). The fan was very noisy, and I reduced it
by elevating
it up from the shelf. I put 4 of my kid's building blocks
beneath the feet
and most of the noise was gone, as if it were in large part
caused by the
rush of air upon the shelf surface. My Ampzilla IIi, never
remained in
repair long enough for me to be bothered the fan noise (which
was far less).
I think you are extremely fortunate in having a working unit.
(None of the
GAS amps generated the current required to drive speakers of 4
ohm
impedance, so mine ended up driving a pair of Stax headphones.)
My GAS unit
is really idling since is too big to use as a doorstop and not
owning a
boat, I'm not in any need of an anchor.

This one started out really original. I bought it from the
original owner, who built it from one of the original kits offered
before GAS got together enough money. The only thing that was not
original in mine was the fan.

Shortly after I received the amp, one channel died. I contacted
the designer, James Bongiorno, and sent him the 'chimney' and he
replaced and updated the circuitry, as well as added a bass servo
unit of his design. I sought his advice on the fan, but since it
was not the original, he was not sure about the proper resistor to
slow it down. He noted that the amp only needed a very small
amount of cooling from the fan, so how slow it was was not an
issue.

I installed the resistor he thought of as his best guess but the
hystersis effect (is that the right term) means it often does not
spin when I turn it on. I finally got tired of having to pull out
the amp and reach up inside it every time I turned it on, and
posted my question here. I am currently leaning toward a German
made Papst fan, since they seem to have the reputation of spec'ing
their noise figures much more accurately than most.

BTW, I am using the amp to drive Dahlquist DQ-10s, and have a
Thaedra for my pre-amp. I got the Zilla and the Thaedra from
different owners over the net. Both are the 'original' model 1,
but I do not know the Thaedra's pedigree.