Hammond-Suzuki XK-3 XK-3c/XLK-3 "Clonewheel" Organ
Last Update
06-25-2025
Since I was eighteen years old, I owned a Hammond Porta-B that I
bought from my piano teacher. I had just started with my first
club band and when I told them my piano teacher was selling his
Hammond organ with Leslie 760 they said "buy it!! buy it!!"
Ow, twist my arm! It was a good price and we were young with
not much money. While the Porta-B is not a "proper" Hammond
like the B-3, it is a screaming organ. I played it for
years and it is currently in a state of disrepair, but in its heyday
it was MUCH easier to lug around than a 300 pound bulky Hammond
B-3. I decided even back in my teenage years that I was NOT
going to ask my bandmates to help move the large console organs, and
that went for the heavier Yamaha CP-70B electric grand piano (this
was way before digital pianos).
The last legacy Hammond tonewheel organ rolled off the production
line in 1974, shortly after founder Laurens Hammond had passed
away. Hammond organs from then on eliminated the
electro-mechanical "tonewheel" generator, and newer organs were
completely electronic which were much cheaper to build and lighter
weight. The later organs did not appeal to the secular
musicians at all - they stuck with the legacy electro-mechanical
"tonewheel" organs. Hammond finally abandoned the organ
business in the 1980s. Around that time, so did Leslie
speakers.
The Hammond trademark (and later Leslie speakers)
was acquired by Suzuki in the late 1980s, to be officially known as
Hammond-Suzuki (for the sake of convention I will use the "Hammond"
to refer to the legacy company and "H-S" to refer to
Hammond-Suzuki). H-S had no intention of reproducing the
electro-mechanical "tonewheel" organ, it would be too expensive to
acquire the tooling and few gigging musicians would buy a brand new
300 pound bulky console organ in that day and age. The
technology at the time made it possible to produce a "clonewheel"
organ (coined by the musicians) in a much lighter much smaller
package.
H-S's first entry in the gigging musician market was the XB-2.
It was a single manual organ (not double manual like the B-3), but
it was widely adopted by gigging musicians - myself included.
While it didn't sound like my Porta-B (frankly ALL Hammond tonewheel
organs sounded different), the XB-2 was a respectable attempt to
sound like a Hammond, albeit compacted down. The XB-2 had the
essential B-3 features such as drawbars, vibrato/chorus and
percussion, and it had a (poor) Leslie simulator built in. You
could program eight user patches. Combined with my Dynacord
CLS-222 Leslie Simulator, I could leave the heavy Hammond and
Leslie stuff at home.
The XB-2 served me well until it developed audio problems. My
tech looked at it and determined that the DRAM ICs were bad and
there was no new replacement parts available. The H-S XK-2 had
succeeded the XB-2 but players complained that it had intonation
problems and certain chords sounded sour (I rented an XK-2 from a
backline company years later and found this to be true, it was not
H-S's finest hour).
Around that time, H-S launched the next product - the XK-3.
Besides fixing the intonation issues, they designed a vastly
improved product. It had a lot of features that were
appealing, but the feature that sold me was the ability to configure
user custom tonewheels, meaning you could match your favorite
Hammond organ (!!!). This was the first time I had purchased a
keyboard product sight unseen, and I was not disappointed. The
retailer offered to trade in my ailing XB-2 for credit towards the
XK-3, so off it went.
I later learned that the DRAM failures were very common with the
XB-2 organs, so buyers reading this webpage are forewarned. To
date it has been YEARS since I have seen an XB-2 for sale or for
auction.
XK-3
Features
The XK-3 is a very authentic reproduction of the sound of
the legacy electro-mechanical "tonewheel" organs. It has that
warm flute sound in the harmonics, the classic scanner vibrato
"purr", the wooden "thunk" of the percussion, the key click, a
decent Leslie simulator (not quite a CLS-222), built-in effects, and
tube overdrive to add some crunch to the sound. Included is an
11 pin Leslie socket for connecting to a real Leslie. The
traditional console controls are laid out in the same order, so a
console organ player will feel right at home on this. Even the
rotary vibrato/chorus dial is there. Full polyphony, waterfall
keys; not quite the same as an old Hammond but I'll be realistic in
that a single manual in an old Hammond weighed 100 pounds
alone. At least the action is immediately adaptable for a
Hammond player like myself, and it isn't that featherlight action
like cheaper clonewheels (Roland, Korg, etc). The waterfall
keys make palm glissandos easy.
