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EXPERT
REPAIR SERVICE FOR THE ARP 2600 |
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This
is a photo of the very rare, blue version of the ARP 2600 with
the matching ultra rare 3604 keyboard. There are approximately
20 of these beautiful machines known to be in existence according
to our estimates. I love the look of the metal cabinet 2600's,
but Alan Pearlman didn't speak highly of the enclosure when I
first mentioned the old metal cabinet 2600s to him when we first
met. "We had an aircraft fuselage engineer design the cabinet
for the very first 2600's, what a nightmare! It was odd looking,
very difficult to service, and the corners tended to crack. I
took the front panel (the front panel layout was designed by Alan
himself) got rid of everything else, and came up with the tolex
covered shuke type cabinet". This was explained to me by
Alan R. Pearlman as he drove me around town and to lunch at a
local Japanese restaurant in his black Saab. The shuke is the
inside angled tolex section that the front panel is bolted to
in a standard 2600P/2601. Over the years, it's obvious that Alan's
cabinet solution made the machine much more roadworthy and serviceable.
But you just can't help appreciating the "Mod" appearance
of the first 2600's. Alan also talked quite a bit about Dennis
Colin and described him as a genius, He was the electronic engineer
who along with Alan, designed many of the 2500 and 2600s critical
audio processing circuits.
The
2600 uses microchip technology in all of its gain stages! The
first 2600's, like the one pictured above, used hi-fi chips (Teledyne)
with a high slew rate. Although these chips sound great, they
were very unreliable and prone to latch up. Early on in 1972,
plagued by failures in the field, ARP was forced to change these
chips to a much more reliable type (National Semiconductor LM-301
or SL-19986) The problem is that they slew the wave shape producing
a muffled sound. The LM-301 is classified as a general purpose
amplifier, and is considered inadequate for audio by present standards.
Nearly all the standard production gray-face 2600's use the LM301.
This is one of the reasons why the legendary Blue Marvins sound
better! If your 2600 doesn't look like the one in the photo above,
and odds are it doesn't, your 2600 is not using the original circuitry
and does not sound the way it was originally intended to sound
by the ARP engineers.
The
C.M.S. Audio path upgrade restores your 2600 to the original performance
specs. If you're going to use your 2600 in a modern digital/analog
studio, we strongly recommend the CMS Audio Path Upgrade. If you
want to keep your 2600 totally original for collector reasons,
CMS offers full restoration and repair services back to ARP factory
spec.
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This
is a photo of the very first portable ARP 2600. The cabinet was
designed and built by Alan Pearlman himself. We recently restored
this unique unit here at CMS for a customer. This is the actual
machine mentioned by Alan Pearlman in the above text that he used
to work out the design of the 2600P. It may seem oddly familiar
to some people. It was instantly recognizable to us as we unpacked
it. This is the exact machine ARP used for many early promotional
photos, instruction and service manuals photos and the 2600 promotional
poster.
If
you look closely, you will notice some notable differences compared
to a standard 2600P: The keyboard uses the ARP 2500 SP module for
the keyboard front panel. The tolex covered shuke that covers the
back of the keyboard is triangular shaped and does not level off
on top. The color of the console panel is a unique and beautiful
light blue gray. The console front panel is mounted further forward
than a standard issue 2600 making the front panel flush with the
edge of the shuke. The lid clasps are in different locations. This
unit also features a tolex covered removable rear hatch for easy
service. There is only one exactly like this in the entire world. |
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UPDATED
: 06/12/2025
UPGRADES
AND MODIFICATIONS FOR THE ARP 2600
These
upgrades are internal audio improvements to the circuitry of the
2600.
Listed
in order of popularity:
POWER
SUPPLY REBUILD - (ALL MODELS) - 219.00
The
power supply in your 2600 is about 30 to 40 years old. Certain
components in the ARP 2600 power supply have a shelf life /
working life of 20 years maximum. If your power supply has not
been serviced in the last 20 years, chances are your power supply
is not up to spec. This can result in excessive noise, ripple,
and instability. Your power supply is removed. All critical
components are professionally replaced. Stability and load are
tested using factory specs. Rebuilt ARP power supplies are available
from CMS but we require the old power supply in exchange.
