Single string triggered switch

[frokost]

Hi. First of all, this forum is great! I've searched around and found a lot of information that I think will help me in this somewhat strange project of mine. I post this to see if I'm thinking in the right direction.

Here's what I want to do: I have a hexaphonic pickup. I want the signal to be passed on to be from only one of the strings UNLESS one other string is plucked. Only one of the other strings, I only deal with two signals here. If what other string is plucked I want the signal from that string to be passed on. Only the signal from one of the strings is supposed to go through to the other end at the time.

I've read about electronic switching and is thinking that some kind of comparator circuit to use as trigger for the electronic switch is the way to go to achieve what I'm trying.

Disclaimer: I'm not that familiar with electronics, just want to make some weird music.

Thanks in advance for all help!

[R.G.]

First, that's a very perceptive and advanced set of objectives.

I spent a while messing with something similar. Here's what you have to do.
(1) get a good hex pickup, with at least 20db separation between adjacent strings. You need the separation so you can automatically select with circuits.
(2) make six sets of the following signal processing, one per string; preamplifier, envelope detector, adjustable threshold and comparator to give a logic-level signal that the string is sounding.
(3) logic that does the selection of one and only one string by some set of logic rules
(4) six analog switches controlled by the logic rules, so that the logic selects only one active string at a time.

It's a lot of circuitry, but it's not hard stuff to build; just a lot of it.

[frokost]

Thank you very much!

Luckily I only need to make two sets of signal processing, as I only need signal from two of the strings. Yes, it's a weird idea, I know.

It seems like I'm on the right track, at least. I was thinking preamp -> comparator (with adjustable threshold) would suffice. Why do I need the envelope detector? I was thinking that I could get away with a logic that said "pass on this signal when present, else pass on this other signal". Sorry if it's a stupid question.

[R.G.]

The only problem with just amplifying and comparing is that the signal out of your guitar is AC. It alternates between a positive voltage half cycle and a negative voltage half cycle. If you only use a comparator, the comparator clicks on on - for instance - the positive half-cycle and then off again on the negative half-cycle. So you get a string of pulses, not a solid "string making sound" signal. You could wind up with an odd set of the strings fighting for half-cycles.

There are ways to cope with that. There are "pulse stretcher" circuits that can be used to stretch short pulses out to cover the in-between times. But then you have to cope with the pulse stretchers, which have their own set of quirks. It can be made to work OK, just a different way.

Envelop detectors tend to be useful for other things, so I will usually go for them. That's why I did that.

[Mark Hammer]

Harry Bissell has done it.  As I recall, he adapted one of the old 360 Systems Slavedriver units to provide string priority.

You can see at least some of it here: http://www.wiseguysynth.com/larry/guitar.htm

I've played it, and it works really well.

[frokost]

Again, thank you, R.G. I didn't think of that - of course I need an envelope detector.

Also thanks to you, Mark. I'll check it out.

This will take a LOT of fiddling on the breadboard to get right, but it has to be done. I'll keep you posted, especially when the time comes when it doesn't work and I'll have to ask again

EDIT: Just realised that I'll get away with only ONE set of circuitry, as I want one signal to just interrupt the other. Lucky me.

[Jaicen_solo]

Lemme guess, you want to build an octave divider that works on your lowest two strings??

If you're going to the toruble of having a hex pickup, why not just have a duophonic device? Saves on loudest string prioritising etc.. Unless of course you're wanting to drive a mono synth or something? In which case, you should check out the synthax stuff on Mr Hammer's site.

[Mark Hammer]

There's actually a string priority circuit for the Roland GR 300 in the service manual.  I have that somewhere.  I got it from a free online source, but I can't remember where right now.  Send me a PM and I'll try and send it along.

[Jaicen_solo]

Shh..., I have that service manual, i'm working on extracting bits from

The loudest string priority thing is just an envelope detector used to drive the VCF I think.

[frokost]

Lemme guess, you want to build an octave divider that works on your lowest two strings??

Good guess! Yes, that's what I'm doing. For now

If you're going to the toruble of having a hex pickup, why not just have a duophonic device? Saves on loudest string prioritising etc.. Unless of course you're wanting to drive a mono synth or something? In which case, you should check out the synthax stuff on Mr Hammer's site.

I'm not sure I understand. Duophonic device?

[StephenGiles]

I'll see what the ARP do dah has to offer..........which pile of nonsense is it in though? I started scanning the circuits months ago but it got put aside.
http://www.4shared.com/file/35991557/fa365de0/avatarE4.html
http://www.4shared.com/file/35991576/bf070ff4/ArpAv1.html
http://www.4shared.com/file/35991590/c8e7874f/ArpAv2.html
http://www.4shared.com/file/35991597/568312ec/ArpAv3.html
http://www.4shared.com/file/35991616/eb1b162b/avatarE1.html
http://www.4shared.com/file/35991822/cdc5acfb/avatarE2.html
http://www.4shared.com/file/35991878/5067b1a0/avatarE3.html
Any help?

[StephenGiles]

Hellooooooooooooooooooooooooooooooooo

[Jaicen_solo]

Tasty looking stuff there Mr Giles, any chance you could mail me the original files of those Avatar pics?? Seem to be re-sized when I save them.

jaicen_solo AT NO SPAM hotmail.com


Frokost, by duophonic, I meant a device that can play two pitches simultaneously. In guitar terms, it would be a two-string guitar. Not to be confused with a dual osciallator, monophonic device I was thinking that you would get pretty good results building say, a pair of Rocktave dividers, driven from a hex pickup (strings E and A). That would mean you could play the E and A with bass simultaneously, and would sidestep the problems associated with loudest-string priority detection (ie, skipping).
In fact, that's something that i'm working on with my pet GR-300. It needs repair, so i'll also be adding octave dividers to each string, probably with PWM. I was also considering adapting the pitch detection routine (quite a simple and elegant design) for use as a mono guitar synth. However, that's all way in the future, if it ever gets done at all.

[DDD]

frokost,
your idea requires a lot of research work with an unpredictable result. As R.G. said, you'll need a lot of circuitry with an unexpected subtleties. It seems you should work hard half an year or your intentions to be in vain :-(
But you can simplify the necessary hardware. For example, six metal plates with six RF capacitive sensors, six integral switches (totally 1+1/2 of CD4066 IC), simple logic circuit that permits only one switch to be open with others closed... it's all! Something  about 4-5 Ics, arranged in a simple and well-known order.
Then, you just slightly touch the metal plate to choose the string you want to play...

[frokost]

StephenGiles: Unbelievable! Lots of useful building blocks there, thank you.

Jaicen_Solo: I think I understand what you mean. But, as long as I only use two of the pickups on the hex pickup, that makes it duophonic, right?

DDD:

your idea requires a lot of research work with an unpredictable result.

Yes, DIY is fun! 

Interesting idea, by the way. But I want the string selection to be automatic based on what string is played. It's not practical to choose string first and then play it.

[Jaicen_solo]

Looks to me like the ARP schems have everything you need for a string trigger detector. Pretty simple rectifer and amplifier, so you could theoretically use it for an envelope effect too with some mods. As I said anyway, if you just use the two pickups on the hex, and feed them to two octave divider circuits, you can use them both simultaneously and not need the priority thing at all.

[frokost]

Ah, but I don't want to use them simultaneously.

[Jaicen_solo]

Well, when you put it like that...