What do you guys suggest I do to rid my amp of radio frequency interference. I followed this build: Mick Feuerbacher Audio Projects and without any source connected, I'm able to hear slight jazz coming though. Gain on my particular 3886 was set to 20 so it's not too loud but still extremely annoying.
Interferences mostly origin from AM radio stations. These become audible, i.e. are demodulated due to nonlinear behaviour of the semiconductors inside your amp combined with its small bandwith compared to radio frequencies.
And I experienced these effects are not restricted to input terminals of the amp but might take place at output terminals, too.
As you wrote that your input is shorted, try to remove the antenna connected to the outputs: shorten your speaker cable and / or insert
a choke of 10~22uH in series, placed close to the output pin of the IC.
And I experienced these effects are not restricted to input terminals of the amp but might take place at output terminals, too.
As you wrote that your input is shorted, try to remove the antenna connected to the outputs: shorten your speaker cable and / or insert
a choke of 10~22uH in series, placed close to the output pin of the IC.
try some bypass caps to ground .1uf or .01uf maybe smaller on signal and power rails to chassis grnd it is been awhile but i stopped rf from getting into fostex 450 mixer using this tech niqe and was able to use with a hi power cb radio station i had to do the same with the effects rack before they would work also good luck i hope this info was of use
Hi,
always fit RF attenuating filters to the front end of all power amplifiers and to the front end of all pre-amps.
All it takes is a tiny 100s pF capacitor after a defined source resistance. This is a single pole filter thats reduces the low MHz interference but leaves the audio signal intact.
I usually add a further 47pF directly across the back of the RCA input socket. This adds a tiny filter that interacts with the natural inductance of the interconnect cable and produces a 2pole RF filter that extends to many 10s of MHz.
Do not use ferrite rings/beads on the audio lines and probably not in any analogue supplies either.
always fit RF attenuating filters to the front end of all power amplifiers and to the front end of all pre-amps.
All it takes is a tiny 100s pF capacitor after a defined source resistance. This is a single pole filter thats reduces the low MHz interference but leaves the audio signal intact.
I usually add a further 47pF directly across the back of the RCA input socket. This adds a tiny filter that interacts with the natural inductance of the interconnect cable and produces a 2pole RF filter that extends to many 10s of MHz.
Do not use ferrite rings/beads on the audio lines and probably not in any analogue supplies either.
i think i know what is happening you have a ground loop situation much like my mixer did. if possible either connect the two grounds together. if there is potenial between them( which there might be because thier seperated) put the cap in between them. but try the cap first as i don't how your circuit is wired but if i saw it i could tell you for sure. in my mixer all of the inputs and outputs were grounded to them selves and the chassis. but not the chassis to the supply grnd causing the chassis and sheilding of cables to become the anttena .its was way back in 1992 and i don't have that mixer any more. what i have now is a mackie 32-8 and msr-16 tape deck with over a mile of cable and same thing there. the shield can only be connected on either the inputs or the outputs but not both.i know this seems strange but that is they way it is.do a search on ground loops and you will find some good info on this subject.good luck.if you have any questions feel free to ask and i will be happy to asist you the best i can.jer p.s. please let me know if it works because imagine having $20,000 worth of superior sound equipment that hums at you somtimes(and i mean somtimes) no matter what the gains are set at.it was a hard lesson to learn but a very vaulable one!
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passive low pass filter.
It consists of an RC pair of components wired into the input signal line as part of the PCB. It is shown on many of the datasheets as optional.
The extra C at the input is an LC 2pole passive low pass filter.
It consists of cable used as an interconnect and a 47pF capacitor.
It can be soldered direct across the signal line terminal and the signal ground terminal of the input socket.
Try to make the leads as short as possible without overheating/damaging the capacitor.
as per instuctions from mick"The signal ground is on the minus pole of the RCA connector. The power ground star is seen in Fig. 15. The two star grounds are connected by a thin and relatively long copper wire in order to lift the signal ground by a small amount."THIS DOES NOT,lift the ground!they are connected.even though the chip is grounded.the signal is not.the ground between and the signal is left floating.i could almost promise you that by connecting the two grounds (as per thin wire) the rf would disapear.however you are correct as to the theoery of how bypass caps work.i have seen this mistake many times and have done it myself when i started playing with opamps.take it for what its worth and good luck.please let us know if and how you manage to solve your problem. jer ,p.s. always learning something new everyday.
So I'm understanding this as a 47pF cap directly soldered from + to - on the RCA inputs?
I'm not sure what you mean by this. You said you're almost sure that by connecting the two grounds the rf would disappear. The two ground stars are connected by a copper wire, I'm not sure how else I can connect them.
I found this on someone's website, maybe this is what you're talking about
The 680 ohm + 470pF filter network is installed at the RCA. This help filtering the high frequency noise before it gets onto the board.
An externally hosted image should be here but it was not working when we last tested it.
post 19 shows the RC input filter moved to the input socket. That is a good place for it. If the cable to the PCB picks up any RF then you still need an RC on the PCB.
I'm suggesting keeping the RC filter on the PCB and by adding one more capacitor, creating an LC 2pole filter operating at VHF on the back of the input socket.
I'm suggesting keeping the RC filter on the PCB and by adding one more capacitor, creating an LC 2pole filter operating at VHF on the back of the input socket.
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