🚀 go-pugleaf

In article <YZwNWoG00VQc8GOWpD@andrew.cmu.edu>, kz08+@andrew.cmu.edu (Ken Zuroski) writes:
> To make a long story short, it seems that the condensor microphone in
> the unit wasn't properly grounded or whatever, and that there is a
> very persistant and annoying sixty-cycle AC hum masking the voices on
> the tape. Uh oh.
>
> Now, the frustrating thing is that it is almost possible to decipher
> the voices behind the buzz. Almost. If you turn the volume up,
> naturally the noise increases as well, and so it's a futile attempt.
> And so I had the idea of using a graphic equalizer to filter out some
> of the noise. Here is what I am going to try to do, and what I would
> like you to comment on as to the possibility of success. I will use
> two tape recorders, the graphic equalizer (when I find one) in line
> between them. I will use headphones to mask out as much of the buzz as
> is possible using the graphic equalizer, and duplicate the equalized
> signal on recorder number two; I'll boost the overall level of signal
> in the process, thus hopefully amplifying the voices. Then, if I still

Ken-- I think you are on the right track, but instead of using a
graphic equalizer, see if you can get a notch filter.  CMU has
plenty of EE's--see if you can find a laboratory filter that you
can use, or have an EE throw together a filter with a couple of
op amps.  The notch filter will have much better attenuation
than a graphic EQ would, and you could tune it to 60 Hz (an
equalizer may not have a slider near that--a parametric equalizer
is another possibility--they allow you to tune the center frequency
of the slider).

The cost of a simple op amp notch filter should be < $10.
If you need schematics for one, let me know, but any op amp
circuit cookbook should have one.

Good luck!!

Paul