@@ -1,111 +1,89 @@-This article was submitted by KonZissis.
------
-!!
Kon's 12AX7 Based
EQ & Overdrive Circuit
for Hammond Organs
+Kon's 12AX7 based
EQ & Overdrive circuit
for Hammond Organs
-My [previous
12AX7 based EQ and
overdrive circuit|KonsOld12AX7basedEQ&OverdriveCircuit] was located after
the [G-G] output terminals of
the [AO-28] preamp because I was able to get a better bass growl and crunch
from this location
compared to the lesser bass growl and crunch
that was previously available if
the circuit was placed between the tone control wiper and
the input grid of the [12BH7] output valve
.
+This
12AX7 based EQ /
overdrive circuit is designed for
the Hammond tone wheel console organs that have valve preamplifiers such as
the B2, C2 , RT2 , B3 , C3 , RT3 , A100 series , D150 series
etc.
It might also
work in the M , M2 , M3, M100 series , L100 series , Porta B etc organs but I have not tried this out.
+I think
that it might also
be adaptable for
the earlier era console organs such as
the Model a , B , BC , BV , CV , D , E etc but I have not tried this out either
.
-One major problem with the previous EQ/overdrive
circuit that was located after
the [G-G] output terminals was that an expensive output coupling transformer was required that would split
the output signal into
a dual balanced line output so that
the output signal could be properly matched with
a balanced line [Leslie] such as
the [
122|Leslie122]
or a HammondToneCabinet
.
+This
circuit connects between
the wiper of the preamplifier Tone Control potentiometer and the input grid of
the output valve which is
a 6SN7 on
the AO10 preamp and
a 12BH7 in
the AO28 preamp, and it uses a 12AX7 valve to create the overdrive effect.
+The quality of the overdrive tone is very good and it does sound similar to an overdriven Leslie
122 or a Leslie147 etc valve amplifier depending on the settings of the EQ controls
. Switching off the passive pre overdrive EQ
-More recently I have experimented with
and I found
a way to get the nice
bass growl
and crunch with the
EQ/overdrive circuit being located between
the tone control wiper and the input grid of the 12BH7.
-The reason why the bass response was being rolled off in my earlier 12AX7 EQ
/overdrive circuit design that was located between the tone control wiper
-and the input grid of the 12BH7 was that the impedance to ground of the input gain control that fed the signal into the first gain
stage of the
-[12AX7] valve would cause the lower bass frequencies to be rolled off from the signal coming from the tone control wiper.
-The tone control wiper needs an extremely high impedance in order to allow the full bass response to pass
and even using
a 1 Meg ohm pot as an
-input gain control causes some of the lower bass frequencies to roll off.
-I overcame the bass roll off problem by not wiring any input gain control between the tone control wiper and the input grid of the 12AX7
-and just having the
passive bass and treble EQ wired between
the tone control wiper and the 12AX7 input grid
.
+This circuit is reasonably simple in operation in that it uses one 12AX7 valve
and a passive ’pre overdrive’
bass and treble tone stack
EQ before
the gain
/overdrive stage and also
a passive ‘post overdrive’
bass and treble tone stack
EQ after
the overdrive stage.
+Both EQ's can be independently activated or bypassed with a 2-pole / 2-position ( DPDT ) switch
.
-I did a careful A/B listening test with the 12AX7 EQ/overdrive circuit switched in and out of circuit and with the gain/overdrive control set to a low level
-to produce the pure clean sound and the master volume control set to the full volume setting so that the volume level of the organ through the EQ/overdrive
-circuit was identical to that of the fully bypassed organ signal.
-After doing this careful A/B listening test, I verified that with the EQ controls set to the flat setting,
-the tonal response of the organ is identical and without any bass roll-off.
-Because of this the newly revised circuit is now simpler and cheaper to build than the version that was located after the GG output terminals
-and that needed the output coupling transformer.
-The quality of the overdrive tone is very good and it does sound similar to an overdriven [Leslie 122|Leslie122] or a [147|Leslie147]
-valve amplifier depending on the settings of the EQ.
-
-This circuit is reasonably simple in operation in that it uses one 12AX7 valve and a passive bass and treble EQ before the gain/overdrive stage
-and also a passive bass and treble EQ after the overdrive stage.
-Both EQ's can be activated or bypassed with a 2-pole / 2-position (_DPDT_) switch.
