Replies to This Discussion

Permalink Reply by mudbelly on April 9, 2017 at 2:57am

So you used 12 volt power? I have built a couple of 9 volts. Could this be a problem?

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Permalink Reply by David Blackburn on April 9, 2017 at 4:11am

Sorry, I should have mentioned, I tried 9 volts as well. Same issue.

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Permalink Reply by David L. on April 9, 2017 at 4:34am

This amp module uses a LM386 chip which can give 20 to 200 amount of gain to the signal. The gain control is the white circle with the slot in the middle - if you use a small screw driver you will find you can turn this white circle. Piezo pickups feedback if the amp module is set on a high gain. Turn the white circle until the feedback stops (full anticlockwise I think, if not full clockwise). This should sort out the feedback issue. You then need to slowly increase the gain until the feedback occurs and roll back the gain to just before this level. You may find the volume isn't particularly loud but that is the limitation of the LM386 with a piezo. With a magnetic pickup you get a nice overdrive sound and will find because it is much harder to get feedback with a magnetic pickup you can achieve a much higher volume.

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Permalink Reply by David Blackburn on April 10, 2017 at 2:11am

Thanks. I can reduce the feedback to nothing by doing that, but at that point the volume is zero. Perhaps it's just a limitation of these little amps but I thought I'd get some sound at least.

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Permalink Reply by Kigar on April 9, 2017 at 3:07pm

Maybe a long shot - I had some trouble with a different 386 amp from a kit.  Turned out I used a cheapo guitar jack and when the cord from the guitar was fully inserted it buzzed. The connection tabs were not quite right, it worked right if the cord was pulled back a 1/8" or so.

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Permalink Reply by David Blackburn on April 10, 2017 at 2:08am

I'll try a different jack. Thanks.

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Permalink Reply by Timothy Hunter on April 9, 2017 at 6:04pm

the pot is input volume. the gain is fixed at 200.if you want to reduce the gain then you are going to have to mod the circuit. R1 is a 0 ohm resistor. Removing this ad replacing it with a 100k pot 1 leg and wiper. then you will get variable gain as well as input volume.

If you are getting a lot of buzzing then your strings and bridge are not earthed to the jack. 

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Permalink Reply by David Blackburn on April 10, 2017 at 2:07am

Thanks for that. I think modifying the circuit on this little amp may be beyond my abilities, but I will see if I can figure that out. As for grounding to the jack, I did that and it made no difference.

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Permalink Reply by David Blackburn on April 10, 2017 at 2:01am

I did, to no effect. 

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Permalink Reply by Jerry Jordan on April 10, 2017 at 9:00am

If you have several boards, and they all do the same thing (buzz), the problem is most likely with polarity or ground. Speaker polarity is important. So is ground reference. I buy a slightly different flavor of this PCB and they work for me. A battery is less noisy than a supply. The input polarity and output polarity must be the same.The problem is most likely how you connect to the circuit. You are using what type of harness to interconnect? Normally LM386's work well. Let us know how you make out !

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Permalink Reply by John Sawyer on April 11, 2017 at 7:21am

Odd... I replied to this yesterday... guess it didn't stick...

Jerry's right here on the power source... if you are using a wall wart, they are super noisy.

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Permalink Reply by David Blackburn on April 11, 2017 at 9:05am

Lots of ideas to try out. I did a quick test with a repurposed computer power supply. It was much quieter than the battery and much, much better at 5V than 12V.  Not sure why that would be. However I hope to get a few free hours at this in a day or so and will report back on what I find.

Thanks to all for your ideas and suggestions.

Cheers.

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