H-S implemented a good Leslie simulator in the XK-3. Better
than other clonewheels. There are two processors for each
horn, which is the way the Dynacord CLS-222 does it. There are
different simulations from the factory that include the classics -
the 122, the 147, the 760, and the 830 models. There are
fast/slow/brake buttons under the pitch/mod wheels for controlling
the Leslie speed, and with all the buttons off the Leslie simulation
is disabled. Three user Leslies can be defined. In the
menu you can vary simulation parameters for each rotor such as speed
(slow and fast), ramp times between speed changes, upper horn
response (flat or honky), mic distance and (for the top rotor) mic
separation with two mics set (X) degrees apart.
If you opt for a real Leslie cabinet using the 11 pin cable, the
Leslie simulation is also disabled and the buttons control the
cabinet (nice touch so I don't have to manually turn off Leslie
simulation in all my presets). If you want to hear my XK-3
through my Leslie 760, check this
out. The top rotor mic is an AKG D321, the bottom rotor
mic is a Sennheiser e609. Both mics positioned no closer than
eighteen inches from the center of the rotor.
The user interface is very easy to use as of OS version 1.20.
The menu system is very intuitive, I found my way around without
referring to the owner's manual (the manual is broken "engrish" with
grammar and spelling errors from poor Japanese to English
translation, but it has enough detail for the Hammond
connoisseur). Like the original, you select presets (user
programs) using the reverse color keys, which is easy to do on the
fly without looking away from your playing. Hold down the BANK
button and you use the same keys to select different banks of
presets. Unlike the original these preset keys don't latch,
but an LED shows you which preset is active. The low C cancels
and silences the organ, but hold it down for a few seconds and you
get an initial organ patch - nice intuitive touch. If you hold
down a preset key for a few seconds, the preset registration
(drawbar settings) is replaced with the current drawbar settings on
the panel while all other preset settings (vibrato, reverb, etc)
remain active. Very few of the other clonewheel organs have
the preset keys.
All the buttons on the panel have LEDs to indicate their
state. A 40x2 LCD display and navigation buttons give you
access to the internal settings. H-S wisely placed the frequently
used controls on the panel; hold down any button for a few seconds,
and the relevant menu appears in the LCD ready to tweak
parameters. This user interface is so well designed that it
should be a model for every music product with a menu system.
The left/right/up/down buttons do double duty, they are context
sensitive like Windows menus. A rotary encoder is supplied to
change menu settings.
A dual tube preamp is included, and the plate voltages run at a
proper 220VDC not the "starved plate" low voltage levels.
There is a 12AX7 tube in each preamp and each preamp can be run in
series or parallel. Parallel mode means each tube processes a
different frequency range, so you can have independent control of
tube overdrive in the bass and treble region. Very nice if you
want bottom end crunch but clear highs. You can specify the
crossover frequency that splits the frequency bands, and yes 880hz
is there for simulating Leslie grunge. Not quite power tube
overdrive of a real Leslie, but it's close enough. An
overdrive knob on the panel varies the grunge amount, and a
tri-color LED tells you how hard you are overdriving. This is
a very cool real time control. Right underneath the knob is a
button to enable/disable the tube preamp (frankly it sounds so
effective that I never turn it off). There is an option in the
menu to vary overdrive with volume pedal amount, so you can back off
overdrive when you let up on volume. H-S really did their
homework. I don't know of another clonewheel with a tube
preamp.
A three band EQ with sweepable mid (discrete, not continuous sweep)
helps you tailor the sound. The EQ settings also impact the
overdrive. Combined with the user custom tonewheels, the EQ is
effective for dialing in "your sound".
Three sets of drawbars give you control over upper, lower, and pedal
registrations - a feature few clonewheels have. The primary
keyboard is the upper manual, and it has a split feature for the
lower manual with selectable split point and octave shift. The
pedal manual is also available with split and can be layered with
lower manual. You get the full nine drawbars for each keyboard
manual, and 16'/8' drawbars for the pedals. You can configure
the manual drawbars as A/B for the upper manual only, with the Bb
and B preset keys selecting A and B drawbars, like the old
Hammonds. Unlike the XB-2, the XK-3 drawbars are always live
so if you punch up a preset you can change the registration.
The XK-3 receives MIDI and can function as a MIDI controller with
its MIDI output. Each manual is velocity sensitive and has its own
MIDI channel. There are NRPN CCs for every parameter in the
organ. Years later when I was building my stage system, I
learned that the low C preset key not only "cancels" the presets and
silences the organ, you can save a MIDI configuration to the low C
preset. This was perfect for controlling other synths.
