I just bought a rather nice electric guitar kit for a hundred bucks that came with a 10 watt amplifier. The guitar is pretty nice but the amplifier has a rather nasty hum. I thought it was a vacuum tube amp but found out it actually has transistors-- or an IC amplifier-- I'm not sure.
The power transformer is pretty close to the circuit and the wires for it were tangled with some of the speaker wires. When I untangled them, the hum disappeared... until I plugged into the jack the guitar cable, then the hum came back. Does anybody have any suggestions for getting rid of this hum problem?
Your description sounds suspiciously like an open shield (ground) connection on the amp's input jack. Open the amp so you can get at the rear of the jack, and look at the solder connections there. I'll bet you find that the shield is loose or has a broken solder connection.
Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
They call it PMS because Mad Cow Disease was already taken.
Darn it, the jack is soldered to the circuit board and along with the headphone jack, the tone and volume controls, holds the PCB to the chassis! Is this fixable?
If you can duplicate the situation where there is no hum from the amp when the guitar lead unplugged then you are halfway home. If the hum occurs only when the guitar is plugged in then the problem is most likely to do with the shield connection in the guitar cable.
Yes, I think you're right. Without the cable, there's no hum. But with the cable it picks up 60 Hz like an antenna. Being new to the electric guitar I guess I thought all cables were shielded to prevent hum, but I see I'm wrong. ;-(
Yes, but the guitar cable should be shielded, and I am prepared to bet that it is. However, the shield connection may be broken and that is what is causing the hum pick-up..
Yet, I've seen ads for shielded cables that are a bit more expensive but said to reduce and/or prevent hum considerably. Ae these cables just hype or is there a qualitative design dfiference between the usual [cheap] guitar cables like the kind that came with this kit, and the ones being marketed as shielded cables?
There is a difference - up to a point - but not enough of a one to make the difference between a cable that's useable, because it's quiet, and one that's not, because it causes too much hum.
All cables supplied for use with a guitar, should be fundamentally quiet, irrespective of their price. However, a more expensive good quality one will have better shielding in that it will have a denser-woven shield wire layer, is likely to be more flexible, will have better quality connectors, and be more mechanically stable, which will result in less microphony when you drag it across, or bang it on the floor. The improved shielding is likely to only be noticable in environments which are electrically very noisy, or have high EM field strengths at line power frequency. Unless you are a professional musician with more money than savvy, the very expensive cables claiming all sorts of esoteric benefits from OF copper and double back-peddling-triple-wound-multiple-plaited-total-150%-shield-construction ( or similar ! ), are unlikely to leave you feeling that you have got value for your money ...
So, it's worth spending 3 or 4 times as much on a good quality cable, but not 10 times or more on a 'snake oil' one.
Ahh... Thanks for clearing that up. I live in a hundred year-old dump of a house and had a lot of noise problems when I tried to practice biofeedback. I don't know if anyone makes a cheap EM field meter, but if they did, it would probably show somewhat more 60 Hz in the environment than that found in newer houses or houses with better/modern wiring. So it would probably be to my advantage to buy a better cable than the one that came with the guitar. I only paid $100 for the guitar, a guitar bag, amplifier, cable, and a DVD on how to play the guitar-- so I didn't expect really *great* quality. So it wouldn't hurt me to plonk down a couple dollars more for a better shielded cable if it cuts down the hum a few dBs.
I'd say that was a pretty fair assumption. Based on the cost of such items over here, I would guess that you should be able to get a cable that's as good as you're going to notice, for $20 tops.
Your statement about a "better" cable cutting down the hum by a few more dB is a little perplexing. It seems to infer that you are still getting, or expecting to get, audible hum even after making sure that the cable shielding is ok.
Provided you have an adequately shielded cable then you should be hearing zero hum at all, except perhaps that which might be audible when you put your ear cloase to the speakers with the volume up a bit. The better quality shielded cables (eg.for guitar use) use construction techniques aimed more at reducing noise generated due to mechanical flexing of the shielding mesh wires (heard a scratching noise when the cable is moved), not so much at reducing hum due to radiated emi pickup which should be very good anyway given the usual construction. Of course, double layer and other types of shielding can marginally reduce radiated pickup better than a single layer mesh can, but the improvement would hardly be dramatic.
I only meant that a new shielded cable would probably solve my hum problem, though it's part of a bigger problem in that this house has a noisey electrical environment that affects every kind of amplifier from the very sensitive ones used in biofeedback equipment to the guitar's amp.
Have you considered having the integrity of the power earth in your house checked by a qualified electrician ? The reason I say this is that it can sometimes be less than good in an old property with old wiring, and dodgy earth connections can be responsible for unwanted signal hum problems. Years ago, many guitar amplifiers had a switch on the back, which disconnected the power earth from the amplifier ground, the intention being that if you went to play in some old barn out in the countryside, and the amp hummed, you tried this switch for a fix !! Needless to say, this was ultimately considered to be dangerous ( ! ), and such switches were discontinued. I still see the odd one for repair now though ...
If you have lots of problems like this with equipment in your house, it might be worth getting the check done just for peace of mind that you and your family are at least safe. I'd hate to think of the sparks flying out of your ears when you graduate to Hendrix-style teeth-playing :-)
BTW, when you respond to posts, it makes it easier to follow, if your reply goes on the bottom rather than the top. That way, if anyone wants to go back and check something in the thread, all the responses are below the one that they are responding to, in chronological order - well that's the theory, anyway. Some groups get really mad at you if you top post.
by "noisy electrical environment" do you mean you experience all sorts of pops and crackles in audio equipment? Noise of this type will most likely be caused by poor electrical wiring and connections. Hum induction is highly unlikely provided good techniques are used in the manufacture of the audio equipment and the house wiring is in good order. Poor electrical wiring can produce loud buzzing and/or hum/static noise due to large potential variations where poor connections occur.
Well, that's the thing: the house wiring is not in good shape. We moved in here about seven or eight years ago, and did *some* re-wiring, but the bulk of the wiring is old and leads to a lot of 60 Hz noise in sensitive equipment. I can't do biofeedback in any room of the house except for my office, where the wiring is new and the 60 Hz noise is nominal. Like I said in an earlier post, this is a hundred year-old house: in 1906 people weren't worrying about audio equipment since there wasn't any. :-)
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