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Buzz On Effects Loop


ROBERTLATHAM1

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hi guys its me again the jcm 800 jone's fool! im get a buzz when i run my effects through my effects loop on my marshall 8100 head. i dont get the noise going through the front end of the amp only through the loop any suggestions?

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Well, you could try using iso transformers on the RP-3's input and output - or you could continue to run it in front of the amp. It might be as simple as cleaning up the power supply rail to the pedal, but inexpensive digital gear isn't easy to mod/repair, and it's easy to destroy, so I'd stay out of it myself. Of course, it could be the loop itself- have you tried anything else in that spot (preferably something analog, and battery powered)?

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If you were able to put some sort of 1:1 Audio transformer after the pedal you'd probably solve the problem. If you don't want to mod your amp (I wouldn't on anything that expensive!), you could actually put in it a little project box wired to 1/4" jacks (like a pedal) and just put a jumper cable over to the primary (which will have less resistance of the two windings in case you have trouble figuring it out) and plug the long cable going to the effects return into the secondary. If you can do basic soldering (literally only 4, maybe 8 solder joints!) and drill and there's an electronic components store nearby (eg. Radio Shack) you could make this for less than $20 USD. It can go right on your pedalboard or you could put velcro on the box and the pedal so they stay together.

When I first made one of these, I seriously thought about how easily I could be reeling in the dough selling these on E-Bay! LOL

BTW, you'd be amazed how much noise gates can help sometimes. I got this DOD FX-30 Noise Gate (older than me probably!) off of E-Bay for $30 and there's a send and return for it, the input signal and the loop signal (where you put the pedals) work in conjunction by adjusting a knob to get you the most natural decay when done right. Kicks serious butt for those high-gain distortion pedals where hum and hiss are an issue! Stopping and starting sounds SOOO killer with it! :D

Edited by Kyle Cavanaugh
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WOW! OK OK WAIT! i am just a poor electrician here this is all greek to me you will have to excuse my ignorance, but if i could see some schematics i might better understand the lingo here. If what is being suggested involves internals of the marshall i want to be d--- sure i know what is going on before i make any mods. lmao! i know its prob the cheapest marshall product ever made but its my first and as i said before poor broke electrician here.

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See if this helps:

iso_loop.png

Notice there's no ground connection between either transformer's primary and secondary. That's how an iso (short for isolation) transformer elimintaes ground loops. This could actually be built in a box separate form both the amp and the RP3, so long as you remember to isolate the inner jacks from the chassis ground on the box. HTH.

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ha! yes i understand this iso transformer concept but the windings must be 1:1 or i could posably even make a little more gain here but this is not neccesary as the marshall has an effects level pot tied in with the loop cicuit anyways. would radio shack would carry a 1:1 iso transformer? thanx for the drawing it makes things much easier for people in my feild as electronics are a different animal than a lighting system or even a motor control center! so thanx again for your help!

Edited by ROBERTLATHAM1
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Wouldn't only 1 transformer on 1 end of the RP-3 (at either the input OR output) work since that would break the ground loop? Is the RP-3 powered by a grounded AC plug or a wall wart. A grounded AC plug would require both isolation transformers, but wall warts are usually isolated from the AC source by their stepdown transformer, and also don't usually ground the unit to AC mains. And if the AC supply of his RP-3 did ground the unit, he would have a ground loop even by running it at the front end.

Edited by Saber
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Reading you were an electrician I was hoping you understood what a n iso transformer was! I'd be wondering if you were actually certified! LOL

The one I've used has 60 ohm and 80 ohm (to make up for losses) windings and says SPT-115 on it. You can pretty much bet the output impedance is only a couple of hundred ohms coming out of the pedal.

Saber I believe you're right, that is what I did with the pedals going into the front end.

Edited by Kyle Cavanaugh
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lmao! yeah unfortunatley i have been an electrician for the better part of 20 years. i do have some electronic know how but very limited. i install whats know as plc's or computer controlers. very elemental stuff until you get to the processor section of the controler . thats when i yank the card and replace it. no component level stuff here lmao! but yes i think the iso trans concept will work. the power supply is not the one that goes with rp-3. it actualy is a tad bit too high of voltage but has not caused any prob for several years now. so i think i might just try to find a shielded pwer supply at the right voltage and amperage for the thing and see how that goes.

poor man! poor toys lmao!

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Yeah installing those doesn't really require deep knowledge in the electronic theory department (electrical of course though), not saying it's an easy job, though. I really need to get into the 21st century with one of those! LOL

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