[sdiy] Now tube type (6SN7) flip-flop circuit.. Thanks !

[Jean-Pierre Desrochers]

For those who would like to hear what an Hammond RT2 pedal Solo board sounds
like :

 

https://www.youtube.com/watch?v=q7M6_kO5S4k
<https://www.youtube.com/watch?v=q7M6_kO5S4k&t=421s> &t=421s

 

Since this is a short demo, the sound is very flat and straight.

My project will use a digital reverb module to add some ‘church’ ambience !

 

Thanks for all your comments.

As usual this will clarify things and help me a lot !

And.. yes this will be a MIDI controlled Pedal Solo generator.

 

Cheers !

 

De : Synth-diy <synth-diy-bounces at synth-diy.org> De la part de Jean-Pierre
Desrochers
Envoyé : 31 janvier 2024 16:31
À : synth-diy at synth-diy.org
Objet : [sdiy] Now tube type (6SN7) flip-flop circuit.. Follow up...

 

I  asked this question about flip-flops because I have a new project in
mind..

I once had a vintage Hammond RT2 organ with a wide church type pedal board.

This pedal board sounded amazingly beautifull !

This pedal board sound was produced by a bunch of successive flip-flops made
out of 6SN7 triode tubes

In a chain distribution.. Producing all the needed pipes sounds (1’, 2’, 4’,
8’, 16’, 32’).
I thought I could reproduce these sounds using a simple CD4040 counter,

Or best, a PIC micro that would have MIDI input and take care of all the
push buttons/leds

That select the actual footages, AND generate all the successive square
waves (yes, these flip-flops have roughly shaped square waves output)
to be filtered using Hammond’s filters design.
Have a look at the below ‘Hammond RT2 PedaL Solo’ schematic ..

As you will see the actual waveforms kept to be filtered are derivated going
down short pulses

>From each flip-flops output like this :



 

These pulse are filtered by successive low pass filters and mixed together
to the final output.

But to be a good Hammond pedal simulation I need to know the actual phase of
each flip-flop outputs

Against each others..

Are these FF’s changing states on each preceding FF on going down or going
up situation ?

I did not measure these waveforms in the past BUT I do know
each FF change state on the ‘going down’ pulse of its pre-driver.

I think using all the 6SN7 tubes output (always inverting their inputs)

I could figure out all the waveforms in this schematic but I’m not sure at
all..

 

BTW, I made a LTSpice simulation using this schematic with all the same
components
including all the necessary 6SN7 (and the two 6J5’s V1 & V6)

And had very bad results.. noisy unreadable waveforms on many places..

 

What do you think about the actual phasings of all the FF’s square wave
output against each others ?

 

JP

 



 

De : Synth-diy <synth-diy-bounces at synth-diy.org
<mailto:synth-diy-bounces at synth-diy.org> > De la part de Jean-Pierre
Desrochers
Envoyé : 31 janvier 2024 10:43
À : synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org> 
Objet : [sdiy] Transistor type flip-flop circuit.. What makes the 'power up'
state of it ?

 

Hi list,

I have a question about the behaviour of transistor type flip-flop circuit

When the DC power is applied to it..

The following schematic of Boss CE-2 pedal shows the flip-flop at the bottom
right.

Why when the DC power is applied :  collector of Q6 goes high (to make the
pedal in the ‘no effect’)

And it’s not Q7 that goes this way instead ?

I know that C23 (.01uf) pull down the trigger input when DC is applied
to put the pedal in the ‘no effect’ position, but why is Q6 selected ?

This is a ‘balanced’ flip flop circuit and both sides should behaves the
same

But some kind of selection is done here.

 

Could someone explain that behaviour ?

 



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