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Electronic Drums: TwinT around CMOS inverter?
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fluxmonkey



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PostPosted: Wed Aug 27, 2008 8:16 am    Post subject: Electronic Drums: TwinT around CMOS inverter? Reply with quote  Mark this post and the followings unread

In the Electronic Drum Cookbook, Tom Henry notes:
Quote:
"One of the earliest methods used to create percussive sounds was the Twin-T oscillator. This kind of circuit was really popular in the 1960’s and all sorts of portable bongo projects using it appeared in the magazines of that time. In those days, the active device which formed the heart of the circuit was the discrete transistor. By the 1980’s, the transistors were replaced by CMOS inverters configured to operate in a linear mode."

Anybody have any example schematics of a TwinT built around CMOS inverters? Sounds interesting.


thx,
bbob

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yusynth



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PostPosted: Wed Aug 27, 2008 11:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Elektor had such twin T CMOS drum oscillator.
C2,C3 and C5 are capacitors that you have to select values for the drum tone you want to achieve.


twinTCMOS-elektor.gif
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twinTCMOS-elektor.gif



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widdly



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PostPosted: Thu Aug 28, 2008 12:58 am    Post subject: Reply with quote  Mark this post and the followings unread

The 808 schematics all have an opamp instead of transistors or cmos. That was in the 80's as well Razz

I guess one advantage of using cmos inverters is the power supply requirements are simpler.

Last edited by widdly on Thu Aug 05, 2010 10:07 pm; edited 1 time in total
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bugbrand



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PostPosted: Thu Aug 28, 2008 1:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I would hazard a guess that you could use a CD4069UB (instead of 4011).
- one thing is that that may give a ?better sound as these are used for CMOS overdrive effects
- you'd also then have two spare gates, one particular use of which could be a simple sum (inverting opamp arrangement) and overall distortion (drive those 4069s!)

I'd like to try out this Elektor one - thanks for posting it Yves.

As a guess / from other TwinT Drum schems, possible C values:

Hi (Woodblock or Tom) - C2 = C3 = 470p or 1n &&& C5 = 4n7
Lo (Bass) - C2=C3=4n7 &&& C5 =47n
--- ie, C5 is generally kept 10 times larger than C2 and C3 (which are equal)

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yusynth



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PostPosted: Thu Aug 28, 2008 2:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Refering to Elektor here are some values

HB : R8=390K C1,C5=33n C2,C3=20n
LB : R8=390K C1,C5=39n C2,C3=12n
BD : R8=100K C1,C5=150n C2,C3=47n
CD : R8=390K C1,C5=56n C2,C3=18n
CL : R8=1M C1,C5=4.7n C2,C3=1.5n

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widdly



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PostPosted: Thu Aug 28, 2008 3:27 am    Post subject: Reply with quote  Mark this post and the followings unread

So in the elektor circuit, what sets the decay?

Also, is R8 effecting the frequency or the volume?

Last edited by widdly on Thu Aug 05, 2010 10:07 pm; edited 1 time in total
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yusynth



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PostPosted: Thu Aug 28, 2008 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

R8 is acting on the volume, it is a simple resistor in series with the output.
The decay is set by resonance (inverse of the damping) of the twin T filter.
it is fed with a brief pulse and the filter auto-oscillates and damps. The damping rate is set by the trimmer P1.

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synthmonger



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PostPosted: Fri Aug 29, 2008 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Couldn't get it to work on a 4011. I swapped it out for a 4069 and used one gate and it worked right off the bat. Pretty smooth sound.

I'm in need for at least a 6 piece drum synth so I'm pretty sure I'll make a module/box out of this. It's easy and really inexpensive to build.
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bugbrand



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PostPosted: Sat Aug 30, 2008 3:45 am    Post subject: Reply with quote  Mark this post and the followings unread

synthmonger wrote:
Couldn't get it to work on a 4011. I swapped it out for a 4069 and used one gate and it worked right off the bat. Pretty smooth sound.

I'm in need for at least a 6 piece drum synth so I'm pretty sure I'll make a module/box out of this. It's easy and really inexpensive to build.


SUPER! Wanna post a demo sound?!

I'd love to get trying out this but have too many other things to focus on for now.
Likely I'd go for four drums, summer circuit and distortion from one 4069 chip. That'd fit nicely into my modular arrangements (four pots vertically per panel)

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synthmonger



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PostPosted: Sat Aug 30, 2008 5:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah I'll mess with it later today and post a sample. Feeling a bit sickly though so it might end up being later ;x
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synthmonger



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PostPosted: Tue Sep 02, 2008 9:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Hrm I think I spoke to soon. Now I'm having problems getting it to trigger on the 4069. I'm running it on a 9V and sometimes it works sometimes it doesn't. It tends to work 90% of the time when I put a pot in series with pin 14 to +9V and adjust it.


Do ya think you could give this is a shot and see if it works 100% for you?
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bugbrand



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PostPosted: Tue Sep 02, 2008 10:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, I'm not quite sure I get what you mean by
'when I put a pot in series with pin 14 to +9V and adjust it.'

I'll see if I get a chance this week.. Things are a little bit cleared up for me now, but still....

I'd been presuming to check with various triggers to see the response - both how wide the pulse is and how the voltage of the trigger changes things. I'd thought probably having a typical trigger converter infront of it would be useful.. stuff to try out myself!

