Hello all.
After spending several months reading about Gainclones on various websites, I finally took the plunge and started to build my first amp.
I built the PSU first, and it seems to be working fine, giving a steady 35V.
I’ve just completed the amp for one channel, and decided to test it before starting the second one.
As advised, I connected a 10 ohm resister across the output and measured 400mV. This was with no input signal. I then connected an old mobile phone via the headphone output, and the DC rose to 800mV.
I’m no electronics expert, but I can read a circuit diagram and am pretty good at soldering.
I have attached the circuit diagrams of the PSU and amp. Any advice as to what the problem could be would be greatly appreciated.
After spending several months reading about Gainclones on various websites, I finally took the plunge and started to build my first amp.
I built the PSU first, and it seems to be working fine, giving a steady 35V.
I’ve just completed the amp for one channel, and decided to test it before starting the second one.
As advised, I connected a 10 ohm resister across the output and measured 400mV. This was with no input signal. I then connected an old mobile phone via the headphone output, and the DC rose to 800mV.
I’m no electronics expert, but I can read a circuit diagram and am pretty good at soldering.
I have attached the circuit diagrams of the PSU and amp. Any advice as to what the problem could be would be greatly appreciated.
Attachments
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I think you will find 400mv is bang on the money given the component values used. It could have been a lot worse if the chip was at the spec limits.
Yes, you need to AC couple your 680 ohm with something like a 220uF. If you make this cap to small then it will become the dominant component in setting the LF response instead of the 4.7uF input cap.
Yes, you need to AC couple your 680 ohm with something like a 220uF. If you make this cap to small then it will become the dominant component in setting the LF response instead of the 4.7uF input cap.
The input bias currents can be up to 1uA for the LM3886. That would develop 22mv at the non inverting input.
It would always be advisable to check for stability issues to. If a scope isn't available then you can always rig a simple filter at the output such as a 10k and 1uF and measure the voltage across the cap. In other words another similar network in parallel to the Zobel one already present, but with different values.
It would always be advisable to check for stability issues to. If a scope isn't available then you can always rig a simple filter at the output such as a 10k and 1uF and measure the voltage across the cap. In other words another similar network in parallel to the Zobel one already present, but with different values.
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