Overdrive Pedal - First Design

[jfrabat]

Hey, guys.  After building a 4 or 5 pedals (most of which are working thanks to support from this site!), I decided to give the first pedal I ever finished a new shot.  The pedal I called the Screechy Cat Overdrive, and to be honest, has been my go-to pedal since I made it (I have made the Ultimate Overdrive, but that one rarely gets used).  I do use my Vulcan Rat, but that is more distortion than overdrive, so it is a bit different.  Anyway, I really like the sound (especially how it cleans up as I go from 10 to 9 in my PRS guitar volume), but I wanted to change a couple of things this time around; (1) get the DC jack working (the original design has no filter and/or protection, so I never connected the DC jack), (2) fit it into a smaller box (I have a Hammond 1590B sitting around that is begging for this project), (3) use better components (not that the one I made sounds bad, but I figured, might as well make it with more quality components, right?), and (4) try out one of the 3PDT Foot Switch with LED Ring I ordered some time back (in green, of course!  Besides, I figured this would allow me to save some space as well... or maybe that's my way of justifying it!), (5) reverse input and output sides (don't know why, but all the pedals I have made are backwards from convention) and (6) etch the board instead of using point to point as I did on the first go around (I figured this will also help reduce the size of the board; I have done a couple of etched boards, and they have come out all right).

Here's a shot of the original pedal (color and graphic style will remain unchanged):



The schematic is actually quite simple; I also borrowed the protection schematic from Ben Lynman:



And this is more or less how it will look like:



I will also use better knobs to give it better aesthetics, but that's purely cosmetic.  Anyway, parts should arrive in a few days (hopefully, before the business trip to Asia, which will leave me out of the building of this pedal for a couple of weeks).  I will post progress here, as well as a sound demo of the original, and at the end, the new version.  If anyone wants the DIYLC file to etch a copy, I will gladly send it (people here have been more than accommodating to me, so I figure I should pay it forward, right?  I know this pedal is very basic and simple, but it does have some good sound to it).  Anyway, I will keep you guys posted on the progress.

[EBK]

What size enclosure is your original in?  It looks close to a 1590B from the pic.

[Renegadrian]

So you build a slightly modified ELECTRA overdrive! simple circuit but great sound! I also made my version some time ago...the ELECTRADRIAN!

[bool]

So you build a slightly modified ELECTRA overdrive! simple circuit but great sound! I also made my version some time ago...the ELECTRADRIAN!

Oh, guity pleasures with elektra ...
I always wondered what makes this ciruit (and the treble boost family in general) record so well - is the polarity flip a contributing factor here?

But back to the OP: you f***d up the gain control. The solution is so simple it hurts - just cut (break) the short between gain pots' 2-3 lugs in your **layout** and solder a 22uF-47uF electrolytic there, "+" to the "3" lug ... the one that goes to the BJT emitter. This will reduce the "scratchy" sounds when adjusting gain.

(Note that you marked the pot lugs differently in your schematic versus your layout.)

[jfrabat]

What size enclosure is your original in?  It looks close to a 1590B from the pic.

I am not sure, but it is slightly larger and taller.

[jfrabat]

So you build a slightly modified ELECTRA overdrive! simple circuit but great sound! I also made my version some time ago...the ELECTRADRIAN!

I will look up the Electra.  I did not even know it existed.  The original idea I got from reading an article about pedal design and it had all the basics...  I just tuned the sound flavor from there...

[jfrabat]

So you build a slightly modified ELECTRA overdrive! simple circuit but great sound! I also made my version some time ago...the ELECTRADRIAN!

Oh, guity pleasures with elektra ...
I always wondered what makes this ciruit (and the treble boost family in general) record so well - is the polarity flip a contributing factor here?

But back to the OP: you f***d up the gain control. The solution is so simple it hurts - just cut (break) the short between gain pots' 2-3 lugs in your **layout** and solder a 22uF-47uF electrolytic there, "+" to the "3" lug ... the one that goes to the BJT emitter. This will reduce the "scratchy" sounds when adjusting gain.

(Note that you marked the pot lugs differently in your schematic versus your layout.)

Thanks for the tip; I will include the pot!  And I will correct the schematics and layout. 

[Renegadrian]

So you build a slightly modified ELECTRA overdrive! simple circuit but great sound! I also made my version some time ago...the ELECTRADRIAN!

I will look up the Electra.  I did not even know it existed.  The original idea I got from reading an article about pedal design and it had all the basics...  I just tuned the sound flavor from there...

