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 Forum index » DIY Hardware and Software
[BEGINNER] - Modulating two oscillators (555)
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KK303



Joined: Feb 13, 2012
Posts: 11
Location: UK

PostPosted: Mon Feb 13, 2012 6:43 am    Post subject: [BEGINNER] - Modulating two oscillators (555) Reply with quote  Mark this post and the followings unread

Hi,

I am fairly new to the world of electronics for music (well, I have spent the last 8 months tinkering but I have a very steep learning curve at anything I do)... my interest is really in trying to make some harsh noise (like the Trogotronics devices) non-musical....

I was experimenting with 2 555 VCO's off the same battery and had 2 questions.

1. When I run 2 555 VCO's off the same battery, one of them has a very small pulse width, the other is almost a perfect square wave (much better than the regular 555 sound). Both were setup identical, 100k pot on 8-7, 10k on 7-6, 0.1u from 2-ground. In terms of how I'm powering them, I don't know if this is series or parallel? Pins 8 and 4 on both 555's are all coming from the + from the battery. I'd like to understand more around the theory of why one is square and the other has a lower (or higher??) duty cycle. I have tried mocking this up in a circuit simulator software but it didn't show the same results.

2. I did some more experimentation, combining the 2 outputs (pin 3) to one junction, then feeding this into a 10u cap and into a speaker. The sound was incredible and just what I am looking for (very glitchy, very harsh, wide range of mangled sounds was possible) but after a while I could smell something burning and eventually sparks started busting out my pots, and little my speaker even started burning (the magnet was red hot!) Smile I'd like to understand why this happening (ie. theoretically why its happening....not because I was being stupid!) I figured I should put some resistors on the outputs before joining them together, but this had more of the effect of a mixer (ie. hearing both oscillators) Even then, adjusting one pot would affect the pitch of the other so I couldn't get 2 stable oscillators off one battery. I know I could probably get this with 556 but I'm interested in using 2 555's, is there a way for the resistors of one 555 not to affect the voltage supply to the other 555?

Also is there any way I can safely combine the 2 output signals of the 555 to allow them to fight against each other (like subtractive synthesis??) instead of the sound being mixed. As mentioned, when it was working for a brief period, the 2 outputs wired into one really was great...I have seen a schematic for a "difference mixer" in one of Forrest Mims handbooks, is this the sort of idea I need? Please let me know if you're interested in a similar sort of thing and have done your own experiments, would be keen to know whats possible....I'm bored of cheesy sounding APC ciruits but it is about the extent of my knowledge just now Sad
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PostPosted: Mon Feb 13, 2012 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Welcome to electro-music.com. You're off to a good start discovering crazy circuit configurations that make neat sounds, but it's not a good idea to wire together outputs. The reason is that they source current and if you connect them together you may get a tremendous amount of current flow in one or both of the circuits. That's probably what caused you to get some magic smoke. Always combine outputs with a mixer, which is what you did but adding resistors.

I suggest that you check out our Lunetta a sub forum. These are cheap little synthesizers that are made for making music based on square waves. Your 555 oscillators would be perfect for driving some of the circuits you find in the Lunetta systems. For example by combining your two oscillators with a logic gate, like NAND gate, you'll get some of the sounds that you for already have been enjoying, but you won't burn out your circuits.

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KK303



Joined: Feb 13, 2012
Posts: 11
Location: UK

PostPosted: Mon Feb 13, 2012 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the advice, this seems to be a new one for me, I hadn't really looked into the CMOS chips yet besides the 4017, my reasoning probably being that I fear the low voltage would mean little sounds like a birthday card piezo...I hadn't thought of using gates either, mostly due to ignorance about what gates are....looks like a whole new lot of info to try and sink my teeth into there, plus some parts that are actually available! (hate reading stuff that leads me to obsolte parts, like the 566!) Thanks...will pick up CMOS chips tonight and have a tinker! Smile
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PHOBoS



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PostPosted: Mon Feb 13, 2012 8:49 am    Post subject: Re: [BEGINNER] - Modulating two oscillators (555) Reply with quote  Mark this post and the followings unread

KK303 wrote:
Hi,

I am fairly new to the world of electronics for music

run while you still can!
Quote:
(well, I have spent the last 8 months tinkering but I have a very steep learning curve at anything I do)... my interest is really in trying to make some harsh noise (like the Trogotronics devices) non-musical....

nevermind the running, too late for that now Very Happy
Quote:

I was experimenting with 2 555 VCO's off the same battery and had 2 questions.