AUDIO
PATH UPGRADE PACKAGE - (ALL MODELS) - 425.00
This
mod replaces all gain stages in the 2600 console with audiophile
grade components for crystal-clear highs and a deep low end,
while still maintaining the distinctive character of the 2600.
Upgraded sections include: lag processor, voltage processors,
reverb stages, pre amp, VCF mixer, output mixer, output buffers,
etc. We also fix the annoying VCA thump. Noise in the reverb
section is reduced by 35%. Filter headroom is increased by a
factor of 2! Stability and sound improvement guaranteed. Later
model 2600s (almost all wood / tolex 2600s) use inferior sounding
gain stages that severely impede the true sound of your 2600.
Earlier 2600's (Blue Marvins and Gray Meanies) use "high
slew rate" chips that sound much clearer. Restore your
2600 back to the specs that the original ARP engineers intended!
Don't be fooled by imitations from "noob techs" or
DIY attempts. If the Audio Path Upgrade is not performed correctly,
it can become unstable and lead to high frequency self oscillation
of all the amplifier sections.
17
INCH REVERB TANK - (ALL MODELS) - 120.00
Ever
wonder why later model 2600s have such a lame reverb? Later
model 2600s use smaller reverb tanks with a shorter delay time
than earlier 2600s made by ARP. The only reason I can find for
this change is economic. Our brand new reverb tanks use 3 springs,
counter wound and placed in parallel for a rich, full sound.
This mod restores your reverb sound back to the original "Blue
Marvin / Gray Meanie" configuration.
MOOG
STYLE FILTER MODULE - 4012cx - (ALL MODELS) - 399.00
The
4012 filter was used from 1971 (blue Marvin) to the middle of
1976. If your 2600 is a gray face, It probably utilizes the
4012 module. The 4012 is a ladder type filter using discrete
transistors. The original 4012 made by ARP is prone to instability.
This causes 2 types of problems when the filter is wide open:
1.
Unwanted high frequency self oscillation
when using resonance. This can cause serious problems in the
recording studio. The high frequency sine wave can wreak havoc
with A to D converters and soak up serious headroom.
2.
Significant gain reduction of the signal
when the resonance is off. This can rob the 2600 of it's classic
powerful punch! Reduction in gain at high frequency settings
can reach 50%.
The
4012 replacement filter by CMS is guaranteed stable yet uses
the exact circuit that ARP used. Better quality components and
personal attention to craftsmanship yield a filter of superior
sonic characteristics! See the Sub-module
section for more info.
VCA
MODULE UPGRADE - (4019) - (LATER MODELS) - 139.00
If your VCA module is un-encapsulated, we can give it crystal
clear highs and a deep low end. Also provides lower distortion
and a faster slew-rate. If you have an encapsulated ARP VCA,
this upgrade is not available, but improved replacement modules
are available, see sub-modules page, model 4019cx.
FILTER
MODULE UPGRADE - (4072) - (LATER MODELS) - 120.00
All
later ARP filters (after 1975) have a cutoff frequency limit
of 11 kHz. This mod upgrades the cutoff frequency range from
11 kHz to 28 kHz. We also upgrade the filter output amp and
control summing amp. This is a necessity for all un-encapsulated
filters. A cost effective alternative to a 4012 module.
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The
rare ARP 2600C restored by CMS.
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STAGE
TWO UPGRADES / MODIFICATIONS FOR THE ARP 2600
These
upgrades / modifications are more extensive and time consuming
than the above. They usually involve partial to complete
disassembly, front panel machining, re-assembly etc.
NEW
- SECOND FILTER WITH SWITCH- 245.00
So
you like the switch-able filter feature on re-issue 2600s
but you don't like the sound. You are not the only one
who feels this way. Because of the surface mount technology
and other methods used in reissue 2600s, the sound cannot
be improved. We have come up with a universal second filter
adapter board that installs in the real ARP 2600 that
permits you to have the best of both worlds. Customers
that have the 4072 can now keep their original second
generation filter and also have the first generation 4012CX
installed, and yes, the reverse is also true. A toggle
switch on the front panel engages the first version (4012)
or the second version (4072) filter. This new mod from
CMS features no changes to the original signal path of
the 2600. Price shown above does not include the cost
of the second filter sub-module.
