Need help determining the Right Capaciter size to stop OVERLOAD!

[Sir_Ian]

Ok, I've determined that I have 9 volts from my battery that momentarily gets sent into my amp when I plug in a jack into the input. (I'm using a stereo jack to wire the battery.....).

So I need to put in a capacitor which will stop the DC current. I'm thinking a .1uf is this the right size? or should I go smaller or bigger? thanks.

[Processaurus]

Your amp almost certainly AC coupled (has a DC blocking cap on the input), and 9v isn't that big of a deal.  It will be a big ol pop, though, if the amp is on, because 9vDC will look like 9vAC for an instant, a giant transient.  But any musician that cares about the amp and speakers their using turn down the volume when plugging stuff in.

I have some plastic switchcraft jacks that are mono, but have an isolated SPST "make" switch that gets used to connect the ground to the battery (-).  It's nice because it doesn't pop as bad, as the power gets turned on before the input is connected.

[Sir_Ian]

I was under the impression (maybe wrongly) that I could put a capacitor  in my A/B switch pedal (the one that pops when turning on) to stop the popping.

Can I, or do I just need to keep the amp off while plugging in? I'd like to make it dummy proof so if I forget or if someone else is using it, no expensive amps get blown.

I was thinking the capacitor would go be inserted between the input jack and the foot switch. Just cut the wire, strip the two ends and attack each one to an end of the capacitor. bada bing bada boom, problem solved. is this rite?

[frokost]

If it's a passive A/B you have a wiring error somewhere. If the battery is for lighting up an LED only you need to check your wiring and look for solder bridges.

[Sir_Ian]

If it's a passive A/B you have a wiring error somewhere. If the battery is for lighting up an LED only you need to check your wiring and look for solder bridges.

This is not the problem. (I don't think). It is only a momentary overload to my amp. I have the battery's negative terminal wired to the ring of the input jack. With the jack completing the circuit so my battery won't drain. And when I plug in my jack, for a split second, the input jack I think is touching the ring to the input, sending 9 volts DC to my amp, causing a BOOM.

[Sir_Ian]

I refound the schematic I used to build it. I got it over at Tonepad.com

http://www.tonepad.com/getFileInfo.asp?id=107

hope it helps.

[frokost]

Well, I'm not sure if there's a problem here at all. - buzz and popping does occur when inserting and removing jacks.

Anyway, there shouldn't be DC anywhere near the input jack - that comes from the red lead. If  you push the jack halfway in, do you read any DC with your DMM? Is that how you determined it?

[Sir_Ian]

Well, I'm not sure if there's a problem here at all. - buzz and popping does occur when inserting and removing jacks.

Anyway, there shouldn't be DC anywhere near the input jack - that comes from the red lead. If  you push the jack halfway in, do you read any DC with your DMM? Is that how you determined it?

Well, sadly I don't own a meter. Too expensive for my blood. The way I determined was I took off the bottom of the box and slowly inserted the input jack and listened for the exact moment it popped. It was right when the tip of the input jack was barely touching both the input ring and the input tip. Somehow, I assumed (maybe wrongly) that some of the DC was jumping the tip of the plug from the ring to the tip and going to the amp. And it's not like the small pop and static you get from inserting a plug into your guitar or anything. It's more of a BOOM and the red overload light on my amp gets all lit up. Do you think thats what my problem is?

[R.G.]

Well, sadly I don't own a meter. Too expensive for my blood.

The real bottom line is that if you don't have some kind of meter, you will quickly find situations where you will -> never <- get the thing to work.

A usable meter can be had for under US$20 and often under US$4.00. I don't know where you are, but deciding that you cannot afford a meter is the same thing as deciding that you will not participate much in making effects.

Things like your needing to assume that some of the DC was jumping the tip of the plug from ring to the tip... AGH! Get a meter and know what you're doing instead of wandering around blindly.

[earthtonesaudio]

The 100% idiot-proof way to find out if the 9VDC is the problem is this: 

1. disconnect all power (that means battery, AC adapter, whatever you have)
2. do the same thing you did before:

The way I determined was I took off the bottom of the box and slowly inserted the input jack and listened for the exact moment it popped.

...but this time with no power.

No pop means you are indeed hearing the DC connection.  Same loud pop means... well, it could mean a lot of things.  Which brings us to step 3:

3. read (and re-read) the troubleshooting/"what to do when it doesn't work" parts in the wiki and on this forum.  There's probably a tiny mistake in the wiring somewhere.

4. Get a meter.  www.harborfreight.com has them for $2.99 (U.S.)

...If all else fails and the switcher is otherwise in perfect order, you could do a couple things.  Large coupling caps will pass your signal and block DC, and large resistors (1M) tied from signal to ground will "absorb" some of the energy of the pop.
The super idiot-proof method is to have the power on a spst switch, and not switched with the jack.

[Sir_Ian]

Once again, thank you all for the help.

I think I will have to pick up a meter. You guys are rite. All the ones I've seen are like 70 dollars, but that cheap one at harbor freight is a steal.

I unplugged the battery and tested it, no pop. Its definately the battery causing it.

With the battery in though, I've found I even get a lil bit of a pop on the mono output jacks (not as big though). Do you think it might be excess voltage going to ground or something? (Behind my leds i have 4 560 ohm resistors wired in series). Should I be having 2 grounds? one for electricity and one for the signal. Because with the schematic I used, there is only one ground? I'm just kinda new to this.

