A fake guitar for your test bench

[R.G.]

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.

[Bad Chizzle]

Cool!

[Morocotopo]

Cool. I´m 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.

[earthtonesaudio]

Nice one.

[danielzink]

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]

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

[joegagan]

i like it.

[soggybag]

Great idea, I love the simplicity.

[PRR]

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.

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.

[diydave]

I just love this guy 

[R.G.]

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

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.

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.

[joegagan]

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.

[stringsthings]

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

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  )

[R.G.]

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. 

I'll upload the corrected page.

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

[R.G.]

Modified page uploaded.

[danielzink]

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

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  )

My hero..

Thanks !

Dan

[KazooMan]

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. !!!  

Life is good.  I found the TL072.  It was a spare I bought for my Tap Tempo Tremolo build.  Forgot I had it.

[R.G.]

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.

[stringsthings]

and a short ( but exciting ) soundclip:

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

at 0:54, echo and reverb are added to the "notes"

[danielzink]

boo hoo...poor me....

pcb or vero ?



Thanks, Dan