FIY I'll suggest you some Electra variants that may interest you, to study the topology and try different solutions!
Joe davisson high gain overdrive
easy fuzz
feel the love overdrive
iibe distortion
le savoreux
moose drive (SOOOO GOOD!)
superlectra
trotsky drive from beavis \m/

I haven't got any links right now but a quick google can give you so many results...

[Kipper4]

Nice font and graphics. Cool.

[rutabaga bob]

Isn't the Woodrow also an Electra variant?

Adriano: a quick Google turns up zero on Moose Drive - more info, please, sir!

[jfrabat]

I will look up the schematics.  I am sure I will include the cap you mentioned, as adjusting the gain does make some noise (by the way, does it make any difference if I use 22uF or 47uF?  I would guess neither affect sound, just how much "buffer" there is for adjusting the scratching, right?)

[midwayfair]

I will look up the schematics.  I am sure I will include the cap you mentioned, as adjusting the gain does make some noise (by the way, does it make any difference if I use 22uF or 47uF?  I would guess neither affect sound, just how much "buffer" there is for adjusting the scratching, right?)

When you hook up the capacitor that way, you maintain a steady DC voltage on the emitter of the transistor because the potentiometer's legs 1 and 3 do not change their resistance. Altering the DC bias is what causes the scratching sound.

The capacitor bypasses, for AC signals only (which is your music), all resistance between lugs 2 and 3 of the potentiometer. As the wiper (lug 2) moves from being shorted to ground (lug 1) toward lug 3 (the emitter of the transistor), the voltage gain for AC signals increases. At the highest gain setting, AC signals above frequencies passed by the capacitor (which is pretty much everything your guitar produces when you use a 22uF) see no resistance between the emitter and ground, so gain is the maximum that the transistor can provide.

For more information, it's worthwhile reading RG Keen's Technology of the Fuzz Face.

Also, the other poster said that you screwed up the control. You didn't. You did something different than they would have done, and something that might not be a best practice all the time but does have an effect on the sound. Your method alters the DC bias, which also alters the waveform's symmetry. It's not preferable because it's less repeatable, and if you ever want to move it with your foot or something, you'll get scratching sounds, but how often do you change the gain while playing? The Rangemaster crackles, for instance, and so does the SHO, and they are both extremely successful designs.

[Renegadrian]

Isn't the Woodrow also an Electra variant?

Adriano: a quick Google turns up zero on Moose Drive - more info, please, sir!

yep you're right about the woodrow

moose drive

[rutabaga bob]

Thank you, my friend!

[jfrabat]

OK, so if I understand correctly, this is the correct schematics and layout I need to build?



And the corrected schematic:



If so, that means I have to edge this:



That sound about right?

What size enclosure is your original in?  It looks close to a 1590B from the pic.

The original is a 125B enclosure size (also referred to as 1590N1 size).  Just checked the site, and measurements match.

[PRR]

> And the corrected schematic:

C5 drawn wrong polarity.

C2 value not given.

Gain and Volume pot values/tapers not given.

_I_ would lean to R3 more like 470 Ohms for better crap-filtering on bad power supplies. I think the difference in delivered voltage and thus "sound" will be nil.

[jfrabat]

C5 I have wrong on both schematic and diagram.  I misunderstood the direction.  The missing values and taper I will also add as per the diagram, which shows them.  So you think 470 is better?  I just dont want to change the sound of the current pedal, which I like, but I could try 470...  It should not make any significant impact in sound, I guess...

[jfrabat]

By the way, going over it, I noticed a typo; C3 is 100nF, not 10nF.

[jfrabat]

OK, more or less finished one (still troubleshooting a short), and making progress on the second...

Here's the one that's almost finished:







The issue I am having is that there is a short somewhere; when I went to try it, no sound goes through either with the effect on or bypassed.  I tested continuity, and there is continuity from the signal to ground (the pots, the case, the ground, all over!).  I took everything out of the case and I still had continuity.  Or do you think the 9V from the battery is making the MM act up?  Just thought of that...  I also checked with the testing cable, and even if I probe the guitar cable jack (when insterted into the pedal jack) there is no sound (it works fine out of the pedal).

Anyway, any help on how best to find that short would be greatly appreciated.  I already went over the entire pedal with a delicate and sensitive analyzing tool (Eyeball Mk. I) and have yet to find any reason for it.

Anyway, this is the second one I am making:



I still need to retouch the paint on that one, so no stickers yet.  I also only had one of those green LED Stomp Switches, so this one uses a traditional LED.

[PRR]

> there is continuity from the signal to ground (the pots, the case, the ground, all over!

"Continuity" is for trailer lights.

We electronic techs have small and large resistors every which way. We need the difference of ZERO Ohms (wire), 10 Ohms, 50 Ohms..... most continuity beepers won't tell that.