Can someone help me figgure this out?

[zurpman]

I'm new to modding pedals and do not have the courage or confidence to build my own stomp box yet.

But, right now I have a Fab tone distortion pedal that I want to mod. One of the Mods I've seen for it suggests replacing R10 with a 470k resistor to allow for more gain potential. This comes from the Wampler book... What I want to do and wonder how it can be done. Is I want to leave the R10's 220k and put in the 470k and maybe another resistor in between those values in there.

And use an Oscillator to switch between the three resistor values at a set frequency, or even better if I could put a Pot in there to control the Oscillator's switching rate. My thoughts is that it will switch between the different gains continuously as I play.

Any suggestions on how this can be accomplished? Would what I'm trying to do cause me to need a different power supply? Is it even possible?

[LightSoundGeometry]

I think you could runs leads from the motherboard to another network of circuitry and then to a rotary switch for control of new nework of resistors back to original circuit?

https://www.taydaelectronics.com/catalogsearch/result/?q=rotary+switch

[Quackzed]

you could use a 'led chaser' typr circuit. it uses a cmos 4017 chip and a 555 timer chip to basically turn each led on one a a time. in your case you would want it to 'turn on' a different resistor one at a time. you can use up to 10 different leds or in your  case resistors, or just three different resistors if you want, you'd just take the 4th on pin and wire it to the reset pin and it'll go 1 2 3 1 2 3 1 2 3 etc...  you'd need to add a 4066 chip to 'switch' each of the 1 2 3 4017's outputs on/off , you'd just take the first 3 outputs of the 4017 and feed each into one of the control pins of the 4066 (it has 4 switches you'd need 3) and add each resistor to its designated 4066 channel, and the 555 timer goes into the 4017's clock to tell it to switch,it could be adjustable with a pot to decide 'how fast' it switches...
here are a few links to look at...
http://www.eleccircuit.com/led-chaser-by-ic-4017-ic-555/

http://www.electroschematics.com/6311/step-switch-selector/

that on is almost what your looking for, but instead of ic1 you'd use a 555 timer chip as an oscillator to 'step' or  'clock' the 4017 through its sequence... ic3's A B C switches would all have one pin of each switch connected going to one end of the 'switched resistor slot' and the resistors would all be tied together on one end going to the other side of the 'resistor slot' with each resistors free leg going to the 'unused' pin of each A B and C switch...

[PRR]

> Is it even possible?

Everything is possible (in some way).

> do not have the courage or confidence to build my own stomp box yet.

What you propose is significantly more complicated than building a pedal from a known good plan. If a 1-resistor mod is "1" complexity, and from-scratch FuzzFace is "5", this radical gain-wobbler add-on is more of a "10". (As Gil's detailed speculation suggests....)

[GibsonGM]

PRR  +1,000,000   

Don't be shy, Zurpman - jump in, build a fuzz, booster or something!  No worries, if you mess it up, we'll help you.   More likely to wreck your existing pedal(s), I think.     

Your gain switching is not a bad idea, it is just complicated.  In time, you will build the skills to do that, if you want to.

Welcome to the forum     

[Quackzed]

Good Point, yeah, the whole electronic switching chapter is pretty steep stuff... you're not likely to get anything but frustration out of it. i guess i dove right in due to having done that kinda stuff in the recent past and it was all still fresh in my mind, i kinda missed your comfort level/experience and went right in!  . build a few fuzzes man, they're a BIT of a pita at first, but you'll learn good stuff in the process and it'll be well worth the effort. i got a big kick out of my first fuzz, i think i eventually modded it to death, but thats due to getting a big buzz out of it!!! ...all the possibilities that is...

[zurpman]

hey guys thanks for all the replies.

Quackzed, Thanks for all the information, this really seems like what I want to do. My brother
is a certified electronics tech and will look this over when I'm done, but I want to do the build.
I will check into the information you gave me, looks like I have some studying to do and this is a
great start. Thanks again!

PRR, yep looks like it is. I honestly had no clue if it would be or not. But, had I done my own
pedal I would still have the same question. This idea came from a random conversation with my brother
about how different electronic components work. I like the idea of a circuit, part, or mechanize
switching the resistors for me either randomly or at a controlled frequency.

GibsonGM, Thanks for the words of encouragement!! I'm actually excited about it being a complicated
build. Let me rephrase something... I do lack the courage and confidence to build my own stomp box
but, I don't mind failure, but nothing ventured nothing gained right?

The pedal I'm modding is my fabtone, which is about 12-15 years old. If I break it in this attempt
That will give me a chance to learn how to fix that. And if i destroy it, then it is just gone

So far I have successfully modded a DS-1 with the synth mod. Any other reading or resources
that you can point me to for this idea would be much appreciated. I just want to see what parts I will need
and yes, I would like to ask questions along the way.

If I commit to this, as I go along I will keep you all informed as I make progress or break stuff.

Thanks again for all the great input so far!!

[Quackzed]

there you go. 