1. When I run 2 555 VCO's off the same battery, one of them has a very small pulse width, the other is almost a perfect square wave (much better than the regular 555 sound). Both were setup identical, 100k pot on 8-7, 10k on 7-6, 0.1u from 2-ground. In terms of how I'm powering them, I don't know if this is series or parallel? Pins 8 and 4 on both 555's are all coming from the + from the battery. I'd like to understand more around the theory of why one is square and the other has a lower (or higher??) duty cycle. I have tried mocking this up in a circuit simulator software but it didn't show the same results.


They way you powered them is in parallel which is the right way to do it. But you have made me curious now
since putting them in series might give some interesting effects (I have to try that sometime, also with
different chips). If you wired them the same as you said than they should produce the same signal. Having said
that, the 555's can produce quite some noise on the power rails and if your battery isn't full that migth be a
cause of how they behave in your circuit. And because your switching at audiorates it might still produce some
extra unwanted effects with a full battery.

Quote:
2. I did some more experimentation, combining the 2 outputs (pin 3) to one junction, then feeding this into a 10u cap and into a speaker. The sound was incredible and just what I am looking for (very glitchy, very harsh, wide range of mangled sounds was possible) but after a while I could smell something burning and eventually sparks started busting out my pots, and little my speaker even started burning (the magnet was red hot!) Smile I'd like to understand why this happening (ie. theoretically why its happening....not because I was being stupid!)


OK, connecting the outputs together was stupid (j/k) Wink
Experimentation is key, and now you know that doesn't work, it could have done something interesting.
What happened is that a 555 switches it's output between + and -. So when you connect them together and one
output is + while the other is - you make a very bad short no no. This means high currents which usually
translates in something getting hot. I'm a bit surprised your pots started burning but it could be that first
the 555's got destroyed making it possible for higher currents to flow through the pot. Not sure how it destroyed
your speaker though since you did have a cap in series, but it's hard to tell what happened.

Quote:
I figured I should put some resistors on the outputs before joining them together, but this had more of the effect of a mixer (ie. hearing both oscillators) Even then, adjusting one pot would affect the pitch of the other so I couldn't get 2 stable oscillators off one battery. I know I could probably get this with 556 but I'm interested in using 2 555's, is there a way for the resistors of one 555 not to affect the voltage supply to the other 555?


I'm not sure if a 556 would be more stable, don't think it would change a lot, but there are some things to improve
your circuit. First of all make sure your battery is full and put a cap in parallel to it close to the battery, say 470uF.
Also place some caps between pins 1 and 8 of each 555, 100uF is a nice value and maybe some smaller ones like 100nF too.
And some 10nF caps between pin 5 and - of each 555.

Quote:
Also is there any way I can safely combine the 2 output signals of the 555 to allow them to fight against each other (like subtractive synthesis??) instead of the sound being mixed. As mentioned, when it was working for a brief period, the 2 outputs wired into one really was great...I have seen a schematic for a "difference mixer" in one of Forrest Mims handbooks, is this the sort of idea I need? Please let me know if you're interested in a similar sort of thing and have done your own experiments, would be keen to know whats possible....I'm bored of cheesy sounding APC ciruits but it is about the extent of my knowledge just now Sad


There are several ways to mix the outputs together, but with most of them you won't be able to drive a speaker directly,
so you will need an extra amplifier. You've got the advantage that the output of a 555 is a digital signal, it's either high
or low. This means you can use logic to mix the signals together: OR, AND, XOR, NAND, NOR etc.
you can use cmos chips for this but you can also do it with some diodes. You can find some interesting info in the lunetta
forum which is probably the place to look for what you want to do anyway (If you haven't found it allready it's here)
Another way would be using an opamp to make a standard mixer which gives you control over the levels of each 555.
like this:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

