iws@rayssdb.ray.com (Ihor W. Slabicky) (02/17/89)
Can anyone send me a schematic or info on broadband noise filters
that will filter out 60 Hz hum on the 120VAC line? Some background:
I use a portable stereo cassette recorder to record music off my
receiver. When the recorder is powered from the AC line, I can hear
lots of 60 Hz being recorded on the tape. Moving the recorder, cables,
or power cord around tends to lessen the hum. When I record using the
batteries, no hum. Also, when I playback, if I put the INPUT switch
on the recorder to the MIC position, no or very little 60 Hz hum is
heard, but when the INPUT switch is set to LINE, lots of hum. Ideas?
Thanks - Ihor
Internet: iws@rayssdb.ray.com
Usenet: {gatech, uiucdcs, decuac, sun, ukma, necntc, spdcc}!rayssd!rayssdb!iwshenry@utzoo.uucp (Henry Spencer) (02/18/89)
In article <2313@rayssdb.ray.com> iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >Can anyone send me a schematic or info on broadband noise filters >that will filter out 60 Hz hum on the 120VAC line? ... The 60 Hz "hum" on the AC line *is* the AC power. There is no way to filter it out; if you want to run your recorder on AC, there will have to be 60 Hz AC going into the power supply. What you need is filtering *inside* your recorder, to keep that 60 Hz out of the signal-handling sections. It's quite possible that you simply have a poorly-designed recorder. The one fix that wouldn't involve digging into the guts of your recorder would be to forget using the recorder's own AC power supply, get a separate power supply that produces the same output voltage as the batteries, and hook that up to the recorder as a replacement for the batteries. This isn't certain to fix the problem but it would probably help. Radio Snack carries plug-in "bricks" of various voltages that might do the job, although you'll probably need a bit of soldering to connect them in. -- The Earth is our mother; | Henry Spencer at U of Toronto Zoology our nine months are up. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
dave@VAX1.CC.UAKRON.EDU (David Stoutamire) (02/18/89)
In article <2313@rayssdb.ray.com>, iws@rayssdb.ray.com (Ihor W. Slabicky) writes: > > Can anyone send me a schematic or info on broadband noise filters > that will filter out 60 Hz hum on the 120VAC line? Some background: One of Radio Shack's `Engineers's mini-notebook's on Op Amps has two 60hz notch filters p. 42. Look pretty easy to build. -= David Stoutamire =-
jeffw@midas.STS.TEK.COM (Jeff Winslow) (02/18/89)
In article <2313@rayssdb.ray.com> iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >Can anyone send me a schematic or info on broadband noise filters >that will filter out 60 Hz hum on the 120VAC line? It's gonna take a hell of a filter to get rid of that 60Hz on the 120V line! :-) [description of problem deleted] OK, "60Hz hum on the 120VAC line" is all one noun. From your description, it sounds like you've got ground loops in your setup. Make sure each piece of equipment has only one path back to ground. Jeff Winslow
ron@ron.rutgers.edu (Ron Natalie) (02/21/89)
Well your average AC adapter/Ni-Cad charger is a pretty cheap thing. What it is is a step down transformer (with enough resistance in the windings to be a current limitter as well) and a diode. When charging NiCad's you don't need filtering and you don't need voltage regulation. When running the calculator/radio/whatever off the charger the battery pack provides the voltage regulation, hence the warning not to operate without the batteries in place. You probably need to add a some nice capacitance accross the rectified AC to smooth it out enough not to be obnoxious. -Ron
nmju@ihlpl.ATT.COM (Urban) (02/21/89)
In article <2313@rayssdb.ray.com> iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >Can anyone send me a schematic or info on broadband noise filters >that will filter out 60 Hz hum on the 120VAC line? You really don't want to filter the 120VAC line directly. I mean, that's what there is on the 120VAC line, 60 Hz. If you get rid of it, you're not going to have much left to power your recorder. Perhaps I'm reading your posting a bit too literally. >... >Moving the recorder, cables, >or power cord around tends to lessen the hum. >... >Also, when I playback, if I put the INPUT switch >on the recorder to the MIC position, no or very little 60 Hz hum is >heard, but when the INPUT switch is set to LINE, lots of hum. Ideas? Ihor, I think you have a grounding problem. These are probably the hardest types of system level audio problems to solve. All I can suggest is that you try a lot of different connections until you find one that works. The fact that the MIC input is noise free is curious. Usually it is just the opposite. A clean MIC input would seem to indicate that the internal power supply in the recorder is doing a good job. Try connecting the chassis grounds of the recorder and the receiver together. Try reversing the polarity of the 120VAC plug at the wall, i.e. - pull it out, turn it over, plug it back in. Try this for the receiver, also. I have had some good success at treating problems of this type. I have also struggled with some that I never did solve. I've never been able to tell exactly what the difference was. Solutions that worked in some cases did not work in others. Good luck, Mike Urban
iws@rayssdb.ray.com (Ihor W. Slabicky) (02/23/89)
