AC Hum in Condenser Microphone hooked to AC Rectified Power Supply

Thread Starter

Homer530

Joined Aug 13, 2017
4
When using 3 Volts battery there is no hum in my condenser microphone but when I hooked it to AC rectified Power Supply it produces hum. Is there any circuit or component that can remove the humming?
 

wayneh

Joined Sep 9, 2010
17,153
When using 3 Volts battery there is no hum in my condenser microphone but when I hooked it to AC rectified Power Supply it produces hum. Is there any circuit or component that can remove the humming?
It's possible that a single electrolytic capacitor across the poles of the rectified supply would do the job if you don't already have one. Hard to tell without a schematic. If that alone is not enough, I'd look to the LM317 as noted, to give you a regulated voltage.

In both cases be careful of your output voltage. Rectified AC still has peaks far above the average voltage and when you filter by using a capacitor, the average voltage output may be that peak voltage. That may be too much for your 3V device. On the other hand you'll need about 6V in order to use the regulator since it needs about 3V of 'overhead'.
 

dendad

Joined Feb 20, 2016
3,909
It also could be a earth loop. Can you put up a diagram of your connection? And make sure there is only 1 earth point in the system.
 

Thread Starter

Homer530

Joined Aug 13, 2017
4
I'm using 5 volts mobile phone charger and a 147 ohms resistor and a 3 volts zener diode across the load.
Can I use a filter choke to remove the AC ripple in the output.
 

dendad

Joined Feb 20, 2016
3,909
Most of those chargers have a lot of coupled noise. Are you using the charger to power the whole lot or just the mic?
Only one power supply should be used. It really is hard as you have still not put up any diagrams of your complete setup. What is the mic connected to?
I don't know why we often have to "beg" posters to give us enough info so we can help.

Filtering out the ripple may not help if it is mains switcher coupled noise. I've had a similar problem. It was trying to run a phone in a car as a music player. The audio connected to the chassis via the amp and the switch mode 5V supply connected too so there was a ground loop with the switcher regulator noise superimposed on it.
 
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Thread Starter

Homer530

Joined Aug 13, 2017
4
What have you got between the rectifier and microphone at the moment?
A regulator, perhaps Lm317L, would help.
Also a capacitor multiplier would make the supply very quiet.
Thank Sir AlbertHall for the link. I will try the Capacitance Multiplier which looks like a series pass regulator with only few components which are available in local stores here.
 

Thread Starter

Homer530

Joined Aug 13, 2017
4
Most of those chargers have a lot of coupled noise. Are you using the charger to power the whole lot or just the mic?
Only one power supply should be used. It really is hard as you have still not put up any diagrams of your complete setup. What is the mic connected to?
I don't know why we often have to "beg" posters to give us enough info so we can help.

Filtering out the ripple may not help if it is mains switcher coupled noise. I've had a similar problem. It was trying to run a phone in a car as a music player. The audio connected to the chassis via the amp and the switch mode 5V supply connected too so there was a ground loop with the switcher regulator noise superimposed on it.
Thanks Sir
 
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