CMS offers a full array of repair, restoration and calibration services for the ARP/Tonus 1000 series modules. CMS has extensive experience repairing, restoring ARP 2000 and 2500 systems. CMS has restored many of the 2500s that are still being used today for teaching at major colleges across the United States such as Brown University and the University of Georgia. CMS has restored ARP 2500s for famous artists like Peter Townshend of the "Who" and Vince Clarke of Depeche Mode to name a few.

ARP 2500 circuit boards are particularly delicate and can be easily damaged by a novice tech. This can actually cost you more money in the long run. We have seen this damage quite a bit lately when we go to perform estimates on 2500s and 2600s. Don't let the local tech ruin your valuable vintage instrument. CMS has in stock, custom replacement boards for several 1000 series modules.

The other typical situation we see with 2500s coming into the shop is incorrect calibration of the 1000 modules. This is usually due to a tech guessing at the calibration process. This problem is compounded by the encapsulated sub-modules used in the 2500 system. CMS has a custom made ARP 4000 series sub-module tester so we can test your sub-modules as part of the initial diagnostic procedure. CMS also makes a high quality line of replacement sub-modules for all the ARP 2500 modules.

Unlike other ARP synthesizers, there never was a service manual published for the ARP 2500. The official story is that they never got around to it. ARP discontinued the 2500 in 1976. The 2500s were made so well, ARP did not get many service requests in the 1970s for 2500s. ARP was out of business by 1981.

Over the years, CMS/Discrete synthesizers has created, and is still writing, it's own extensive and detailed service manual for the 2500. Please don't bother asking for a copy, It is not for sale at this time. We plan to publish this sometime in the 2020s.

Send your 2500 system to CMS for a free detailed estimate, proper service and more importantly proper calibration. See the link below for 2500 packing tips. Call or email Phil at CMS to send in your 1000 series modules, or your entire system for repair, restoration and calibration.


MAIN POWER SUPPLY REBUILD -------------------------------------295.00

Much of the noise and cross-talk in a stock 2500 is due to the age of the power supply, not due to the matrix switches! The power supply in your 2500 is 33 to 40 years old. Linear power supplies have an average shelf / operating life of about 20 years. Chances are that your power supply is not up to factory specification. This can result in excessive noise, ripple, and instability rendering the instrument useless in a modern digital/midi studio. Without any de-soldering, you can disconnect your existing 2500 power supply and send it to CMS for a complete rebuild to ARP factory specifications.


LAMP POWER SUPPLY REBUILD------------------------------179.00

The 2500 features a separate 12V regulated lamp power supply that we can service also. Minimal de-soldering is required to send in your lamp supply. Lamp supplies that are malfunctioning can actually affect audio performance.


MAIN POWER SUPPLY UPGRADE----------------------------499.00

Much of the cross-talk, noise and pitch instability in a 2500 system can be eliminated by upgrading the power supply to a modern high speed, low noise unit designed specifically for high fidelity audio applications. Even if you rebuild your 2500 main supply, there are limitations inherent in the older designs that permit noise and VCO waveforms to contaminate the power supply rails and subsequently distort the audio signal. To remedy this, we recommend the power supply upgrade. This mod replaces your unit with a high power, highly stable, military spec power unit. The overall sound quality, oscillator purity, stability and keyboard tracking are noticeably improved. You must send your cabinet to CMS to install the power supply upgrade. A 230V version is also available.


LAMP POWER SUPPLY UPGRADE ------------------------------379.00

This upgrade is usually required if you have a very old cabinet. It is also critical if you are a european customer and want to run the 2500 cabinet correctly from 230V.






We have an extensive stock of hard to find, original equipment manufacturer parts to restore your modules to brand new ARP factory specifications.

We also manufacture a complete line of high quality ARP sub-module replicas for the ARP 1000 series modules.




Many of the calibration points on the ARP 1000 series modules do not have trimmer potentiometers. Calibration of ARP 1000 series modules involves a process known as "component selection calibration". It starts with testing the module to see if it passes ARP factory test parameters, selecting specific components and soldering them in place, then re-testing the module to see if it meets factory specifications. CMS uses the original ARP factory test documents and blueprints directly from the ARP engineering department for the selection and calibration process.

Send your 2500 to CMS for a free detailed estimate, proper service and more importantly, proper calibration. See the new 2500 packing tips page for detailed information on packing and shipping an ARP 2500.


1004 OSCILLATOR CRITICAL RE-ALIGNMENT-----------------------------------------175.00

ARP 1004 oscillators use special custom made temperature compensated exponential converters that drift out of specification from decades of use. Waveshapes and keyboard tracking linearity are often found to be way out of spec when we perform estimates on ARP 2500 systems. This critical re-alignment procedure also upgrades certain components to give you trouble free operation, accurate waveforms and precise keyboard tracking for decades to come.


1004 OSCILLATOR HF TRACKING UPGRADE -----------------------------------------125.00

Early ARP 1004 oscillators do not have a high frequency adjustment. We install a high frequency trimmer as well as upgrade certain components to improve oscillator tracking using ARP factory methods and documentation.


1005 MOD-AMP UPGRADE -----------------------------------------375.00

This mod includes upgrading the audio path in the 1005, increasing slew rate and reducing noise, adding a separate output for the balanced modulator and adding an additional audio input to the VCA section. Vastly improves the 1005 module functionality. Now includes installation of a 1/4" auxiliary output jack on the back of the module for a low noise, direct connection to your mixer.


1006 FILT-AMP UPGRADE ------------------------------------------375.00

This upgrade replaces certain cheap components in the audio path of both the filter and the VCA with high quality hand selected parts. This upgrade also includes increasing the filter headroom by a factor of 2. Improved noise and slew rate for the VCA section. Includes cap replacement and calibration. Now includes installation of a 1/4" auxiliary output jack on the back of the module for a low noise, direct connection to your mixer.



updated: 12/14/2017

Since the ARP 2500/2000 is so rare, here are some sound samples to illustrate this great sounding synthesizer.


"Pre incision"

This cut shows off the the ARP 2500 sequencer, ring modulator and using the matrix switches to "play" the instrument. By the way, the stories about the matrix switch cross talk are grossly exaggerated and are mostly used to rationalize not owning a 2500.


"Countdown Warning"

Here is another track where the ARP 2500 matrix switches are "played" by selecting different modulation routings in time with the music. The bass uses the 1047 multimode filter.


"Multiple Madness"

This insane and raw clip might also make you smile a bit. The ARP 2500 sequencer coupled with a madman at the keyboard produces this. Not recommended for the ears of "people on the edge".


"Searchlight 7"

This track is from my band National Razor. I wanted to include this because it features a Roland TR-808 being processed by ARP 1047 multimode filters from the ARP 2500, in stereo.


older clips:

"2500 Duet in stereo" - 2/10/06

This is a live cut - no overdubs. The thick bass sound is a 2515 main cabinet with 7 vco's. The surprisingly realistic piano sound is a 2508 wing cabinet with 3 vco's and 3 multimode filters. The controller was a Rhodes/ARP Chroma via a Kenton Pro-2.


Ennio Morricone's - "Once Upon a Time in the West"

This was quickly arranged on a PC using sonar. This uses the same 2500 patch as above. I added some 2600 percussive rhythms and a Roland 808.


More sound clips to come

©2006 -2017 Phil Cirocco



1023 variations, replica



1026 replica




This early version of the ARP 2500, the 2002 was made in 1970

2500 Matrix Switch Color Code

Running a ARP 2500 / 2000 from a MIDI converter


e-mail: filter@discretesynthesizers.com
phone: 912-727-2195 ©2017 Phil Cirocco