Death By Audio Robot

[aaronwahlmusic]

Built a Death By audio Robot Pedal. Sounds wicked, but I get a high pitched constant noise when I roll down the volume knob on my guitar. I previously had a very very similar problem with a 1-knob colorsound fuzz pedal. Now, on both pedals I would turn the volume knob (on the pedal) and it would give me that scratchy sound (usually means a bad pot, right?). So from that, I gathered that maybe in both devices I just needed to replace the pots. Is this a likely culprit? Do mammoth pots tend to not work sometimes? Thanks guys, let me know.

[Dr Satan]

A scratchy pot can be indicative of dc voltage on the pot, not necessarily a bad pot. As for the whine, I think that's an impedance mismatch issue. I've experienced it before but I forgot where and what I did to remedy it.

[aaronwahlmusic]

What do you mean by Impedance mismatch? used this layout. http://1.bp.blogspot.com/-QbkA3stWJAk/U ... ot+Mod.png
And by DC voltage on the pot, do you mean on the back of the pot or on one of the lugs?

[jurioste]

" Q - Why doesn't my Robot pedal work with my multi-pedal power supply?

A - The main chip inside the Robot uses positive and negative power. This is usually incompatible with standard multi-pedal power supplies. It will work with any standard (one pedal) 9v adapter.
"

[aaronwahlmusic]

@Jurioste - I've tried it just by itself and I still have the same issue.

[aaronwahlmusic]

I'm having trouble with high pitch noise again. HELP? Could I possibly put a volume trimmer on the input of the circuit so that the volume is never max? Also, the switch pops when I press it. Please help, somebody, I'm kind of lost on this one.
Here's the board and everything.

[aaronwahlmusic]

Also note that when I took the 2nd pic, I hadn't finished the off board wiring yet.

[eatyourguitar]

I think its your layout and long wires. if you had a 2-layer pcb with ground plane and pcb mounted pots your problem would be less likely. after all, it is a correct schematic right? check the tagboard effects blog and see if anyone actually tested this layout. check it against any info you find on FSB. they sometimes make mistakes at tagboardeffects

[aaronwahlmusic]

I don't think it's the layout. it's verified at tagboard. Im building the rotary switch version which works better. Idk, but I'm convinced it's a bad volume pot, because I've had this problem before with a fuzz, and it's volume pot.

[Dr Satan]

It could be the pot, it could be that you heat up the lugs too much when you solder them, or you don't have the dial rotated all the way in one direction or the other, or solder dripped in it from soldering at the wrong angle or something. There are all sorts of things that could cause it. I'm pretty sure I've ruined a pot or two myself before I got a good method down. It's part of learning so don't take offense, I'm not downing you or anything.

Have you ever built or used an SHO? That "crackle OK" is from DC on the pot. And because of the way that design is, you hear it in the audio path. AC and DC can and do travel on the same wires. Caps block DC (mostly) and are used to couple gain stages and whatnot in amps and effects (transistors are often used as just little amps) but you can't always just couple them directly or the voltage present on one part of the circuit will effect the next part, so you put caps between them so that the audio (AC) can pass through, but not the DC (or at least not enough to matter, nothing is perfect and caps do "leak", as in some DC voltage passes through them but very minimal) If there is DC on the output of whatever in your pedals there and it goes to the volume pot, you'll hear a crackling when you turn the pot. So between the last output or last input or both (depends on the circuit) and the voltage divider for the volume, you need caps to block DC. These types of thing are much easier to spot in a schematic than a layout. Nothing wrong with following a tagboard layout or whatever, but you will be much better equipped to troubleshoot if you have a schematic that you can read along with it.

Impedance is basically an AC load. Like a resistor, but for AC, but basically when you have a mismatch, the device isn't properly loaded. You may be able to just put a resistor in line. Or you may need a voltage divider. Typically you'll see a 100K to ground followed by a 100Ω in line (voltage divider) on the output of an op amp if it is a buffer that is post volume. Which I think is what's going on with your the Death By Robot or whatever.

As for switch pop, yet another mismatch but this time by means of DC offset. Mr. Black explains it best so I'll direct you there.http://www.mrblackpedals.com/blogs/straight-jive/6629778-what-really-causes-switch-pop

[aaronwahlmusic]

Thanks SO much, I will look into that. and my SHO clone does have that similar crackle.