-
-_
Baxandall_
type EQ's and I have simply copied the bass and treble tone stack that BobSchleicher
-[
schematics section of his website| http://www.tonewheel.com/schematics.htm]
(see http://www.tonewheel.com/Schematics/tonecontrol.jpg),
-however I have disregarded the low gain cathode follower circuitry that BobSchleicher
's circuit uses and I have simply wired the EQ tone stack
-
+The passive bass and treble EQ's are Baxandall type EQ's and I have simply copied the bass and treble tone stack that Bob Schleicher
displays on the schematics section of his website (see http://www.tonewheel.com/Schematics/tonecontrol.jpg ),
+however I have disregarded the low gain cathode follower circuitry that Bob Schleicher
's circuit uses and I have simply wired the EQ tone stack before the input grid and after the master volume control of the EQ/overdrive circuit.
+Both stages of the 12AX7 valve are wired as simple cascaded gain stages
.
The pre-overdrive EQ affects the tonality of the signal going into the 12AX7 valve.
-This is useful if your organ has a weak bass response and you want more of a bass growl and grind or if you want more distortion from
-
+This is useful if your organ has a weak bass response and you want more of a bass growl and grind or if you want more
distortion from the organ treble frequencies.
The post-overdrive EQ shapes the sound after it has passed through the overdrive stage.
-This can give you a nice fat bass but without distortion because it is located after the gain/overdrive stage.
-You
can simulate the deeper bass response of a Leslie connected together with a [
PR-40]
Hammond tone cabinet.
+This can give you a nice fat bass but without a muddy
distortion because it is located after the gain/overdrive stage.
+With this you
can simulate the deeper bass response of a Leslie connected together with a PR-40 Hammond tone cabinet or the fatter bass sound heard on some recordings where the miked up signal had a bass boost added via the recording console EQ controls or the final mix and mastering process
.
-There
is an additional modification to the treble capacitor of the post overdrive EQ treble control
.
-You can use a DPDT switch to select either the original 470 picofarad (_
pf_
) capacitor or a 1 nanofarad
(_
nf_
) capacitor.
-The 470 pf capacitor produces the true flat response sound when bass and treble are set to the _"flat"_ position.
-For the bass control, the _"flat"_ setting is the 12 o'clock position and for the treble control the _"flat"_ position is at around the 2 o'clock position
.
+Although the passive bass and treble tone stacks are similar to those shown on Bob Schleicher’s website , there
is an additional modification to the treble capacitor of the pre overdrive and
the post overdrive EQ treble controls
.
+You can use a DPDT switch to select either the original 470 picofarad ( pf ) capacitor or a 1 nano farad
( nf ) capacitor.
-With the
470 pf capacitor, turning
the treble control
to the full
position results in the higher treble frequencies being emphasised thus making the distortion more raspy sounding
.
-When
the 1 nf capacitor
is chosen there is a discernible increase in
the lower midrange warmth when
the treble control is set at
the _
"flat"_
2 o'clock position
-and when you turn
the treble control to
the full position the upper midrange as well
as the treble is emphasized for more presence and _"scream"_
.
-This can
be useful if you have a muddy sounding Leslie or a Hammond tone cabinet or an external amplifier or speakers.
-If you want to you can add this same capacitor switching option to
the pre overdrive EQ treble control
.
+The
470 pf capacitor produces
the true flat response sound when bass and
treble are set
to the "flat"
position.
+For
the bass control, the "flat" setting
is at around
the 12 o'clock position and for
the treble control the "flat" position is at around the
2 o'clock position. In actual use this might vary depending on
the taper characteristic of
the actual potentiometers that are used
as the bass and
treble controls
. There might
be variations in
the taper between 1 mega ohm potentiometers from different manufacturers
.
-With the pre-overdrive EQ switched on
, you can get a fully clean sound even with
the expression pedal at
the full volume
position when
the gain/overdrive control is set at a low setting
.
-With
the pre overdrive EQ swithed on , setting the gain/overdrive control to the fully clockwise position will produce a heavily ovedriven Leslie 122 / 147 simulation when the expression pedal
is at the full volume position.
