ARP 2600 with CMS Mods / Upgrades

images via this auction
"ARP 2600 semi-modular synthesizer, with full complement of CMS modifications and upgrades.

This auction includes the 2601 Console (s/n 26010788) and 3620 Keyboard Controller (s/n 36200788). Not only is this 2600 in outstanding cosmetic and functional condition, the numerous modifications and upgrades performed by Phil Cirocco at C.M.S./Discrete Synthesizers make this a truly phenomenal instrument. Here is a list of the work performed, with descriptions from the CMS web site:
AUDIO PATH UPGRADE PACKAGE
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, preamp, 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!

MOOG STYLE FILTER MODULE - 4012cx
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.

VCA MODULE UPGRADE - (4019)
If your VCA module is unencapsulated, 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 unencapsulated replacement modules are available, see submodules page, model 4019cx.

POWER SUPPLY UPGRADE
The power supply in your 2600 is about 20 to 30 years old. Chances are that your power supply is not up to spec. This can result in excessive noise, ripple, and instability. This mod replaces your unit with a high power, highly stable, military spec power unit with remote sense regulation. The overall sound quality and oscillator purity are noticeably improved. Rebuilt ARP units are available for 125.00 (50.00 core charge).

17 INCH REVERB TANK
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 6 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.

1/4 INCH LINE LEVEL JACKS
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.

SYNC SWITCHES
Two independent miniature toggle switches that sync vco-2 to vco-1, and vco-3 to vco-1 This setup enables dual sync (two separate harmonics) if desired.

ENVELOPE GENERATOR RANGE EXPANDER SWITCHES
Miniature 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.

VARIABLE VCF KEYBOARD TRACKING
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 miniature rotary potentiometer that adjusts the tracking ratio from 0 to 1v/octave

LED INDICATORS
providing visual feedback on both E.G. outputs (red), s/h clock (green) and envelope follower (yellow). Requires power supply upgrade.

24Db DUAL MODE FILTER - MODEL 2621
The one key element missing in a 2600 is a highpass filter with resonance and associated coupling circuitry. The CMS 2620 is a dual mode, 24Db (Lowpass/Highpass), discrete, transistor ladder filter from the CMS 9000 series modules, Installed in the left speaker section. This original CMS design features a beautiful "raspy" resonance. Complete with anodized face plate, high quality controls, 1/8 inch Switchcraft normalized patching. Special switch links both filters in your 2600 together for a truly remarkable sounding bandpass function (24Db x 24Db). The resonance on the highpass function is also very unique and distinctive. Requires power supply upgrade. Now comes with voltage controlled resonance.

VCO / 4 CHANNEL MIXER / INVERTER - MODEL 2627
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. Requires power supply upgrade.
In addition, the following mods are present:
• The AR has been converted to an ADSR for even more CV potential;
• All three oscillators have been fitted with -1/0/+1 "octave" switches. This switch will transpose the oscillator by the amount predefined by the "Interval" pot (up to one octave)
• An additional set of multiples have been added in the lower left, now giving you 2 x 4 mults;
• Voltage Processor sections 2 & 3 have positive outputs available as well as the conventional negative;
• External trigger input for the Sample & Hold."

Custom MacBeth M5N "Blue Meanie" / "Blue Marvin"

via Ken MacBeth:

"Hi Matrix! ...well to continue with the custom panel thread- a prolific german client asked to have 2 M5N synths built for him- but with a special blue color that I ordered in- this color was swatched against the color type of the very first ARP 2600s. We discussed whether or not they originals were called 'blue meanies' or 'blue marvins' - maybe the viewers of the matrix synth blog know this stuff! I am currently offering direct sales of two Process Red M5Ns (...there will be a fire in the disco!) that go as a pair-both hand built by myself, and not the factory I'm using- there is a premium for this- but interested parties can enquire- pics to follow soon. Best To All- Ken Mac."

click here for more pics. Regarding the "Blue Meanie" vs. "Blue Marvin," if you know, feel free to comment. Via this post: "The very first model 2600 was produced in early 1971 and is known as The Blue Marvin. It has mistakenly been called the "Blue Meanie" but according to Alan R. Pearlman, the Blue Marvin is so named after Marvin Cohen, head of engineering at ARP at the time."

ARP 2600

Click here for shots via this auction. Note the cartridge modules on the inside shot.

Update via John Levin in the comments:
"For what it's worth, this one has the Tonus logo on it, as opposed to the Arp w/ cable logo. This means it's the first cut at the grey meanie after the blue meanie."

Update via Micke in the comments:
"It appears to be a model 2600P V2.0 (in production between 1972-72).

This model differed to the 2600P V1.0** (1971-72) in that the front panel was increased in height and that the VCOs changed from 4027 to 4027-1.

** the first version after the Blue Marvin and Grey Meanie

Micke"

CLICK FOR MORE »

ARP 2600 with MIDI

via this auction

Details:

"Much of the following info can also be found at discrete synthesizers.

2600:
The very first model 2600 was produced in early 1971 and is known as The Blue Marvin. It has mistakenly been called the "Blue Meanie" but according to Alan R. Pearlman, the Blue Marvin is so named after Marvin Cohen, head of engineering at ARP at the time. It came in a bright blue aluminum case with a funky and fragile wooden enclosure. It used an entirely micro-chip based voice path but the chips they used wound up being highly unreliable, although they sounded great! Only a few of these were made (approx. 25) and they were mostly built in a garage.

2600C:
Next, the factory produced 2600C Gray Meanie (pictured above) appeared in 1971 and can be identified by the rectangular 'ARP' logo on its right speaker grille. About 35 of these were made.

2600P:
Later in 1971 came the 2600P V1.0 which featured the same metal case (housing the same electronics as the original models) now enclosed in a much more roadworthy suitcase-style enclosure (similar to the pic below). In 1972, ARP switched out the unreliable (Teledyne) VCO chips for the model 4027 and 4027-1 (National Semiconductor) VCO chips in the 2600P V2.0 and 2600P V3.0, respectively. These new VCO chips sounded weak and nowhere near as good as the originals. A new duo-phonic keyboard (3620) with LFO was introduced with the 2600P V4.0 in 1974. The 2600P V3.0 and V4.0 models are denoted by the "G-clef" ARP logo and are the most common models out there with roughly 1700 2600P's produced during 1971-1974. Unfortunately, further changes to inferior parts were just around the corner. The Model 4012 filter used in the all the 2600's through 1976 used a design that was a copy of Moog's patented ladder-filter design. This led to a law-suit between Moog and ARP which forced ARP to design their own filter for their next version.

2601:
The Model 4072 filter, a four-pole low-pass designed to replace the original 4012 was widely considered to be faulty. The frequency response of this filter only goes to about 12kHz, giving this model a duller sound than models with the Moog style 4012 filter. The early 2601 V1.0 models were still using the disputed 4012 filters during 1975-76. In 1977 ARP started using their new 4072 filter in the model 2601 V2.0 with the modern orange-on-black design (pictured below). Around 1978 ARP unleashed a whole new line-up of their synthesizers using this new orange-on-black look. These were produced from 1977 through 1980. Very late 1980 versions of this model featured un-potted submodules, making them easier to maintain (but they are more rare).

There were also three versions of the remote keyboard: The Model 3601, which is a very rudimentary version with just Portamento and Tuning controls. The Model 3604 is similar but adds adjustable scaling and was used until 1974. The duo-phonic Model 3620 (pictured at top and bottom) which adds a dedicated LFO, latching and some other very useful features was introduced with the 2600P V4.0, and used with all subsequent models from 1974 to 1980."