However be warned that the XK organs transmits a constant MIDI
Active Sense command, which has caused some MIDI devices in my
system to malfunction - and there's no way to turn off Active Sense.
The volume pedal on old Hammonds was tapered in different frequency
bands to compensate for the Fletcher-Munson curves of the human ear
- the XK-3 offers this as an option in the menu.
Vintage tonewheel generators were not perfect and the tonewheel
pickups can pick up motor noise and tones from adjacent
tonewheels. The menu includes "Leakage" and "motor noise" to
simulate these "defects".
"Extra voices" can be accessed using a button combination on power
up (press and hold Brake, Control, Tone buttons then scroll up to
menu page "F"), but these were "not ready for prime time" as playing
the extra voices would sometimes crash the XK-3. You also can
only use organ tones or extra voice - not both - and the extra voice
can only be played from the upper manual. The Clavinet voices
are very useful (the attack is right on and it has the goofy release
tail), and I can use a sustain pedal - something that is impossible
on a real Clavinet. The other voices are rather poor. I
wouldn't even use the acoustic piano or electric piano voices in
rehearsal.
There's a lot of little features I haven't mentioned, I don't want
to re-write the owners manual.
A Compact Flash port lets you store all your settings and user
custom tonewheels, so you can sit at another XK-3, plug in your CF
card, and it's your own customized Hammond. The XK-3 uses 32MB
CF cards; these are now hard to find, and higher density CF cards
will not work. I had an old 4MB CF card that worked. The
weird thing is that all user configurations are stored on CF cards
and transmitted over MIDI Sysex, but user configured Leslies and
user custom tonewheels are not transmitted over Sysex. top
XK-3c
Features
H-S succeeded the XK-3 with the even more authentic XK-3c
clonewheel. Very similar user interface, so no learning
curve. The MIDI implementation has been improved for
integration into a DAW, the tube overdrive and Leslie simulation
have been improved, and vibrato/chorus can now be split between
upper and lower manual. The tube overdrive is very effective
not just for distortion but when used at lower settings it can shape
the tone of a preset that EQ or drawbar setting cannot do. The
biggest reason why I added the XK-3c is to pair with the XLK-3 lower
manual.
"Extra voices" are now standard on the XK-3c, and they don't
crash. There are acoustic piano, electric piano, and other
simple voices that can be played from either manual. The
Clavinet voice is especially good (I used to own a real one), and it
can be routed through the tube overdrive for that vintage biting
snap that is been so elusive with Clavinet samples. top
XLK-3
Features
H-S offered the optional XLK-3 lower manual, with pins to set an
XK-3 or XK-3c right on top to comprise a bona fide dual manual
Hammond. It works with the XK3 but with some limitations:
- MIDI channels are forced to channels 1 (pedal), 2 (lower), and
3 (upper). This was a problem with my MIDI system as I had
other devices assigned to those channels.
- MIDI channels need a MIDI processor with "channel bump" to use
for MIDI recording/playback. This was not worth the
trouble.
- XK-3 does not have split vibrato/chorus per manual.
- The "extra voices" do not work on the lower manual and they
can't be layered with organ tones.
When a used XK-3c became available, I grabbed it to use with the
XLK-3. That pairing was much better and it eliminated the
limitations with the XK-3. A way cool XK-3c feature is that
you can assign the extra voices to either manual, so I assign it to
the XLK-3 lower manual and layer the Clavinet voice with a Hammond
registration.
A weakness of the XLK-3 is the flimsy bottom wood panel, I feared it
was thin enough that it could break without much handling. So
I ordered a custom road case such that the bottom lid of the case
served as a much sturdier bottom for the XK-3c/XLK-3 system, and
they both stay on the bottom lid. I also pre-wired MIDI cables
between the two using right angle MIDI plugs so that the case cover
can enclose the setup without removing or breaking MIDI plugs.
Thus the XK-3c /XLK-3 is ready to gig at any time, but I won't drag
it out unless I am playing a LOT of Hammond parts that require
techniques using both manuals. It's not a lightweight setup,
but much lighter than a vintage console organ and is the closest
clonewheel to a B-3 in my arsenal. top
How Does It Sound?
First I'll discuss the selling point for me - user custom
tonewheels. When I read of this feature in a magazine review,
this sold me on the XK-3 without even trying one in a store.
