This Arp is here for several reasons. Although a basic repair has already been done before it came in (S&H replaced and some other typical tasks for the 2600), but there is a lot of work to be done. Here’s a first impression of the Arp

There are may modifications, some not yet fully understood. The main problem are several broken potentiometer levers – original parts are not available, nor aren’t rebuilds of similar quality. Therefore we are evaluating levers and knobs made using 3D printing techniques. This work is carried out by drucke3d.de and the parts are now waiting for installation.

Here are some photos of the major modifications and additions:

This is a simple 2 transistor astable multivibrator which is actually not connected to any parts of the Arp.
The output signals are routed to separate jacks and may be used for modulation purposes.

A 2nd order RC filter with switchable corner frequency. The filters are passive with an buffering op amp in between.

One of the two transpose circuits connected to each of the two VCOs. Two switches expand the transpose possibilites by fourths and fifths.

During repair, all modifications will be reverse engineered and documented. For now, here’s an overview of the modules in the Arp: