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245/246 vs 281 - odd AD vs ASR interaction
MUFF WIGGLER Forum Index -> Buchla, EMS & Serge  
Author 245/246 vs 281 - odd AD vs ASR interaction
So I just got my freshly built 246, and did some testing along with an older 245 and a pair of rev 1 281's.

I'm experiencing some odd interaction between the 246 and the 281's in AD mode, and I'm hoping for help in determining where the problem might lie.

First, I'm only talking about the actual pulser output, not the stage/gate outputs. This is connected directly to the pulse input on the 281's.

When connected to the 245, in ASR mode the 281's track the pulse length control as the sustain segment of the envelop, and in AD mode they ignore the pulse length control - expected functionality.

When connected to the 246, in ASR mode the 281's track the pulse length control as the sustain segment of the envelop, but in AD mode they also track the pulse length control as the sustain segment of the envelop.

There is one other difference between the 245 and 246 which may or may not be related.

On the 245 when the pulser output is connected to the sequencer advance input and a 281, some of the 281's channels won't trigger in AD mode but others will. And all will trigger in ASR mode. Using the ref output to trigger the 281's works fine though.

On the 246, the pulser output will trigger all of the 281s' channels regardless of whether it's also connected to the sequencer advance input.

So I really can't tell whether the problem is with voltage levels/pulse shape on the sequencers' side, close-to-threshold voltage sensitivity on the 281s' side, or some combination thereof.

And insight would be greatly appreciated!
But wait, it gets even better!

Further testing shows that the stage/gate outputs on both the 245 and 246 result in ASR functionality on both of the 281's regardless of whether the mode switch is set to AD or ASR.

And even weirder, on both the 245 and 246 the ref outputs also exhibit some ASR functionality regardless of the 281's mode switch setting, but the pulse width is shorter on the AD setting in both cases. Still longer that the assigned AD times though.

So in conclusion, I'm even more confused than before. As far as I can tell, the only proper AD functionality from either module occurs with the 245's pulser outputs - as long as it's not also connected to the sequencer advance.

Dead Banana
Have you looked at the "Is my 281 working properly?" thread on here?
here it is

My rev 1 (I think?) 281 didn't work properly as built. One of the main issues I had was that they would sustain even while in AD mode.

My guess is that what is happening is that your 281 is essentially always in ASR mode (as mine was) but with a different sustain threshold between the two modes.
Thanks for that - I had a vague memory that thread was regarding a later rev, so I will go back and review.

But what you're describing is pretty much exactly what's happening - except for a direct connection from the 245's pulser output. In that the one instance the AD envelope appears to be properly tracking only the attack and decay times and completely ignoring the pulse length. Which has made troubleshooting this oh so confusing...

I've got a V1.1 of the latest batch of 281 PCBs (gold colored traces) built with Dave Brown's mods (removing the 100K, adding the resistor/cap and diode) and using a 244's Manual Trigger (which is +12V so long as the switch is held) the 281 does not sustain in either one-shot or ASR mode. I do not have a 245 or 246 present.

However: when I input +15V to a trigger input the modes operate as expected. In one-shot it follows the AR curve to the end. In ASR mode it sits in sustain so long as the +15V is applied.
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