Transistor position to turn an effect on and off

[frets]

Hey Doods,
I’ve been meaning to ask this question; however, it’s difficult to convey.  I think I’ve mentioned doing mini pcb push-pull face boards for onboard guitar effects. The issue I’m having is the positioning of the NPN transistor in the circuit to turn the effect on and off simultaneously when the push pull is pulled up.  In other words, power comes into the effect when the push pull is pulled up, power goes off when the push pull is down.  I’m trying to create a push pull that does tone in the down position and effect in the up position.  I know you all like diagrams but this AutoCad file is double sided and I don’t think would be helpful.
Again, the basic question is power comes into the effect from the 9 volt simultaneously with the pull up, off with the push down. How would the switching transistor be positioned to activate the effect in the up position? I don’t “get” the concept of a switching transistor with the on/off on a push pull.   I know the transistor has to be positioned at the beginning of the circuit; but, how can the current simultaneously turn on and off with the transistor and a dpdt.  I’m having difficulty explaining this conundrum. I  realize this is one of my odder questions.

[thetragichero]

how're you planning to power the transistor that does the switching?

[thetragichero]

the other bugaboo is that you'll want the effect powered before putting it in the signal path, otherwise the volume will drop and then rise and the filter capacitor(s) charge
easiest thing to do is just wire the push/pull as true bypass (assuming you don't need an led to indicate it's on: pot being pulled up should be enough of an indication)

[thetragichero]

if you're concerned about battery draining, a simple trs output jack on the guitar (issues of the normal ts) will go a long way. connect battery ground to the ring terminal and it will be disconnected when the cable is removed

[sumgai]

frets,



Let me see if I've got this right - you want to apply power to the transistor that's doing the amplification job when the p/p is up, and turn off that power when the p/p is down, is that correct? That's a no-brainer, to be sure.  (This is an assumption, because your title does imply that you want to use a transistor as power control relay, which is also a no-brainer.)

Sadly for you, thetragichero is correct - you should be using a true bypass, or else the circuit loading will be highly noticeable when the p/p is down (whether or not it's powered up at that point).  However, a true bypass and a separate power control requires a 3PDT switch, as found in many better-designed stompbox pedals.  In light of adhering to the K.I.S.S. principle, my suggestion would be to leave the effect powered up whenever the MONO (standard) cable's plug is inserted into the output jack.... said jack being a TRS type, wired to act as a switch for the battery's negative lead.  Careful attention to component choices can give you a design with an easy 100 hours of operation before the battery can't do the job any longer.  (Probably 70-80 hours for a rechargeable type.)  That gives you an easy path to a true bypass, and your signal when the p/p is down should be "as desired", and not some funky dark tone.

Wait! Wait a minute!!   Did I read this correctly:

Nov 14, 2020 12:16:07 GMT -5 frets said:

I’m trying to create a push pull that does tone in the down position and effect in the up position.  I know you all like diagrams but this AutoCad file is double sided and I don’t think would be helpful.

Aside from the power and loading issues you have to deal with, are you also intending to use the "tone" pot as the "effects" control when the p/p is up?  Hoo boy, you're not asking for much here, are ya?

Please confirm that last, or correct it as needed.  Or post an image-capture of your ACAD file.  (You could just attach the file, but I'd be one of the very few who could see it and make sense of it - better to let everyone have a look-see at the thing.)

HTH




sumgai

[frets]

Trag and Sumgai,

Ashcatit had recommended the Jack solution a while back. But I don’t want to do that. It’s a challenge trying to do it my way. I guess I need to fix up the file so you guys can see both sides.
And I am confirming that I am trying to attempt a Volume/Effect and a Tone/Effect. Giving two push pulls with a passive function and an active function. On push pulls. I think it can be done. Somehow. I will work on the file. Thanks guys🦃🦃 Thanksgiving is coming!!

[Yogi B]

Am I right in thinking that your after some kind of variation on "Millennium Bypass"?

It should be noted that is usually only used to switch power to the LED, not the entire effect circuit for the reason outlined by thetragichero. But using only battery power (DC) you should be able to reduce or eliminate the filter cap, but going too far could introduce popping when switching due to inrush current. And while power-filtering caps are tend to be the largest value in an effect circuit (thus are responsible for the largest proportion of inrush current) coupling caps will also need to charge to their relevant DC offsets before an effect is fully functional.

[JohnH]

I think its very difficult to switch power to a circuit at the same time as actually engaging its effect - and I have tried. There's just too much of a surge, at an instant in time when the circuit is not yet in equilibrium, causing a 'thump' or a 'crack' or other nastiness. Need to find a way to let the circuit be fully powered, before switching signal through it. Some delay is needed between circuit getting power and signal coming out of it. Switching off is no problem, just remove power and let a cap on the power supply drain gently over a short time.

[frets]

The Millennium Bypass is what I was basing this idea off of. But it is a bit complicated for me in the translation to a faceplate push pull. I did foresee the switch pop problem, I did not think of the need for an upfront delay of some type. I guess the idea of “why” I want to do this is a variable. The reason is: 1. It’s a challenge; and 2. I’d put them in the guitars I build. A huge variable holding me back is my lack of any electrical engineering knowledge. Given this looks to be more complex than I anticipated, I do need to diagram the circuit as it would appear on the actual board.

