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how important are the cooling fans for the 2400-2600 series amps
being used in a home environment

Dear Jim,
As the designer of that series using my radical horizontal heat sink
radiator I can tell you that it is very efficient. However, as the power
output goes up, obviously the disappation goes up correspondingly. The
average temperature rise is solely dependent on the amount of dynamic range
that you want from your system. Those SAE amps were designed with industrial
uses in mind ie; rock concerts, discos, etc. where the dynamic range is much
more limited than in the home. Even a great many people found that my
earlier Ampzilla could be run without the fan. It all depends on how loud
you listen and the efficiency of your speakers. Remember that a mere 20 db
of dynamic range, which is not a lot, is a power factor of 100 times.
Therefore, a nominal 200 watt amp would be running an average power level of
around 2 watts. A 30 db dynamic range would have an average level of 200
milliwatts!
The only way for you to tell in your system is to disconnect the fan and
after say an hour of listening, see how hot the power transistors get (NOT
the heat sink). If you can KEEP your finger on the case of the devices
without feeling pain, then you are probably OK. If however, after a second
or two, you have to pull your finger off so as not to get burned, then the
temperature is too hot necessitating the fan.
James Bongiorno

jim albert wrote:

From: "jim albert" <tbirdsc@...>

how important are the cooling fans for the 2400-2600 series amps
being used in a home environment

What would have been nice was a temp sensor that turned on the fan when
the heatsink reached a certain temperature.

The thing about the 2500 and 2600 is that if you took off the top cover
and remove the fan, you could run the amp in free air and get good
cooling airflow. The heatsink airflow would be identical to the MKIIICM
(200Watts/Chan) and the MK31B(50 W/chan same as the 3100) amps which do
NOT have fans. The airflow would be backwards compared to the forced
airflow direction of the 2600 not that really means anything. In my
opinion you would not have any problems in a reasonable home environment
unless you really like pushing your amp on long stretches. However, I
could not state with any certainty it would work well under all
conditions. That would require testing. I ran my 2600 at 133W/Chan 1K
sinewave into a resistive load and the amp got really warm even WITH the
fan. Running an amp continuously at 1/3 of its rated power is a good
thermal test. So I sure the amp can get very hot if pushed. There is a
thermal cutout on the AMP that removes AC power if the heatsink gets to
hot. So there is some level of protection.

I do not think you can run the 2400 series if amps without a fan at all
even with the cover off. It looks like the heatsink assembly was almost
designed from the ground up to require forced airflow. However, it would
be an interesting comparison of that heatsink configuration with the
Dynaco 400 heatsink, maybe it could work.

You could build a thermal cooling circuit into the 2600 that monitored
the temp of the heatsink and turned on and off the AC fan accordingly.
Use the 6.3VAC power that drive the front panel bulbs as the input power
source for you circuit. A simple voltage comparator and 5V regulator
would be all that is needed in terms of IC circuitry. Configuring the
thermistor in a voltage divider would allow you to generate a voltage
that is proportional to temperature. The comparator would monitor the
thermistor voltage relative to a voltage trip threshold that would be
created by a another fixed resistor divider. I would also add about the
equivalent of 10C of thermal hysteresis to prevent frequent fan power
cycling. The comparator's output would drive the relay which drives the
fan. You could mount the circuit on the big ground bus bar which also
supports the 120VAC connection terminal strip.


Best Regards,

Mark Gurries

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