I received one of the boards from Jan this week. (Thanks, Jan!) I
compared it with the schematic. The schematic incorrectly labels almost
all of the pins on the three op amps, U5, U6, U7. But the board is
correct. For example the three sections of U7 that buffer the tone
outputs are indeed voltage followers. Be careful when installing U7!
It goes in the opposite direction from the other ICs. This orientation
of U7 is correctly indicated on the silk screen.
All the outputs are in 0-10V range. For the CV outputs: STEPPED,
SMOOTH, WOGGLE, I think this is fine; the all-positive voltages are
nicely suited for control purposes. However, I prefer audio outputs to
be centered about zero. Capacitors in the range of 100nf to1uf placed
in series with R37, R38, and R39 would do the trick for centering the
tone and ring mod outputs.
I am a bit puzzled why the board designer used surface-mount pads for
the bypass caps. It looks as if there is plenty of room for
plated-through holes in those locations.
Don't forget to read these notes by Ryan Williams:
http://diy.czmok.de/mod/gbuy/wogglebugparts.txtYou should add a 4.7nf cap to ground at the end of R35 that connects to
the cluster pot, as described there. I used a 1K for R35, as well.
This makes the LF398 more stable when it is reading its own output
(cluster pot wiper all the way over to R35).
Richard Brewster
http://www.pugix.comMark wrote:
> On 3/1/08, Grant Richter put forth:
>
>> > Also, I took a look at the schematic. According to the above
>> > website, this module uses 0 - 10V, and I wanted to see how easily it
>> > could be adapted to the -5V/+5V that MOTM generally uses. It looks
>> > like all the op-amp outputs are wired as comparators (ie. with
>> > positive feedback). If that is a mistake, perhaps it should be
>> > corrected.
>>
>> Orcad library op-amp symbols have the minus input on the bottom, and
>> the positive input on the top, don't ask me why. Don't assume
>> op-amp symbols are always drawn with the negative input on top, it
>> has become conventional recently, but different schematic software
>> may not follow that convention, and there are no regulatory bodies.
>>
>
> These are drawn according to that convention, with the negative input
> on top. It's labeled with a "-" and the number 2 (which is an
> inverting input on a TL072). The feedback goes from the output
> (labeled 1, which is an output pin on a TL072), along the bottom, to
> a an input labeled with a "+" and the number 3 (which is a
> non-inverting input on a TL072). So I don't think I'm assuming
> anything in suggesting that if it isn't meant to be a comparator,
> then perhaps the schematic should be corrected.
>
> http://diy.czmok.de/mod/gbuy/wogglebug-schem.pdf
>
>