A fake guitar for your test bench

[Ripdivot]

I use my MP3 player for testing. I recorded a guitar part and looped it over and over for about 5 minutes. Works great and gives me a better idea of what the pedal sounds like. I feed the pedal into an amp. I guess I'm just re-amping...

[darron]

i'm hanging out to hear a sound clip of how this sounds!

i can't imagine it having all the richness of a real guitar (harmonics, or a power chord etc.), so it might not suite me for wanting to prototype distortions/fuzzes but it sounds excellent to add to the test rig!

maybe a magician could make a few oscillators which then modulate, so there's a wider frequency range to test. not complaining, this is some awesome work which has kindly been made free (:

[slideman82]

So, I'm lost. What does this thing do? How does it sounds?

[darron]

So, I'm lost. What does this thing do? How does it sounds?

maybe i'm wrong. it was my impression it generates a tone and then fades it away and repeats, like a guitar string being plucked over and over. it might not actually sound like it but for testing purposes it would be more useful to see how the circuit respond to a decaying signal than a simple pure sine wave.

[danielzink]

So, I'm lost. What does this thing do? How does it sounds?

There are sound clips on both pages one and two of this thread......

[darron]

There are sound clips on both pages one and two of this thread......

thanks. there i was hanging out. it's been a while since the thread was last bumped. sounds pretty useful in the seconds clip (page 2).

now will we make effects for the fake guitar and build them in? hehe

[DavenPaget]

All this while i just use my friend's cover of my favourite song .
http://soundcloud.com/djdestiny-2/bc-cover-by-syn-humbucker-mode

[jwmallett]

First of Thank you R.G. for providing this info for online use, it is a great Idea and will be a great addition to my bench!

I am attempting to sandwich this idea with the beavis board. Basically take out the spst of the beavis board and add another 1/4 jack and a 2 switches. Switch one To bridge terminal in/outs if I am using an already built effects pedal instead of breadboard and the other to turn the oscillator off/on if I want to test an instrument instead. The jack would be amp out and guitar in(effect in if using oscillator) but the third jack would be oscillator out(to effect in) and lastly, turn one of the terminals into an oscillator out for the breadboard. This way I can test built pedals and breadboard projects.

Anyway, I am about 80 percent of the way done with the wiring of the box. I saw the PCB image of the wiring layout by Dave, btw thanks man! I am still perplexed about wiring this thing up. I looked at the vero layout and compared it with R.G.'s Schematic. I figured out as much as the wiper on the volume would be the output. I was confused about how to hook up the length and speed pots. At first I was thinking I had to do something from the switch sort of like Dave did. However, looking at his layout raises more questions. I see he has Tone and Note Lengths, but no speed pot? From R.G.'s Schematic I would presume that dave used a standard pot instead of a trimmer for the notes? Ok but is this the correct way to wire these pots up? or is this a good alternative?

I am not very keen at tracing a layout from a schematic, I am getting better. From RG's schematic I could gather that 3 and 2 of the Length pot would be hooked together but from the vero layout there is no specifics on how to wire the switch/pots. Sure, I see "1 a, lug 2" etc, but it left me hanging with which lugs on the pots and also whether or not the lug 1b or 3a got any attention.

I saw R.G. say he was gonna post a layout, did I read that correctly? I feel so ignorant, many people have built this it seems but I seem to be the only one confused?  

Can someone shed some light on this? when my 3pdt toggles come In I am ready to hook this baby up.

[R.G.]

First of Thank you R.G. for providing this info for online use, it is a great Idea and will be a great addition to my bench!

You're welcome. Glad to help.

I figured out as much as the wiper on the volume would be the output.

Yep, correct.

I was confused about how to hook up the length and speed pots. At first I was thinking I had to do something from the switch sort of like Dave did. However, looking at his layout raises more questions. I see he has Tone and Note Lengths, but no speed pot?

I really should have explained that more I guess. It's kind of cryptic.

