Xref: utzoo sci.electronics:5254 rec.audio:10990 rec.ham-radio:8840
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cwjcc!tut.cis.ohio-state.edu!osu-cis!att!ihlpl!nmju
From: nmju@ihlpl.ATT.COM (Urban)
Newsgroups: sci.electronics,rec.audio,rec.ham-radio
Subject: Re: 60 Hz hum filter
Message-ID: <9143@ihlpl.ATT.COM>
Date: 20 Feb 89 19:00:45 GMT
References: <2313@rayssdb.ray.com>
Reply-To: nmju@ihlpl.UUCP (55244-Urban,M.J.)
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 37

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