A fake guitar for your test bench

[egasimus]

Well, there are 3 capacitors that determine the frequency. You can simulate a variable capacitor, but you're gonna needs about as many parts as the rest of the circuits, and on top of that you'll need a triple-ganged pot to control the 3 capacitors simultaneously.
This oscillator is made to be simple and easily put together - you can only go so far with it. You'll have a better chance starting off with some other circuit, for example something based on the XR2206 or perhaps the harder to obtain ICL8038.

By the way, I made a layout for this oscillator on my layout spree some weeks ago. Gonna post it when I get around to it.

[ayayay!]

My fake guitar is called an RC-20XL.

[PRR]

> hopefully not stupid question..is it possible to modify the circuit so the sound frequency is controlled with only one pot?

If R.G. had wanted that, with sine-wave output, he would not have used this nice simple oscillator.

It's a real problem for simple audio sources, and I'll have to work it out.

What do you want? If you just want a semi-tone of pitch and only "tone" output, change R3 to like 6K8 plus 5K pot.

Even then, because of how R4 trims the gain to 1.00000...., any change in R1 R2 R3 will want a change in R4's trimmers.

And if you take this idea further, the oscillator will get unhappy, quit or go square.

The "right" way is to change all three capacitors C1 C2 C3 in proportion. You can't get trim-caps this value. You could try switching values, but the C and R interacts so if the ratio of the capacitors changes even a little, you are back to trimming R4 every time you switch.

Not "only one pot", not with this plan.

The real "problem" is to get a Sine with one pot frequency. Most wide-range solutions use two pots on one knob plus an automatic gain trim to keep it oscillating despite minor mis-match between pots.

For many audio workbench uses, a triangle would be just as good, sometimes better,

But not here. R.G. uses self-oscillation and marginal-self-oscillation to get the "Notes" mode. The simple triangle generators don't oscillate like this, they are function generators.

Sure, it is "possible" get just what you want. Let the tone generator run steady, with whatever to control frequency. Use a variable gain scheme to make it loud/soft according to an LFO or whatever shape/rate you want.

But design thought has cost. If we pretend that R.G. worked 10 hours and is worth $10/hour that's $100. He's surely worth much more. Your ideas might take longer to think-up. Would the result save $100 in your time and labor?

A gated square is dead simple, two 555 chips. You may find plans as "555 beeper" or "2-tone siren".

[darron]

nice bump on this one from 2010...
not something that i need... but i'd make one for sure if there was a pcb layout for it.... ?      hopefully it would annoy the neighbours slightly less prototyping...

[Cap]

Thanks PRR for your explanation! I'll search for something more appropriate but I'll also try this circuit on my breadboard

[CodeMonk]

This is cool.
When I get a few of my other projects done (Sometime in the next millennium) I'm gonna build this thing.
Hmm...build 3 to 6 of them and set their freqs. to simulate a chord

Wonder if this could be used for breaking in speakers?

[deadastronaut]

my guitar dont sound like this?...if it did i wouldnt be playing it...

but seriously...this 'replicates' a guitar pluck...?...what a hard whack, with a hard pick?.....or a light finger pluck?....bridge or neck pickup?....humbuckers or single coils?....

sorry for the dumb questions.

[boogietone]

The point, I believe, is not to be a guitar synth, but to provide a somewhat controllable "distorted" signal with a simple circuit for basic testing purposes.

[Paul Marossy]

I haven't seen this until just now. Cool idea RG. 

[R.G.]

my guitar dont sound like this?...if it did i wouldnt be playing it...

Yeah, I know. My guitar does sound like this; it's why I went into electronics.   

but seriously...this 'replicates' a guitar pluck...?...what a hard whack, with a hard pick?.....or a light finger pluck?....bridge or neck pickup?....humbuckers or single coils?....

