ARP Synthesizers

[ARP 2600 VCO-2] ARP Instruments, Inc. existed from 1969 to 1981 and produced some of the most wonderfully musical synthesizers ever. I've always loved these instruments, they were clearly built by some very talented and clever folks.

This is a page of resources and articles on ARP Synthesizers. I'm also including resources for the ARP/Rhodes Chroma, the synthesizer ARP was working on as the company went out of business; they sold the design to Fender/Rhodes, who put it into production.

This collection is not meant to be complete -- only select technical, historical, and practical resources with closest historical accuracy are included. (Suggestions are welcome, of course.)

ARP Web Resources

Below, a collection of ARP technical, historical and support resources on the web.

ARP Articles

Below, a bibliography of ARP articles.

ARP Patents

Reviews of all the patents I could find associated with ARP Instruments, Inc.

Upgrading the Rhodes Chroma Power Supply

The "Nuclear Powered Chroma", my adventures replacing a Rhodes Chroma power supply with a modern switching unit.

Rhodes Chroma Pedalboard

A nice pedal arrangement for the ARP/Rhodes Chroma.

ARP Web Resources

Manuals, Schematics and Technical:

	ARP Patents Don Tillman reviews many ARP patents.
	ARPtech Joachim Verghese's ARP Synthesizer technology page is the single most useful technical ARP site and includes descriptions and schematics for all the modules, including the mysterious potted submodules. (Later... The ARPtech site has disappeared twice, so I have a copy of it hosted here now.)
	Cloned Analog Gear Anders Sponton's site has the ARP 2500 Manual in PDF format including operating notes on all the modules. (Look under "sundries".)
	E-Music DIY Archive Tony Clark's site has copies of the ARP 2600 User Manual, the ARP Odyssey Service Manual and the ARP 1601 Sequencer Service Manual.
	The Emulator Archive ARP 2500, ARP filter, ARP Quadra articles, manuals, other stuff.
	Guitar Fool's Synthesizer Page ARP 2500 schematics, ARP 2500 and ARP 2600 manuals.
	Jim Michmerhuizen ARP 2600 Owner's Manual reprints are available from the author.

Historical:

	120 Years of Electronic Music A listing of ARP products from the 120 Years of Electronic Music web site.
	Synthmuseum Photos and information on all the ARP models, and excerpts from Mark Vail's book Vintage Synthesizers.
	Vintage Synthesizers by Mark Vail, published by Backbeat Books. A must-have for synth fans, this book contains three chapters devoted to Moog synthesizers as well as a couple other chapters written by Bob Moog.

Support:

	Archive Sound Rebuild kits for the Pratt-Read keyboards used on many ARP and Moog synthesizers.
	ARP Odyssey Resource Page Rob Williams' ARP Odyssey resources and email list.
	ARP Explorer Page Rob Williams' ARP Explorer resources.
	CMS/Discrete Synthesizers Phil Cirocco is an ARP guru. He performs ARP mods and builds synthesizer modules very much in the spirit of the ARP 2600.
	Music Machine's ARP Site Some resources from those wacky ravers at Analogue Heaven.
	Rhodes Chroma Chris Ryan's ARP/Rhodes Chroma site is very complete and very impressive. Patches, information, links, buy-and-sell, articles, etc. Chris also has an email list for Chroma fans.

ARP Articles

The ARP Synthesizer-A New Instrument for Musical Composition and Performance
David Friend
Preprint 742, 39th AES Convention October 12-15 1970
(Copies are available from the Audio Engineering Society for a minimal fee.)

A description of some of the philosophy and features of the ARP 2500, including extra-stable wide-range oscillators, matrix switches replacing patch cords, three-note split keyboards (2-note main + 1-note bass), multiple function modules (including an entire synth voice in a module).

An Integrated Guitar Synthesizer for Live Performance
David Friend
Preprint 1289, 58th CAES Convention, November 4-7, 1977
(Copies are available from the Audio Engineering Society for a minimal fee.)

A block level description of the ARP Avator with a number of interesting features. The instrument is monophonic, but they use a hex-pickup. The hex pickup allows for the hex-fuzz sound of course, but it also enables more accurate pitch detection as a multiplex circuit selects only the most recently played string and noises on other strings do not interfere. Also, the pitch detection circuit goes through a variable speed shift register to get extra-accurate conversion at the initial note transient, but adds a delay as the note progresses to ignore the change in pitch as the finger and string leave the fret.

The Electrical Design and Musical Applications of an Unconditionally Stable Combination Voltage Controlled Highpass, Bandpass, Lowpass, Band Reject Filter/Resonator
Dennis Colin
Preprint 786, 40th Audio Engineering Society Convention, April 27-30 1971
Journal of the Audio Engineering Society Volume 19, Number 11, December 1971

An analysis and block diagram for the ARP 1047 VCF module on the ARP2500. This is a basic biquad filter with some nice features and presented as an alternative to the Moog filter. Unfortunately schematic details of the voltage controlled stages are not included.

LP, HP, BP and BR outputs are all available simulatenously. There is a potentiometer on the notch output to tune the zero above or below the pole, altering the shape of the resonse curve greatly. The Q is voltage controllable. Switch selectable input gain for either a unity gain pass band or a unity gain peak. A keyboard gate input with a second Q control to set two separate Q's; one for for key up and one for key down. Pretty featureful.

The Rise and Fall of ARP Instruments
Craig R. Waters, Keyboard Magazine, April 1983
based on the article in Inc. Magazine, November 1982
and reprinted in Vintage Synthesizers by Mark Vail.

Great historical account.

Rhodes Chroma: They Synth that Survived ARP's Fall
Mark Vail, Keyboard Magazine, October 1993
and reprinted in Vintage Synthesizers by Mark Vail.

An interview with Phil Dodds about the Rhodes Chroma, including a lot of insights about the design.

The Apple II / Rhodes Chroma Interface
Bob Moog, Keyboard Magazine, September 1982.