[HAM] DC filtering to the heater filament voltage of the AO28

[Keith H Clark]

Kon,
    The final revelation would be to listen through a PR-40 as it has a much
superior bass reproduction.The difference,if any,would be readily apparent.
Keith

-----Original Message-----
From: hammond-bounces at zeni.net [mailto:hammond-bounces at zeni.net] On Behalf
Of Kon Zissis
Sent: Saturday, December 22, 2007 10:05 PM
To: hammond at zeni.net
Subject: [HAM] DC filtering to the heater filament voltage of the AO28

Hi Scott.
There is nothing wrong with the AO28 of my 1965 C3  , however because I
am currently rebuilding it , I was curious to try out the DC filtering
for the heater filaments  because some techs have mentioned that they do
this modification to minimise hum.
 
l did an A / B listening test by setting both the AO28 and the  Leslie
122 at full volume and then I switched between the stock AC filament
wiring and then  the  filtered DC voltage wiring that used four IN5822
Schottky diodes as a bridge rectifier followed by a 10000 uf smoothing
capacitor .
 
I could not hear any real difference  in the level of the subtle  normal
hum so therefore I concluded that the AO28 does not need the DC filament
voltage so I rewired the  filament voltage back to the stock AC voltage
set up .
 
Even though this experiment with DC  filtering for the heater filaments
proved unnecessary , it was a learning experience that at least
satisfied my curiosity about this.
All the best.
Kon
 
Scott Hawthorn wrote:
I confess to being puzzled by this whole discussion. It's just that I
have 
never known hum to be a problem with AO-28 amps, unless the amp is
broken. 
Of course it has been famously said that these organs are not HI-FI 
equipment. I guess if somebody wants to phool around with it, then
that's a 
fascinating hobby, but really, the bottom line is that it's pointless,
IMHO.
 
 
 
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