If you want to drive a speaker directly you would probably have to make a mixer using one or more transistors, but that
could get a bit more complex.

edit: ah, in the time I was writing mosc allready replied Razz
edit2: you might like this too Cool

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KK303



Joined: Feb 13, 2012
Posts: 11
Location: UK

PostPosted: Mon Feb 13, 2012 9:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, that answered a lot, although Im still confused on the different pulse widths of the 2 555's...I'll try it again with a different battery..I'm sure it was a fresh battery I was using however....it was interseting for me because it was the first time I had heard what sounded like a pure square wave from the 555....

I definitely need to investigate the use of CMOS chips and the Lunetta schematics, that does look right up my street with regards to what I've been doing so far.

The mixer schematic looks like a summing amp, I'm wondering what a difference amp will do.... (see attached) ... I guess I just need to try it and see....but can you tell me what difference this would make from the schematic you posted? Would it be more like phase cancelling using the diff-amp? That might not be the effect I am after...

Funnily enough, that link you posted is what brought me to this forum via google! Smile I'm gonna try that out now! The case looks awesome also Very Happy

One thing tho...

Quote:
First of all make sure your battery is full and put a cap in parallel to it close to the battery, say 470uF.
Also place some caps between pins 1 and 8 of each 555, 100uF is a nice value and maybe some smaller ones like 100nF too.


I maybe still don't understand fully all about capacitors, I know to tie pin 5 to ground with a very small cap (I forgot to mention I had this already, as it fixed some stability) but what does the cap near the battery do, and why one from 8 to 1 (positive to negative?) [/quote]


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PostPosted: Mon Feb 13, 2012 1:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey KK303,

Have you ever played around with the Falstad Java Circuit Simulator?

http://www.falstad.com/circuit/

There are a lot of examples that use 555 timer circuits in there, and you can see exactly what is going on within the chip, including any power filtering capacitors. And you can mess with logic stuff.

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KK303



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PostPosted: Mon Feb 13, 2012 2:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey there! Yes, I certainly have used that!! (thats one of my fave resources and is primarily what I've used to learn as I have no scope!! Smile The only problem is theres no pin1 in the simulator, so i tried adding the cap to pin 8 and then grounding 8, but not really sure whats happening. I tried it on the breadboard too, never really noticed any difference although after reassembling my circuit I have lost this freak square wave one side thin pulse the other, and both oscillators and sounding exactly the same....maybe it was just the battery! Smile

I tried mixing the outputs into a 741 but it didn't get the sound I wanted....

I've attached a video of me messing around using Tassman....I know this is pretty sophisticated software, but I just want to have an oscillator than modulate another, but I also like there being noise in the mix aswell. In Tassman I used a whitenoise generator on the modulation input and just so slightly applied it, it got a sound not too unlike what I got when I had the two oscillators wired direct to the speaker. I'd love to be able to build something that could replicate this, not particularly interseted in strict 1v/oct tracking etc.... this is another idea of the sort of sound I'm after..I think these devices are something of a black box, but does anyone know what it sounds like is going on? WIth some reverb and delay on this it can really sound amazing! Smile

http://www.trogotronic.com/666%20solo%201.mp3


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PHOBoS



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PostPosted: Mon Feb 13, 2012 3:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

KK303 wrote:
The mixer schematic looks like a summing amp, I'm wondering what a difference amp will do.... (see attached) ... I guess I just need to try it and see....but can you tell me what difference this would make from the schematic you posted? Would it be more like phase cancelling using the diff-amp? That might not be the effect I am after...

In this case I don't think it would matter much because of your signals
(but don't take my worth for it), allthough I'm not sure if you can use the
- of your battery as ground or if you need a virtual ground aswell.

Quote:
Funnily enough, that link you posted is what brought me to this forum via google! Smile I'm gonna try that out now! The case looks awesome also Very Happy

thanks, nice that it brought you here Smile

Quote:
I maybe still don't understand fully all about capacitors, I know to tie pin 5 to ground with a very small cap (I forgot to mention I had this already, as it fixed some stability) but what does the cap near the battery do, and why one from 8 to 1 (positive to negative?)

