CabSim Noise - Help

[kinski]

So I built the Simple CabSim Rev2.0. Its sounds pretty good. But I'm getting a good amount of white noise along with it when engaged. Perhaps this is just in the design? Any way to get around this?

[iainpunk]

it shouldn't introduce that much noise because is has no gain, is it adequately shielded form outside noise? are all transistors connected the right way around? are all cuts made correctly? pictures?

how does it sound if you ignore the noise?
it should scoop the mids slightly and roll off some low end and treble!, and it should be less loud then without it.

https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

cheers, Iain

[kinski]

Yeah, everything looks good on the bored. And sounds exactly how you described. Just the background has some white noise. I put a small value cap on the output that helped a decent amount.

Might try slapping a Huminator on the power to see if that helps.

[iainpunk]

maybe put a big (100nF) cap on the power rails, between the 9V and ground.
have you checked if the grounds are connected from in to out to the board?

cheers, Iain

[kinski]

Yeah, it all seems fine. The huminator didn't work at all. Speaing of the volume drop, could I replace that 4.7k resistor on the output with a jumper to get more volume?

[kinski]

Removed the 4.7k and it gave a good volume boost. Still a little under but not too bad and its not like I'll be switching it on and off all the time. I think Im happy where it is now. Still plenty bright with the cap I put on the output to get rid of some of the hiss.

Thanks for your help/input.

[iainpunk]

no, don't take out that resistor. its to protect the last transistor. if you want more volume, you need a booster on the end, something like the LPB1

you're welcome

cheers, Iain

[kinski]

Really? How does it protect the last transistor?

[iainpunk]

the last transistor has a huge amount of gain on tap, its not used here, but its there. if there is a short to ground, that transistor will try to make its emitter a certain voltage, but the ground short prevents that and makes it pump out a huge amount of current on the positive cycle, which kills the transistor.

cheers, Iain

[kinski]

Thanks for the explanation! I'll put the resistor back and add a booster.