[sdiy] Transistor type flip-flop circuit.. What makes the 'power up' state of it ?

[Tom Wiltshire]

It's not a reliable feature, just a side effect of whatever values your particular unit has. People complain about it all the time. For example:

https://www.harmonycentral.com/forums/topic/1591085-boss-pedals-way-to-defeat-auto-on-when-turning-power-on/ <https://www.harmonycentral.com/forums/topic/1591085-boss-pedals-way-to-defeat-auto-on-when-turning-power-on/>

OP in this thread has two Boss pedals that power up to On and two that power up to Off.

There is plenty of stuff online about how to modify the flip-flop circuit to ensure it does come up in one state or the other though, if you want to modify it. Basically, you need to introduce some inequality that's bigger than the "naturally occurring" inequalities found due to component tolerances.

HTH,
Tom

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



> On 31 Jan 2024, at 15:43, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
> 
> 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 ?
>  
> <image001.jpg>
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