Hum and noises from ungrounding amp

Hello to everyone here .. i was on vacation this time , and i decided to make something simple .. i found an old speaker monitor in my storage and thought of making it into a guitar amp .. i made a simple amp with tda2030 and a higain preamp .. everything works perfectly and i designed it too front panel on the 3d printer, but the problem is the following. the whole box is plastic and besides that if I feed it with a transformer that doesn't have a ground, a hum noise is heard,, does this solve the problem somehow or do I have to put a transformer with ground,, to be more clear, I mean the transformer I have put it, it does not have a ground plug in the wall AC, it only has the 2 terminals., thank you
 

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Keep transformer far away from sensitive input circuitry.
Transformer could be located near the mains power socket and low voltage wire to the amp (like a laptop supply).
Even better, use a laptop supply if the voltage is suitable.
Have you determined if the hum is radiated from the transformer or does the DC to the amplifier have ripple?
 
it is very clear that it is from the transformer, because the transformer has no ground and I just ground it with a wire with the amplifier with the AC outlet. the noise stops immediately! .. it's not a big issue, I just don't have another transformer, should I put it now,, if I put batteries in it, will it work? I mean if I put 2x 9volt batts in parallel. will it have enough amperes to keep playing?
 
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You can't parallel 9V batteries, but you can series connect them.
Batteries will run down quickly in a guitar amp, though.
Agree a laptop supply is best, if you can work out how to use one.

How do you connect the ground wire at the amplifier end, and to what?
 
2030 will take 18-24 V, laptop supply with 100 pF filter will work.
Or two 12V batteries in series, 7 A-h and up.
Best use a wall wart or laptop supply, 2 to 4 Amps rating.
Old laptop supplies are easily available.

Or join 4 x Lithium cells in a holder, gives about 15V, and about 3 A-h, adequate for practice.
Or change to a 12 V car radio amp chip, in fact an old car cassette player can be easily converted.
Have fun.
 
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I would get some aluminum HVAC tape and stick it to the inside of the box. I would use an IEC connector for power and run a ground to the shielding and to a ground point in the circuit. Or do the same and use a laptop PS. They come ungrounded and a lower amount which has a ground pin. The ground continues to the output jack and can be run to the shield as well as the circuit.
 
A metal cabinet would not need HVAC tape.
And that tape comes off after some years, so I would not use it near an exposed circuit.

But yes, the ground connection to an earth connection in the wall or to a metal pipe / spike should be there, and of a type unlikely to fail.
An open earth can cause all sorts of feedback issues, hum, squealing, and others.

I would run the connection up to the guitar, sometimes that wire can become a receiver of unwanted signals, which are then fed to the amp section.

You can see what they do in cars for this issue, if you need your system to be portable.
 
A metal cabinet would not need HVAC tape.
And that tape comes off after some years, so I would not use it near an exposed circuit.

But yes, the ground connection to an earth connection in the wall or to a metal pipe / spike should be there, and of a type unlikely to fail.
An open earth can cause all sorts of feedback issues, hum, squealing, and others.

I would run the connection up to the guitar, sometimes that wire can become a receiver of unwanted signals, which are then fed to the amp section.

You can see what they do in cars for this issue, if you need your system to be portable.
Uh,"whole box is plastic", guessing the OP would like the circuit in where he has it. Also working in the HVAC industry I have seen it stuck for 20 years. The stuff is a pain to get off the tape is also used on ductwork that gets warm so it is better than most other types of tape.