via this Reverb listing
"Amazing deal alert! This vintage ARP Quadra has just been serviced in April 2025 by Synthchaser, the foremost expert on ARP Quadras! Work done included new sliders, recap of all tantalum and electrolytic capacitors, new touch sensor, new key bushings, reliability enhancements, fresh batteries, and installation of the Synthchaser MIDI Adapter.
The ARP Quadra is one of the coolest looking synthesizers ever made, and packs a duophonic lead synthesizer, ARP Omni-style string synthesizer & polyphonic synthesizer sections, and a monophonic bass synthesizer, along with a unique sounding phase shifter and other bells and whistles. The addition of the Synthchaser MIDI makes this venerable beast useful again in a modern studio.The synth is in good condition. There are some scratches on the front panel, and the top layer of the membrane panel has some cosmetic cracks near the "5" program button (see photos). The membrane panel works perfectly, and replacement membrane panels are available for purchase through Synthchaser should it bother you or you wish to stock a "survival kit".
Work completed on the synth included:
Synthchaser ARP Quadra MIDI adapter - Provides MIDI capability to all 4 sections of the synth (bass, strings, polysynth, and lead). Via MIDI in, aftertouch is processed over the full 5 octaves of the keyboard, not just the top 3 as in the original design! MIDI IN and OUT jacks have been fitted.
Synthchaser Precision slider upgrade - All 35 of the old original sliders have been replaced with new, smooth, high precision sliders. The difference in the way these sliders feel and perform compared to the originals is a huge improvement. New slider caps have been fitted.
All polarized capacitors replaced - The original tantalum capacitors in ARP synths are ticking time bombs, and 45 year old electrolytic capacitors are past their prime. All of the 150+ tantalum and electrolytic capacitors in this synth, including the power supply, have been replaced with new electrolytics to help provide stable operation for years to come.
4075 Filter Enhancement - The ARP Quadra uses the same 4075 filter submodules found in the Odyssey, Omni, Avatar, and Pro DGX which was designed with a calculation error that limited the cutoff frequency. Both of the 4075 filter submodules (for the lead synth and the poly synth) have been recapped, and corrected to provide superior frequency response, and tested for proper operation in the Synthchaser custom test fixture.
New aftertouch sensor - The original aftertouch sensors are a common failure point-- the aftertouch sensor has been replaced with a new long-lasting one to ensure the aftertouch will work for years to come
New key bushings
Oscilloscope calibration - Calibrated to factory spec using oscilloscope and frequency counter.
PCB Interconnect reliability upgrade
Batteries relocated - ARP Quadra presets are preserved by alkaline batteries mounted to the microprocessor circuit board. In the majority of Quadras, these batteries have leaked and damaged both the microprocessor board and also the keyboard electronics circuit board below. There is no battery damage in this synthesizer, and to keep it that way, I've relocated the batteries to a battery holder in the bottom of the chassis, a standard upgrade I make to all Quadras that I refurbish."
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