[Quackzed]

a few caveats:
-----i did't figure the speed range, so r1 and vr1 will probably need to be changed 'my gut says r1 10k vr1 100k will be in the ballpark and have too fast and too slow available at the extremes, but why should i hog all the fun! 
-----also some kind of on/off switch would be nice, bypassing the sequencing as well as killing the osclillation maybee? more fun!
-----i'll guess it won't pop (i may be wrong) not sure about the internal switching of the 4066 as far as speed or transients but it might be fine w/out any pop resistor added... not sure.  are we having fun or what?!?
i'm gonna throw this up in its own thread as it's a pretty neat little add on circuit and isn't too bad as far as parts, other than the chips theres not much to it...

[smallbearelec]

I'm a little surprised that no one mentioned this: Don't commit this to solder and expect it to work right off the rip. Especially because it's experimental, Breadboard It First! If you don't have a breadboard, adding a small one to your order for chips is a small investment. Get it working on the breadboard, and then Get Help (maybe from your brother) with turning the prototype into a suitable layout. This step is major and loaded with minefields. I don't mean to discourage, do want it clear that you have chosen a steep learning curve. Let us know how it goes.

[zurpman]

Quackzed, Thanks! This is exactly what I am looking for! I'm ordering parts this week and smallbearelec I am going to breadboard this. I even considered trying to build the entire fab tone on breadboard, but I think I'll stick to making this circuit on breadboard. Then testing it in my pedal.

As far as an on/off switch I have a couple of ideas for that. I'd kind of like to put a potentiometer from one terminal where the stock resistor was. And add an on/off switch to the other terminal, that way I can switch from having the circuit on to by passing it in the off position and having a potentiometer (I have an extra 10k pot in the mail). If this works out I could turn the circuit off, then have a pot active to have control over the gain.

This does indeed look like a lot of fun and frustration on the way!!  Thanks again guys I'm off to order what I need for this circuit!

[zurpman]

Oh one more thing... I know I will need a power source for the breadboard. But, if this all works out and I can move it to the pedal will I need another power source? Or will this tie into the pedals power source?

Thanks!

[balkanizeyou]

this circuit is running on 9V power supply, so you just connect the 9V point of the schematic to the 9V rail of the pedal, same goes with ground, no need for any additional power supply.
You can power the breadboard with a 9V battery and a battery clip.

[thermionix]

switch between the different gains continuously as I play.

Not trying to be a jerk, but...why?  I'm having a hard time imagining how this could be useful.

[zurpman]

balkanizeyou, Thanks like I said I am new to this and not too sure on how all this works just yet 

thermionix The reason why is simple because its there and can be done. this is all about fun and learning. but let me just ask you something you read this thread right ? is there any advice or anything you can add to help me out ? Thanks !

[zurpman]

Hey guys,

Just a quick update on this mod attempt. I used the circuit Quackzed posted and it worked! But, it was far to fast to distinguish any changes. So I put another 0.1 uf capacitor in parallel with the one in the sequencer that was posted. I also replaced R1 from Pin 7 of the 555 timer with a 470k resistor. The three leading from the 4066 and being switched out I used R1 10k R2 100k R3 470k.

Now I have it slow enough to tell a difference in sound. The problem I ran into was it is introducing noise in the form of a loud thump about 7 or so times a second. The pulse seems to be in line with the switching speed and is always there even when idle.

I'm working on an alternative solution because the effect I'm going for is a ramping level of distortion at a controllable  rate.

Do you have any other advice on something to try, or a good project to learn with? I'm having fun so far!

[robthequiet]

Good project. Had a flash of inspiration, maybe you could fork this project into a "tone sequencer", aka a [sort of] sample & hold ring modulator? Probably done by someone in this forum already, of course, but it's great to see how one guy does it a certain way. When you get to something you like, it would be cool to have an audio or video show and tell. Rock on.

[Quackzed]

Heres a Version 2 attempt, to try to get rid of the 555 thump and have a better range of speeds...
uses a schmidt trigger inverter oscillator instead of the 555 and  adds a bias network for the 4066...

[smallbearelec]

The problem I ran into was it is introducing noise in the form of a loud thump about 7 or so times a second. The pulse seems to be in line with the switching speed and is always there even when idle.

I should have foreseen this. The 555 is notorious for dumping noise onto its power feed when it switches states. I discuss this some in this article on my tremolo:

http://diy.smallbearelec.com/Projects/TremBear/TremBear.html

The ideas in there may give you some help with getting rid of the ticks.

I'm working on an alternative solution because the effect I'm going for is a ramping level of distortion at a controllable  rate.

Try subbing a photocell for the resistor that controls the distortion level and exciting the photocell with an LED ramping up-and-down like in the trem. I can't tell you which photocell

http://smallbear-electronics.mybigcommerce.com/photocells-cds-5mm-diameter/

would work best, but they are cheep enough to experiment with. You Will still need to pay attention to filtering and grounding of the 555 circuit.

[zurpman]

Hey everyone,

Thanks for the info and help with this! This is pretty fun stuff to experiment and learn with.  Quackzed I will try the revised circuit, just need to order a few parts to make it.  I will update both this thread and your original thread of the resistor sequencer schematic with my results once I'm done and have tested.

Smallbearelec, My other solution idea was exactly that! I wanted to use a LDR + led to get around the thump. I will try Quackzed's new schematic, and this solution too. Also thanks for the article man, I will read it and use anything I learn from that as well. This is all a learning experience for me.

Thanks again everyone, I will keep you posted!