Andy 40's Madbean Snarkdoodle (Overdrive Pedal)

[Andy40]

Thanks Mick, I'll give that a go and see. I thought it may have been the diode but i don't have another one to try.

[DrNomis_44]

Fourth time lucky....

would you believe?
Attachment 19047
Thank the electronic gods...i needed a win.

Sounds pretty good, my only complaint is that it totally craps out if the gain is turned up to full. Clearly the circuit cannot handle it.

It might have something to do with my substitute parts.

First, I used a CMOS IC 4049 (Hex Buffer) instead of a CD4049UBE as the IC;
Second, I used a 1N4004 instead of a 1N5817 as the Diode.
The rest of the components are about the same.

If anyone has any ideas about how I can limit (smooth out) the gain, let me know.

It shouldn't make much difference if you use CMOS 4049 instead of a CD4049UBE, the CD4049UBE is a Hex Inverter IC, that's made using CMOS (Complimentary Metal Oxide Semiconductor) technology, the "CD" in the IC type number indicates that it is a CMOS Device, it may be that the CMOS 4049 might have suffered from ESD (Electro-Static Discharge) damage, which most of the early CMOS devices were prone to until manufacturers started incorporating ESD protection in them.


You could also try using a CD4069 because it is a Hex Inverter too, although the pinout might be different, they are both functionally the same.


The 1N5817 is a Schottky Rectifier Diode with a forward voltage drop of about .3V as compared to a 1N4004 which is a standard silicon rectifier diode with a forward voltage drop of about .6V and a PIV (peak inverse voltage) rating of 400V, that really shouldn't have much effect on the operation of the circuit.

[Andy40]

Thanks doc. That was an awesome explanation. Have you any suggestion regarding the issue? If you need a sound sample I can put one up

[DrNomis_44]

Thanks doc. That was an awesome explanation. Have you any suggestion regarding the issue? If you need a sound sample I can put one up

Might be a good idea to put up a sound sample so we can hear what's going on, when you turn up the gain, does it sound like it's going into self-oscillation?, if it does, you could try connecting the metal plate of your breadboard to circuit ground and see if that fixes it, I had that happen to me once when I was breadboarding a circuit on one of my breadboards, soon as I connected the metal plate to circuit ground the circuit started behaving normally.

[DrNomis_44]

From looking at the Snarkdoodle circuit, it looks like it is based on the Tube Sound Fuzz circuit that was designed by Craig Anderton, who included it in his book "Electronic Projects For Musicians", I've built the circuit before and managed to get it working pretty well on a piece of Veroboard, I might have a go at building the Snarkdoodle one day.


Sorry for the double-post, Firefox was behaving a bit weirdly and wouldn't let me edit my previous post cause the keyboard wasn't responding, had to restart my laptop to sort it out.



Anyway, in the Snarkdoodle circuit each of the used inverters are actually not used as inverters, they are actually being used as amplifiers by being made to work in their linear region, in the circuit diagram, you can see a resistor (R3 in conjunction with a 1M pot, and R5 1M) going from the output of each of the used Hex Inverter stage to the input of that stage, this negative-feedback resistor sets the overall gain and makes the inverter work as an amplifier.


The pot in series with R3 gives us a way to control the gain of the first inverter stage, you will also notice that there's a small value cap in parallel with the resistor, this is to prevent the inverter stage from going into self-oscillation, to further stabilize the circuit, I would put a large value cap across the points where the 9V battery connects, maybe say a 100uF to 470uF/16V cap.

[mjg]

I think it already has the 100uf cap - it is c6 in the schematic?

I reckon play around with the r3 and gain pot, see if a different value will get the sound you want. As DrNomis said, they are setting the gain factor on that first stage.

You might also find that the circuit is quieter and less distorted once you get it on the PCB. I find that bread boarding will sometimes introduce a whole bunch of noise due to the wires going everywhere.

[Andy40]

Wow Doc! its like someone turning a light on in the dark! totally makes sense.

The gain pot doesn't do a lot till you turn it waaay up.

Heres a link to a sound file. https://soundcloud.com/andy40-923020...k-doodle-test1

Sorry is not a real amp, but it sounds the same going into my Blues Cube. Its going into my Zoom G3X Pedal. I think I just used a tweed amp simpulator with some reverb and my Pitbull ST-1 going into the Sanrkdoodle circuit.

For the first minute, I have the gain turned right down to 0 and I am just increasing the volume up at stages.

From 1:00 min I turn the volume down a bit and turn the gain right up, then I increase the volume at 1:25min and you can hear it start to not handle it - that's my problem right there.

[DrNomis_44]

Wow Doc! its like someone turning a light on in the dark! totally makes sense.

The gain pot doesn't do a lot till you turn it waaay up.

Heres a link to a sound file. https://soundcloud.com/andy40-923020...k-doodle-test1

Sorry is not a real amp, but it sounds the same going into my Blues Cube. Its going into my Zoom G3X Pedal. I think I just used a tweed amp simpulator with some reverb and my Pitbull ST-1 going into the Sanrkdoodle circuit.

For the first minute, I have the gain turned right down to 0 and I am just increasing the volume up at stages.

From 1:00 min I turn the volume down a bit and turn the gain right up, then I increase the volume at 1:25min and you can hear it start to not handle it - that's my problem right there.

You could try reducing the value of the coupling caps between each of the inverters, that will reduce some of the bass frequencies, I'm assuming that's what the problem is, too much bass in the tone, I'll have a look at the circuit again and post some suggested cap values to try.


Okay, you could try reducing C3 to 22nF (.022uf, or 223), and C5 to maybe 100nF (.1uf, 104) and see if that sorts it out.


I may need to breadboard the circuit so that I can see if I can figure out exactly what's going on and maybe tweak some of the component values.


Update:

I just had another listen to your demo and I made sure I paid careful attention to what I was listening to as it got to the 1:25 mark, and I see what you mean, it seems to go a bit glitchy there in comparison to the smoother sound you get at lower gains, hmmmmm.....try giving those cap values I suggested a try and see if that gets rid of the problem.

[Andy40]

I think it already has the 100uf cap - it is c6 in the schematic?

Yhep, you are right C6 is a 100uf 16v electrolytic cap

You might also find that the circuit is quieter and less distorted once you get it on the PCB. I find that bread boarding will sometimes introduce a whole bunch of noise due to the wires going everywhere.

Yhep again Matt, there is definatley an overall buzzin that i thought may be reduced once on the PCB and boxed.

alright I'll try changing R3 to either 50k or 200k and I think ive got a 500k pot somewhere here too! I'll also try connecting the metal plate of my breadboard to circuit ground

I'll also try reducing C3 to 22nF (.022uf, or 223), and C5 to maybe 100nF (.1uf, 104)

Thanks guys you really are helping me out!

[DrNomis_44]

Yhep, you are right C6 is a 100uf 16v electrolytic cap



Yhep again Matt, there is definatley an overall buzzin that i thought may be reduced once on the PCB and boxed.

alright I'll try changing R3 to either 50k or 200k and I think ive got a 500k pot somewhere here too! I'll also try connecting the metal plate of my breadboard to circuit ground

I'll also try reducing C3 to 22nF (.022uf, or 223), and C5 to maybe 100nF (.1uf, 104)

Thanks guys you really are helping me out!

No worries mate, hope that sorts it all out, when I get round to breadboarding the circuit I might make some mods to it, like maybe add a tone-stack of some kind to it, I'll post the mods in this thread.