The section of IC1 with R1/2/3 and C1/2/3 on it is a sine wave oscillator with a fixed frequency. R1/2/3 and C1/2/3 set the frequency. It is a characteristic of this kind of oscillator that it has to have a very, very specific gain to oscillate without distortion. If the gain is too high, it distorts and is no longer a pure (-iish!) sine wave. If the gain is too low, it will start to oscillate at turn on, or at any disturbance, but it doesn't quite have enough feedback to keep itself going. If the gain is ***perfect*** it oscillates with a pure sine wave.

R4 plus either the "length" control or TR1, depending on where the switch is set, let you adjust the amount of feedback.  The idea is that if you flip it to "Tone", by which I meant "steady, non varying tone" and finely adjust TR1, you can get a nearly pure sine wave out. The reason a sine wave is useful is that your ear can hear the difference between a sine wave and a few percent of distortion. TR1 lets you get a steady test tone.

If you flip the switch to "Length", you can adjust the amount of feedback so that when the circuit is disturbed by the "disturber" part of the circuit, the tone starts up, but dies away. The length pot lets you set this so it takes a goodly fraction of a second to die away, faking the sudden start, then trailing off of a guitar string being plucked. It's the electronic analog of pulling a pendulum away from rest, then letting it go, and coincidentally of plucking a taut string. You can, of course, set "Length" and TR1 both to do either always-on oscillation or dies-away notes. They do the same thing electronically. The difference is just how they're set and which one you put on the front panel.

Both pots cause longer ringing, getting into steady tones, at the biggest resistance. The little dot on the pot in the schematic is the clockwise-most terminal. When you turn the shaft full clockwise, it's closest to the dotted terminal. What that tells you is that the schematic intended for the pots to be hooked up so maximum clockwise rotation was biggest resistance. The connection from wiper to dotted/CW terminal is optional. You could leave off the connection to the dotted terminal of these pots and just connect the counterclockwise terminal and the wiper, ignoring the clockwise terminal, and the thing would work the same.

From R.G.'s Schematic I would presume that dave used a standard pot instead of a trimmer for the notes? Ok but is this the correct way to wire these pots up? or is this a good alternative?

"Notes" means "you get repetitive notes that die away" instead of a steady tone. "Tone" means "you get a steady tone that doesn't die away".

I saw R.G. say he was gonna post a layout, did I read that correctly? I feel so ignorant, many people have built this it seems but I seem to be the only one confused?

No more confused than I am. I had to go back and read what I wrote. By the way, you did make me find a mistake I put in there. The Speed pot is shown wired backwards. As it is, it gets slower as you turn the knob toward CW. The wire from wiper to CW/dotted terminal should go to the non-dotted/ CCW terminal instead, so the resistance goes down as you turn it clockwise.

For this one, the simple thing to do is get your pots, based on how you want the mechanics to look, and for the pots that probably means a front panel knob for speed, and maybe for length. I would use a trimmer for TR1, myself, but nothing says it can't be a front panel knob too. It's just that I didn't see adjusting it very often. When you get the pots, get out your meter, set to ohms, and connect one lead to the wiper. Hook the other lead to one of the outer lugs, then turn the shaft clockwise. If the resistance goes to nearly zero, that's the clockwise/dotted outer lug you're on. If it goes to the full nominal pot value, it's the non-dotted/CCW terminal. If it doesn't change, you guessed wrong about the wiper pin and have the meter on the CW and CCW pins.

[jwmallett]

Wow, your response was more in depth than I ever expected. I tend to want to know how things tick and why they do what they do and will spend LOTS of time trying to work it out in my mind. Although, many see this as a disadvantage and wastes precious time getting things done and just "accepting" the rules and move forward. I cannot completely disagree with them, but this is how I am. Anyway, Thank you for that!

I still struggle with all the different ways to draw schematics etc. I started to draw a vero from your schematic, but then I found "stringsnthings" vero all nice and neat, checked a few placements and thought. Why finish tracing your schematic if one is already done? So I printed his:




Perhaps, this was my downfall. Because the wires do not quite match up with the schematic. I have a better understanding about the dot to clockwise and will admit that the speed did look backwards to me, which being new at tracing schematics, confused me.

