Computer Interfacing
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Balance Input for audio

difference ground betwen two system can cause serious noise/humming problem.


       Computer Interfacing Forum Index -> Input circuits and filters
Author Message

Sep 24, 2008 4:12 pm

humming is one of other problem in audio system that must be take care. there is a theory that humming was caused by power supply system that not filtered well. is there any guarantee that well design power supply can solve that problem?
in my experiences in audio system design, i have opinion that well filtered power supply will be the expensive one. but the problem is not about power supply, because when system stand alone that problem is not reveal. that problem just rise when connected with other system. so the problem is on input part, to solve that i always design input part in the form of differential amplifier, even though that will be little expensive cause that was build by OPAMP.
in this forum i like to ask, is any alternative way to designing differential input without using OPAMP? Sad
Site Admin

Joined: 13 Mar 2007
Posts: 145
Location: Netherlands and Kazakhstan

Sep 24, 2008 10:43 pm

To make a differential amplifier without opamps, you need at least two bipolar transistors and some resistors. You can find an example circuit here at the University of St. Andrews. I doubt if this option is cheaper than a simple opamp.
Full Member

Joined: 02 Mar 2008
Posts: 38
Location: Vaasa, Finland

Sep 25, 2008 12:04 am

Depending what are ones audio sources one might have cheap solution for humming... If your other source is TV or radio tuner you can get galvanic isolator for that, this way you won't have antennacable ground and poweroutlet ground on same system with their potential diffirence (modern electric design prevents this by connecting antennaground to common ground at 'fusebox').

2 examples of such device:

Galvanic isolator with F connectors
IEC galvanic isolator

This is just for the info for other possible viewers that might come across here seeking help for hummingproblems; Original post is very valid noting that diffirential/"balanced" system is most noisefree in itself.

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