In my studio there's lots of RF polution, so I was trying with a combination of resistor and cap at input and that produces good results.I can see it on the scope.
But today I was thinking about using something better, like ferrite beads or little inductors plus cap inmediately after the input connector, like most of the microphone inputs have in pro level mixers.
Can somebody tell me who's selling that little inductors?. What spec are we needing here?
Another related question would be: As we are talking about very hi frec. here, little caps are needed. We know that garden variety ceramic caps are a no-no in the audio path, but what about in this situation as a shut? Still bad?
cherrs
Ric
But today I was thinking about using something better, like ferrite beads or little inductors plus cap inmediately after the input connector, like most of the microphone inputs have in pro level mixers.
Can somebody tell me who's selling that little inductors?. What spec are we needing here?
Another related question would be: As we are talking about very hi frec. here, little caps are needed. We know that garden variety ceramic caps are a no-no in the audio path, but what about in this situation as a shut? Still bad?
cherrs
Ric
Unfortunately, Ceramics are really your only choice for RF filtering. The mylar types preffered for the audio signal path (polyester, polyethylene, etc.) do not behave well at RF frequencies... too much parasitic inductance. Only a ceramic satisfies the requirements. You can rest easy knowing that the cap is not "in" the signal path, but rather from signal to ground, and of course, in audio frequencies, its impedance is so high it should have no effect.
RF
Hi
You can get small inductors at rs, but I think the best way to solve your RF-problem is to place a small capacitor (like 220 PF) between the +input and -input of the (chip-)amp you are using.
You can also limit the bandwide of your amp by placing a small capacitor across you feedback-resistor. If your resitor is 20 kohm a 100 pF would limited it to around 80 khz.
Try the 220 pF first.
THomas
Hi
You can get small inductors at rs, but I think the best way to solve your RF-problem is to place a small capacitor (like 220 PF) between the +input and -input of the (chip-)amp you are using.
You can also limit the bandwide of your amp by placing a small capacitor across you feedback-resistor. If your resitor is 20 kohm a 100 pF would limited it to around 80 khz.
Try the 220 pF first.
THomas
Re: RF
The first suggestion is the better way to go. The second one will reduce the gain below 10 thus making the opamp unstable at those frequencies and it may start oscillating.
I'd add, if you can kill the noise at the input RCA connectors would be the best ( Place the RC right on the connector). That way the RF is not going to sneak inside the housing (I assume it's all well shielded/gnd'ed).
tlmadsen said:
The first suggestion is the better way to go. The second one will reduce the gain below 10 thus making the opamp unstable at those frequencies and it may start oscillating.
I'd add, if you can kill the noise at the input RCA connectors would be the best ( Place the RC right on the connector). That way the RF is not going to sneak inside the housing (I assume it's all well shielded/gnd'ed).
killing rf
this did the trick for me. I tried using a normal (polar) 220 pF cap across the + and - on the rca plug. This didn't give satisfactory results so I tried a non polar 220 pF. This did the trick for me.
The amp is dead quiet. No hum, no RF. Nothing. Perfect!
this did the trick for me. I tried using a normal (polar) 220 pF cap across the + and - on the rca plug. This didn't give satisfactory results so I tried a non polar 220 pF. This did the trick for me.
The amp is dead quiet. No hum, no RF. Nothing. Perfect!
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