In article <2313@rayssdb.ray.com>, iws@rayssdb.ray.com (Ihor W. Slabicky) writes: > > Can anyone send me a schematic or info on broadband noise filters > that will filter out 60 Hz hum on the 120VAC line? Some background: > I use a portable stereo cassette recorder to record music off my > receiver. When the recorder is powered from the AC line, I can hear > lots of 60 Hz being recorded on the tape. Moving the recorder, cables, > or power cord around tends to lessen the hum. When I record using the > batteries, no hum. Also, when I playback, if I put the INPUT switch > on the recorder to the MIC position, no or very little 60 Hz hum is > heard, but when the INPUT switch is set to LINE, lots of hum. Ideas? Well, thanks to everyone who responded. The two problems suggested are: 1 - a ground loop or faulty cables. Recommendations were to check the cables and switch around the plugs at the wall or to other outlets. I tried both of these, and this did not solve the problem. So... 2 - filtering capacitors going bad in the tape recorder's power supply (AC to DC) conversion. This may be the problem. The recorder is almost 15 years old. Before I go and take it apart, any ideas on how to test the capacitors using a volts/ohms/DC amps meter to see that they are bad? Any ideas on which type of capacitors to use as replacements (obviously same or higher ufd value and same or higher voltage value) Thanks for your advice - Ihor Internet: iws@rayssdb.ray.com Usenet: {gatech, uiucdcs, decuac, sun, ukma, necntc, spdcc}!rayssd!rayssdb!iws
moto@cad.Berkeley.EDU (EDIF Committee) (02/24/89)
In article <2322@rayssdb.ray.com> iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >2 - filtering capacitors going bad in the tape recorder's power supply > (AC to DC) conversion. This may be the problem. The recorder is > almost 15 years old. Before I go and take it apart, any ideas on > how to test the capacitors using a volts/ohms/DC amps meter to see > that they are bad? Any ideas on which type of capacitors to use > as replacements (obviously same or higher ufd value and same or > higher voltage value) If the recorder is that old (and especially if it hasn't been used much), then the electrolytic cap. are probably dried out. It is often possible to "re-form" the barrier, but for the price of new caps. at this voltage I would simply replace every single one. Just the electrolytics (polarized) ones! The others should be ok unless physically damaged somewhow. The same or higer volt/ufd is fine, but try to stay within about +20%, since the actual capacitance will vary some with too low a voltage and too high a capacitance (e.g. 100X) can give you problems with leakage. Be careful with over heating the PC board and good luck! Mike Waters AA4MW/7 * Motorola CAD Group * Witty remark goes *HERE* Mesa, AZ ...!sun!sunburn!dover!waters * OR moto@cad.Berkley.EDU *
myjak@home.csc.ti.com (Mikie) (02/24/89)
In article <2322@rayssdb.ray.com> iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >In article <2313@rayssdb.ray.com>, iws@rayssdb.ray.com (Ihor W. Slabicky) writes: >> >> Can anyone send me a schematic or info on broadband noise filters >> that will filter out 60 Hz hum on the 120VAC line? > >Well, thanks to everyone who responded. The two problems suggested are: > >1 - a ground loop or faulty cables. >2 - filtering capacitors Rats! I was hoping someone wound mail a realy useful reply to this one. I have the same (similar?) problem when I hook up my Mac to the Stereo via the Mac's audio digitizer. Everything I playback has a terrible 60/120 hz. hum in it. Sure, the filter caps on the mac aren't the greatest, but there still good, and besides, replacing them with mega-farad caps would void the warranty. I was hoping someone would mail in the schematics so's I could build an in-line, black box trap to clip everything below 120hz. Rats! 2 /\/\ Computer Virus: n., pl. -ruses. 1) Any of various post-compilation pathogens consisting essentially of a core of hexadecimal characters surrounded by a benign software coat, having the ability to fit through a pinhole in the condom of security and replicate within a computing environment.
dave@onfcanim.UUCP (Dave Martindale) (03/13/89)
In article <1989Feb17.172352.5088@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: > >The one fix that wouldn't involve digging into the guts of your recorder >would be to forget using the recorder's own AC power supply, get a >separate power supply that produces the same output voltage as the >batteries, and hook that up to the recorder as a replacement for the >batteries. This isn't certain to fix the problem but it would probably >help. Radio Snack carries plug-in "bricks" of various voltages that >might do the job, although you'll probably need a bit of soldering to >connect them in. Unfortunately, most of the Radio Shack bricks (and those of other manufacturers) do not put out pure DC. It's AC that has been full-wave rectified and filtered somewhat, but there's still 120 Hz hum sitting on the DC voltage. Thus, you may find that you get hum with a "brick" when you don't with real batteries. If hum persists with a "brick", you can entirely eliminate the hum from the DC power supply by starting with a brick whose output is 3V or more above the voltage you need, and using a monolithic voltage regulator like a 78XX or LM317 to drop the voltage to what the recorder needs.