MATRIXSYNTH

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"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."