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Old 13th November 2012, 04:40 PM   #1
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Default Input line 120hz on speaker output in class A?

Does the 120hz rectified ripple couple directly on the output of a class A amp?

For example if your rectified voltage is 20V with 200mV of ripple, and you feed that into a voltage regulator, will you see that 200mV of ripple directly on the output?

I haven't had time to debug it, but in the amp I built as I increase ibias I start to get the 120hz hum at the speaker output.

If this is the case, in general do you just need enormous power supply caps for class A amps?
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Old 13th November 2012, 06:35 PM   #2
lineup is offline lineup  Sweden
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What voltage regulator do you have?
Describe your power supply.
If everything is in order you will not hear any hum.
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Old 13th November 2012, 10:36 PM   #3
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Quote:
Originally Posted by lineup View Post
What voltage regulator do you have?
Describe your power supply.
If everything is in order you will not hear any hum.
Even if you have significant ripple at the input to the regulator? I only hear it when I use a large ibias (thus more input ripple). I just have a full wave rectifier, 45000uf cap on each rail, and a +/- 12 TO220 vreg (L78S12CV and L7912CV).
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Old 13th November 2012, 10:59 PM   #4
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I guess in theory I could be current clipping my regulators (I just read it has internal limiters). Would that make sense?
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Old 14th November 2012, 10:07 AM   #5
DF96 is offline DF96  England
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It would make sense if you showed us a circuit diagram. Otherwise we are just guessing, based on a few snippets of random information you have given us.

However, a few general points can be made. Voltage regulators, when used properly, reduce ripple as well as stabilising DC. Class A is not particularly difficult with respect to hum, but single-ended is. Increasing bias might increase SE hum, as the active device has smaller impedance so the load sees a greater proportion of the supply rail ripple.
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