Author Topic: A fake guitar for your test bench  (Read 17529 times)

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R.G.

A fake guitar for your test bench
« on: June 26, 2010, 08:04:32 AM »
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.
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

Re: A fake guitar for your test bench
« Reply #1 on: June 26, 2010, 08:10:29 AM »
Cool!
I dig hot Asian chicks!

Morocotopo

Re: A fake guitar for your test bench
« Reply #2 on: June 26, 2010, 08:27:58 AM »
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.
Morocotopo

earthtonesaudio

Re: A fake guitar for your test bench
« Reply #3 on: June 26, 2010, 08:35:16 AM »
Nice one.

danielzink

Re: A fake guitar for your test bench
« Reply #4 on: June 26, 2010, 08:54:24 AM »
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

stringsthings

Re: A fake guitar for your test bench
« Reply #5 on: June 26, 2010, 10:02:08 AM »
thanks R.G. .... this falls under the "good to make one day when i get tired of fuzz boxes" circuits !  :icon_mrgreen:

joegagan

Re: A fake guitar for your test bench
« Reply #6 on: June 26, 2010, 02:55:17 PM »
i like it.
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

Re: A fake guitar for your test bench
« Reply #7 on: June 26, 2010, 05:01:31 PM »
Great idea, I love the simplicity.

PRR

Re: A fake guitar for your test bench
« Reply #8 on: June 26, 2010, 07:13:58 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, 07:16:07 PM by PRR »

diydave

Re: A fake guitar for your test bench
« Reply #9 on: June 26, 2010, 08:27:40 PM »
I just love this guy  ;D

R.G.

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

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

Re: A fake guitar for your test bench
« Reply #11 on: June 27, 2010, 05:09:53 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.
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

Re: A fake guitar for your test bench
« Reply #12 on: June 27, 2010, 06:28:01 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: )

R.G.

Re: A fake guitar for your test bench
« Reply #13 on: June 27, 2010, 08:03:05 AM »
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:
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.

Re: A fake guitar for your test bench
« Reply #14 on: June 27, 2010, 08:20:59 AM »
Modified page uploaded.
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

Re: A fake guitar for your test bench
« Reply #15 on: June 27, 2010, 09:12:20 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: )

My hero..

Thanks !

Dan

KazooMan

Re: A fake guitar for your test bench
« Reply #16 on: June 27, 2010, 11:41:28 AM »
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, 11:47:47 AM by KazooMan »

R.G.

Re: A fake guitar for your test bench
« Reply #17 on: June 27, 2010, 11:44:46 AM »
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.
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

Re: A fake guitar for your test bench
« Reply #18 on: June 27, 2010, 01:32:58 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, 01:41:43 PM by stringsthings »

danielzink

Re: A fake guitar for your test bench
« Reply #19 on: June 27, 2010, 02:35:52 PM »
boo hoo...poor me....

pcb or vero ?

 ;D

Thanks, Dan