First attempt at seriously modding a circuit ( aka HALP)

[nightendday]

So I've built an electra distortion... And I'm wanting to mod it in a few ways. First I want a variable input cap, so I tied lugs 1-2 together and placed a .0047 on that, then a .1 cap on lug three, tied the leads togeth and soldered it all in, can't hear much of a difference while sweeping the pot... pot value is 100k. Next I took the resistor between the emitter and diodes, and made it a pot, this acts as a gain control, which is pretty cool.
My questions are, why doesn't my input cap work, and am I correct in thinking that the resistor between the base and collector of the 2n3904 controls how much signal comes from it? would my gain control be better suited there? ex. Less resistance would equal more gain, thus more signal hitting the clippers. 

[Jdansti]

Welcome to the forum!

Here's some discussion on what you're trying to do:
http://www.diystompboxes.com/smfforum/index.php?topic=71397.msg575780#msg575780

The simplest thing would be to use a rotory switch with a range of caps. I've used as many as 6 caps on a 6 position switch. While it's not continuously variable, you can get some pretty good in between values with 6 positions. Just experiment with a range of caps to decide which ones you want to use on the switch.

[nightendday]

Welcome to the forum!

Here's some discussion on what you're trying to do:
http://www.diystompboxes.com/smfforum/index.php?topic=71397.msg575780#msg575780

The simplest thing would be to use a rotory switch with a range of caps. I've used as many as 6 caps on a 6 position switch. While it's not continuously variable, you can get some pretty good in between values with 6 positions. Just experiment with a range of caps to decide which ones you want to use on the switch.

Thank you very much! I'll grab one of those and test it out!

Any idea on the gain?

[Jdansti]

If you could please post a pic of the schematic you're working from I'll take a look. Even better, someone else who's smarter than I am about this would be able to give you a better answer. 

[nightendday]

Here's what I plan on doing, If I'm way off base on this, just let me know.



schem

[Jdansti]

Aha!  You caught the DC wiring mistake and edited it before I could comment on it!

I'm looking at your layout vs the schematic and I'm a little confused. Your layout has two transistors, but the schematic has only one. The schematic has some diodes and the layout has none. Also, what are the four green circles on the layout?  Maybe these aren't the same circuit?

[nightendday]

Aha!  You caught the DC wiring mistake and edited it before I could comment on it!

I'm looking at your layout vs the schematic and I'm a little confused. Your layout has two transistors, but the schematic has only one. The schematic has some diodes and the layout has none. Also, what are the four green circles on the layout?  Maybe these aren't the same circuit?

Those little green guys are 4 3mm LEDS. I added the transistor as another gain stage. I started with the schem and was basically seeing if I was on the right track to mod the bajeepers out of the pedal.

[Jdansti]

Got it.

One leg of the 0.1uf cap and the jumper next to it aren't connected to anything. I assume that they are supposed to be connected to each other.

So if I understand correctly, you have omitted the volume pot and added a 1M gain pot at Q2.  You want to know if this is the best place for the gain pot, correct?

[nightendday]

Got it.

One leg of the 0.1uf cap and the jumper next to it aren't connected to anything. I assume that they are supposed to be connected to each other.

So if I understand correctly, you have omitted the volume pot and added a 1M gain pot at Q2.  You want to know if this is the best place for the gain pot, correct?

Yea they should be connnected, I'm tired lol
I was asking if the added gain stage was set up correctly, and then yes, if that was the ideal spot for a gain control. I assumed it was, as it would control how much of that signal was hitting the LED clippers.

[nightendday]

I think this one is more what I want, still unsure of how to do the gain pot though.

[Jdansti]

First, I'm not sure about the arrangement of the two transistors. They are essentially piggy-backed and the two 2m2 resistors are in parallel giving you 1m1 ohms. 

Second, you can adjust the amount of diode clipping with a pot. There are many ways to do this.   Below are several ways to do it from this article by Jack Orman:  http://www.muzique.com/lab/sat.htm  Please see the article for a description of each technique:

[nightendday]

First, I'm not sure about the arrangement of the two transistors. They are essentially piggy-backed and the two 2m2 resistors are in parallel giving you 1m1 ohms. 

Second, you can adjust the amount of diode clipping with a pot. There are many ways to do this.   Below are several ways to do it from this article by Jack Orman:  http://www.muzique.com/lab/sat.htm  Please see the article for a description of each technique:

First, thank you very much for all the help. I tested it, and it works, and has more gain, but I've noticed that it definitely does NOT respond well to the volume knob, volume dips VERY fast as it's rolled back... Is this a product of the 3904 I'm using? or are my mods causing this?

[artifus]

could be due to the audio taper of the pot - try a linear. for the transistors you may want to try a darlington pair arrangement: http://en.wikipedia.org/wiki/Darlington_transistor

[Jdansti]

+1

Also depending on which clipping diodes you use, they can cause a serious drain on the signal.  I've built a passive clipping box that takes the output of gain pedals and adds clipping. I've got 6 sets of clipping diodes connected to a rotary switch. Each set of diodes is a different combination of diode types. The volume can be greatly reduced depending on which set of clippers I choose.

It might be necessary to put a buffer on the back end of your circuit to boost the signal back up to at least unity.

[nightendday]

Mpsa13 saves the day!   I always thought LED clippers were the loudest... Maybe i'm wrong though, I'll draw up another layout with a darlington pair and see how I like that one!

[artifus]

I always thought LED clippers were the loudest...

diode voltage drop