ARP Quartet- Owned from December 2000-present, traded for Siel DK 70

I traded one broken crappy synth for another. This Quartet had seen better days, it was really dirty, the sliders were awful (2 were replaced with potentiometers and the other ones needed it), there was a pretty signifigant dent in the back panel, the brass section didn't work, the organ section had a buzzing sound, and the power transformer would emit smoke and burning smells when turned on (primary short I think). At first I ignored this and turned it on, and after fiddling with it for 30 seconds I figured out that the entire case had filled with smoke- it smelled awful. I removed the transformer to measure the voltage but it died as soon as I plugged it in. It took some searching but I found schematics and ordered the appropriate 20 volt transformer for $6 from a surplus website. I replaced the transformer, power cord, filter capacitors, and fuses, and rewired the pair of potentiometers added to the front panel by the previous owner to replace the sliders. It worked now, at least the string and piano sections. I traced the problem in the brass section to a faulty ribbon cable but a little after that the cable broke completely. The ribbon cables used in the Quartet are really low quality and they'll break if the cover is opened too many times. I haven't messed with it since then, but I know it needs all new ribbon cables and probably all new decoupling capacitors and CMOS chips.

The Quartet was the same thing as the Siel Orchestra, rebadged and sold as the ARP Quartet around 1979-1980. It is regarded by some as one of the worst synths ever made. I don't think it deserves such a bad reputation as at least the string sounds are good.

It's big and ugly, made of wood (actually particle board with fake wood veneer) sides and bottom, with a brown metal top/back. There are a few sliders but most of the controls are weird feeling flip switches that have a nice fast action. It's got a 4-octave keyboard with a crappy feel and a tune control on the right side. There's just a mono output, no midi or anything like that, but there's a DIN socket on the back for some sort of pedal that I don't have. Opening it up is very simple, the front panel and the keyboard assembly are hinged for easy access.

Synth-wise it's got a brass section with 2 footages that can be combined, a brightness slider (non-resonant 2-pole lowpass filter), a brass attack slider (filter attack), and a vibrato switch/slider. Then there's a string section with 2 footages, a "percuss" switch which just changes the envelope and a "solo" switch which takes off the chorus. There's an attack slider which I think only applies to the string section. The organ section has an organ switch and a celeste switch which is the same thing only an octave higher and with a chorus effect (different from the string chorus). The piano section has piano and honky tonk switches, both the same only with chorus on the honky tonk, both sound pretty bad. Then there is a sustain (more like release) slider. The sounds can be combined but it doesn't really stack sounds because it's all coming from the same circuitry, it just gives variations on the sounds, so you can get something like a brass sound with the celeste chorus effect, etc. String sounds are nice, piano sounds aren't very good, organs are okay, I don't really know about brass.

Inside it's rather poorly made but conveniently all of the chips are socketed. The master oscillator is under the keyboard, and like most string machines there are 12 divider chips and simple envelopes under each key. 4 different footages are output from the keyboard. These are mixed differently depending on the sounds selected. There's a non-resonant 2-pole lowpass filter with its own envelope, and 3 independent BBD-based chorus circuits using TDA 1022 chips. Each chip has its own clock oscillator and LFO. When "celeste" or "honky tonk" is selected, the second chip gets the inverted LFO from the first instead of its own, for a different effect. The outputs from all of these are mixed together and amplified for output. All of the signal routing, envelope control, etc. is controlled by simple CMOS logic chips.

If I ever get around to fixing it, I'll be sure to modify it so that it has a lot more control over the waveform mixing, chorus circuits, etc.

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