slacktave - truth table

[egasimus]

Can anyone repost the "Truth Table" schematic by @frequencycentral? It's an octave down/guitar synth closely based on the Slacktave. Found it just the other day, and now the link is dead. Wish I had saved it.

On a side note, lotsa cool stuff in @frequencycentral's photobucket.

[frequencycentral]

I see the Truth Table schematic in that thread - maybe Photobucket was down when you looked?

http://www.diystompboxes.com/smfforum/index.php?topic=76695.msg627710#msg627710

Lots of other interesting ideas there too.

I never followed through on that (re) design though.........

[egasimus]

Great stuff, thanks a million.

That design you never followed through, you mean the square/tri/saw waveshaper?

[frequencycentral]

I vaguely remember breadboarding part of the whole circuit......but had no concrete results, I got sidetracked into another project........

[egasimus]

Well, I tried simulating it in Paul Falstad's sim, and it didn't seem to work. I've figured out a pretty nice way to shape a square into a ramp/saw though.

However, I have read that the Slacktave seems to have a limited input range, and, outside it, wouldn't be the perfect square wave source for the guitar/bass monster synth I'm thinking about. That's really sad, it sounds great in its own right. I wish it would cover the full range of guitar and bass guitar, or at least have a switch to choose either range. Compression would probably help, but, the craziest thing I've thought of is a wide VC band-pass at the input, which would be controlled by a frequency-to-voltage converter (although I can't seem to come across the schematic for such a converter when I need it). But trying that out is way above my level for now.

Any ideas on how to widen the input range?

[slacker]

The slacktave should work over the whole guitar fretboard. It's difficult to make something so simple that will track bass well though.

[egasimus]

Hmm, that's both good and bad news. I'm really keen on making a synth from this, and will probably soon build a Slacktave and start experimenting. Do you think that using a schmitt trigger instead of a comparator would make the tracking any better, though? I was really hoping to get this thing going with bass.

[Skrogh]

A schmitt trigger might work better, but you could also try the pitch-detector form the OC2. Tracks pretty well for me on bass, as long as I don't need long sustained notes.

[egasimus]

Hmm, I'd need some help with that. I've looked at the OC-2 schematic before, too, and I can't make head or tail of it, really.

[slacker]

A Schmitt trigger won't help the tracking, the thing limiting the tracking performance is the filtering before the comparator. The filtering just about works over the whole range of the guitar to make it work with bass you could try doubling the size of the 100n and 10n caps in the filter that will lower the overall frequency response.

[Skrogh]

Here is my explanation of the OC-2:



1: Input-buffer and filtering

2: Phase-shifter for first octave down
3: Lowpass-filter for 1 down

4: Phase-shifter for second octave down
5: Lowpass-filter for 2 down

6: Output-buffer

7: Filter before pitch-tracker
8: Pitch-tracker (consists of positive and negative envelope-follower, comparators and a J-flipflop. Works as a Schmitt-trigger, with the envelope as its "boundaries")


If you are going to use this nr. 7 and 8 is what you need. Tell me if you need more help

[egasimus]

Thanks for the explanation, sure does clean things up. I can understand how this works I intend to extensively experiment with different guitar to square to multiplier to saw configurations and see if I come up with anything usable.

But, meanwhile, I wanna build myself a Truth Table, and I want it to have some sort of low pass filter, too. I've added the low pass filter from the Drone Lab (http://casperelectronics.com/finished-pieces/drone-lab/) after the mixing resistors and before the final opamp, too, but I'm not really sure what I'm doing. Any advice on whether this is a viable configuration? And, if not, I'm looking for a simple low pass with variable cutoff and resonance.

[slacker]

That should work fine I'd just replace the last opamp with the filter. You might need to increase the size of the mixing resistors or decrease the 1k to ground on the front of the filter to get it to work properly.