Anwsers]

[Harry Bissell]

Hi Jeremy:

Jeremy <jmartin at ixks.com> wrote:
I have very little electronical knowledge, due to my lack of experience
with it, although I've been interested in electronically generated
sound/music for years now, I just recently scraped up the $ to buy a
FatMan. I know very little synth acronyms, or at least, cannot seem to
remember what they stand for as I have not heard them repeated enough,
although I've read what they stand for before. Anyway, I would appreciate
it if some of you kind hearted folks would help explain this to me.

>I was reading the manual during class a while ago, kinda bored with the 
>teacher lecture I guess, and the manual says that the Fatman's VCF is a 
>multimode. So I went through my notes and used this info for a mod. The 
>Fatman's VCF is not only a LPF but a BPF as well! not only that but the mod 
>was done in only 5 min. 

1) I know VCF is voltage controled filter, and that it is what is applied
to the sound to filter out different frequency ranges, right? So what is a
"multimode" VCF, in the first place? 

>Voltage control sets the frequency where the filter begins to cut or boost
frequencies. LPF (Low Pass Filter) cuts everything above the filter "Cutoff
Frequency" and passes everything lower (Low PASS, capiche??)
High Pass Filter (HPF) does the opposite. BPF (Band Pass Filter) cuts out all
frequencies above and below a (usually) narrow band around the "Center
Frequency" (was cutoff in HPF and LPF) Notch cuts out a narrow band of
frequencies around the center frequency, passing everything higher and lower.



2) LPF and BPF? I think this has to do with filtering out frequencies above
a certain frequency, and filtering out frequencies BELOW a certain
frequency, but I'm not sure. Am I right? Which is which?

>First remove the positive side of C23 and attach that to the center pole
of a 
>SPDT switch. Then run a wire from the the board where you just removed C23
to 
>one of the other poles on the switch. Connect a lead from pin 8 of Ic17 to
the 
>last remaning pole on the switch, and now you have a choice of either LPF or 
>BPF mode! 
 
3) What does SPDT stand for in an SPDT switch? Is that something that they
would have at Radioshack, or do I need to order it from Mouser? Do I just
waltz in the door, and say, "hey, I need an SPDT switch"? 

>Single Pole - Double Throw. Yes Radio shack has them. Get a miniature or
subminiature Toggle switch.

4) I also purchased the machined face palte thing for the FatMan. Once I
finish this mod, where would I attach the newly integrated switch? Just
leave it loose someplace, or is there a better way to more securely attach
it to the metal face thing?

> You find a blank spot where ther is room, and drill a hole in the panel. It
should be somewhere that makes sense (like near the filter controls.) Its a
good idea not to run wht wires too far... Try the mod first and if you like
it, then drill the hole. IMHO the LPF is the most important thing to have, but
BPF is the 2nd important thing. I'd do the mod :-) Harry

Thanks! I apologize for my current ignorance in these matters. :) 

> Get the search archive utility (look for the Synth-DIY Grey Pages) and
search on some of these topics. They have been gone over B4 and sometimes in
great detail. Then if you have more questions e-mail me.

___________________________________________________________________________

      Jeremy Martin - jmartin at ixks.com ; IXKS, Inc. - Internet Kansas
                    785.842.9996 - http://www.ixks.com
                  P. O. Box 1761, Lawrence Kansas, 66044
____________________________________________________________________________


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