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Amp help please

I'm a newbie to CBGs and amplifiers so there's a whole lot I don't know. This forum has been great in helping with most questions, but I am having an issue I haven't been able to resolve.

As an experiment to go electric I got a couple of pickups and these little amps (LM386 DC 5V-12V Mini Micro Audio Amplifier Module Board Mono AMP Module HIFI)

Wired it all up with a piezo pickup and a 12 volt battery for power and I get severe buzzing from the speakers. Sometimes the tone will come through a bit but then it degrades into a buzz. Based on advice from this forum I have tried the following - all to no avail.

1. Tried another amp (same type).
2. Tried better speakers.
3. Tried a different guitar with a magnetic pickup rather than the piezo.
4. Checked and rechecked all solder joints.
5. Grounded strings to the jack.
6. Reversed pickup leads (getting desperate now - trying everything I can think of).
7. Turned off all fluorescent lights.

So all I'm left with (I think) is the amp itself. And since I tried a couple of them it must be a design issue rather than a specific fault in the amp.

I have a different type of amp on order but I'd really like to resolve this issue as I think these should work. Does anyone have any sage advice?

Thanks all.

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Permalink Reply by John Sawyer on April 11, 2017 at 9:28am

If it is noisy on a battery, then going to a plugin power supply can only get worse...

Do you have a pic of the wiring?

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Permalink Reply by David Blackburn on April 11, 2017 at 9:31am

That's what I expected, but it was cleaner on the power supply than on battery. I need to do some playing around to make sure I've got everything wired up right. No wiring pictures, but I'll put together a rough schematic when I get back at it.

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Permalink Reply by Timothy Hunter on April 12, 2017 at 1:46am

that is weird.. maybe a photo or two would help us see whats going on. running from a battery should be the least noise.. is the battery new? if its old and the voltage drops it possibly could do weird things.

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Permalink Reply by JL on April 12, 2017 at 2:18am

One out-of-the-box-sides thought...if it's a "HI-FI" amp board that might means it is designed for LINE level signal, which is much stronger than a piezo pickup can make.

as a test: take your favorite mp3 player with the aux cable plugged into the earphone jack, touch the tip to the "IN" and the sleeve to the "GRND" and see what the output sounds like.

(side note: very useful to have a set of jumper wires with alligator clips on each end for troubleshooting)

If the MP3 player sounds a lot better than your git, than an in-line powered EQ will probably help, like the one CBGitty sells that shane turned into a stand-alone eq in a box.

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Permalink Reply by David Blackburn on April 26, 2017 at 2:02pm

Just wanted to get back to everyone who offered advice and suggestions with an update.

First problem - I had a crappy battery. A fresh battery made a world of difference.

Then I went over all the connections to make sure they were tight, no cold solder joints, etc. Joined all the grounds together in a star ground (including the strings).

And now the buzzing is gone. Hooray!

The sound is a bit "tinny" to my ear, but that could be a tone issue. I will pick up a tone pot and hook that into the circuit next.

So, progress.

The sound is still good with the computer power supply I'm using, especially if I take it off the 5 volt lead. Problem is it's too bulky to fit in a small box, so I'll be looking for another power supply, perhaps one off a laptop rather than a desktop unit. That way the transformer is actually out side the amp.

Still lots to play with, so I may be back. But thanks for all the help and advice. This is a great group for that.

Cheers.