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 re: Fatman Anti-phase-lock modification linearity problem 
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Joined: Wed Jan 01, 2014 1:36 pm
Posts: 61
Location: Toronto
Post re: Fatman Anti-phase-lock modification linearity problem
I have tried several times to get this to work but always end up with the same problem.

I can tune the vco for the top and bottom note fine but all the notes in between are wrong. seems like a linearity problem.

any thoughts?

Billb


in case I missed something obvious, the components I changed were
33k -> 10 meg
22k -> 220k
.01u to 1nf
100k pot to 1 meg pot
lm op amp to TL074 (dont have an 084)


PAiA 9308 FatMan modifications
VCO Anti-phase-lock modification, for long, slow beats between the vcos (minimizes the tendency for them to lock together and sound as one, plus fixes undesirable pitch changes with adjustment of Glide (both VCOs) and VCO#1 Offset (VCO2). Lee Diode Mod, complete


Thu Apr 24, 2014 9:37 am
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 726
Post Re: re: Fatman Anti-phase-lock modification linearity problem
Here's a little different way of doing the tuning that I use here.:

Before calibrating. Set the #1 offset to minimum (to be very different from VCO2 because when they are very close, one might be pulling towards the other - like when they are set for low beat frequencies and they phase lock).

Press the lowest C and adjust the Pitch control to so the sound is in tune with the MIDI controller's if you need the reference. (I usually just set the pitch to about a 9:00 setting without any reference and it's fairly easy to pick out the octaves on the subsequent adjustments).

Press the highest C and adjust the DAC Tune for a pitch four octaves higher.

Press the next C down and adjust Oct 3 for a pitch three octaves higher.

Press the next C down and adjust Oct 2 for a pitch two octaves higher.

Press the next C down and adjust Oct 1 for a pitch one octave higher.

Now, when you press the lowest C, it's pitch will be different and the Pitch control should be adjusted to bring it back to the original pitch.

Repeat the process beginning with the adjustment of the DAC Tune and after two or three iterations, no further adjustment will be necessary.

Tuning may need to be optimized by repeatedly playing a C, C#, D, and D# one after the other listening for the best relationship while tweaking the DAC Tune one way or the other slightly.

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Scott Lee
scott@paia.com


Thu Apr 24, 2014 4:57 pm
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Joined: Wed Jan 01, 2014 1:36 pm
Posts: 61
Location: Toronto
Post Re: re: Fatman Anti-phase-lock modification linearity problem
my non modified oscillators are in tune, its the anti phase lock modified one that is wonky.

are the "standard" oscillators incompatible with the anti phase lock oscillators?

Billb


Thu Apr 24, 2014 5:15 pm
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 726
Post Re: re: Fatman Anti-phase-lock modification linearity problem
There might be some noise mixing with the pitch cv and it is throwing off the setting for the added circuitry.

Maybe just selecting a different ground node for the wire to the added circuitry will correct the response.

Notice on the FatMan schematic, the VCOs get their pitch cv from R34-2 while the pitch CV output is full-range, right off the de-multiplexer s/h.

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Scott Lee
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Fri Apr 25, 2014 10:32 am
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