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AM 4034 - ARP 24dB Low Pass VCF
 Overview
This is a classic "moog" transistor ladder low pass filter with the usual 4-poles and 24dB cutoff. In 1974 ARP went back to their "moog" filter design and updated it to use transistor array chips and put it into the Explorer 1 as the 4034.
Original Circuit The original design is very similar to the ARP 4012 filter in the 2600, with the same ladder design, but using 4 transistor array chips (CA3086). A dual FET buffers the ladder into
the usual LM301 Op Amp. Another LM301 is used to sum the control voltages and provide CV scaling. The CA3086 were selected by ARP, presumably to match the transistors.
AM Circuit
This AM module is actually based around an original ARP 4034 potted module from an Explorer. The synthesizer has had a hard time, in fact it was in a fire...It was donated by Jim Burdon in Canada in July 2005.
The 4034 module has been removed from the VCF/VCA and ADSR PCB and mounted onto a Veroboard which has the CV Op Amp summer and some passive components for the audio input and out. The CV Op Amps have been updated to an OP177.
Front Panel The front panel is an AM High Density design, 90mm wide, 3mm thick aluminium, 4U high, with black lettering. Controls pot spindles are 3.18mm in diameter, knobs are 27mm, 19mm
and 13mm in diameter - black and chrome, the switch is a sub-minature slide model and 3mm LED's are used.
An audio signal LED monitor is fitted with a 10 LED bar graph, this is a separate and optional sub
module. More details on the Signal Level Sub Module (SLSM) are here. more »
Build History The 4034 was tested in July on the PCB to see whether it survived the fire...
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