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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  A fake guitar for your test bench 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: A fake guitar for your test bench  (Read 14258 times)
R.G.
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Posts: 16015


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A fake guitar for your test bench
« on: June 26, 2010, 12:04:32 PM »

I had the need for a test oscillator when I was away from my signal generator, so I trotted out the Q&D oscillator, which had been broken by its storage.

So while tinkering, I did some things to it I'd intended to do for a while. I made it fake a repeated string pluck by adding an adjustment to make the oscillation decay to zero over a second or so, and a "plucker" to fire off repeated notes.

http://geofex.com/FX_images/Fake Guitar Oscillator.pdf

You can flip it to a constant tone, too. I think this constitutes the world's most accurate, if boring, assistant guitarist.

One dual opamp and a few other parts.

I notice in looking at it that I still can't type. I'll fix some of the misspellings someday.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
Bad Chizzle
Posts: 151

Charles D


Re: A fake guitar for your test bench
« Reply #1 on: June 26, 2010, 12:10:29 PM »

Cool!
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I dig hot Asian chicks!
Morocotopo
Posts: 773

Ariel F. - Argentina


Re: A fake guitar for your test bench
« Reply #2 on: June 26, 2010, 12:27:58 PM »

Cool. Im just making a circuit test "station" (well, really just a piece of wood with two jacks and a proto board...) and this is a perfect addition to it.

Thanks for sharing, R.G.
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Morocotopo
earthtonesaudio
Posts: 3596


Alex


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Re: A fake guitar for your test bench
« Reply #3 on: June 26, 2010, 12:35:16 PM »

Nice one.
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I gotta cut down on my (ab)use of parentheses.
danielzink
Posts: 485



Re: A fake guitar for your test bench
« Reply #4 on: June 26, 2010, 12:54:24 PM »

Oh AWESOME !!!

I've been using an Atari Punk as a tone generator for quite some time - this one would actually let you test delay pedals as well - what with the "plucking" and all.

If some could lay this out to vero or PCB - I'd be forever indebted.

Dan
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stringsthings
Posts: 363

David Y.


Re: A fake guitar for your test bench
« Reply #5 on: June 26, 2010, 02:02:08 PM »

thanks R.G. .... this falls under the "good to make one day when i get tired of fuzz boxes" circuits !  icon_mrgreen
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joegagan
Posts: 3153



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Re: A fake guitar for your test bench
« Reply #6 on: June 26, 2010, 06:55:17 PM »

i like it.
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my life is a tribute to the the great men and women who held this country together when the world was in trouble. my debt cannot be repaid, but i will do my best.
soggybag
Posts: 1465

Mitchell H


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Re: A fake guitar for your test bench
« Reply #7 on: June 26, 2010, 09:01:31 PM »

Great idea, I love the simplicity.
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PRR
Posts: 5823


Paul R. - Maine USA


Re: A fake guitar for your test bench
« Reply #8 on: June 26, 2010, 11:13:58 PM »

Looks real useful.

> I still can't type.

The only mechanical errors I see (6/26/2010 11:24am version) are 2 mis-spaces and a z/x slip.

Quote
line 4: look like aguitar signal
line 10: R1...R3 and C1...C3 determinethe feedback null
last line: All rights rexerved.

Text reads well.

Circuit looks to be drawn correctly. (I assume the twin-T inverts at center frequency? Too tired to work it out.) FWIW, the OUT jack is not marked as such.
« Last Edit: June 26, 2010, 11:16:07 PM by PRR » Logged
diydave
Posts: 93


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Re: A fake guitar for your test bench
« Reply #9 on: June 27, 2010, 12:27:40 AM »

I just love this guy  Grin
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R.G.
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Posts: 16015


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Re: A fake guitar for your test bench
« Reply #10 on: June 27, 2010, 09:06:05 AM »

The only mechanical errors I see (6/26/2010 11:24am version) are 2 mis-spaces and a z/x slip.
Quote
line 4: look like aguitar signal
line 10: R1...R3 and C1...C3 determinethe feedback null
last line: All rights rexerved.
Hey, thanks for nailing those down. I noticed the "rexerved" as I posted it, but didn't catch the others. I'll go fix it.

