Comment

Comment by David L. on June 20, 2016 at 12:34am

Hi Denis,
It sounds like you have narrowed it down to the guitar
Are the strings on the guitar grounded?
Also if your avatar photo is the guitar you are using, it looks like you have a lipstick pickup which is non-hunbucking. When guitars with single coil pickups are played you do get some electrical hum passing through to the amplifier. Adding some shielding can help (which is why even the cheapest stratocaster copy has some aluminum tape added to the back of the scratch plate). I find resting the side of my palm on the bridge whilst I strum helps lower the level of hum.

Comment by Paul Craig on June 19, 2016 at 11:14am

If your plugging in something else with good results then it's got to be in the plug, cord or guitar.

Comment by Denis U on June 19, 2016 at 11:07am

Thanks Paul,

I do get the (non)grounded wallwart issue and that was my initial thought of getting the whole thing grounded. But why does it work like a dream with the phone as input if it's a problem with the wallwart or the rest of the house wiring/equipment? Doesn't that mean that it's a problem with the lead, and only the lead, or am I missing something in my ignorance?

Comment by Paul Craig on June 19, 2016 at 10:34am

I wish they would put a ground lug on the plug of walwarts.

Your problem could be the cord your using, a walwart that's going bad or producing a lot of RF noise or the wiring in the house(relay type sockets used in bathrooms or dimmer switches) and even fans.

Could also be a internal problem with the amp.

Comment by Denis U on June 19, 2016 at 9:59am

OK Gurus, I need some direction please.

I got a 3.5 stereo lead and wired the other end to a 1/4 inch mono jack with the left and right going to the tip, and ring to ring. Plugged it into the TDA7297 stereo amp which works fine with a very clean output when the headphone socket on my phone is plugged in. With the guitar and the new lead, I get a real buzz as well as the guitar sound. The buzz increases with both guitar volume and with increased treble  - both controlled from the guitar's pots.

Remembering another post here, I switched off the fluorescent lights and not a blind bit of difference. The amp is in a plastic enclosure and is powered by a wallwart that's not got a ground connector - it has, but it's plastic, so I know that doesn't count.

What can I try to get rid of the buzz, please?

Comment by Denis U on June 18, 2016 at 1:07am

Hermit,

Do an ebay search for TDA7297 Mini Digital Amplifier Stereo Audio that will find you a load of them. The exact one I bought is no longer  available, but I guess it's one factory bui;ding them and loads of different sellers.

I always set my preferences to lowest price when I am buying from China. It's worked for me so far.

Comment by GARAGE HERMIT on June 17, 2016 at 11:56pm

Denis U , dont suppose you have a link to the amp, i'd like to try one, cheer's,,

Comment by Denis U on June 17, 2016 at 10:26pm

This looks rather like the amp I got last year to use with my phone to get music in my garage. I was really suspicious about the price - less than 2GBP, but it works really well as a stereo beast no noise at all, just loud music.

I've not yet tried it with a guitar - that's on my to do list.

Comment by Paul Craig on June 17, 2016 at 7:34pm

Testing polarity first is a great idea with these kind of amps with questionable build quality. Maybe a couple of leads to a single AA battery, cause a brief hookup with 1.5 volts will do very little damage if any when the power is hooked up wrong. Compared to 9 or 12 volts anyway.

Comment by Paul Craig on June 17, 2016 at 10:08am

That's a stereo amp. If your using a mono plug input only one of those speaker outputs will work, guessing it's the one by the battery connections.

If you accidentally hooked the battery leads backwards, it could have fried the chip.

Your speaker may be bad.

Try to post a pic of what you got hooked up so far.

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