Buit an A/B switch with LEDs, and the 9 volts gets sent to amp when plugging in.

[Sir_Ian]

Hi, I'm new here, so be kind, thanks. I think this is the right place for the question, but if it isn't, I'm sorry, and I'd ask if you'd please point me in the correct direction.

I built a simple A/B switch, and I'm using a stereo input to make a complete circuit for the battery, so it doesn't drain. If I have it all turned on and going to my amp and I plug in my guitar to the input, it overloads the amp, and I'm 99% sure that this is because for a split second it is sending the 9 volts to the amp.

From all my reading, I believe solution is to put a capacitor on the input wire to stop DC current. Is this right? If so, what size capacitor will work. I'm thinking a .1uf, but I don't really know. I just saw that that is what the "debugging" tool uses, and I assume its for this reason.


Also, I do have another question. I build a talkbox, and I know most people drive theirs with a practice amp. I have two practice amps and neither of them has a line out like my 100 watt amp does. Are people just disconneting their spearker and running the signal to their talkbox. If so, I have a good idea on how to do it (attach jacks for quick and easy connections) but if not, how do I.

Thanks in advance for any help. Its much appreciated.

[R O Tiree]

You are using the negative wire from the battery to the stereo socket? Had to ask.

The only other thing I can think of is inrush current, as the LED lights up. It's certainly one source of popping in pedals.

A schematic would help, along with a picture of what you've hooked up.

[Sir_Ian]

I have it wired correctly with negative going to the input jack ring. (it's ok that you asked, I'm not offended).

I think i need to be more clear. It only overloads the amp for a split second, and that second is as I am pluging in my cable to the input jack. For a split second, I believe the tip and the ring are making a connection, thereby sending the 9 volts to the amp. Once I have the jack all the way in, the problem is solved. So, as long as I plug in the input first, and the output second, I'm fine. And I could know this and life would be ok. But I'm thinking of giving the pedal to my brother and I don't want him to someday forget and blow something on his Fender DeVille. He'd hate me.

I think this is the same problem all guitar pedals would have if they didn't have a capacitor to block the voltage. I'm just not sure what size capacitor I need.

If would help, I could put up a pic or schematic, but its just a simple a/b switch, and everything is wired correctly, because it works fine. As i said, the problem is only for that split second.

[R O Tiree]

OK, experiment time. Take the battery out. Now plug everything in and switch the amp on. Lastly, connect the battery.

If you get a pop as you connect the battery, it's inrush current into the LED and I can point you at a circuit to tame this.

If you don't get a pop as you connect the battery, then it's the jack.

[Sir_Ian]

Ok, I plugged it all in and disconnected the battery and connected it back it. I got a few crackles, but not the big BOOM I get when I put in the input jack.

So I think I might have both problems, but the input jack is definately a major problem that needs fixed. Would you also point me in the direction of a schematic to stop the inrush to LEDs as well?

thanks

Do you mind me asking you one more question? I'm thinking after this I want to try building a guitar pedal (this A/B switch has been relatively painless). The question is, is it cheaper to buy all the parts seperately online, or just order a kit from someone like Build Your Own Clone?

[Sir_Ian]

I know this is a shameless bump, but I don't want to make a whole new topic. Since my problem is for sure the 9 volt battery going to my amp for a split second....

will a  .1uf capacitor due the trick? or should i use smaller or bigger?

thanks