What happens is that when a 555 switches it needs power (current) which
has to come from somewhere, in this case your battery. And because of
this sudden need for current the supply voltage can drop a bit, which has
to do with the internal resistance of your battery. This drop in voltage will
cause a frequency change in the other 555.
(This doesn't happen if you would have an ideal power supply which is
usually the case when using software to simulate a circuit)

Caps are like batteries but are able to deliver current much faster so
by putting a cap directly across each 555 you give them both a little
buffer. You can think of it as filling a bucket with a waterhose, in this case
the bucket is your cap and the waterhose your battery. By doing this you
can use more water at once, but you have to wait for the bucket to fill up
again. A cap across the battery does basically the same thing, and it can
help a bit if your battery isn't completely full.

If you look at CMOS circuits you will notice that in most cases they all have
their own 100nF cap across the powerpins, which is there for the same reason.
It also works the other way around btw,. the caps can keep noise on the
powerlines from entering the chip.

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Last edited by PHOBoS on Mon Feb 13, 2012 4:24 pm; edited 1 time in total
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KK303



Joined: Feb 13, 2012
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PostPosted: Mon Feb 13, 2012 3:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey thanks, that really sort of explains it to me, I think I got it now! I noticed the whole thing becoming a lot more musical now, now the two oscillators keep stable pitch while being adjusted and I can get a nice unison sound...hmmm its not what I initially intended (maybe it was the noise interfering that was the sound I enjoyed!) but very cool nonetheless and has demonstrated the power of caps...I always just thought they were like a delay , but I knew the current could be offloaded to the other plate very quickly, just didnt see what the point of this was before now.

Heres how it looks on the breadboard...Im using 2 batteries (orginally was using 3 batteries, but I found a little circuit lying around that I built which uses the exact same technique as above (caps across the voltage) and also creates a virtual ground, so I used that for the op-amp (couldn't get the 555's to work off it)....thanks for all the advice so far!! Ordered up some CMOS chips so will need to wait a few days till I can get my teeth into these lunetta circuits, certainly looks to be some very interesting stuff going on in that forum!! CHeers for now!


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PHOBoS



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PostPosted: Mon Feb 13, 2012 4:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

KK303 wrote:
Heres how it looks on the breadboard...Im using 2 batteries (orginally was using 3 batteries, but I found a little circuit lying around that I built which uses the exact same technique as above (caps across the voltage) and also creates a virtual ground, so I used that for the op-amp (couldn't get the 555's to work off it)....thanks for all the advice so far!! Ordered up some CMOS chips so will need to wait a few days till I can get my teeth into these lunetta circuits, certainly looks to be some very interesting stuff going on in that forum!! CHeers for now!

looks good, glad to hear it worked Smile
something you could do for now to make it more interesting is wire pin 3 of one
555 to pin 5 of the other (maybe with a potentiometer in series) and remove
the cap attached to pin 5 from that one.

I just noticed that you're driving the speaker directly from the opamp,
be carefull with that it might not like it (you can feel if it gets warm)
but it can work sometimes. Unless it's an LM386 but that's not really an
opamp and that should be wired differently anyway.

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KK303



Joined: Feb 13, 2012
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PostPosted: Tue May 01, 2012 3:15 am    Post subject: Reply with quote  Mark this post and the followings unread

In case anyone comes across this while searching on using two 555's....I think I found the trick....using the output of one 555 into PIN 7 on another (replacing the resistor from PIN 8 to PIN 7) seemed to work great. For a bit of variation of the output from the first 555, i connect the output to pin 2 of a 10k potentiometer, with a 100u capacitor across pins 2 and 3 of the pot. Pin 3 also goes to ground and pin 1 goes to pin 7 of the 555, this makes for a useful pseudo waveshaper (square to slightly triangular) there is a trade off in pitch also but it works well for my purposes, and can blast out some mangled sounds as well as slight vibrato...a vactrol on pins 6 and 7 of the 2nd 555 gives some ability to almost play something musical aswell! Smile
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