-With the pre overdrive EQ switched off ,
there will be some distortion
in the first gain stage of the 12AX7
when the expression pedal
is at the full volume
position regardless of the setting of the gain/ overdrive control
and
- setting
the gain/ overdrive
control to the fully clockwise
position will produce a heavy level of saturated overdrive similar to
the early 1970's Deep Purple Mark 2 albums such
as 'Machine Head'
and Made in Japan ' which featured Jon Lord's Hammond C3
organ played through
a heavilly overdriven Marshall valve
amplifier.
+With the 470 pf capacitor
, turning
the treble control to
the full position the higher treble frequencies are emphasized more resulting in more top end brightness and key click
.
+When
the 1 nf capacitor
is chosen
there is a slight increase
in the lower midrange warmth
when the treble control
is set
at the "flat" 2 o'clock
position and when you turn
the treble
control to the full
position the upper midrange
as well as the treble is emphasized for more presence
and "scream".
+This treble boost can be useful if you have a dull sounding
organ or a dull
sounding Leslie or
a Hammond tone cabinet or an external
amplifier or speakers
.
-I recommend that
the post
overdrive EQ is normally left
on because
when it
is bypassed
the signal levels from
the EQ
/ overdrive unit
will be extremely high and they will overload
the final
stage of the organ preamp
.
+With a stock organ, when
the pre-
overdrive EQ switched
on, you can get a fully clean sound even with the expression pedal at the full volume position
when the gain/overdrive control
is set at a low setting.
+With the pre overdrive EQ
switched on , setting
the gain/overdrive control to
the fully clockwise position will produce a heavily overdriven Leslie 122
/ 147 simulation when the expression pedal is at the full volume position.
+With the pre
overdrive EQ switched off, there
will be some distortion in
the first gain
stage of the 12AX7 when the expression pedal is at the full volume position regardless of the setting of the gain/ overdrive control and setting the gain/ overdrive control to the fully clockwise position will produce a heavy level of saturated overdrive similar to the early 1970's Deep Purple Mark 2 albums such as 'Machine Head' and Made in Japan ' which featured Jon Lord's Hammond C3
organ played through a heavily overdriven Marshall valve amplifier
.
-BY THE WAY after some more recent experimenting
I noticed
that the two 10 K resistors that are shown in series with the grid pins 2 and 7 in the schematic are not really necessary after all and you can get a subtle increase in the very high treble if you omit these two resistors
because the 10 K resistors in series
produce a subtle roll off in
the very high treble. However if you switch off
the pre ovedrive
EQ bass and treble tone stack
you
will then get a sagging or 'coughing' effect when
the first
stage of the 12AX7
is overdriven and
a 10 K ohms resistor
wired in series with the grid pin 2 will help to stop this effect. If
you want you can wire this 10 K ohms resistor
to be on the
bypass section of
the 'pre
overdrive EQ' on / bypass switch so
that the 10 K series resistor is in circuit only when the pre overdrive EQ is switched off.
- The 10 K ohms resistor is not needed in series with the grid of the second stage of
the 12AX7 ( pin 7 )
.
+I recommend
that the post overdrive EQ is normally left on
because when it is
bypassed
the signal levels from
the EQ / overdrive unit
will be extremely high and they will overload
the final
stage of the organ preamp if the Master Volume control
is set to
a loud
setting but if
you do
want to bypass the post
overdrive EQ then I recommend
that you at first set
the Master Volume control to a very low setting and then set it to
the desired setting
.
-The two cathode bias internal gain
pots determine
the total internal gain level of the two gain stages of the 12AX7 valve. In my own circuit in my 1962 C3 l have found that the best sounding
overdrive tone is created when
the 25 K ohms
cathode gain control of
the 12AX7 gain stage 1
is set at slightly less than
the full position. I have
the 10 K ohms cathode gain control
of the 12AX7 gain stage 2 set at the full gain position
. If both cathode gain
controls are set to the fully clockwise
position for maximum gain then the distortion has
a harder sounding quality
to it but when the cathode gain control pot
of the 12AX7 gain stage 1
is set at slightly less than the full position such as between the 3 o'clock and the 4 o'clock position , the valve breathes better and the distortion sounds more natural
. The trick is to
set the
cathode bias internal gain controls to the setting that produces the maximum amount of distortion that you want
when the gain /
overdrive control
is set to the fully clockwise setting. If you only like a mild distortion
, then you can set
the 25
K ohms cathode bias
gain control
of the gain stage 1 to a lower setting so that when
the gain /
overdrive control
is set to
the fully clockwise position there
will only
be a milder level of distortion
.
