ASM-1 Life

[Dave Fulton]

I finished constructing the 1st of 3 ASM-1's tonight, I took it downstairs 
to test it out (mixers,AMPs,powersupply etc. live down here) of course 
with a pad of paper to note errors in wiring. A couple of things struck me 
as odd so I would like to present the problems here and hopefully attempt to 
solve them on thursday (I have an 18hour shift tommorrow).

1) The LED I added to the LFO appears to effect the pitch of the OSC.
2) AS does the ones I added to the ADSR's.

I added the LFO LED in the fashion the was suggested by Gene in the ASM 
docs, the LED's monitoring the gate inputs were added based on Chris List's
plans. I quickly changed the 3.3K to 10K (As I did to the Gate LED's) & 
reduced the effect. When I noticed that the pitch of the OSC's were 
modulating the filter cutoff. Starting to sound like a Power Supply problem?

Could be. I am using a HP6236B bench supply. It should be fine. I did 
note that even though the LED's when on consumed more current, the voltage 
appears to remain constant. LED's draw only from the + supply, could this 
unbalancing of the load create this effect? But what about the crosstalk 
between the OSC's & the Filter? I ask this because I have heard of others 
having strange effects when using HP supplys.

Other than the a couple of controls wired backwards (The Sustain & 
Release Pots on both ADSR's) all other controls work correctly. 


Of course the trimmers are just center slotted at this point or quickly 
adjusted to get sound out of it.

Any thoughts? 

Dave Fulton
Oregon Public Broadcasting
Engineering Dept.