I have guys repeatedly ask me about on board effects. I think that is interesting given the pedal market. Typical answer to that question is “a delay or distortion are basically the same and it would be nice to have them in the guitar.” They don’t seem to be too interested in the features offered by pedals. I find this weird.

[thetragichero]

very weird, part of the appeal of pedals is how modular they are (for most stuff the reverb goes last but for shoegaze-type music putting it before distortion sounds aces)

remember just because something is a challenge doesn't mean it's worth doing. normal true bypass is nice and easy and with all the other "moving" parts is nice to not have to troubleshoot a @$_#& switching circuit. i also don't know if I'd want to lose my tone control just to use an onboard effect (although for the record mine almost always stay on 10 like my volumes because more louder is more better)

[sumgai]

Nov 14, 2020 18:31:21 GMT -5 thetragichero said:

I also don't know if I'd want to lose my tone control just to use an onboard effect....

It's worse. What if you have the Tone turned down about half-way, and you trade it out for the effect control?

First, the signal is suddenly opened up to full treble. Second, the effect's "control" is sitting at half-way - is that where it was desired? What if it was last used at full-blast, and such was expected again, when next engaged....

frets, I hate to say it, but while the idea of simplicity is attractive, I think this scheme is going to be a bit too simple. Take a poll of your customers, and see just how much control they're willing to give up, in order to "sound cool" while making heads turn because the guitar looks stock.

However, if you were to instead use a dual concentric pot with a p/p, that might be an idea worth fleshing out.

HTH




sumgai

[newey]

Nov 14, 2020 21:28:07 GMT -5 sumgai said:

However, if you were to instead use a dual concentric pot with a p/p, that might be an idea worth fleshing out.

I know someone posted a dual-gang pot with a P/P. Have we seen a concentric P/P?

[Yogi B]

Nov 15, 2020 7:57:40 GMT -5 newey said:

Have we seen a concentric P/P?

Yup, but they're on the pricey side.

[thetragichero]

dang it better play guitar for me at that price

was chatting with my dad Friday about amp/effects in guitars and the thing that's always stopped me is the controls start to resemble one of those ussr guitars (which i do happen to like). i wonder if a little trap door cavity for effects parameters wouldn't go a long way to keeping the external controls tidy

[ashcatlt]

So anyway, I guess the transistor sits with the collector and emitter in series with the battery hot on its way to wherever that goes in the actual circuit, and you use the appropriate type of transistor such that pulling the base up to a positive voltage opens it up...or I guess closes the circuit...brings the collector>emitter resistance as low as it goes. To avoid too much of a pop, you could have a cap from base to ground to slow the whole switching action down, and for extra protection probably another BAC across the effect’s power supply. With a battery you usually don’t actually need any filtering there, but we want it to slowly ramp up in power rather than just banging up all at once. I suppose the transistor could interrupt either end of the battery really, but...

[frets]

Thanks Ash,
I should have a diagram by Thanksgiving.

[ashcatlt]

I have to say I don’t think it’s a great idea either, but I noticed this thread had gone quite a ways without actually answering the relatively simple question. I don’t have much practical experience with transistors, but I get the theory, and I’m pretty sure it’ll work.

[thetragichero]

oh you do-gooder, you

[frets]

I plan on having the tone in the down position and when the effect is turned on (the pull up) a tone cap will be present in the circuit. C’mon, it’s a fun experiment. We have to have some out of the box projects and discussions.

[sumgai]

Nov 16, 2020 1:19:09 GMT -5 frets said:

I plan on having the tone in the down position and when the effect is turned on (the pull up) a tone cap will be present in the circuit.

OK, and just how much resistance were you planning interjecting into that "tone cap will be present" sleight-of-hand? To be sure, you are now switching not just a control module in or out, but you're attempting to ameliorate the tonality by inserting yet more components in place of what was dropped, as part of the "switch up" operation. I think ChrisK would approve of this Zen thought: Complications are.  (Though to be fair, I can see where you'd just swap the Tone pot's resistance for a fixed resistor value, one that sounds good with the effect turned on.  Or better yet, a mini trim pot - set it and forget it.  But that adds yet more complexity in that another switch pole will be needed.)

C’mon, it’s a fun experiment. We have to have some out of the box projects and discussions.

I'll agree, experiments sometimes lead to potential income sources, but they nearly always lead to more knowledge and a deeper understanding of, and appreciation for the art. Fortunately, discussions don't cost nearly so money out of the wallet as actual bench time.


But my major beef here is logic/electronic problems, it's the usability factor.  I repeat: if the effect is used at 75% rotation at one point in time, and the next time it's engaged the pot has been rotated because the Tone value had been changed, it won't be the desired 75%, but some other value.  The question is, will the player like that?  Will he/she have to rotate the knob back to what he/she wants, as they pull up the knob?   (It shouldn't seem so strange that someone who has coded both front- and back-ends to various programs will tend to think in terms of user friendliness.  User-hostile programs can be the most productive things on the planet, but they tend to not get sold if the user spends more time cursing them than getting any work done.)