Listed
in order of popularity:
SYNC
SWITCHES - 225.00
Two
independent high quality miniature toggle switches that
syncs VCO-1 to VCO-3, and VCO-2 to VCO-3 This setup enables
dual sync (two separate harmonics) if desired. Stability
guaranteed, unlike the factory version.
Explanation:
Some people think this mod is used to simply synchronize
2 VCOs together. Not so. That is pointless since they
end up sounding like 1 VCO. This mod is used to obtain
the classic "ARP sync sound" found on some other
ARP synthesizers. Basic patch: 2 VCOs are synchronized
together. Modulation is applied to the slave oscillator
(usually ADSR). The output of the slave VCO is fed to
the filter etc. to obtain the sync sound. Sounds best
with a square wave. The effect appears on all the waveform
outputs of the slave VCO.
You
must have at least 1 un-encapsulated VCO to install this
mod.
ENVELOPE
GENERATOR RANGE TIME EXPANDER SWITCHES - 79.00 each
Miniature
high quality toggle switches that provide 2 additional
time ranges for the attack, decay and release time of
the ADSR generator and the attack and decay time of the
AR generator.
ADSR:
The ADSR is quick in a stock 2600. The 3 position switch
we install gives you a x1(factory speed), a x2 and a x3
speed, providing much longer times previously unavailable
on a 2600.
AR:
Conversely, the AR generator in a 2600 is quite sluggish
in certain situations. In addition to the normal X1 mode,
the high quality 3 position switch provides a new high
speed mode for sharper attacks, as well as a X2 mode for
longer attack and release times.
AR
ENVELOPE GENERATOR UPGRADE - 149.00
This
mod is a critical upgrade of the AR circuit in the 2600.
The AR in the 2600 suffers from a sluggish response time
and a poor input impedance. In addition, the output voltage
can change depending on the gate voltage used to trigger
it. It can also put a drain on your gate supply especially
if you are feeding that gate to multiple destinations.
The gate input is permanently linked to the ADSR input
so you can't independently trigger the AR from another
source like a VCO etc. This CMS mod fixes all of those
issues but still maintains the original core circuitry
of the 2600 AR. Comes complete with a separate high quality
gate input jack that conveniently separates the inputs
of both envelope generators for independent operation.
1/4
INCH LINE LEVEL JACKS - 120.00
Professionally
installed 1/4 inch Switchcraft jacks at line level (designed
to interface with your studio mixer etc.) on both main
outputs, VCA output, and pre amp input. 4 jacks total.
VARIABLE
VCF KEYBOARD TRACKING - 85.00
The
filter tracking on a 2600 is fixed at 1v per octave. This
is quite limiting especially if you are shooting for natural
textures. This mod provides a high quality miniature rotary
potentiometer that adjusts the filter tracking ratio from
0 to 1v/octave. Now features a high quality 2500 control
knob.
NEW
-
REVERB
DRIVE CONTROL - 85.00
This
mod provides a high quality miniature rotary potentiometer
that adjusts the reverb driver gain from 0 to overdrive.
Now features a high quality 2500 control knob.
POWER
SUPPLY UPGRADE - (ALL MODELS) - 425.00
The
power supply in your 2600 is about 30 to 40 years old.
This upgrade features a professionally installed, high
power, highly stable, military spec power supply. This
power supply features a high speed regulation circuit
that reduces cross-talk between sub-modules in your 2600
system. The overall sound quality and oscillator purity
are noticeably improved. Warning: These power supplies
must be installed by a professional. Incorrect installation
of a power supply upgrade can lead to system instability.
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STAGE
THREE UPGRADES / MODIFICATIONS FOR THE ARP 2600
These major upgrades / modifications are
very extensive and time consuming. These mods are designed
for users that are seeking to professionally "Hot
Rod" their ARP 2600 to the max. They require complete
disassembly, front panel machining, rewiring, and the
power supply upgrade.
Listed
in order of popularity:
VCO
OCTAVE SWITCHES - 135.00 each
This variable version octave switch has
a position toggle and a potentiometer to dial in any desired
interval over a 2 octave range. This upgrade uses the
same high quality miniature toggle switches, military
spec potentiometers that were used on the ARP 2500 system
including a high quality 2500 style knob.
