Hi! Just to preface this- I'm a bit new to electronics and am by no means a pro. I've designed an AB amplifier that's meant to power a 30ohm transducer in a spring reverb tank, hence the push-pull power stage to provide with much needed current. I've tested the circuit on a breadboard and got it working fine, sure I had quite a high noise floor and some distortion but it functioned for its purpose. Once I got a working prototype on the breadboard I made the schematic you see accordingly and drew up a perfboard design.


I've now soldered everything on the perfboard but now it's not working. When I plug the board in all I get is a loud random noise and distortion and no audio signal from the guitar I'm testing with. The noise seems to be completely random and fluctuates and increases in volume every now and then. It starts quiet but then when I take a chord with my guitar chaos breaks loose, but the noise that's sounding has no characteristics of my guitar, it's completely random.





When I look at my power supply the positive-supply draw about 14-80mA and the negative seems stable at around 10mA (the negative supply is older and has less accurate monitoring, so it might be the same). I figured that since the negative-supply current is lower there might be an issue with the PNP transistor on so I replaced it but no difference. I've also tried a new NE5532 but the issue persists. I've checked for poor solder connection, shorts or wrong wiring but everything seems fine.



Is there an issue in my schematic or layout? I've gone over it 1000 times now but I can't seem to find an issue in them. Does anyone have any insight or see the issue? any tips or help is very much welcomed.



Thank you!

 

How did you connect the half of the NE5532 that you are not using?
Where exactly is "earth" in your circuit? How does its voltage relate to the positive and negative power supplies?

 

V1 needs to be referenced to ground.
Otherwise there's no path for the load current to the supply.

You then will need to add a large electrolytic capacitor (e.g. 1,000µF) in series with the output (- to load) to block the DC offset.

 

And why the variable feedback?
What is the total supply voltage?

 

V1 needs to be referenced to ground.
Otherwise there's no path for the load current to the supply.

You then will need to add a large electrolytic capacitor (e.g. 1,000µF) in series with the output (- to load) to block the DC offset.

Thank you for the reply! When you say i need to reference V1 to ground what pin are you referring to and how and why do i need to do that?

 

How did you connect the half of the NE5532 that you are not using?
Where exactly is "earth" in your circuit? How does its voltage relate to the positive and negative power supplies?

Sorry that might be a bit vague in the schematic. Ground is set up at the 0v between +12v and -12volt on a dual power supply.

When it comes to the other half of the NE5532 i did leave it floating initially but have connected as a buffer with the output to ground, but the issue is still there.

Thank you for replay

 

hi g4,
Are you now confirming that the dual PSU is connected as per this image?
E

 

hi g4,
Are you now confirming that the dual PSU is connected as per this image?
E

View attachment 350854

Hi,

Yes that is correct!

 

Does adding a resistor (say 30Ω or so) in series with the transducer improve things?

 

Is the TS able to measure voltages relative to the "ground" level??Are the positive and negative supply voltages equal?? and why not have some capacitors from the supply voltages to the common???
There could easly be a high frequency oscillation with coupling from the outputs to the non-inverting input.