Upgrades & Service for the ARP 2600

The Blue Marvin


This is a photo of the very rare, blue version of the ARP 2600. 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. Dennis passed away last November (2015) and he will be missed.

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. Around 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-1998) 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 the main reason 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.




These upgrades are internal audio improvements to the circuitry of the 2600.

Listed in order of popularity:


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.



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!



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.



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. 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.



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.



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 un-encapsulated replacement modules are available, see sub-modules page, model 4019cx.


The ARP 2600C restored by CMS.





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.

Listed in order of popularity:



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. You must have at least 1 un-encapsulated VCO to install this mod.



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. This mod now includes an upgrade of the AR circuit. 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.



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 preamp input. 4 jacks total.



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.



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.





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:


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 - 59.00 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 - 389.00

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.



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.



The electronic switch in the S/H section of the 2600 is almost never used because it is missing many functions. This new upgrade we call the "Swiss Army Knife" mod for the electronic switch. It greatly increases the usefulness of the electronic switch in many ways. It's a real pain to install, that is why it is pricey. It consists of:

1. An external trig/gate input jack to toggle the switch
2. A toggle switch to connect / disconnect the clock trigger
3. A dedicated push-button to manually toggle the switch
4. 2 LEDs that indicate what side of the switch is active.

It can be used to obtain a clock pulse at half the FC of the 2600 clock for triggering purposes.

The opposing gate signals can be used to drive envelope generators or VCAs etc. for externally triggered panning effects.

You can also use it as an audio Fc octave divider (up to 1Khz) if you patch a pulse wave from any VCO into the external trigger input.



This useful circuit is sometimes called a trigger detector or gate detector. It is typically used to trigger the envelopes when controlling the unit externally by guitar or any external source. This circuit often frees up the envelope follower so it can modulate the filter for an auto wah wah effect, synced VCOs etc. An LED indicator also provided. The input jack is normalized to the output of the envelope follower.


VCO RAMP/PULSE SELECTOR SWITCHES / AUX OUT JACK- 60.00 for each VCO / 90.00 w aux out jack

This mod provides a convenience switch that selects either pulse or sawtooth for routing to the filter audio inputs. This high quality toggle switch has a center off position so you can quickly disable or enable the VCO outputs for easier tuning of multiple VCOs. We also install an auxilliary output jack next to the switch that features ramp and pulse outputs at +5/-5. The standard factory ramp and pulse outs are 0 to +10v with a 5v dc voltage present so the aux jack offers an alternative modulation source as well as a better balanced audio source.


24Db DUAL MODE FILTER - MODEL 2621- special order - call

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 / INVERTER - MODEL 2627 - special order - call

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.



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.
    e-mail: filter@discretesynthesizers.com
  phone: 912-727-2195   ©2007 - 2011 Phil Cirocco