And ash's note is correct, we really haven't answered the OP question, about turning on or off the power supply to the transistor.  I can handle that, as I'm sure others can as well, but I'd like a good reason to do so, something more than "it's an experiment, just for grins and giggles".  And for the record, the so-called Millennium Bypass was intended to power an indicator lamp, not the actual active component(s) in the circuit .  In point of fact, it will still exhibit some current draw from the battery, just not as much.  This is evidenced by the use of pull-up or pull-down resistors - they simply direct power to a destination, which might have the effect of enabling/disabling an active component, but some current draw is still going on.  IOW, you don't want to leave the battery in-circuit when the player puts the instrument down for the night, the battery will still continue to discharge to an unusable level.  Chalk it up to "Best Practices" and all that.

HTH





sumgai

[thetragichero]

i was mainly joking on ash for answering the question
and i hope i don't come off as discouraging, just sort of a feasibility check and warning about rabbit holes that may not be fruitful (sort of like me wanting to make a tube-based, sweepable mid control on an amp: fairly easy with a few op amps but mapping that over to tubes could easily double the tube count. suppose that's why i was having such a hard time googling for tube-based gyrator tone controls)
i have also had the experience of discussing with a potential client for a custom stomp box and the difference between what he though he wanted (which would've been a TON of knobs and switches and an enclosure larger than a 1590bb) and what would actually be useful. sort of like probably everybody's first "nutz-influenced" guitar where it has ALL the sounds and is difficult wrangling something *useful* out. I've learned a lot about wiring and switching and impedances in my time around here but the most valuable stuff has been the zensunni-like wisdom from folks such as ChrisK. sometimes all you need is a single pickup guitar plugged straight into a nice-sounding amp

so by all means getcher breadboard out and have some experiments with transistor switching, microcontrollers and relays, etc. just keep in mind a lot of the effects boxes using that type of switching (boss, dod, etc) rely on momentary rather than latching switches

[sumgai]

Nov 16, 2020 14:48:09 GMT -5 thetragichero said:

just keep in mind a lot of the effects boxes using that type of switching (boss, dod, etc) rely on momentary rather than latching switches

And the reason for that is they are using the momentary switch to trigger a solid-state switch, which is a late 20th century version of a bog-standard mechanical relay. You know, where a low voltage controls a high voltage.  Only here, we're concerned with the fact that control is taking place, the voltage levels are not of concern.

(Digitally speaking, this is exactly how the first calculators worked. (They weren't called computers back then, a "computer" was a person who operated the calculator.) A signal voltage was keyed in, a clock pulse was sent to every stage, and a resultant value was read out to the indicator lamps (or to a tape punch).)

Now doing this has the very slight drawback of needing a battery, but since we're already using one to power the effect circuit.... The complexity in design increases, but the parts count doesn't - a simple CD4016 quad switcher is used for this function so often that there are whole design books published on how to do this. Super simple, low power consumption, reliable into the next century at minimum, what's not to like. Well, it'll take up some room on your circuit board, but other than that, it'll make things a lot easier all the way around.

Tag, you're it!





sumgai

[frets]

Hi Guys,

Trag, don’t feel like you were discouraging, you’ve all given me good perspectives and advice, let’s face it, most of my stuff is “out-of-the-box” and fringe impossible (or impossible🧩).

I’m working on the circuit, I should have it done by Thanksgiving. Let me try and figure it out given what y’all have shared. I know what I will present will be wrong but it will give us a target. I am working it so the 22nF tone will be present in both passive modes, functioning as a True Tone pot on the “push” and Static Tone (tone that is “just there” in the effect) on the “pull.” The simplest circuits for effects are distortion and delay. Those will be the two I will be focusing on. As much as I would love to have a chorus, there is no way I can conceive it without the pot being ringed in by boards.

This project now has become more of an exercise to see if a quality distortion/delay can be placed on a push pull tone pot. Kinda just to see if it can be done. Then, who knows. Maybe a chorus could be conceived. Ha!! The CD4016 is a great consideration.

[thetragichero]

lemme know how deep you wanna go with those 4000-series cmos chips. you can get some cool octave up/down sounds outta them

[sumgai]

frets,


The beauty of a digital switch, particularly one with 4 poles (the 4016 and variants), is that you can now achieve a full bypass operation, which is a good thing. Not to mention that you can also insert a cap/resistor combo to knock down the thump when turning the power on or off.

Without that full bypass operation, you're going to find that keeping any kind of "common" 22nF Tone cap in the circuit will result in Excedrin Headache #8. And possibly higher numbers, who knows. I'll let you fight that battle as it crops up and bites you on the derriere.

I do have to say, I don't see your anticipated mods going into a Tele cavity without some wood being hogged out. But for just about all other styles of electric guitar, what you envision should be a salable item. That's also a good thing.

HTH



sumgai

[frets]

Thanks Sumgai,
I’m actually excited about you guys vetting this circuit (when I get it done)