On 4/13/07, contact@... put forth:
amp, so I went and looked that up. Pin 8 is V+ and pin 4 is V-, which
is the same as a TL072.
various mods.
It's my understanding that a a 1V/Oct input and exponential FM input
would be the same thing.
I had thought the "Ext Excite" was an input for an external VCO to
clock the filter (although that might not be a bad feature). If
that's true, then a 1U expansion module would seem unwise as that 1U
could be used for an MOTM-310 or some other 1U VCO.
Now I'm thinking that it might be an additional audio input for the
filter. Is this the case?? So if the saw output is normalled to the
"Ext Excite" jack, following the chickenhead selector:
EXT -- saw
1 -- square
2 -- square, F/2
3 -- square, F/4
4 -- square, F/8
are the inputs to the filter, is that correct?? So one way of
looking at is that the "Input" and "Excite" knobs have the same
function for their corresponding inputs??
I took another look at the schematic for the VCO output
daughterboard. I'm thinking that it taps the sawtooth going into the
CMOS counter, and the first op-amp servers as a follower. Where does
the 560K with the down-pointing arrow go?? Then I'm thinking that a
square wave is generated by the massive gain (2M/2K) of the second op
amp by driving it into the rails. Although, afaik, a TL072, unlike
the LM358, doesn't like going to rails. I'm not sure about positive
outputs, but the common mode voltage getting too close to the
negative rail of a TL072 can cause phase inversion and latch up. I
apologize if I sound overly critical, but for educational purposes,
I'm not sure why another comparator circuit was not used.
>I'm sorry, I still don't get it. The schematic shows an LM358 op
>I'll clear up the confusion. For the daughter board, the schematic
>is correct. The - and + pins on one op amp are swapped, basically. I
>use a CGS simple mixer PCB, which needs to have those physically
>swapped, as the ground trace is a bit too big there to simply cut.
>You then run jumpers to the points those pins need to go to. Those
>jumpers are wired directly to the pins of the TL072. If doing it on
>your own, you could use protoboard or a Tellun MUUB-2 if my solution
>seems inelegant :) It works well with my bracket, though, and is
>not hard to do.
amp, so I went and looked that up. Pin 8 is V+ and pin 4 is V-, which
is the same as a TL072.
>By the by, a great place to get the tap from the oscillator core isYes, I think it is most excellent that he deliberately adds room for
>very close to the "Sync" pad, on the closest "extra cap hole" if you
>use a .2" cap. I'll try to get a pic up if anyone wants to see that.
>
>As an aside, kudos again to Ken for providing extra holes for
>different size components!
various mods.
>I think Jim means that the power _header_ is backwards, compared toOK, thanks for clearing that up. I was scared to leave the house :)
>MOTM modules -- that is, +V and -V are opposite of what you may be
>used to. However, if you put the header in according to the
>silkscreen, everything is fine. I supply friction lock headers, so
>as long as the headers follows the proper silkscreen, you can't put
>it in backwards. The silkscreen may be hard to cipher, though, since
>it's made for MOTM and .Com power headers; I triple check my own
>each time I make an assembled module :)
>I did indeed sacrifice the Linear FM for the oscillator outputs, andAt this point I feel as though I must be confused about a few things.
>a 2U module instead of 3U.
>If there is ever interest, I could add a 1U expansion. This would
>include Linear FM, PWM square output, and VC Bandpass. It still
>needs to be tested, the PCB made, etc...
It's my understanding that a a 1V/Oct input and exponential FM input
would be the same thing.
I had thought the "Ext Excite" was an input for an external VCO to
clock the filter (although that might not be a bad feature). If
that's true, then a 1U expansion module would seem unwise as that 1U
could be used for an MOTM-310 or some other 1U VCO.
Now I'm thinking that it might be an additional audio input for the
filter. Is this the case?? So if the saw output is normalled to the
"Ext Excite" jack, following the chickenhead selector:
EXT -- saw
1 -- square
2 -- square, F/2
3 -- square, F/4
4 -- square, F/8
are the inputs to the filter, is that correct?? So one way of
looking at is that the "Input" and "Excite" knobs have the same
function for their corresponding inputs??
I took another look at the schematic for the VCO output
daughterboard. I'm thinking that it taps the sawtooth going into the
CMOS counter, and the first op-amp servers as a follower. Where does
the 560K with the down-pointing arrow go?? Then I'm thinking that a
square wave is generated by the massive gain (2M/2K) of the second op
amp by driving it into the rails. Although, afaik, a TL072, unlike
the LM358, doesn't like going to rails. I'm not sure about positive
outputs, but the common mode voltage getting too close to the
negative rail of a TL072 can cause phase inversion and latch up. I
apologize if I sound overly critical, but for educational purposes,
I'm not sure why another comparator circuit was not used.
>I must say that this filter is very deep. Sound destruction and such
>are easy to do, as well as some very subtle effects. Small changes
>in bandpass and frequency can lead to very different sounds. I made
>some sound samples -- they should be on my site next week, after my
>web guy catches up w/ all the new stuff...