Lastly, if using a capacitor is the way to go. Which size should I use?

[earthtonesaudio]

The cap should be large enough to not cut into your signal.  0.1µF should be plenty.  But stay away from electrolytics as they may color the sound unfavorably.  Unless you use tantalum electrolytic for the extra "mojo" they supposedly add...    But still, troubleshoot first.

[brett]

Hi
without knowing the details of the cause, it might be transient DC (ie a variation on AC), some or all of which may pass through a cap.
Try to drain the swamp rather than out-wrestle the alligator. 
cheers

[frokost]

Since you seem to have determined that the battery is causing it, it seems like you have miswired something. Buy a meter and find out what. You really need to get one. Don't think about anything else for now.

[Sir_Ian]

Ok, I followed all the suggestions, but I'm still having PROBLEMS!!!

A little update. I boughta voltmeter. Checked everything. Electricity is only going where it is supposed to.

I cut the wire that carries the signal from the input jack to the switch and I put in a .1 uf capacitor. Plugged it all in, and still had the POP, and my overload light blinked angrily at me.

So here is what I've done:

I thought for a second, "Hey maybe, I did wire it wrong and the DC is getting added later, maybe like on the switch." But I'm pretty sure this isn't it because I've quadruple checked my connections, and everything is good. And when I plug in the Wall Wart (which dissconnects the battery) I don't have the problem.

Which brings me to my next point. The AC adaptor works, and I get no popping. So then I thought, "Hey somebody said something about LED rush in something or another." So I disconnected the battery, and plugged my guitar in and than ran it to the amp, played a note, and then plugged in the AC adaptor and got no pop. So it is not LED whateverness.


To sum it up!
So I'm convinced that somehow the battery is still sending its charge to the amp for that split milisecond when plugging in. I studied the jack and for a brief moment, the Ring part of the jack is touching both the tip and the ring part of the plug. So this means that Ground, Ring, and Tip are all connected, which means that the electrical circuit with the battery is complete and it is also sending it to the amp.

I don't know a ton about electronics, but from what I understand, a capacitor takes a certain amount of time until it charges, and until it does, it will pass DC current through it. So maybe.....I just need a different size capacitor? I'm not sure. Any suggestions. Thanks a ton.

One last note
well, you know how I said teh AC adapter elimanted the pop. Well....about 1 in 10 times with the ac adapter it still popped. I was thinking that maybe it was because the 9 volt adapter I was using isn't reallly for guitar pedals and it didn't even fit in perfectly all the way, so maybe it just wasn't disconnecting the battery.....I'm not sure (even then, I still don't think its this because I hooked up my meter and set it to amps, and used it to connect to the battery in series, and it showed that the battery was sending out 0 amps with the ac plug in. Then again....I didn't check this everytime...so maybe one of the times it didn't fullly work, and thats why I got the pop). I'm going to go run some tests on this. (I'm going to unplug the battery, then plug in the ac, then hook it all up to the amp). But 9 out of 10 times with the AC adapter, I got not pop. NONE. So I still think its that dang battery.

Lastly
Thank you for all the help and suggestions. If there is anything I can do to help you help me. Let me know. I think I've been pretty precise about what I've done, but if there is anything you need to know about what I'm doing. Just ask. Thank you!!!

[earthtonesaudio]

Good job on buying a meter, but holy smokes, you got that thing FUBAR'ed.  Wrong size adaptor

But a quick bit of electronics theory might save you some time.

First, in your application, caps BLOCK dc.  Well, more accurately, they block low frequencies (and dc is zero Hz) and pass through higher ones.
Second, if your BOOM is audible, it's in the audio frequencies (and therefore higher frequency than zero Hz) and the cap will pass it through just fine.
So, the cap is not blocking your BOOM at all.  That's what pull down resistors are for.  They give that BOOM somewhere to go (ground) other than through the signal wire and into your amp.  One resistor on each end, tied from signal to ground, will stop pops, or at least tame them to levels that won't make your amp freak out.

Well, this may be a little jumbled and perhaps the facts are wrong, but I still think you need some pull down resistors.  Large value, such as 1M ohm.

The caps still couldn't hurt, though.  Don't beat yourself up for putting them in there.  You have already partially solved the problem.  The rest of the solution is pretty easy.  Just a 1M resistor from tip to sleeve on your jack.  Easy.

[Sir_Ian]

Earthtoneaudio,

Thanks for the response and help.

I understood everythign you said except for "FUBAR'D".....is this some pop culture reference, and I'm just missing it.

And secondly...the pulldown resistor. Do I put one on each output jack or just one on the input jack? thanks

[Zben3129]

If you ever need to test if you are getting dc through something, just take the output and plug it into a junker speaker. If the cone just goes all the way up and makes not good noises, you have DC. And please, don't do this with a celestion greenback, DC+Speaker=Bad if there is enough DC

[earthtonesaudio]

Fouled Up Beyond All Recognition. 

Just joking, not being demeaning to your pedal.

[Sir_Ian]

Yea, your right...it is all fouled up.

I was popping of the battery snap and I accidently touched the wrong side of the LED and I blew it....lol. So now I have to spend another 25 cents on a new LED