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

[Jean-Pierre Desrochers]

Tony,

Very good and informative details here you gave us all..

I thought about this 'in phase' leading edges importance to get all the

Generated footages alligned and mixable but I was not sure
looking at the Hammond schematic and the  flip-flop stages

Here is why:

 

If you look at each freq divider sections you will notice

They are all made out of a pre-driver/inverter that produce
a going down pulse to trigger its associate FF and make it trip.
(They are : V3-pin 2, V3-pin 5, V6-pin 3, V8-pin 2 and V8-pin 5)

Then you have their triggered FF itself using 2 stages of 6SN7.

 

The problem I have is the following :

For example if you look at the 2nd freq divider,

To produce a going down pulse at V3-pin 5 you need

A going up pulse generated by the preceding FF stage output.. here V4-pin2.
Ok.

But to make all the following freq dividers ‘in phase’ each FF’s

should produce a going up pulse at their outputs to drive the next connected
pre-driver/inverter..

(FF’s outputs are : V5-pin2, V7-pin 5,  V9-pin 2 and
 oupss !!! they chose
V10-pin 2 instead of  V10-pin 5 !!!) Why ???

Despite the fact Hammond chose pin2 instead of pin5 of V10 on the last FF,

And following my first interrogation on transistor FF’s on how they start at
first

How can I understand what makes all these freq dividers allign ?

To make all of them alligned each divider section must :

** input : receive a going up pulse

** output : generate a going up pulse too !! (But how Hammond’s engineers
could know what section of their FF will generate the right pulse phase ??)

 

These were and still are my interrogations


 

BTW, My PIC project won’t have to deal with these Hammond ‘original FF’s
behaviours’

But will simply generate in phase pulses who will be passed thru the same HP
filters Hammond used in this schematic..

 



 

> -----Message d'origine-----

> De : Synth-diy <synth-diy-bounces at synth-diy.org> De la part de Tony
Allgood

> via Synth-diy

> Envoyé : 1 février 2024 05:36

> À : Synth DIY <synth-diy at synth-diy.org>

> Objet : 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

> 

>  <http://www.oakleysound.com> www.oakleysound.com

> 

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