Aries AR-332
Dual VCO

Aries modules were available both as kits and factory modules.  This module did not appear in the 1975 catalog and sold in 1977 for $179.00 in kit or $295.00 assembled.  This module appear to be a kit due to the build and solder quality.

I combined specifications from Robert Leiner (with permission), my photos, and a reverse engineered schematic into a PDF document.

AR-332 Dual VCO Document

 

Each ramp VCO is in a large potted module with a sync and 1V/Octave input.  The other pins consist of +/-15V, ground, output, and the timing pin so a larger capacitor can be paralleled for LFO operation.  The PCB circuitry consists of a dual op-amp for control voltage summation and ramp to pulse generation.  I was not able to tune this module to 1V/Oct with the single turn 50K trimmers and replaced them with 20K 20 turn trimmers (the VCO tunes to 1V/Oct with the trimmers set to around 10K so I reduced the value from 50K to 20K).

 

The PCB is a single sided tin with no solder mask.  Care is required when doing repairs as the pads do lift easily.  The VCO-B ramp output had low amplitude and significant DC drift which is unrepairable without depotting the module.  The extra op-amp and circuitry on the rear of the PCB is an AC coupled gain circuit to bring the VCO B ramp output back to 10V pk-pk and center it at +/-5V.

 

This scope image shows the VCO B potted module ramp output.  The amplitude has decreased to 7.4V pk-pk and it is centered around -6.5 volts.  This renders the pulse generation circuitry useless as it is outside the comparator range.  By AC coupling and bringing the signal back to 10V pk-pk the pulse circuitry operates correctly.

 

I AC coupled the ramp instead of using a DC level shift as I believe the DC drift might continue with time.  AC coupling makes the ramp output in LFO mode very non-linear but the pulse output can be used for narrow pulses at low frequencies.  This image shows VCO B in LFO mode at 0.117 Hz with a very nice pulse output.  Because of the AC coupling the ramp output has shifted negatively but still has a 0 volt DC average.

 

 

Epilog

Years later this module came back again for repairs. The ramp output had decreased slightly so I increased the gain. I also adjusted resistors so the PWM controls would not cut out.  The biggest issues were the two VCOs tended to lock and the coarse controls were really unstable. I could verify the VCOs locking with the oscilloscope so I ended up decoupling the +/-15V to each potted module with a 47R series resistor into 100 F. and that eliminated the locking. The coarse controls would change frequency with sideways pressure on the knob and turning one knob tended to move the other. I tried cleaning the potentiometers and even replaced them with a NOS mod pot but it had the same sensitivity issues. I finally replaced the coarse and fine controls with single 10 turn potentiometers which work well. I glued the small knob to the large knob to preserve the look of the module.

 

 

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