PuzzleSounds RC Booster. First project fail!

[lutherd672]

Bought a kit from PuzzleSounds.  Info below.

https://puzzlesounds.com/wp-content/uploads/docs/effect-pedals/doc-rc-booster.pdf

Got e wet thing hooked up correctly for the most part. It calls for 2 led's.  I broke one but put a jumper in it's place till I can replace it.  Confusing part is it calls for 1uf cap for c2 and c9.  These slots are not for electrolytics but that's what the kit came with.  I put them in there but there's no indication for polarity like in the other slots for the electrolytics.  They just don't seem to go where the manual states.  In the pics of the manual they use film boxes.

Anyway, checked for continuity and everything seems to be connected.  The led comes on when the foot switch is engage and signal is coming through when bypassed just NOT when effect is turned on.  Goes silent.  Any tips would be appreciated.  This is my first build so I'm aware I'm not a master at soldering yet but I'm fairly sure everything is receiving connection.

[iainpunk]

welcome to the forum,

i suggest you lookt at this link:debugging guide

cheers, Iain

edit: i can't seem to find a schematic, do you have it?

[lutherd672]

The schematics are different than what the list says so I don't know what is what.

[idy]

Welcome

I'm failing to see the manual, slow net here, but....

Sorry they sent you caps that don't match the PCB, and pots that don't have PCB solder pins... let's hope everything else is OK. Do the two transistors have the same numbers as the ones in the schematic? *Any* NPN transistor will work for these buffers but they don't all pinout the same.

Assuming this is a clone of the Xotic RC/AC...

You didn't show us the wiring side of the footswitch, a very likely source of this kind of problem.

Replacing the LED (there are three diode spots on the PCB, you have only one filled) could also kill things. You put in two jumpers. Likely one of those is OK in that if connects to the LED, but the other is shorting things out. The effect probably calls for an "asymmetric" arrangement with two in series in one direction and one in the other direction. You could pull both jumpers and even the LED and you would have an even cleaner booster with high gain introducing Opamp clipping instead of diode clipping. This is also confusing because the RC had 6 diodes and the AC had three... so things may be a little mixed up. The "Puzzlers" offer separate boards for the two effects, everybody else just tells you how to build either way on a single PCB.

You will need to make sure those electrolytics are in right way 'round. You could wreck them. You could try measuring the voltage on each side of a cap. The - sign should be attached to the lower number. Those are probably in the audio path, the RC had a 1uf after the first transistor and a 10uf after the second. If these are the ones you mean, the + side should be attached to the emitters of the transistors.

You also jumpered one of the capacitors. That's suspicious...on the RC there is a cap you leave out (compared to AC) but you don't jumper it...that would also short out your sound.

[iainpunk]

that schematic helps a lot!
the issue is that LED replaced by wire, that shorts all signal to ground, instead of clip at a certain threshold. replace it with a diode, any diode, that would probably fix that problem.
even taking the wire out and leaving it open, nothing in the holes is an option, lots more headroom.

cheers

[lutherd672]

Thanks for the replies! The jumper in the diode section and the cap on c4 was something I tried after the initial fail.  It's since been removed but you guys are saying I could take that whole section out and it would be ok?

Yes the transistors are the same as in the schematic. 

The foot switch isn't wired.  It's connected by pins. Doesn't stay connected very well. I suppose that will improve if it is mounted so I just removed it in the pics. 

[lutherd672]

Ok so I removed the diode jumper and the led and it fired right up! Thank you so much! So now what would be the benefit of replacing the 2 leds on the pcb?

[idy]

So congratulations!

You should do some reading about maybe tubescreamers or opamp overdrive pedals, they are many variations on a simple plan. Try the famous GEOFEX article

http://www.geofex.com/article_folders/tstech/tsxtech.htm

The opamp boosts the signal;, as you turn the drive knob you get more gain. This is because you are varying the resistance in the "negative feedback loop.' Essentially if the "inverting" (negative) input is getting the same signal that the "non inverting" input gets, the opamp is satisfied and doesn't boost any. If you "lose" some of that signal (turn it down with that gain knob) the inverting input gets "not enough" and the Opamp begins boosting until the level is back up to where it is on the other input.

The diodes are also in that loop. When the signal gets above their forward voltage (1.2v? 2v?) they switch on and begin conducting, immediately bringing the gain back down, where they switch off again. This happens on every cycle of your signal and that on again/off again is clipping.

With the diodes removed you have a very loud clear booster, although you can probably turn it up far enough that the opamp itself clips by trying to make the output bigger than the supply voltage (impossible.)

Putting the diodes in will give you a distortion pedal. You can use myriad types of diode (Ge, Si, zener, Schottky), and even transistors (mosfets popular here) to do this, and they each have their own fingerprints. People describe LEDs as loud (higher voltage than regular diodes) and crunchy (subjective.)

Asymmetry is where you put a different combination on the two directions of clipping, making one side of the wave clip at a lower level than the other . Some people talk about different harmonics, I hear it as some of the original sound is preserved even as the sound starts to break up. You still hear the character of your guitar in addition to the fingerprint of the diode(s).

[lutherd672]

This is all very helpful thanks!  I do believe I want it to clip considering it has a gain knob.  So I'll probably put the LED's in.  Side note: is there a way to bypass all the questions required to leave replies?

[duck_arse]

This is all very helpful thanks!  I do believe I want it to clip considering it has a gain knob.  So I'll probably put the LED's in.  Side note: is there a way to bypass all the questions required to leave replies?

yes - post more. that way, Aron knows you aren't a spambot, or similar, and he lets you in easy.

[idy]

If you replace the diodes you will want to figure out which diode is attached to the jumper. Or rather which two diode spots are "in series."
There are three diode spots and you need to fill all three either with diodes or jumper one.  Jumper the wrong spot and no-workie (short.) Leave the third empty and you will get asymmetry, you might like....