I’m very new to all this so please be gentle. I built the SSO today and got everything working (almost the first time). Really cool! I had a lot of fun and I’m pretty pleased that I got it right despite using a different transistor (BC337) etc.
What I’d like to do next is add a gate input so I can turn it on and off with my SQ-1. I’m not expecting it to be super musical but I feel like this should be quite possible.
My idea was to add another transistor after the output and connect the gate input to the base. This … doesn’t seem to “work” or, at least, it doesn’t do what I hoped it might. I will go recheck what I’ve done but is this even vaguely a feasible approach? I tried a BC557 and I had a voltage divider to drop the gate input from the SQ1 from 10V to 5V.
Thanks for reading and even more thanks for any help anyone can throw my way. I’m having fun messing around whether I get anywhere or not.
Edit: thought immediately after posting - would it make sense to connect the transistor between the output and ground?
If you upload a drawing showing the way you modified the original schematic, that will make it easier to see what it is you are experimenting with for people reading your question.
Hi mabu . welcome to our space , no need to worry we are of all skill levels here . dam you got the SSO working right off thats a good start , there are a few of us including me that had a heck of a time with that thing .
Thanks! No doubt it’s beginners luck that I got this far…
I’m attaching a draw of what I’ve tried to do. I’ve not shown the SSO circuit itself because that is actually working but let me know if that would be helpful. I strongly suspect that what I’m aiming for here is just me thinking about the problem completely wrong.
In my diagram the orange parts are what I’ve added; everything else was working. My thinking was:
the SQ-1 is 10V by default and 0V when playing a note (this can be reversed but it seems reasonable) - so my thinking was that when nothing is plugged in it should behave as it was, when there’s 10V it should mute
I’ve added the two 1k resistors as a voltage divider so I’m expecting 5V at the base of the transistor (I should measure this, didn’t do that)
I’m not at all sure that it’s possible to use a transistor like this but the idea is that when there’s 0V at the base then whatever voltage there is at the collector will also be a the emitter and then when there’s 5V at the base then the transistor is like an open switch and there will be no audio. I’m thinking this was wrong.
I’m not 100% sure I’ve drawn the transistor the right way around - I did try it in both orientations but neither did what I wanted.
What actually happened: I didn’t get nothing at all but I didn’t get what I hoped for either. I got something like noise for every gate which is interesting but I guess I broke the sound output itself.
The more I think about it the more I’m thinking audio is not a static DC voltage and the idea of ‘letting it through’ a transistor is wrong. Would it make more sense to have something like this second drawing? I’d need a different transistor here to short the audio output to ground (or let it through) depending on the gate input.
In your first diagram, you’ve drawn an NPN transistor but the BC557 is PNP. BC547 is NPN.
A voltage divider doesn’t work like that. If you want to reduce 10 V to 5 V apply it to the top of one resistor, the bottom connects to the top of another (equal) resistor, and the bottom of that is ground; take the 5 V from the junction of the resistors.
That sounds perfect but TBH “Painfully Simple” is probably still a stretch for me - it’s basically what I was going for though. I’ll see if I can grab a BC107 on my way home and try it later.
Thanks so much everyone. I got it working with a BC547! I didn’t manage to get any BC107s yet so, per the link, there’s quite a loud pop for each “on step” from the SQ-1 (which I guess is expected).
I will order in some BC107s to try too but does it make any sense at all to try a capacitor before the base of the BC547 so that it opens and closes more slowly?
You’ll need a resistor in series with the base, and a cap from the base to ground.
This way, as the cap charges thru the resistor, the transistor will conduct progressively more and more.
Then you probably need a way to discharge rapidly that cap when the gate goes low.
Maybe a diode in series with some current limiting small resistor in parallel to the cap ?
As for the values, well, I’m still learning too and can’t enlighten you here…
It depends what you call ‘reasonable’. In your sketch what you are doing is shorting the audio to gnd, which stops it from reaching the 3.5 mm socket. But that is quite a harsh way of stopping a signal. You could alternatively choose to disconnect the signal from the 3.5 mm socket by inserting an analog switch (or a single FET) like the ones you can find in a CD4066 between the SSO’s output and the 3.5 mm socket. This resembles your first idea, but will probably work better because the analog switch can switch an AC signal and is easier to control by the signal on the gate input.
