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G8MNY > TECH 05.05.21 10:45l 117 Lines 4601 Bytes #999 (0) @ WW
BID : 32926_GB7CIP
Read: GUEST
Subj: Variable Speed Fan for AF PA
Path: IZ3LSV<DB0ERF<DB0RES<ON0AR<GB7CIP
Sent: 210505/0841Z @:GB7CIP.#32.GBR.EURO #:32926 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Nov 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have often been annoyed by fan noise from powerful AF PA gear, or the
opposite, red hot gear with inadequate cooling.
Here is a solution I adopted for a 100W RMS (4ê/100V line) PA amp that had the
heatsinks inside a metal box, with little chance of proper ventilation.
SPLIT RAIL SYSTEM
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄo-oÄÄÂÄÄ +32V @ 4A
R1 ³ ³
³ 1N4004 ÚÄÄÁÄÄÄ¿ ³
ÃÄÄÄÄÄÂÄÄR2ÄÄ´<ÃÄÄÄÄÂÄij PA ³ ³
_³_ ³ ³ ³OUTPUT³ ³
/ + \ ³ ³ ³ STAGE³ ³+ Transformer
³ 12V ³ +³1000uF ³\__³ ÀÄÄÂÄÄÄÙ === & Bridge
\FAN/ === ³LS_ ³ ³ Rectifier
~³~ ³25V ³/ ³ ³ ³
ÀÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄ)ÄÄÄÄÄÄÂÁÄÄ 0V
³ ³+
³ ===
³ ³
ÀÄÄo-oÄÁÄÄ -32V @ 4A
The small fan was from a scrap PC PSU (mounted inside on the top panel spaced
off 3mm to reduce blade hole noise), to push air into the box, the only exit
was from holes near the heatsinks.
R1 is select to just start & run the fan, I used a 2W 390R & that gave about 9V
on the fan. R2 is selected to speed up the with typical program to give the fan
12-14V, as you like it. the value I used was 5R6 5W.
Although this approach is not a good as a thermal switch, it is simple & the
added DC load to speed up the fan a bit, on a 100W PA is insignificant.
BRIDGED or STEREO
In this case use two diodes into R2 from each phase/channel to share the load.
SINGLE RAIL SYSTEM
This should work as well, as long as the 1/2 rail point is not too high above
the fan voltage.
RESULT
The fan starts up & runs very quietly on 9V & gently runs faster from 50W peak
to very fast at 200W peak (clipping).
Of course it is possible to only power the fan from the LS voltages, & this is
one way to cool a Test Dummy Load!
SB TECH @ WW
Variable Speed Thermal Fan
By G8MNY (Updated Jul 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I have often been annoyed by fan noise from over powerful fans in gear. Here is
a solution I adopted for a 12V PSUs & 400W HF PAs. Small 12V fans can be found
in a scrap PCs etc & draw about 70-100mA depending on speed & size.
2x PNP CIRCUIT (Germanium NPN can be used E-C reversed)
use idiot diode & fuse if fan manually wired up.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´<ÃÄo-oÄÄ +12V
e\³Silicon
PNPÃÄÄ¿ FANS
/³ e\³PNP Small ÚÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ Ã Germanium Sponge fill ³ Tab³~³ ³
³ /³between fins gap so fan..ÀÄÄÄÄÄÄÄÄÄÄÄÅÄÅÄÄÄÄÄÄÄÄÄÄÄÙ.
ÃÄÄÄÄÙ blades kept Þ Þ Þ Þ Þ Þ ÞºÞ Þ Þ Þ Þ Þ Þ
_³_ away from Þ Þ Þ Þ Þ Þ Þ²Þ Þ Þ Þ Þ Þ Þ
/ + \ For a quieter fan, fins for ÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛ
³ 12V ³ try 2 in series, min noise. ³ ³
\FAN/ or use a 24V one! ³ P A / P S U ³
~³~ ³ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 0V ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
It uses a high gain (x100) tab silicon NPN or PNP controlled by a leaky
Germanium PNP or NPN placed between the hot heatsink fins (test a germanium
with a soldering iron for resistance change & Fans on/off). I used an all
plasic Tab silicon cable tied to the fans, with the insulated geramanium
transistor E & C leads twisted (make sure it's case is isolated or insulate) &
exposed connections in heat shrink etc.
Fan operation is typically from @ 50øC with a slow variable speed action until
cool!
The fan can be in the earth path or +12V side...
Silicon NPN & Germanium PNP CIRCUIT
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´<ÃÄo-oÄÄ +12V
_³_
/ + \ For a quieter fan,
³ 12V ³ try using 2 in series,
\FAN/ or use a 24V one!
~³~
ÃÄÄÄÄ¿
³ e\³PNP Small
³ Ã Germanium
\³ /³betweens fins
NPNÃÄÄÙ
e/³Silicon
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 0V
RESULT
In high use (waffle mode with processing on or a pile up) the fan starts up &
runs very quietly from about 5V across it, & gently runs faster if the heatsink
gets hotter.
See TECH bul "PA & PSU Fan Noise"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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