I've built a few electronics projects recently (mainly LED based stuff) and had good results but this latest one has me a bit stumped. I'm still very much learning and this is my first audio project.
I have built a CMOY type amplifier based very much on Tangent's tutorial, using at the moment an NE5532 Op-amp (mainly so I don't damage the more expensive OPA2132 I have. I have some very large 0.47uF 250v Metallised Polypropylene Capacitors as Input caps in the circuit.
I first built the circuit on breadboard with the standard 10x Gain 1K resistor on the Op-amp and after some silly issues I got it working and it sounded awesome, going very loud and without any distortion.
Moving on I then built the same circuit on Matrix board, and while I made a bit of a mess of the track joining (never used Matrix board before) the circuit itself looks fine but is presenting me with strange issues. With the input capacitor in position the sound is totally messed up at anything but minimal volume, and even then could just be so quiet I can't detect the distortion.
However if I stick my fingers on the bare LED wires and touch the Op-amp tracks the sound magically clears, and returns to distorted shortly after I remove my hand.
At first I'd thought I'd destroyed the polyprop during soldering but after trying several different capacitors and they all seem to distort the sound.
I've also found that removing the input caps from the circuit and shorting the connection clears the sound up.
I've tried swapping the Op-amp for another with no change.
I've also tried adding in two more electrolytic caps in parallel with the existing power supply capacitors and that has had no effect. I can see the voltage dropping on these once I switch the power off.
I've added bypass 104 ceramic caps to the +v and the -v, both going to Virtual ground, with no effect.
I've cleaned all traces of flux residue away with good IPA and a toothbrush.
I've also checked resistance from the 8 pin IC socket and they are equal to each other and correct as per schematic.
I also noticed that when the input capacitor was in place the voltages on the 'rails' were massively unbalanced. On a 12.4v source (regulated) it was 10.7v on the one side with 1.7v on the other, yet when the circuit it no fitted with the Op-amp it's more or less dead centre at 6.1v/6.3v.
Ideally I'd like the Input cap to close down any DC-offset as I'd hate to destroy my headphones.
Source at the moment is an iPod Touch with a Fiio E1 at low volume.
Any insights as to why when I have the input cap fitted and touch the LED and the rear of the Op-amp contacts that the sound clears?
I can take pictures if that would help but be warned the soldering is pretty bad in places and I've pulled a few tracks off and slaved resistors and caps in place trying to fix the issue.
Thanks.
I have built a CMOY type amplifier based very much on Tangent's tutorial, using at the moment an NE5532 Op-amp (mainly so I don't damage the more expensive OPA2132 I have. I have some very large 0.47uF 250v Metallised Polypropylene Capacitors as Input caps in the circuit.
I first built the circuit on breadboard with the standard 10x Gain 1K resistor on the Op-amp and after some silly issues I got it working and it sounded awesome, going very loud and without any distortion.
Moving on I then built the same circuit on Matrix board, and while I made a bit of a mess of the track joining (never used Matrix board before) the circuit itself looks fine but is presenting me with strange issues. With the input capacitor in position the sound is totally messed up at anything but minimal volume, and even then could just be so quiet I can't detect the distortion.
However if I stick my fingers on the bare LED wires and touch the Op-amp tracks the sound magically clears, and returns to distorted shortly after I remove my hand.
At first I'd thought I'd destroyed the polyprop during soldering but after trying several different capacitors and they all seem to distort the sound.
I've also found that removing the input caps from the circuit and shorting the connection clears the sound up.
I've tried swapping the Op-amp for another with no change.
I've also tried adding in two more electrolytic caps in parallel with the existing power supply capacitors and that has had no effect. I can see the voltage dropping on these once I switch the power off.
I've added bypass 104 ceramic caps to the +v and the -v, both going to Virtual ground, with no effect.
I've cleaned all traces of flux residue away with good IPA and a toothbrush.
I've also checked resistance from the 8 pin IC socket and they are equal to each other and correct as per schematic.
I also noticed that when the input capacitor was in place the voltages on the 'rails' were massively unbalanced. On a 12.4v source (regulated) it was 10.7v on the one side with 1.7v on the other, yet when the circuit it no fitted with the Op-amp it's more or less dead centre at 6.1v/6.3v.
Ideally I'd like the Input cap to close down any DC-offset as I'd hate to destroy my headphones.
Source at the moment is an iPod Touch with a Fiio E1 at low volume.
Any insights as to why when I have the input cap fitted and touch the LED and the rear of the Op-amp contacts that the sound clears?
I can take pictures if that would help but be warned the soldering is pretty bad in places and I've pulled a few tracks off and slaved resistors and caps in place trying to fix the issue.
Thanks.
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