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fluxmonkey
Joined: Jun 24, 2005 Posts: 708 Location: cleve
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Posted: Wed Aug 27, 2008 8:16 am Post subject:
Electronic Drums: TwinT around CMOS inverter? |
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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 _________________ www.fluxmonkey.com |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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widdly
Joined: Jun 25, 2007 Posts: 268 Location: singapore
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Posted: Thu Aug 28, 2008 12:58 am Post subject:
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The 808 schematics all have an opamp instead of transistors or cmos. That was in the 80's as well
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
Joined: Nov 27, 2005 Posts: 846 Location: Bristol, UK
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Posted: Thu Aug 28, 2008 1:51 am Post subject:
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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) _________________ http://www.bugbrand.co.uk
http://www.bugbrand.blogspot.com |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Thu Aug 28, 2008 2:13 am Post subject:
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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 _________________ Yves |
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widdly
Joined: Jun 25, 2007 Posts: 268 Location: singapore
G2 patch files: 2
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Posted: Thu Aug 28, 2008 3:27 am Post subject:
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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
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Thu Aug 28, 2008 4:21 am Post subject:
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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. _________________ Yves |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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Posted: Fri Aug 29, 2008 3:26 pm Post subject:
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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
Joined: Nov 27, 2005 Posts: 846 Location: Bristol, UK
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Posted: Sat Aug 30, 2008 3:45 am Post subject:
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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) _________________ http://www.bugbrand.co.uk
http://www.bugbrand.blogspot.com |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
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Posted: Sat Aug 30, 2008 5:28 am Post subject:
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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
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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Posted: Tue Sep 02, 2008 9:50 am Post subject:
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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
Joined: Nov 27, 2005 Posts: 846 Location: Bristol, UK
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Posted: Tue Sep 02, 2008 10:39 am Post subject:
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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! _________________ http://www.bugbrand.co.uk
http://www.bugbrand.blogspot.com |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
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Posted: Tue Sep 02, 2008 1:23 pm Post subject:
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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
Joined: Mar 09, 2014 Posts: 104 Location: Taiwan
Audio files: 4
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Posted: Tue Aug 05, 2014 4:18 pm Post subject:
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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! _________________ https://soundcloud.com/ruebezahl |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Wed Aug 06, 2014 5:51 am Post subject:
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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
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
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Ruebezahl
Joined: Mar 09, 2014 Posts: 104 Location: Taiwan
Audio files: 4
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Posted: Wed Aug 06, 2014 9:05 am Post subject:
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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 Thanks for yo Help anyway... _________________ https://soundcloud.com/ruebezahl Last edited by Ruebezahl on Wed Aug 06, 2014 9:53 am; edited 1 time in total |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Wed Aug 06, 2014 9:37 am Post subject:
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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. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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Ruebezahl
Joined: Mar 09, 2014 Posts: 104 Location: Taiwan
Audio files: 4
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Posted: Wed Aug 06, 2014 10:43 am Post subject:
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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
btw: cool mushroom-drums _________________ https://soundcloud.com/ruebezahl |
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Ruebezahl
Joined: Mar 09, 2014 Posts: 104 Location: Taiwan
Audio files: 4
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Posted: Thu Aug 07, 2014 5:13 pm Post subject:
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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? _________________ https://soundcloud.com/ruebezahl |
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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Posted: Fri Aug 08, 2014 6:54 am Post subject:
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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. _________________ Revenge is a dish best served with a fork... to the eye |
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Ruebezahl
Joined: Mar 09, 2014 Posts: 104 Location: Taiwan
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soundust
Joined: Sep 13, 2015 Posts: 2 Location: forbidden planet
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Posted: Sun Sep 13, 2015 8:13 am Post subject:
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Hi everyone,
I am new to the forum, and an amateur in electronics. I would like to pick your brains a little in regards to the twin T CMOS drum oscillator circuit posted by yusynth.
First, what is the purpose of the inverter in that circuit? What happens when the inverter is feeding back on itself?
Second (in relation to PHOBoS' Shroom Drums http://electro-music.com/forum/post-392036.html#392036), are all diodes in the circuit supposed to be Shottkies or just the one marked? What is the purpose of BAT85 and other diodes in this circuit?
Third, how would you adjust the circuit if you wanted to change the decay time of the tones?
I made an LTSpice model based on PHOBoS' Shroom circuit, but I am not getting good results: http://oi60.tinypic.com/2i27gg5.jpg
Any advice on my simulation? |
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LFLab
Joined: Dec 17, 2009 Posts: 497 Location: Rosmalen, Netherlands
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Posted: Mon Sep 14, 2015 6:34 am Post subject:
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No advice on your simulation, but the inverter will act as an oscillator when fed back.
If you want a more controllable damping circuit, you could try to somehow adapt the schematic of the CGS chime circuit, it has a transistor which is damping the output. |
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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Posted: Mon Sep 14, 2015 8:50 am Post subject:
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https://en.wikipedia.org/wiki/Schottky_diode#Voltage_clamping
The BAT85 limits the voltage triggering the twin-T to that diode's forward voltage. I believe an ordinary silicon diode could be used without ill-effect.
Quote: | Third, how would you adjust the circuit if you wanted to change the decay time of the tones? |
I've had some success with a pot in series with the cap to ground between the two 68k resistors. That, however, could only shorten the decay. Another possibility is to vary the 1M feedback resistor. That may or may not interact with pitch.
Quote: | Any advice on my simulation? |
Yeah; never trust simulations, particularly when using logic devices in the analog domain.
so many Edits _________________ Revenge is a dish best served with a fork... to the eye |
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