I assume a DPDT switch a one side b the other with 1 2 3 being the same on each side so that isn't a big deal. Looking at dave's drawing, there is no speed, but in your schematic and on this vero, there clearly is a speed knob. There is no indication on this vero that pots are hooked up to or from the switch. As I said I figured volume out by looking at your schematic. Speed is self explanatory on the vero. Length on the other hand, only shows Lug one being connected. Looking at your schematic and realizing that speed IS backwards, I now gather by connecting the Length 1 wire to the proper lug on the pot allows flow from the Length pot to the TR1 Trimmer. So the next question is where is 2 and 3 on this vero to connect from the board to the pot for continuity? Using Dave's Image:



At first glance clears it up, but then confuses me since clearly he is using single channel I.C's and to top it off, no speed pot. I realize there are so many different ways to wire circuits up that will achieve the same goal, but for a newb like me who likes to think things through while doing it, the lack of experience AND deciding to use 3 different methods to piece it together was not the wisest approach for me. I am not complaining or saying it SHOULD have been provided, but I was wondering if I missed a gutshot picture or wiring diagram from the vero or even the original schematic. If not, good, I feel better I didn't do all this cause of haste or lack of research. I want to learn things on my own, but when I get stuck I know it is better to ask for help and I don't always explain myself thoroughly and I am sure it is so simple for some of you that you wouldn't assume a particular something is all I need. This is a learning experience for me and I appreciate you all making this available online so people like me can learn this in our own time.  I want to be able to transpose a schematic into a layout. Perhaps I should have just finished my trace and went with it first, who knows, might have been the same amount of head banging  . I also, know that creating layouts can be like fingerprints and it is that, which I have learned from this instance, what NOT to do hastily  . I think when I complete this one, I will build take the lessons learned and trace my own and see what I come up with. At this point, I am pretty confident that building stringsnthings vero will work, hook speed up the way it shows and where it says (Notes) attach that to lug one on my pot then lug 2 and 3 on the same pot would lead to switch 1a lug 3? Although there is a Length 1 on the vero already, which I just remembered, so just attach the wire that says (Notes) to the switch like it says, then on the Note Length pot, hook lugs 2,3 to 1a lug 3?? Thanks for any help.  

[jwmallett]

Ok It was 1a lug 3 and I got it working. Thanks for all of your input! Many of the concepts I had forgotten since the last build I know have a better grasp on, and I have learned a lot on this one. I have built about five or six pedals so far and each one has given me lots of trouble! The 3 band parametric EQ actually gave me the least and was the most complex, go figure!   Still want to play with the Tone length and get it longer, as in before I turn speed up to the point where it sounds like a space radio dialing In to my station   .

A couple of things I have noticed and would like to know if this is normal, My switch is a DPDT (on off on) When I am switched to tone, it is signifigantly lower than the Notes and the decay seems a bit longer, but BARELY noticeable AND when I switch the position to off it is a solid tone like when a tv station goes offline, which seems normal. Also, the decay on notes is noticeable but it does off quick, I remember seeing something about that and I will go back and read if there was a solution to give a little more decay, but that really isn't necessary and I guess at this point the time put in would be for learning experience.  My box is pretty crammed and I'm using sharpies at the moment to label stuff, but Ill post a pic of my beavis/fake oscillator smashup once I'm done tinkering, and maybe post my findings.

All in all pretty cool gadget and it is setup with a switch to allow guitar in jack to be on or switched to osc injected instead, then I have a dedicated OSC out jack (for effects already jacked up (pun intended   ) that would then go to my mini fender tone master amp. There is also an amp out jack. Basically if the LED is on, then that means the signal routes to the Terminal block, for breadboarding, then to the amp out socket, when it is off, it goes straight to the amp out and I can choose whether I want the  FGO or guitar as an input, which means the FGO out may be redundant and I have two terminal blocks leftover since I decided against the built in switch that the beavis board layout suggests. Maybe I can make a saucer shaped box and paint it like a ufo and put FGO on it (with included space radio modulator) and submit it for the contest! or maybe not, it's probably over anyway. I'm too lazy to go look before I post. Peace

[jwmallett]

I have finished boxing up my beavis board with FGO inside. I am sure it will come in very handy. I know this is elementary to most of you, but my comment earlier on increasing the length, would not be possible, I think, by adding resistance, because less resistance means longer lengths, therefore I cannot just do this via a pot, perhaps there is another way besides using all gold/silver components    Also, I have no idea on increasing decay, but as I said, it isn't a big deal, so I guess it is time for me to move back to my Echo Base Delay and figure out which component isn't soldered right. And Thanks to RG and BeavisAudio, this will make my troubleshooting ALOT easier!

