Xref: utzoo sci.electronics:5541 rec.audio:11520 rec.ham-radio:9358
Path: utzoo!utgpu!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: sci.electronics,rec.audio,rec.ham-radio
Subject: Re: 60 Hz hum filter
Message-ID: <17755@onfcanim.UUCP>
Date: 13 Mar 89 06:37:02 GMT
References: <2313@rayssdb.ray.com> <1989Feb17.172352.5088@utzoo.uucp>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Followup-To: sci.electronics
Organization: National Film Board / Office national du film, Montreal
Lines: 21

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.