Seriously, no. Not like any of those. It doesn't sound much like any real guitar, nor was it intended to. It's just an intermittent oscillator that makes a test signal for seeing whether a pedal/circuit is working kinda correctly without lashing up a guitar, cable, amplifier and *person to pick it*. It's a quick and dirty aid for a test bench.

When I get frustrated with a test setup, I often think "hey, I need a box that does this to help me with the test". The box usually doesn't exist, so I make one.

The problem you're talking about I solved before, in a different way. I have a friend who had a vintage guitar store. The idea was to take a laptop with a sound input into the store and make high quality recordings of vintage guitars with pickups of all kinds at various control settings and picking types. The recordings would be cleaned up and spliced together into really, really dull "songs" of repetitive notes on a CD at inter-consistent levels as a reference signal tool for making pedals. (If I had been able to get this done, I'd probably have pressed CDs and sold them, perhaps through Small Bear, although they'd be pirated instantly and the totals sales would have been about 7 discs. But that's another story.)

I have a personal problem. I can't stop inventing stuff, of all kinds. I literally woke up this morning with a solution to a problem I'm having. I have board fences on the entry way to the property. The fences have posts every ten feet and four boards running laterally between posts at about 1 foot spacing vertically. Over time, the boards split at the places where they're nailed to the posts. Takes a few years, but it eventually happens. So you gotta go nail up and replace boards every 5-6 years. It occurred to me that the problem is that the nails force the wood to split, and once it splits, it gets worse. Drilling a hole for the nail only helps until the weather makes it split there. I woke up with the image in my head of a washer with a hole for the nail, but with teeth bent down around the edges. You put the nail in the washer, then nail it in, teeth to the board side. The teeth are arranged to dig in about 1/3 of the board's depth and force the board back toward the nail. This prevents most splits, and reinforces any that do happen to prevent the board from falling off until it's really, really bad.

[Gus]

R.G.  maybe you could use a tee-nut?  Drill a clearance hole for the center part and then hammer the tee nut into the board from the front and nail the board tee nut(s) assembly to the post thought the hole.

http://en.wikipedia.org/wiki/T-nut

[Thomeeque]

If I had been able to get this done, I'd probably have pressed CDs and sold them, perhaps through Small Bear, although they'd be pirated instantly and the totals sales would have been about 7 discs. But that's another story.

Yep, I'd probably burn one T.

[R.G.]

R.G.  maybe you could use a tee-nut?  Drill a clearance hole for the center part and then hammer the tee nut into the board from the front and nail the board tee nut(s) assembly to the post thought the hole.

Yeah, a second after I visualized a spiked washer, a T-nut came to mind. T-nuts have two big issues. First, building fences in Texas heat with a drill in hand is a true PITA. Second, all the T nuts I've seen have three prongs. You really want four, two on each side of the central hole, and not one of the three reinforcing the tendency to split with the central hole. I was after the ability of the toothed washer to bite into and actually reinforce the board toward the central nail hole by slightly angling the prongs outward. Driving them in forces the wood toward the central hole.

I may have to see if there's a shop that will make a die for me. 

[boogietone]

May be more trouble than washers, but how about using bigs$$ staples above and below each nail. With a decent staple gun, it should go pretty quickly, which of course is the key in the Texas sun.

[Fender3D]

Just a little bump to this thread 

But this is a real challenging DIY ... http://player.vimeo.com/video/36981447?title=0&byline=0&portrait=0

enjoy it 

[seedlings]

My fake guitar is called an RC-20XL.

Mine is named Jamman delay.

CHAD

[DavenPaget]

Probably deserves a PCB layout - unchecked .

[stringsthings]

this circuit is one of the most useful tools i've ever owned ( let alone built ) ... with the oscillator hooked up to a circuit, it frees up your hands to do testing/reading voltages/etc .... i use it just about every time i get a build ready for testing ...

[ORK]

What I need is not a fake guitar, but rather a fake guitarist.

[R.G.]

What I need is not a fake guitar, but rather a fake guitarist.

Kewl! I've been told many times that I'm a fake guitarist.