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208 pulser offset
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author 208 pulser offset
papz
The 208's pulser ramp output at the yellow banana sockets oscillates between 1.5V and almost 15V and doesn't reach 0V.
The offset voltage depends on the period time, the wave moves with respect to 0V : when the period is in audio range, with the slider set to the max, it's about 0.5V only.

Although not a problem in most uses, a customer reported that he couldn't clock his Keen Association 220 keyboard with his 208p's pulser because of this.
It also gives a snappier sound when the pulser controls a LPG.

Adding an offset circuit on board 4 between IC1 pin 12 and IC4 pin 8 makes it possible to move the ramp bottom to 0V. Of course the former trace should be cut.
The circuit can be on veroboard and mounted with a short standoff to the back of the board.

When the trimpot is adjusted to cancel the 1.5V offset, the ramp bottom goes to -0.5V when the pulser runs in audio range.

This offset schematic by Jeroen Baars works fine.





ArguZ
That is very elaborate, thank you smile
Question, wouldn't a simple resistor change to the input of IC1 (pin14) or a value change to R41 work too ?
We need to lose around 1-1.5V only.
papz
I first tried to change R41 value but it didn't help.
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