The XK-3 and XK-3c has 96 virtual "tonewheels" (five more than the
original B-3, but who's counting?) that produce the Hammond
"voice". On the old Hammonds, the tonewheels were calibrated
manually at the factory and no two organs sounded alike. Alas,
the factory had different calibration standards over the years so
there is much debate over whether 1950s B-3s sound better than
1960s. All subjective.
XK-3/XK-3c come from the factory with standard tonewheel sets to get
you off and running, ranging from Hammond tones with subtle
differences to 1960s combo organs (Vox, "junky" Farfisa, the old
Hammond X-5). I used to own a Vox Continental - the A/B test
revealed that the 16'/8'/4' drawbars sound the same, but that "IV"
drawbar remains elusive. I have yet to hear a keyboard that
does an authentic Continental. The "IV" drawbar is a combined
mix of 2-2/3', 2', 1-3/5' ,and 1' harmonics on the Vox. While
the Hammond has the same drawbars, I couldn't match the tone of the
"IV" drawbar. I sold the Vox twenty years later and never got
around to a forensic study of how the "IV" drawbar is done. On
the upper half of the Connie, the "IV" drawbar really pierces while
the XK-3/XK-3c still sounds flutish. The Connie's waveforms
are triangle and the Hammond/XK-3/XK-3c are sinusoidal, but the "IV"
drawbar is pretty biting for triangle waveforms. I think the
Connie scales the "IV" mixture across its keyboard, which can't be
duplicated in the XK-3/XK-3c. But it's still a fair
impersonation. The Connie's vibrato is faster than a Hammond,
so you'll need to increase the vibrato frequency on the XK-3/XK-3c
to emulate that weedy sound.
There are even different tonewheel sets for the pedal manual.
One of them is a synth style bass, like an ARP Odyssey synthesizer
with the "4023 module" 12dB/oct VCF set at slight resonance and
being spiked by an EG. While not tweakable, it sounds pretty
good. The standard Hammond tonewheel for the pedal manual is
REALLY beefy, a strong fundamental that is almost too loud (I set
the pedal drawbars at 6 instead of 8). Fortunately the pedal
manual is not processed by the vibrato/chorus which is crucial for
bass parts.
If you own a vintage Hammond that has a great sound, you can do a
calibration procedure to collect amplitudes of the 91 (or 96)
tonewheels, then dial up the contours in a user custom tonewheel in
the XK-3/XK-3c. It REALLY works. My Porta-B is a
screaming organ with really bright drawbars that I exploited for
comping sounds, and I succeeded in duplicating that in the
XK-3/XK-3c. To date I do not know of another clonewheel with
this feature.
Here is how you calibrate the XK-3/XK-3c to your favorite
Hammond. I had the service manual for my Porta-B which
included a chart showing tonewheels related to drawbars and
keys. You need the chart and a dual channel oscilloscope (do
NOT probe inside a vintage Hammond unless you are an experienced
tech, there are lethal voltages inside and I assume zero liability
upon any personal injury or death). On the XK-3/XK-3c, turn
off the overdrive, the EQ, the vibrato/chorus, and any
effects. On your Hammond, turn off vibrato/chorus and if
applicable turn off the reverb. Open your owner's manual to
the section for custom tonewheels to navigate the XK-3/XK-3c menu
(with the arrangement of the rotary encoder and menu buttons, it
isn't hard to advance through each XK-3/XK-3c tonewheel without
turning away from the 'scope).
While monitoring your Hammond with the 'scope, cycle through each
tonewheel from lowest to highest pitch (refer to the chart for key
and drawbar) and identify the loudest one - for the sake of the
XK-3/XK-3c, that is your "zero dB reference pitch" because it is
much easier to attenuate tonewheels. Then while holding the
reference pitch on your Hammond, monitor the XK-3/XK-3c on the
'scope, play the same reference pitch and adjust the volume so that
both organs have the same amplitude on the 'scope. Both organs
are now "normalized" for the calibration process.
Then for each tonewheel on both organs, adjust the amplitude on the
XK-3/XK-3c using the menu system while watching the signals on the
'scope. When the amplitudes on the 'scope are matched, advance
to the next tonewheel.
By the time you finish, save and name your new tonewheel set.
