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

[Mike Bryant]

Actually on a pipe organ, the phase rarely matters as all the octave spaced pipes are only in perfect phase sync at 21 degC.  As they are such different sizes at any other temperature there is a difference in frequency variation across each pipe, which is why some organs can sound quite crap in the morning, sort of ok for afternoon weddings and absolutely glorious in the late evening.
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From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Tony Allgood via Synth-diy <synth-diy at synth-diy.org>
Sent: 01 February 2024 10:35
To: Synth DIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Now tube type (6SN7) flip-flop circuit.. Follow up...

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<http://www.oakleysound.com>

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