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synthmonger



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PostPosted: Tue Sep 02, 2008 1:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

bugbrand wrote:
Hmm, I'm not quite sure I get what you mean by
'when I put a pot in series with pin 14 to +9V and adjust it.'

I'll see if I get a chance this week.. Things are a little bit cleared up for me now, but still....

I'd been presuming to check with various triggers to see the response - both how wide the pulse is and how the voltage of the trigger changes things. I'd thought probably having a typical trigger converter infront of it would be useful.. stuff to try out myself!


A pot that acts as a voltage divider to pin 14, y'know like a "starve" control sort of thing. I didn't measure the voltage at which it started working since it was different each time. I've been sick so I haven't done too much testing. ;x
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Ruebezahl



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PostPosted: Tue Aug 05, 2014 4:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey folks,

For my new Project, a modular drum machine, wich topic you can find here, i was thinking about implementing this circuit as one of the drum voices. Now i built it, with a simple 47HC17 as a clock. But it doesnt really work. What i hear at the output is pretty much the ticking of the clock, but just every second tick. but it's really just the short ticking. I was experimenting with different values for the capacitors C1 to C5, but that didn't really change anything *sigh*
Do you have any idea what could cause this problem? Thanks!

edit: I am thinking: My problem might be, that i don't quite understand, what is needed if a drum voice has a trigger in. i have experience building sequencer driving a 40106 Oscillator, but the input there was certainly not a trigger but a gate. so i wondering how to actually create a clock wich puts out trigger signals? And if you feed a designated "trigger in" a gate signal, what actually happens. I thought if you put a gate into a trigger, the Envelope of the Synth will just not work, but there will be Sound. But could it be, that instead, there is just clicking, like in my case? PLEASE HELP!

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elmegil



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PostPosted: Wed Aug 06, 2014 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

it's pretty easy to convert a gate to a trigger for testing.

http://cgs.synth.net/modules/cgs24_gatetotrigger.html

I would expect that subbing in a schmitt trigger inverter for the op amp and ignoring the comparator bits would work fine (though your pulse would have to be inverted again).
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PHOBoS



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PostPosted: Wed Aug 06, 2014 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

what chip did you use ? I didn't have much success with the 4011 but the 4069 worked for me (used it in my RGB Shroom drums).
I don't think you need a seperate gate > trigger converter as that's already taken care of in the circuit.

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Ruebezahl



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PostPosted: Wed Aug 06, 2014 9:05 am    Post subject: Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
what chip did you use ? I didn't have much success with the 4011 but the 4069 worked for me (used it in my RGB Shroom drums).
I don't think you need a seperate gate > trigger converter as that's already taken care of in the circuit.


Hm, i did it with the 4069 right away, since i read this information in the thread already. I maybe scribble a schematic and make a pic of the breadboard, maybe then you can help me find the error. Thanks so far.

btw: what does the (D) in the schematics mean? If it means connect it to the negative side of the battery, i am right.

edit: it's working now, it was completely my fault, just couldn't read the schematics in the right way Very Happy Thanks for yo Help anyway...

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Last edited by Ruebezahl on Wed Aug 06, 2014 9:53 am; edited 1 time in total
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PHOBoS



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PostPosted: Wed Aug 06, 2014 9:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Ruebezahl wrote:
btw: what does the (D) in the schematics mean? If it means connect it to the negative side of the battery, i am right.

The letters are most likely marked pads on a PCB or points that are referred to in the text that goes with it (in the orginal book).
So you can ignore it, but yes it connects to the negative side of the battery. But it's not that "D" has a universal meaning of being that.

Have you tried triggering it with standard CMOS ? it might be that the 74HC series output isn't suitable for this circuit.
Also it's usually powered with 5V and I don't know if the drumcircuit works correct at that voltage,
I expect it would do something though. If you are using a seperate supply then don't forget to connect the GND's together.
The drum circuit powered from a battery with only the trigger input connected to a seperately powered circuit won't work.

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Ruebezahl



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PostPosted: Wed Aug 06, 2014 10:43 am    Post subject: Reply with quote  Mark this post and the followings unread

as i edited in my last post, its working now! i forgot one connection in the schematics. sorry for that. gonna check double tripplie next time Wink

btw: cool mushroom-drums

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Ruebezahl



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PostPosted: Thu Aug 07, 2014 5:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

So as i said, its working now. I was experimenting around with some of the capacitor values, and have a nice bassdrum sound i like. but there is one thing wich annoys me: After every drumhit you can hear a little click. its always exactly halfway between two hits, so i suspect it to be the clock-sqarewave going back to zero. Any ideas how to fix this?
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richardc64



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PostPosted: Fri Aug 08, 2014 6:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Ruebezahl wrote:
After every drumhit you can hear a little click. its always exactly halfway between two hits, so i suspect it to be the clock-sqarewave going back to zero. Any ideas how to fix this?


I'm surprised that all you hear between hits is a click: Those twin-T circuits will trigger on the rising OR falling edge of a pulse. If the pulse is too "wide" you'll get two hits from one pulse.

Try decreasing C1 or R2, or both in the Yusynth schematic, or increasing R3.

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Ruebezahl



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PostPosted: Sat Aug 09, 2014 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you, increasing R8 helped Smile
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