via this auction
"8 ARP MSL (modular synth lab) modules. These were supposed to be used for teaching synthesis in the '70s and are basically slimmed down ARP 2600/Odyssey circuits, but with ins/outs just like a modular synth. As you can see from the sticker in the photos, these lived up to their purpose some 25 years ago!
* 1501 ADSR envelope generator
* 1502 Low Frequency Oscillator
* 1503 Noise generator
* 1504 Voltage Controlled Oscillator
* 1506 Voltage Controlled Filter
* 1507 Sample/Hold
* 1509 Voltage Controlled Amplifier
* 1511 Speaker/Amplifier
* Original patching cables.
There is hardly any info on these on the net, except for this site: http://www.synthmuseum.com/arp/arpmsl01.html"