Audio noise with op-amp. Need recommendations.
Audio noise with op-amp. Need recommendations.
(OP)
Hello -
I am using a LM324 op amp to amplify an unbalanced signal and am getting a large amount of hum. I suspect this is due to the power source for the op-amp because when we take the op-amp out of the loop and listen to un-amplified audio, it sounds fairly clean. Perhaps the power noise is passed directly through the internal FET of the op amp?
My question is: Is there an established way to power an audio op amp when noise is a concern? I can't use a battery for this application, but am open to any power filtering, etc schemes. Right now, it is being powered by a 9V linear regulator which is fed off of a switching regulator package from TI.
Thanks,
I am using a LM324 op amp to amplify an unbalanced signal and am getting a large amount of hum. I suspect this is due to the power source for the op-amp because when we take the op-amp out of the loop and listen to un-amplified audio, it sounds fairly clean. Perhaps the power noise is passed directly through the internal FET of the op amp?
My question is: Is there an established way to power an audio op amp when noise is a concern? I can't use a battery for this application, but am open to any power filtering, etc schemes. Right now, it is being powered by a 9V linear regulator which is fed off of a switching regulator package from TI.
Thanks,





RE: Audio noise with op-amp. Need recommendations.
TTFN
RE: Audio noise with op-amp. Need recommendations.
RE: Audio noise with op-amp. Need recommendations.
Having said that it is worth confirming that the regulator is not oscillating.
RE: Audio noise with op-amp. Need recommendations.
Mike Halloran
Pembroke Pines, FL, USA
RE: Audio noise with op-amp. Need recommendations.
RE: Audio noise with op-amp. Need recommendations.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Audio noise with op-amp. Need recommendations.
RE: Audio noise with op-amp. Need recommendations.
Posting pictures: FAQ238-1161
This would probably propel the discussion forward.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Audio noise with op-amp. Need recommendations.
Also, are you using two supplies (pos and neg)? Opamps don't operate rail-to-rail so that could be messing up the signal if it is AC coupled or goes within about 1.5 V of either rail.
What are the ranges (amplitude and freq) of your input signal?
RE: Audio noise with op-amp. Need recommendations.
What has not been asked, or stated, is the gain that the circuit is configured for: the 324 has an open-loop gain in excess of 90dB, so any mains hum will really get in there!
Also how is the input to the 324 configured (presumably single-ended) but where is the ground side referenced?
RE: Audio noise with op-amp. Need recommendations.
Thanks for the help
RE: Audio noise with op-amp. Need recommendations.
1. Substitute an appropriate load resistor for the audio cable and optimise the amp for hum. Do this by ensuring that the input signal path does not share any common conductor path with either the power supply ground return or output signal return to power and filtering power.
2. If possible use a shielded twisted-pair for the audio input cable as this offefs much better opportunity for noise protection than single shielded/coax.
3 If the input signal source is isolated from ground then keep it that way, connecting the twisted pair to the signals and the shield to ground at the signal source only.
4. If one of the signal source connections is grounded, then connect the shield to this ground as well as one of the twisted pair.
RE: Audio noise with op-amp. Need recommendations.
RE: Audio noise with op-amp. Need recommendations.
Of course, it may be because it doesn't know the words.
RE: Audio noise with op-amp. Need recommendations.
Thanks!