+If you switch off
the pre
overdrive EQ bass and treble
tone stack
you might then get a sagging or 'coughing' effect
when
the organ preamplifier Tone Control
is set to
the full brightness
position and
the expression pedal is set to full volume thus causing the first stage
of the 12AX7 to be overdriven
. You can minimise
this ‘’coughing effect
by
wiring
a 10 K ohms resistor between
to two ‘bypass’ poles
of the pre overdrive EQ
‘on / bypass’ switch
which would normally be shorted out with a direct wire link
. With this revised
set up
when the passive pre
overdrive EQ tone stack
is switched out of circuit
, a 10 K resistor will be
then activated in series with
the input
grid pin 3 of the 12AX7.
+This 10
K resistor
will not affect the overall
gain levels but there might
be a subtle slight mellowing
of the very high frequencies.
+When
the passive pre
overdrive EQ
is switched on in circuit ,
the 10 K resistor
will no longer
be in circuit
.
-Next to the 100 k ohms plate resistor of the second gain stage of the 12AX7,
-labeled
as _
"Variac simulator"_
.
-This 1 M pot can lower the HT voltage going to the second stage of the 12AX7 valve in order to starve the plate of the second gain stage
-
-When it is set to the fully clockwise position,
-
+When the pre overdrive EQ is switched off , if you feel that he input stage of the 12AX7 is overdriven too much , you can then lower the gain by turning the 25 K “Cathode -A Bypass Internal Gain potentiometer to a slightly less than full gain setting until the ‘’coughing ‘’ effect is minimised or the excessive distortion is tamed down.
+
+There is an 820 ohms resistor wired between the “Cathode –A Bias Internal Gain” control and the actual Cathode- A pin 3 of the 12AX7 and there is an 820 ohms resistor wired between the Cathode – B Pin 8 of the 12AX7 and the ground.
+The 820 ohms value resistor is commonly used as the cathode resistor in many valve circuits. Many valve circuits also have a 330 uf or a 470 uf capacitor wired in parallel with the 820 ohms resistor as a cathode bypass capacitor and this results in the maximum gain levels in the 12AX7 valve and originally this overdrive circuit also had the 470 uf cathode bypass capacitors wired in parallel with the 820 ohms cathode resistors, however after doing some experimenting I noticed that the distortion sounded smoother and less harsh when the 470 uf cathode bypass capacitors were disconnected. Disconnecting the 470 uf capacitors resulted in slightly less gain so that there was not as much extreme distortion available but the slight loss of gain still allowed for a full heavy level of distortion but the valve “breathes’” better now that I have disconnected the 470 uf cathode bypass capacitors.
+This is a matter of personal taste and if you do like the absolute maximum gain levels and a harsher sounding distortion then you can wire up 470 uf capacitors in parallel with the 820 ohms cathode resistors.
+
+
Next to the 100 k ohms plate resistor of the second gain stage of the 12AX7,there is a 1 M ohms pot wired in series and it is labelled
as "Variac simulator".
+This 1 M pot can lower the HT voltage going to the second stage of the 12AX7 valve in order to starve the plate of the second gain stage for a very squashed and dirty sound if this is desired.
+When it is set to the fully clockwise position, the full HT voltage goes to the plate B for the loudest output level.
Even with this setting you can still get a full overdrive sound when the gain overdrive control is set to the fully clockwise position.
+Using the “Variac simulator” to lowering the HT voltage going to the plate B will result in a more distorted sound but it will also result in lowered output levels when you set it to produce a very squashed sound so therefore if you do use the Variac Simulator control you might then need to switch off the Post Overdrive EQ in order to have a reasonably loud output level.