As a test, I duplicated drawbar settings (I have many "acid tests")
between the XK-3/XK-3c and my Porta-B. Both were going through
my Leslie via my stompbox preamp. I played them both and there
was NO A/B DIFFERENCE BETWEEN THE ORGANS. That was the single
feature that sold me on the XK-3/XK-3c sight unseen, as I had been
looking for a clonewheel that could impersonate my Porta-B. It
really works. Clonewheels can nail the percussion, the
vibrato/chorus, the flute tone, the Leslie - but the missing gap was
duplicating your favorite Hammond registrations using the user
custom tonewheels. I tried my registrations on other
clonewheels (I am a "drawbar artist" and use many registrations
other than 888000000) and they could never sound the same.
Percussion has that classic wooden "thunk" which is seldom heard
from other clonewheels. There are buttons for slow/fast, soft,
and second/third harmonic. Unlike the original, you can
combine both harmonics. You can fine tune the percussion in
the menu system, it even has an option to attenuate the drawbars
when percussion is not set to soft, just like the original.
Key click is variable in both down and up keystroke and you can vary
the attack/release of the voice for simulating pipes.
The vibrato/chorus is dead on, it nails that mechanical scanner
vibrato purr. A crucial XK-3/XK-3c trait that is missed in
other clonewheels is that the LFO waveshape for the scanner is trapezoidal
not sinusoidal. It also gets a little brighter with the
vibrato engaged, which is noticeable when used with a Leslie at fast
speed. You get the traditional V1/V2/V3/C1/C2/C3 varieties
plus an on/off switch, and the vibrato speed can be changed in the
menu.
Vibrato/Chorus can't be split between upper and lower manuals on the
XK-3, it affects both manuals at the same time. If you plan to
go with dual manuals using the XLK-3 lower manual (unfortunately
long out of production and hard to find today), then use the XK-3c
which can split vibrato/chorus between both manuals. For this
reason, I reserve the XK-3 for gigs where I don't need both manuals.
Between the tube preamp and EQ, the XK-3/XK-3c can sound really
ballsy. It can even approach the "Jon Lord" heavily distorted
organ sound, which he made famous with Deep Purple.
I'm a stickler for Leslie simulation (most Hammond players are), and
the XK-3/XK-3c is better than a lot of clonewheels. It's
convincing in stereo, but when I tried it in mono with my stage amp
it lost some authenticity. That's where my Dynacord CLS-222
and Neo Ventilator II
have the edge. Not only do both sound good in stereo or mono,
they both have better animation of the Leslie sound and - crucially
- both model the peculiar frequency response, as Leslie cabinets are
far from flat frequency response. You can hear the XK-3 with
the CLS-222 here.
But the XK-3/XK-3c simulation is still good in a pinch.
Unlike earlier clonewheels, the leslie simulator and vibrato chorus
can be used at the same time. An effects loop allows you to
use the effect of your choice, and the return is
pre-EQ/Leslie/Reverb.
Digital effects range from various reverb algorithms (rooms, halls,
plates, church) and delay effects include mono and ping-pong.
There is a reverb/delay combination also. Not much to tweak
and the reverbs aren't Lexicon class, but they're not terrible and
they're not muddy like cheap digital reverbs. The delay times
are optimized for short delays - the time settings are fine for
short delays, but as delay times get longer the settings are
coarser. If you desire to use delay sync'd to tempo, use an
external one in the effects loop. The delay times can reach
into the very short HAAS delay regions, which is handy for changing
the timbre (via comb effect) or to give the voice some ambient
space.
If you own a Dynacord CLS-222, I'll share a modification
that allows the CLS-222 rotor speeds to be controlled from the organ
using the 11 pin Leslie socket. Not shown are the audio and
ground connections from the 11 pin connector to the CLS. Seek
the services of a competent tech for this modification - I assume
zero liability upon any personal injury or death, or of any damage
to your music gear. top
Epilogue
I have tried many clonewheels - Roland, Korg, Voce, plugins.
While the Roland VR-760 was the better clonewheel running, I was
turned off by the fact that there are no separate outputs for organ
and other sounds - if I use a real Leslie cabinet for the organ
sounds, I don't want the onboard piano/synth sounds routed to the
Leslie. While plugins have many conveniences, I prefer having
immediate access to the drawbars and controls under my hands in
front of me when I play a controller, not under a mouse.
The XK-3/XK-3c blew them all away in authenticity, balls, and
simulation of the classic Hammond vibrato and percussion. They
even simulate the "voice robbing" of a real Hammond that attenuates
the volume as more drawbars are pulled out and you play thicker
chords. Subtle effect but effective. H-S did a complete
ground up redesign of the OS user interface, which is one of the
most intuitive I have used. Far better than my XB-2 and their
XK-2. I did buy the optional EXP-100F volume pedal, which is
an optical volume pedal with integrated spring-loaded "kick switch"
for changing Leslie speeds. I could never get comfortable with
the kick switch while standing (when I play I do not sit down) so I
removed the switch, leaving just the volume pedal.
