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 Forum index » DIY Hardware and Software » PAIA Equipment
Fatman FM.
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reve



Joined: Feb 23, 2008
Posts: 147
Location: USA

PostPosted: Sun Aug 07, 2011 12:25 am    Post subject: Fatman FM. Reply with quote  Mark this post and the followings unread

Hey guys.

So after a couple years of modular building, I revisited the piece that started me down this dirty, dirty road of SDIY -- the PAIA Fatman. I did the more obvious mods of adding sync, isolating the VCOs, and doing the bandpass switch thing.

I started figuring out what additional circuitry would be required for PWM, subosc, etc., but after seeing the guy who replaced the 8051 with an Arduino (Fatduino) I realized that I was going to wind up with an MS-20 style semi-patchable thing.

Anyway, I'm curious if anyone has implemented some sort of rudimentary FM in the fatman? I assume since the oscillator swings between -12 and -4 v I'm going to have to bias it up by 8v? Anyone try this yet?

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JovianPyx



Joined: Nov 20, 2007
Posts: 1247
Location: West Red Spot, Jupiter
Audio files: 161

PostPosted: Thu Oct 27, 2011 2:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

The PAiA Fatman pitch control voltage tops out at a little over 6 volts coming from the microcontroller pitch voltage generator. It should not go below zero volts. So yes, you'd have to add level shifting by 12 volts and then also attenuation. I don't see why the voltage couldn't go all the way to 8, perhaps it can at the VCO CV input.

I haven't done it, but I think it's worth a shot.

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patrickvf1976



Joined: Aug 08, 2011
Posts: 182
Location: Gig Harbor

PostPosted: Thu Nov 24, 2011 1:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

I was thinking that since the fatman uses two 555 ICs, you could simply cross modulate them by hooking one 555's output to the cv in of the other 555. At least that's what I did when experimenting with 555 ICs, but I'll have to take a look at the citcuit since it could be a totally different configuration.
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JovianPyx



Joined: Nov 20, 2007
Posts: 1247
Location: West Red Spot, Jupiter
Audio files: 161

PostPosted: Thu Nov 24, 2011 1:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just don't try to use the 555 timer's "FM input". It's not really FM in that it doesn't tolerate and FM input signal at a higher frequency than the VCO frequency. I tried that - and got crap. The reason is that it changes the threshold at which the oscillator resets. It does NOT change the slope of the wave form as it should it real FM.

What you propose sounds like it would work, using the actual pitch CV input. Since it's linear you should get FM. Not sure what it will sound like tho. I've messed with FM in an FPGA synth, but that was based on sine wave operators, not sawtooth. With saw, you start out with lots of harmonics anyway. With sine you start out with only one.

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FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.
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BTW, Do these genes make my ass look fat?
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patrickvf1976



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Location: Gig Harbor

PostPosted: Thu Nov 24, 2011 4:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

hmm.. I think if you take the signal directlly from one of the 555's, it should be a pulse of squarewave singnal. you propably could condition it with a simple RC lowpass filter, to make it more sine like., then use that for a modulation source. I think you should be able to do the same with the other 555 and use that as the audio source. Haven't tried it that way yet, it might or may not work.
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