-After the signal has passed out of the second stage of the 12AX7 it goes to the output warming control. This is basically a passive high cut control similar to a passive tone control but there is a sweet spot setting at lower end of the range at around 9 o'clock where there is the effect of a bottom boost which adds depth to the sound and the top end of the distortion is smoothed out for a sweeter, more '' vintage '' sounding overdrive effect because this output warming control brings a grounding 22 nf capacitor to the signal coming from the plate of the 12AX7 valve and it affects the way that the treble distorts when the second stage of the 12AX7 valve is overdriven. I normally play my 1963 C2
in my room at a comfortable volume level and at these mild volume levels , setting the output warming control to the 9 o'clock position produces a very nice sounding chunky bottom end combined with a sweeter overdrive tone that sounds very pleasant. If you do set the output warming control to the 9 o'clock position then setting the post overdrive EQ bass control down to around the 9 o'clock position
+After the signal has passed out of the second stage of the 12AX7 it goes to the output warming control. This is basically a passive high cut control similar to a passive tone control but there is a sweet spot setting at lower end of the range at around 9 o'clock where there is the effect of a bottom boost which adds depth to the sound and the top end of the distortion is smoothed out for a sweeter, more '' vintage '' sounding overdrive effect because this output warming control brings a grounding 22 nf capacitor to the signal coming from the plate of the 12AX7 valve and it affects the way that the treble distorts when the second stage of the 12AX7 valve is overdriven. I normally play my 1962 C3 organ
in my room at a comfortable volume level and at these mild volume levels , setting the output warming control to the 9 o'clock position produces a very nice sounding chunky bottom end combined with a sweeter overdrive tone that sounds very pleasant. If you do set the output warming control to the 9 o'clock position then setting the post overdrive EQ bass control down to around the 9 o'clock position
will produce a more or less '' flat '' bass response.
All of this is a matter of personal taste, the actual Leslie or external amplifier that the organ is being played through and the room acoustics.
-*
By the way*
, although I have specified a 22 nf capacitor on the output warming control , you can experiment with other capacitor values to get the type of sound that you like. I have added a 1 pole , 12 position rotary switch with the following capacitor values: 1 nf, 2.2 nf. 3.3 nf, 4.7 nf, 5.6 nf, 8.2 nf, 10 nf, 15 nf, 22 nf, 33 nf, 47 nf, and 82 nf.
+By the way, although I have specified a 22 nf capacitor on the output warming control , you can experiment with other capacitor values to get the type of sound that you like. I have added a 1 pole , 12 position rotary switch with the following capacitor values: 1 nf, 2.2 nf. 3.3 nf, 4.7 nf, 5.6 nf, 8.2 nf, 10 nf, 15 nf, 22 nf, 33 nf, 47 nf, and 82 nf.
This variable capacitors rotary switch adds a lot of flexibility to the output warming effect of the overdrive sound.
-If you have a modern treble driver such as the Hammond Suzuki 100 watt ferro fluid driver that is too bright sounding in your Leslie, you can
use the output warming control to help compensate for this.
+If you have a modern treble driver such as the Hammond Suzuki 100 watt ferro fluid driver that is too bright sounding in your Leslie, you might be able to
use the output warming control to help compensate for this because the output warming control will tame down the excessive upper midrange response.
.
-After the output warming control there is the master volume control and after this there is the passive post overdrive EQ bass and treble controls.
-
+After the output warming control there is the master volume control and after this there is the passive post overdrive EQ bass and treble controls. Set the amount of overdrive level
that you want with the setting of the expression pedal and the gain/overdrive control and then set the master volume to what ever listening volume level that you like.
-An optional wiring modification is to add a sweetening switch that brings either a 100 nf or a 150 nf or a 220 nf capacitor across the [
G-G]
output terminals of the [AO-28] preamp
.
-Even though the 12AX7 EQ/overdrive circuit is not connected to the G-G output terminals of the AO-28
,
+An optional wiring modification is to add a “
sweetening”
switch that brings either a 100 nf or a 150 nf or a 220 nf capacitor across the G-G output terminals of the organ preamplifier
.
+Even though the 12AX7 EQ/overdrive circuit is not connected to the G-G output terminals of the organ preamplifier
,
the audio signal in the organ passes through the G-G outputs before going to the Leslie or the tone cabinet
and consequently the sweetening capacitor wired across the G-G outputs will result in a sweeter,
-more rounded out treble response which will make the treble harmonics of the overdrive effect sound sweeter because any
-
+more “vintage” sounding
rounded out treble response which will make the treble harmonics of the overdrive effect sound sweeter because any fizzy sounding higher harmonics of the overdrive effect are rolled off.
The sweetening switch and the actual capacitor nf value chosen is also a matter of personal taste and also a matter of what Leslie or other amplifier and speakers are used.
The stock Jensen V21 in my 1971 Leslie 122 is brighter sounding than the V21's in other Leslies 122 cabinets that I have played and I like the sweetened sound when the 150 nf or the 220 nf capacitor is switched across the G-G output terminals. On other Leslies with mellower sounding V21's ,the overdrive sounds nice without needing the sweet switch.