Quote
Circuit looks to be drawn correctly. (I assume the twin-T inverts at center frequency? Too tired to work it out.) FWIW, the OUT jack is not marked as such.
Again, thanks. I did this in about half an hour; I have to finish things like this before I get pulled off to other stuff I have to do. Twin T has an infinitely deep null at center (if the Rs and Cs are tuned just right, these aren't perfect values) and a dramatic phase reversal at center. The null lets the opamp go almost open loop at center and the phase change does the rest. Single transistors make OK Twin T resonators and oscillators, although you have to be very careful with loading effects if you do that. PAIA did several variations of the Twin T as a ringing oscillator (bongos simulator) and resonator (wind/surf simulator) wah ( Poptronics article, 1969 I think), and fake "Leslie", the Synthespin, which was a Twin T resonator/wah driven by an LFO. It's quite flexible.

This thing owes its heritage to the drum simulators mostly.

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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
joegagan
Posts: 3153



WWW
Re: A fake guitar for your test bench
« Reply #11 on: June 27, 2010, 09:09:53 AM »

rg, interesting. a few weeks ago i went on a surfin safari diving deep into fifties and sixties organ schematics. the signal generator portions for drum sounds were interesting. how many ways to make white noise into a cymbal? fun stuff.
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my life is a tribute to the the great men and women who held this country together when the world was in trouble. my debt cannot be repaid, but i will do my best.
stringsthings
Posts: 363

David Y.


Re: A fake guitar for your test bench
« Reply #12 on: June 27, 2010, 10:28:01 AM »

i've got a layout and a build that's working nearly 100% ....  icon_biggrin

i'll be posting the layout and a soundclip tonight ... the tone/notes switch is incredibly handy ... with the parts that i had on hand, the frequency of the tone is somewhere between 700 and 800 Hz ...

thanks again, R.G. for providing the schematic .... it's a hassle having to plug the guitar in for testing out fuzz boxes ... ( BTW, a sine wave run through a simulated fuzz box sounds kind of nice  icon_mrgreen )
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R.G.
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Re: A fake guitar for your test bench
« Reply #13 on: June 27, 2010, 12:03:05 PM »

I can't believe you guys let me get away with that. There's DC on the output. I left out a blocking cap to the output jack - which I have now corrected.  icon_biggrin

I'll upload the corrected page.

'Course, I got the chance to put in NEW errors, too.  icon_lol
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
R.G.
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Posts: 16015


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Re: A fake guitar for your test bench
« Reply #14 on: June 27, 2010, 12:20:59 PM »

Modified page uploaded.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
danielzink
Posts: 485



Re: A fake guitar for your test bench
« Reply #15 on: June 27, 2010, 01:12:20 PM »

i've got a layout and a build that's working nearly 100% ....  icon_biggrin

i'll be posting the layout and a soundclip tonight ... the tone/notes switch is incredibly handy ... with the parts that i had on hand, the frequency of the tone is somewhere between 700 and 800 Hz ...

thanks again, R.G. for providing the schematic .... it's a hassle having to plug the guitar in for testing out fuzz boxes ... ( BTW, a sine wave run through a simulated fuzz box sounds kind of nice  icon_mrgreen )

My hero..

Thanks !

Dan
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KazooMan
Posts: 321


Re: A fake guitar for your test bench
« Reply #16 on: June 27, 2010, 03:41:28 PM »

Wow!  This is great.  I have almost resorted to strumming with my feet so I have two hands to tweak the dials.  I am certain I have all the parts on hand except perhaps the proper IC.  

Thanks  R. G. !!!  icon_razz

Life is good.  I found the TL072.  It was a spare I bought for my Tap Tempo Tremolo build.  Forgot I had it.
« Last Edit: June 27, 2010, 03:47:47 PM by KazooMan » Logged
R.G.
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Posts: 16015


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Re: A fake guitar for your test bench
« Reply #17 on: June 27, 2010, 03:44:46 PM »

Wow!  This is great.  I have almost resorted to strumming with my feet so I have two hands to tweak the dials.  I am certain I have all the parts on hand except perhaps the proper IC. 
In a pinch I'd use any dual opamp I had on the bench. It would probably work fine.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
stringsthings
Posts: 363

David Y.


Re: A fake guitar for your test bench
« Reply #18 on: June 27, 2010, 05:32:58 PM »



and a short ( but exciting ) soundclip:

http://soundclick.com/share?=songid=9330932

at 0:54, echo and reverb are added to the "notes"
« Last Edit: June 27, 2010, 05:41:43 PM by stringsthings » Logged
danielzink
Posts: 485



Re: A fake guitar for your test bench
« Reply #19 on: June 27, 2010, 06:35:52 PM »

boo hoo...poor me....

pcb or vero ?

 Grin

Thanks, Dan
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