[HAM] DOWN AND DIRTY EQUALIZER POOP

[Kon Zissis]

Hi everyone.
An  ordinary  graphic equalizer or a parametric  equalizer connected
between the AO28  tone control wiper and the input grid of the 12BH7
should indeed work very well  in helping to  provide a very wide
variation in tone and this will help to compensate for problems such as
weak bass  or  excessive treble or weak treble.  The only thing to
consider is that  the power supply voltage of the EQ should  be high
enough to allow  for clean headroom with the very  high signal levels at
the tone control wiper  stage when the expression pedal is set at  full
volume 
  A 9 volt based graphic EQ such as the well known  Boss GE-7  would run
into distortion but a  12 volts  based EQ will allow more clean headroom
and it should be OK for situations such as churches or living rooms
where the organ is not played at full volume  but a + / - 15 volts based
EQ   would  allow a whole lot more clean headroom at full volume.
Because common op amps such as the TLO71 can handle   up to +/- 18 volts
DC,  they  should work well in  a home made EQ  designed  from a audio
hobbyists circuits book. 
The input impedance should be very high such as 1 mega ohms  in order to
avoid reducing the bass response  and also to allow the tone control to
work properly . If the EQ has a lower input impedance , a very simple
unity gain FET buffer with a very high input impedance   can be built
and placed before the input of the EQ.
 
For  the people  who love the overdrive sound , a stereo  EQ would be
very useful  because one channel of the EQ could be used as a ''pre
overdrive EQ'' to shape the sound going into a tube based or  a solid
state based n overdrive unit and then the other channel of the EQ could
be used as a 'post overdrive EQ''  to shape the sound coming after the
overdrive unit. This set up would be ideal  if for example you want a
real deep bass response but still have a  non muddy  overdrive sound.
You can keep the  bass  in the pre overdrive EQ  set at flat or reduce
the bass if the sound becomes too muddy with the overdrive effect  and
then  you can boost the bass after the overdrive  section  so that you
can  get a  deep and  cleaner bass. With the post overdrive EQ you can
also remove  unwanted  raspyness of the   overdrive sound and simulate
that warm dirty and sweeter sounding  overdrive  heard on the old Jazz ,
Blues and Rock albums  of the 1950's , 60's  , and 70's.
 
In my own 1962 C3 I  have built a  12AX7   based  EQ and overdrive
circuit  with a pre overdrive EQ and  a post overdrive EQ and these work
very well . These passive bass and treble pre overdrive and post
overdrive EQ tone stacks are very useful  but a graphic  EQ  or a
parametric EQ  would allow for even more  tonal variety. The schematic
and instructions for the 12AX7 based EQ / overdrive  unit  is freely
available  on Hammond Wiki  ( ''Kon's 12AX7 based EQ / overdrive unit''
) so that anyone can build it.
 
 I have also built this  12AX7  based EQ / overdrive unit  into Ray
Vanderby's 1959 C3 and  this is a key part of  Ray Vanderby's  sound.
Ray  Vanderby previously  had a Chicago style Blues band called '' Ray
Vanderby and the Raynettes''  but now he has gone back to what he really
does best with  his hard edged   Progressive Rock/ Psychedelic Rock
group ''Cosmic Nomads'' whose influences include Uriah Heep , Deep
Purple , King Crimson , Hawkwind , Emerson Lake & Palmer , The Who  etc.
The ''Cosmic Nomads''   have  just recorded their new album ''Vultress
''  these past three  days at Atlantis Sound studio in Melbourne,
Australia and  this album is full of aggressive dirty Hammond C3 through
a Leslie 925.  The12AX7 based  EQ / overdrive  unit combined with the
spring  reverb unit that I built in Ray's C3   were used to create some
very trippy  and ominous sounding feedback  effects and thunder crash
effects and space ship effects  for some of the tracks on the ''Vultress
'' album.
All the best.
Kon 
 
Mike Fulk and Scott Hawthorn wrote:
 
>I bought a car equalizer from radio shack, and a 12 volt power supply;
>installed it at 12BH7,,,,,,,, for a church..NO HUM
>About $25.00.........8 years ago.............everybody was happy.
>Fulk
 
>Now THAT'S damned interesting! :eave it to Fulk, I always say....