-November 2006 update.
-If you want to hear recorded examples
of what this
EQ / overdrive unit sounds like through a
1959 C3 organ played through a Leslie 925 cabinet , you can hear it on
the songs
that have been posted on the My Space website of the Australian Progressive Rock/ Psychedelic Rock band
''Cosmic Nomads
'' who are led by the Hammond organist Ray Vanderby.
-The Cosmic Nomads My Space link is :
-www.myspace.com
/cosmicnomads
-Click on this link and
listen to
the songs from the album
''Vultress
' that have been posted there
.
+I am the Hammond tech and roadie
of the Dutch born Australian Progressive Rock organist Ray Vanderby and I have built the 12AX7 based
EQ
/ overdrive into Ray's
1959 Hammond
C3 organ. Because of
the work
that I
have done with Ray
's C3 and Leslies , Ray calls me
''Professor Kon
'' and he refers to the12AX7 based
EQ
/ overdrive unit as
the ''ProKon EQ / overdrive unit'
'.
-I am
Ray Vanderby's Hammond tech
and roadie and I have built this 12AX7 based EQ
/ overdrive
into Ray's 1959 Hammond C3 organ
. The tonewheel
generator of Ray's 1959 C3 has been recapped with new capacitors in order to more or less restore the original stock sound and Ray plays his C3 through two solid state biamped Leslie 925 cabinets which have a JBL bass speaker and a JBL 2482 treble driver.
-In October 2006 'Cosmic Nomads' recorded their new album ''Vultress '' at Atlantis Sound Studio in Melbourne , Australia and this album prominently features Ray's 1959 C3 through the Leslie 925 and the 12AX7 based EQ / overdrive unit is used on all the songs . The 925 was played reasonably loud but still clean sounding in the studio and all the ovedrive heard on the songs is from the EQ / overdrive unit. Because of the work that I have done with Ray's C3 and Leslies , Ray calls me ''Professor Kon'' and he refers to the EQ / overdrive unit as the ''ProKon EQ / overdrive unit''
.
+Ray Vanderby is the band leader of the Australian Progressive Rock band “ Cosmic Nomads” ,
and in
May 2007 Ray Vanderby added me
into his band as the rhythm guitarist of the Cosmic Nomads
.
+
The tone wheel
generator of Ray's 1959 C3 has been recapped with new capacitors in order to more or less restore the original stock sound,
and Ray plays his C3 through two solid state biamped Leslie 925 cabinets which have a JBL bass speaker and a JBL 2482 treble driver.
-Here below
is my hand drawn schematic of
the 12AX7 based EQ / Overdrive circuit
.
+In October 2006 'Cosmic Nomads' recorded their Progressive Rock album ''Vultress '' at Atlantis Sound Studio in Melbourne , Australia and this album prominently features Ray's 1959 C3 through the Leslie 925 and the 12AX7 based EQ / overdrive unit is used on all the songs . The 925 was played reasonably loud but still clean sounding in the studio and all the Jon Lord / Ken Hensley – like heavy overdrive sound heard on the songs
is from
the 12AX7 based EQ / overdrive unit
.
+In late August 2007 the Cosmic Nomads began to record new songs for the next album and this again prominently features Ray’s 1959 C3 with the 12AX7 based EQ / Overdrive unit providing all the overdriven sounds.
+
+The Cosmic Nomads My Space link is :
+www.myspace.com/cosmicnomads
-[http://www
.dairiki
.org/hammond/pics
/KonsNewEQOverdrive
.png]
+Ray Vanderby sometimes posts audio samples of the Cosmic Nomads songs on his Cosmic Nomads my space page and he also sometimes posts live film footage or promotional film clips of the Cosmic Nomads on YouTube
.
+Go to YouTube and type the words “Cosmic Nomads” in the search bar and there might be some Cosmic Nomads clips available on YouTube
. Any Cosmic Nomads clips dated as of 2006 and after will feature Ray’s C3 organ with the 12AX7 EQ
/ Overdrive unit creating the overdrive sounds and the C3 is being played through his Leslie 925
.
-Also see KonsZenerDiodeBasedOverdriveCircuit
.
+Here below is the schematic of the 12AX7 based EQ / Overdrive circuit
.
