I have a large monobloc amp I use for for subwoofing and I want to add a
simple but reliable temperature controller for the fan. For the main output
heatsinks, is there a general temperature value that should not be exceeded,
or is this highly specific to the output devices? Also, would a high
quality fan controller designed for computer use be suitable?

- Magnusfarce

Most of the analog semi houses now manufacture fan control IC's -- you
can't simply use a thermal sensing device and an IC since the fan needs a
threshold voltage to "get going" -- one of the simplest of these is to use
an LM3524, modulating pulse width mode controller chip and a small fan --
the duty cycle is adjusted in relation to the temperature sensed -- the
LM3524 has a built in error-amplifier and you control the V(error) with a
sensor like an LM34.

The temperature you don't want to exceed will be specified in the
manufacturer's datasheet -- it is usually specified as the maximum junction
temperature -- but it gets a little complex since it is virtually impossible
to measure the junction temperature in real life. Instead, an approximation
is made for the "case temperature", and the difference between this and
ambient.


put "fan control" into the search engine at www.analog.com and you will come
up with a lot of neat implementations!

"Magnusfarce" wrote in message
...
I have a large monobloc amp I use for for subwoofing and I want to add a
simple but reliable temperature controller for the fan. For the main
output
heatsinks, is there a general temperature value that should not be
exceeded,
or is this highly specific to the output devices? Also, would a high
quality fan controller designed for computer use be suitable?

- Magnusfarce

"Magnusfarce" wrote in
:

I have a large monobloc amp I use for for subwoofing and I want to add a
simple but reliable temperature controller for the fan. For the main
output heatsinks, is there a general temperature value that should not
be exceeded, or is this highly specific to the output devices? Also,
would a high quality fan controller designed for computer use be
suitable?

- Magnusfarce



You could mount a microwave oven thermoswitch on the heatsink. These will
handle a fair amount of current and are rated at 250volts so you can drive
a fan directly. Cheap and reliable. I know of one amplifier manufacturer
that uses a setup like this.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

The simplest way, and the method a lot of pro power amps use, is a
bi-metallic switch bolted to the heatsink. This can switch mains or low
voltage DC, it's just a mechanical switch. They come in a variety of
flavours - 25, 40, 50, 60, 70 degrees C and higher. I've never found one of
these switches that has failed.

I wouldn't work on the maximum recommended temperature of the output
devices, as running anything near that is likely to shorten their life and
is just risky. Heat is the biggest enemy of a power amp.
I'd choose a nice comfortable setting of 50 or 60 degrees C. Then the amp
isn't cooking and will love you for ever. Incidentally, 60 degrees is
pretty hot to the touch.

Gareth.


"Magnusfarce" wrote in message
...
I have a large monobloc amp I use for for subwoofing and I want to add a
simple but reliable temperature controller for the fan. For the main
output
heatsinks, is there a general temperature value that should not be
exceeded,
or is this highly specific to the output devices? Also, would a high
quality fan controller designed for computer use be suitable?

- Magnusfarce

I would put a standard whisper fan that will easily fit, and let it run all
the time. A DC operated fan would be the best, to not radiate any hum or
noise back to the amplifier circuits that may be near by to it.

The above is what I do in my own equipment. I don't like to get over
complicated with thermo control, and etc. The simpler this is the more
reliable it would be.

--

Jerry G.
======


"Magnusfarce" wrote in message
...
I have a large monobloc amp I use for for subwoofing and I want to add a
simple but reliable temperature controller for the fan. For the main
output
heatsinks, is there a general temperature value that should not be
exceeded,
or is this highly specific to the output devices? Also, would a high
quality fan controller designed for computer use be suitable?

- Magnusfarce

In , on 11/24/04
at 06:37 AM, "Jerry G." said:

I would put a standard whisper fan that will easily fit, and let it
run all the time. A DC operated fan would be the best, to not radiate
any hum or noise back to the amplifier circuits that may be near by
to it.

The above is what I do in my own equipment. I don't like to get over
complicated with thermo control, and etc. The simpler this is the more
reliable it would be.

There is some advantage to keeping the noise down by monitoring the
heatsink temperature, but, overall, I would agree with the keep it
simple approach.

One point to consider is the how the fan noise enters the room. Mount
the fan such that noise conducted to the room is minimized. I've used
fans that, when held in your hand, could barely be heard, but, when
mounted to a cabinet anchored to the wall, could be clearly heard in
the next room and down the hall. Don't be over aggressive with your
airflow. High flows bring high noise. I've been more successful with
DC, ball bearing, slow speed fans.

If the amplifier, as designed, is able to safely dissipate its heat,
but you are uncomfortable with the temperature, then a very small fan,
always on, will work wonders.

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"Barry Mann" wrote in message
om...
High flows bring high noise. I've been more successful with
DC, ball bearing, slow speed fans.

It's not the air volume so much as the air velocity that increases noise.

If the amplifier, as designed, is able to safely dissipate its heat,
but you are uncomfortable with the temperature, then a very small fan,
always on, will work wonders.

A small fan is not the quietest approach. A bigger fan running more slowly
usually gives the same air flow with less noise.

TonyP.