[sdiy] Now tube type (6SN7) flip-flop circuit.. Follow up...

[Tom Wiltshire]

> On 31 Jan 2024, at 22:02, Donald Tillman <don at till.com> wrote:
> 
> On Jan 31, 2024, at 1:31 PM, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
>> 
>> What do you think about the actual phasings of all the FF’s square wave output against each others?
> 
> Doesn't matter.
> 
> (?!?)
> 
> In a set of octave square waves there are no harmonic or fundamental frequencies in common, so there will be no summing or cancellation happening.

If the waveforms are reduced to pulses, then there will be even harmonics as well, so there will be some summing. But I agree with Don, I don't think it matters.

The phase relationship between the different outputs is fixed, so as long as you make sure that you use the same output from each of your flip-flops (e.g. don't use Q from one and then !Q from the next one!) then it'll be the same as your old Hammond.

I think your idea of doing this on a PIC is viable. It's a set of monophonic bass pedals. The pitches are low, so a divider-based pitch generation should be accurate (errors are worse for higher frequencies with that method) and the PIC has timer/counters that could do that. It's a DCO without the difficult ramp integrator part! You only need accurate semitone pitches, so you don't need to worry about digital stepping. As long as the steps line up with your required semitones, you'd be fine with only 12 steps per octave. So there's no worrying about pitch stepping between divider values being audible required here. The final output is a simple binary count, of which you need five bits.
That's your basic pitch and square waves done, on a single chip. Can you get it to run a MIDI input as well? Probably, if you've got a prescaler+timer doing the actual frequency generation so that the uP itself doesn't have to.

Since one square wave sounds very much like the next square wave, irrespective of whether it was generated by tubes or a uP, I would expect this to give a good sonic result. The sound of these pedals is going to be mostly due to those filters and any subsequent stages.