ASM-1 Triangle wave....

[Christopher_List at Sonymusic.Com]

Hi List - - -

John, I think I figured out what your problem was with the "flattened"
triangle wave using the transistor saw-to-triangle trick.

First off, make sure you are using the 0 to +5 sawtooth wave coming from
the ASM-1's "unused" op-amp buffer - DO NOT use the -5 to +5 output
sawtooth wave.

Second, when I first hooked it up I had the output going to an inverting
summer for the amplification and level shift. I used a 47K input resisitor.
This is too low! It seems to screw up the output - must be sucking too much
current away from the collector / resistor connection. I had the same
results you did - a flattened triangle wave...

I switched it to 100K input resistor and it worked fine. The resistor on
the top half was 10K and on the bottom half it was 39K + 20K trimmer. I
used a 3904 PNP tranny. With a 100K resistor to the inverting summer, a
620K feedback resistor and a 470K input resistor to -V is approximately
what you need for centering around +/-5v output. Fiddle with these values
to get it perfect. Such high resistor values will add noise to the wave,
but I didn't notice it....

This works much better than op-amp FWR of the sawtooth as that method has a
switching glitch on one half of the triangle wave...

- Chris