Buchla Cards 1-5

Almost halfway with the 12 cards. Nothing special with card 2 (Random Voltage). This card has one jumper wire.

Cards 3 (Envelope Generator) and 4 (Pulser) can have problems with bleed into the audio. This is caused mainly by LEDs that take a lot of current. I cut the traces on bottom side to the driver transistors 2N1711 and soldered 1k resistors across the cuts to drop the currents. In card 3 I also added a 100pF capacitor across IC1 pins 12 and 14 to tame possible oscillations. Card 3 has two jumper wires.

Card 5 (Balanced Modulator) has seven vactrols. Vactrols 1/2, 3/4 and 5/6 need to be matched. With this simple test-circuit I measured the on-resistance of the LDR.

Resistance keeps rising as long as the LED is on. This is because the LED warms the LDR and this changes the resistance. I measured the lowest resistance when the vactrol was fired on. On REV2.1 cards there is a small pad added that indicates where the positive (+) lead of the vactrols LED should be inserted.

Buchla 208 Sequencer

Nothing special in this card. I added the decoupling capacitors to the bottom side to ensure trouble-free operation of the sequencer.

Buchla 208 clone

From these parts I am trying to create a working clone of Buchla's Stored Program Sound Source Model 208. I still need some components from Mouser, spring-tank and a front panel. PCB's are from Electric Music Store. uA726 replacement PCB is my own design. Hardware and NOS-parts are from SAMODULAR.

mA726 Proto

This seems to be working! Next test is going to be inside Buchla 208 VCO's.

Moog Prodigy and AS3046

With these SOIC to DIP adapters I managed to change the LM3046 chips with AS3046 SMD drop-in replacement chips. Next I must re-calibrate Prodigy and see how these SMD-chips behave.

mA726

Here is my version of drop-in replacement for uA726 part used in Buchla Easel. I have tested this before here. I ordered the first proto-batch from Eurocircuits. Because of two SMD-parts it's very compact (width = 37mm and height = 17mm). For LM3046 replacement I use ALFA-parts AS3046 (Vbe is matched five times better for the NPN pair than in the original with +- 1mV).

Buchla 208

I am considering the possibility to make my own clone of Buchla 208. Here is the first sketch of the motherboard.