[x86guru]

Hello Folks,

I have a question about guitar amps with an overdrive channel. I have two small amps (Marshall MG15DFX and a Fender Bullet 150). Both amps have intolerable levels of noise/hum/feedback when using the overdrive channel with the gain turned up.

I typically get excessive noise/hum if the volume is higher than 1/4 on the overdrive channel.

I'm wondering if you need a special extra shielded guitar cable when using the high gain/overdrive channel? If I completely disconnect the input source from the AMP then there isn't any noise/hum so the guitar cable appears to be collecting a lot of RF/EMI.

If I simply need a better shielded cable, what brand(s) do you guys recommend?

Thanks,

Adrian

[fly135]

No special cables, although I would try switching cables to make sure that one isn't flawed. High gain invites hum. Humbucking pups are named that because they exhibit less hum than single coils. Also on a strat the 2nd and 4th switch positions are usually wired to reduce hum. I have to stand away from my computer monitor to reduce hum. So much so that I'm thinking of getting an LCD screen. Fluorescent lights cause hum.

External distortion boxes can be tamed with noise gates. They may work in front of your amp as well. A noise gate shuts off the signal when the input level drops below your setting. Most MultiFX units have a noise gate. You could get yourself a cheap MultiFX and just use the clean channel on the amp. Get your gain from the FX box.

Lastly, your guitar can cause hum from poor shielding or faulty wiring. My Tele had a poor ground that caused hum. Does the hum subside when you touch the strings or controls on your guitar?

[x86guru]

I have several cables and two guitars and I've tried all combinations with more or less the same level of noise/hum so I guess it's just the nature of the beast. I'm not sure how clean my playing area is (RF/EMI wise). If I just plug in the cable to the amp without the guitar connected (High impedance) the hum/noise gets a little louder so the impedance of the guitar must be quite high. I haven't measured but I'm guessing the guitars are around 1meg ohm(?).

I like the idea of using the clean channel and something inline between the guitar and AMP instead of using the overdrive/gain on the amplifier.

I don't have any experience with any of the inline FX units. Are there any units that you could suggest?

Thanks,

Adrian

[felixdcat]

Originally Posted by x86guru

Hello Folks,

I have a question about guitar amps with an overdrive channel. I have two small amps (Marshall MG15DFX and a Fender Bullet 150). Both amps have intolerable levels of noise/hum/feedback when using the overdrive channel with the gain turned up.

I typically get excessive noise/hum if the volume is higher than 1/4 on the overdrive channel.

I'm wondering if you need a special extra shielded guitar cable when using the high gain/overdrive channel? If I completely disconnect the input source from the AMP then there isn't any noise/hum so the guitar cable appears to be collecting a lot of RF/EMI.

If I simply need a better shielded cable, what brand(s) do you guys recommend?

Thanks,

Adrian

Could be your pickups? Guitar electronics? If it's humming when there's only cable plugged in, and not the guitar, it's normal, if when they're both in, could be electronics. Try googling for solutions, but you could try to shield your guitar cavities (inside) with aluminium (like the one your mother uses), it's a trick I read recently, and can't wait to see if it works...

[P-90]

There are conductive paints for that too, they're kind of expensive, but are easy to apply, and some of them are quite effective.

Of course, neither approach will work if the pickups are where the hum's coming from. All you can do then is to try and keep a distance from computers and fluorescent lights, and avoid sharing electrical outlets with them (unless they are on UPSes, or other RFI-filtering electrical hookups).

[fly135]

"I don't have any experience with any of the inline FX units. Are there any units that you could suggest?"

Here are some great deals on low end multiFX that sound good...

Buy Toneworks AX3G Guitar Modeling Signal Processor online at Musician's Friend
Buy Toneworks AX5G Guitar Modeling Signal Processor online at Musician's Friend

Other than that it depends a lot on your budget, whether you are willing to buy used, if you have good deals locally on Craigslist, etc...

You can even use both your amps, as most mutifx have a stereo output. I like the GNX series if you can find a deal on a used one. A GNX2 for $100 would be a good buy. Things to consider when looking are....

- Computer editing of presets.
- A display that shows enough characters that you can name your presets
- Rhythm (drum) machine.
- USB hookup for recording.

Most multifx can be tweaked to give you a good tone for bedroom playing and recording.

[P-90]

Originally Posted by x86guru

If I just plug in the cable to the amp without the guitar connected (High impedance) the hum/noise gets a little louder so the impedance of the guitar must be quite high. I haven't measured but I'm guessing the guitars are around 1meg ohm(?).

I like the idea of using the clean channel and something inline between the guitar and AMP instead of using the overdrive/gain on the amplifier.

A belated thought...

You'll probably find that overdrive pedals are about as bad WRT noise as your dirty inputs are. They may make better sounding distortion, but the advantages often end there.

There IS something you can do which addresses both issues... but it's one of those things which will void your guitar warranty. It's the addition of a tiny preamp (usually a single transistor) and 9v battery to your guitar. This will boost the signal, typically by about 5x, while dropping your output impedance from hundreds of thousands of ohms to a tiny fraction of that. Some of them, particularly those that use op amps, can eat batteries pretty quickly, but a single J201 field effect transistor (for example) can run on a 9v for 400 hours or more. Parts count can be very small; one JFET, 2-4 resistors, 1-2 capacitors, a battery clip, an on-off switch, and about a square inch of perfboard, and cost for them can be under $3, if you're handy with a soldering iron and inclined to DIY.

Just thought I'd throw that out there in case your x86 expertise extends to hardware hacking.

Example schematic at: Discrete FET Guitar Preamp

[x86guru]

Thanks for all of the info guys! I've reduced the hum to acceptable levels by moving things around.

fly135, thanks for those links! I'm going to buy one of those just to play with since they are practicably free

P-90, thanks for the preamp idea. I was thinking about embedding a small TI MSP430 in the guitar and sampling the guitar's output at ~44khz with one of the 12bit ADCs, then send down a digital bitstream (probably manchester encoded data over LVDS) to my amp. Inside the amp, I'd have another TI MSP430 which receives the manchester encoded bitstream and source the AMPs input with one of the 12bit DACs at ~44khz.
Thanks,

Adrian