LED INDICATORS - 69.00 each
Miniature LED indicators providing visual
feedback on both E.G. outputs (red), S/H clock (green)
and envelope follower (yellow). Requires the power supply
upgrade.
DUAL
LFO - 399.00
We install
2 LFOs below the voltage processors. They have triangle
and square outputs and also have LED indicators included.
This mod, as all our others for the ARP 2600, features
high quality Switchcraft jacks, military spec potentiometers
and ARP 2500 style knobs. Requires the power supply upgrade.
COMPARATOR
/ DISTORTION - 199.00
This can
be used to square up a waveform. It also makes a good
distortion device according to John McEntire from Tortoise.
Includes LED indicator.
NEW
- TRUE STEREO REVERB - 379.00
We can install
a second reverb tank, driver and pickup electronics in
your 2600 to give you a true stereo reverb. The second
tank features a longer delay time and 3 springs. This
mod utilizes the existing left reverb output slider and
has an additional dedicated output jack. The sound improvement
to the reverb is quite remarkable.
24Db
DUAL MODE FILTER - MODEL 2621- no longer available
- see our euro-module 1047
The one key element
missing in a 2600 is a high-pass filter with resonance
and associated coupling circuitry. The CMS 2620 is a dual
mode, 24Db (Low-pass/High-pass), discrete, transistor
ladder filter from the CMS 9000 series modules, Installed
in the left speaker section. This original CMS design
features an innovative circuit that extracts a high-pass
response from a 24BD discrete ladder filter circuit producing
a unique sound and beautiful resonance quite different
from the existing low-pass filter in the 2600. In addition,
the volume of the filter output does not drop off drastically
as the resonance is increased as all other ladder filters
do. This also makes the low-pass output quite useful as
an alternative sounding 24db low-pass filter. Complete
with anodized face plate, high quality controls, 1/8 inch
Switchcraft normalized patching. Special link switch enables
the coarse frequency control knob of the 2627 to control
both filters for a truly remarkable sounding band-pass
function (24Db x 24Db). The resonance on the high-pass
function is also very unique and distinctive. Requires
the power supply upgrade. Now comes with voltage controlled
resonance.
VCO / 4 CHANNEL MIXER - MODEL 2627 - no longer
available - see our Euro Rack section - module
1004
Installed in the right speaker
section, this VCO utilizes the same exact circuitry used
in the other VCO's in your 2600 to assure exact tracking
and pitch stability characteristics. All four waveforms
are available as well as pulse width modulation. Low frequency
mode and normalized patching are also provided. The mixer
section serves as a high quality audio mixer with the inputs
either normalized to all 4 outs of VCO-4 or externally patched.
The mixer can also be used as a voltage summer or inverter.
This major upgrade uses high quality Switchcraft jacks,
military spec potentiometers and ARP 2500 style knobs. Requires
the CMS power supply upgrade.
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MODIFICATIONS
FOR THE ARP 3620 KEYBOARD
INTERVAL SWITCH - ALL MODELS
- $59.00
The
switch provides a easy and fast method of locking the pitch interval
of the second voice without the use of a foot switch. Useful for
instantly setting up precise intervals or octaves of selected
VCOs.
LFO
FREE RUN SWITCH - $79.00
Most people do not know this, and it is probably because it was
never mentioned in the ARP 3620 owners manual but the 3620 LFO
is re-triggered or restarted when you hit a key on the 3620 keyboard.
This can sometimes be annoying especially when using a slow LFO
to modulate something like a filter for example. You can actually
disable this function by setting the trigger mode to "SINGLE",
however the LFO will always restart in the "MULTIPLE"
trigger mode. When this mod switch is in the "free run"
position, playing the keyboard will not restart the LFO under
any circumstances.
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A
fully modified 2601
Many of our customers
prefer to have their machine in original condition. We offer full
restoration services that restore your 2600 to original ARP factory
specifications. Call or email Phil at CMS to schedule a free estimate
on your ARP 2600. Every 2600 restoration varies widely depending on
condition, road use, storage conditions, poor servicing, substandard
aftermarket sub-modules and moisture damage. Estimates are not available
by phone or email. |
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