BTW for those of you who haven't read about the Helping hand +++ instructable(instructables.com) I basically bought a black and decker workbench vise on ebay and figured out tapping the plastic holes on the brackets that hold the boards onto the table with a 3/8-24thread tap you can screw in the connector directly onto this table, a little modified micro or mini irwin quick clamp and you now have a little (and portable) Bench to use the grip to hold your box and the vise to hold boards. This makes it so much easier to remove components and works WAY better than a standard helping hand since it is much heavier and versatile.

Ok, I said I would post some pics and I know my wiring schemes aren't the tidiest, or the whole build for that matter   so here they are:


http://www.facebook.com/media/set/?set=a.3801130118388.148490.1581372303&type=3&l=9b0236078a

One day I will brush up on my gimp2.0 skills and create some stick on decals, but this will do for now.

[mattthegamer463]

Threw together a 2-sided PCB for this one, 2" by 2" size with on-board 16mm alpha pots, switch, LED.  Works surprisingly well in virtual simulation.  If there's interest I might order a batch and sell them to members. 

[asatbluesboy]

That's amazing, and will seriously solve my issue with cables being too heavy and making the whole board fall down, break wires and whatnot...

[tca]

I've been planning in doing something like that... but I always though of building a small synth. I have the schem some where in a old book (have to look for it), if I recall it correctly it as also a vibrato option that could be changed to a slow decay.

(edit)

Here it is; the text is in Portuguese and it is a translation from the French edition of "Les gadgets electroniques" by B. Fighiera 2ed.

The oscillator part uses two BC108 and the vibrato a BC109. The values of the resistances allows a range of one octave.

[pringe]

Hi guys - resurrecting this old thread as it is directly linked to my build of this great little circuit! Hoping you guys (especially R G Keen?!) are still around to point me in the right direction with this one!

I have pretty much finished the unit, but am having a couple of issues:

1. When on the constant (tone) setting, the disrupter part of the circuit is still audible - if I turn the speed pot I can hear the clicks speed up. I'm thinking that this shouldn't be possible since the switch should break the second half of the IC circuit?

2. The constant setting is also quieter than when on the 'note' setting....this may be related to issue 1?

I have visually checked all the veroboard connections for continuity and cleaned the gaps between the tracks to ensure there's no solder shorting out the tracks. I've also double and triple checked all switch and pot connections and tallied them up with the original schematic that R.G.Keen posted (I followed the v1.1 strip board layout when building and referred to the schematic for double checking).

If anyone could offer any advice I would be very grateful - this is one of my first builds aside from FX pedal kits and so I am on a steep learning curve at the moment!

Thanks,

Steve

[PRR]

Welcome.

> disrupter part of the circuit is still audible

Are your C7 C8 *good*?? Large value, proper solder, short ground path?

The oscillator is rather violent. R.G. took care to isolate power and reference so it would not bleed.

With Out Thinking: looks like the unused terminal of SW1 could be grounded to give a small added filtering. Or it may foul something? I don't see how it could smoke.

[pringe]

Thanks for the reply PRR.

C7 / C8 are both fine, correct values, soldered following the vero layout, checked continuity with a meter.

It just occurred to me that I have housed this in a plastic lunchbox for now (all that was to hand!) - could there be any grounding issues here? i.e does the case being physically connected to the pots provide some kind of grounding improvement? I don't know much about best practices for grounding points in circuits...!

Also I just noticed that the TR1 trimmer has to be pretty far to the end of its travel for oscillation to begin, and I don't get into audible distortion territory, something that from reading RG's posts should be possible even though undesirable?

Thanks!