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

[Tom Wiltshire]

One advantage of doing it in something like a PIC using a counter would be that you get this synchronisation for free. All the edges line up when the counter wraps back to 00000. Or if you *really* need rising edges, count down and wrap back to 11111.

It's an incrementing one-byte counter and a write to a port. That part is dead simple.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 1 Feb 2024, at 10:35, Tony Allgood via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> If you are creating pulse waves, or a pulse like wave, from the output of the flip flop, it is important to consider the phase relationship of the flip-flop outputs all together. Phase matters not if you listen to these derived pulse outputs individually, but on an organ, or string machine, octaves are mixed together, either by playing octaves on the keyboard or using the footage mixers. If you don't have the correct phase relationship the resultant mix will sound weak.
> 
> Using a cascade of flip-flops to divide down will result in a set of square waves. If the pulse is being created by a standard differentiator, a high pass CR circuit, then it is the position in time of the leading edge of the output square wave that is important. Those leading edges must line up, so that the leading edge of the lowest frequency must be synchronised with all the others. That is, when the lowest octave square wave goes up, then so must all the others.
> 
> Note that the propagation delay within the chip itself is minimal and can be ignored.
> 
> How do I know this? I designed a SAJ110 octave divider replacement board for string machines. The scope outputs looked perfect. But it sounded like pants because every other octave when played together destructively interfered and sounded wrong. It used the 4520 to divide the octaves.
> 
> The problem was solved when I ensured the leading edges of all the were synchronised. I could have done this with additional invertors, but it was smaller to do it with a couple more 4520 stages. Now when you mixed octaves the sound become louder.
> 
> At this point I should present a diagram to show this. But I've lost my original sketches I did on graph paper to show how the waveforms add together. If I find it I'll post it.
> 
> Tony
> 
> www.oakleysound.com
> 
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