The best Hammond clonewheels yet, and essentially the complete
package. Hammond later released the XK-5 which added TWO sets
of drawbars for each manual, but the tube preamp was replaced with a
digital overdrive which sounds like a ratty sounding fuzzbox.
Currently I have no compelling reason to replace my XK-3/XK-3c so I
stopped browsing with clonewheels. top
Known Faults
Batteries have a finite life and need to be replaced periodically,
about every ten years. User settings are retained using a CR2032
battery when the power is off (CR2032 batteries are not
rechargeable). If you lose the battery, a NO BATTERY message
appears on the LCD and the organ won't function. If you lose
user patches when the battery is gone, you can use the CF card or
sysex file to restore them (you DO backup your user patches, don't
you?!?). Seek the service of a competent tech to replace the
battery - it's not an expensive job, and the battery can explode
from too much heat of a soldering iron. The original battery
is soldered to the PC Board and it is highly recommended that you
have a battery holder installed - it saves the trouble on future
solder work, and you can use generic CR2023 batteries from many
stores which are much easier to find.
On one occasion I turned on my XK-3 to be greeted with a NO BATTERY
message on the LCD. However on this occasion, a new battery
did not resolve the NO BATTERY message. And I could smell
faint electrical smoke.
Pop the hood, battery is perfectly seated. Faint smell of
electrical smoke from somewhere. No sign of caps about to pop
their tops. Re-seated the battery, tested with DMM.
Restored from CF card again, power cycle, works fine. Turned
it off. Checked after I came back from work each day, no
battery loss. No idea why the battery flaked out so I put it
back together.
"NO BATTERY" again. And no audio... big audio POP whenever I
plug a cable in any output. That's a telltale sign of
DC. Turned on the 'scope and found (+)14VDC on any audio
output - that is not good!!!
Pop the hood again and check the power rails - the (-)15VDC rail is
gone. Found a 4r7 ohm 1/2 watt resistor that was burnt, that
was the smoke I was smelling. This resistor is a protection
device against excess current on the (-)15VDC rail.
Checked for direct shorts or low resistance to ground on the
(-)15VDC rail, none found. Looked in my surplus and found a
4r7 ohm resistor, but 5 watt and I didn't have any in 1/2
watt. There are two protection resistors, R78 and R81. I
ordered replacement 1/2 watt resistors of the same value, but this
time I suspended them above the circuit board so that heat could
dissipate better (they were originally flat on the PC board which
had scorch marks from high heat). As long as I don't have a
bad rail it is good enough to test for the rail, then for
audio. Isolate each board on that rail and test by briefly
powering up and verifying the (-)15VDC rail, then re-connect each
board and repeat. Rail is fine with all boards. The new
resistor is not even warm, which means no excess current.
Turned it on, tested for audio, and it works.
Educated EE guess is the original resistor began heating up from
inadequate dissipation, which changed the resistance value higher
and higher until the organ could no longer function. Good ol'
thermal runaway. When that happens, the 4r7 ohm resistor turns
into a ~5Kohm resistor because it burns up from excess power (Ohm's
law, power is the product of resistance and the square of current).
Suspending the resistors solved the problem, the XK-3 has been fine
since then.
If you use the EXP-100 or EXP-100F pedal, with age the maximum
volume becomes unstable. You can verify this by going to the
CONTROL menu and navigate to the expression pedal, where you can
observe the setting of the pedal in real time. With the pedal
all the way down (max volume), the readout should be "127" - any
other value means the pedal is out of calibration.
There's a trimpot inside the pedal to adjust the maximum volume
value. But the trimpot can go bad with age and the maximum
value won't stay steady. You can confirm this by mechanically
bumping the pedal with the handle of a screwdriver while watching
the value on the menu.
Unfortunately the trimpot is a weird 300K value which is not a
common part. So I replaced it with a 100K trimpot, and
replaced the resistor to pin 2 of the opamp with 220K. This
also reduces the trimpot range which makes it less vulnerable to
mechanical shock, especially for a foot pedal on the floor.
You should also replace the electrolytic caps with same value but
higher voltage rating - the originals have a voltage rating (16V)
that is too close to the power rails (15V). Just be careful
that the caps are not installed backwards. top
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