And so it came to pass, on 03-28-97 12:39,
   that Kenneth Parrish spake unto Matt Ion:
 KP> Are erase and bias wave forms asymmetric for efficiency?  
MI>> Hmm, can't say as I've ever seen a tape deck that used Hall effect
MI>> device playback... interesting concept!
 KP> What are these?
Essentially a semiconductor that responds to changes in magnetic fields (the 
Hall effect).  Most are simple on/off devices, although linear versions exist 
as well.
 KP> Dual turntables used them for speed sensing.  A Spacebase (tm)
 KP> article says NASA flies one or more in a current satellite.  I
 KP> think they're used in data disc drives and maybe Hitachi used them
 KP> in a cassette deck (for recording and playback?  ). 
For playback, yes, but not for recording.
 KP> I've seen integrated circuit Hall devices.  Hall units are used in
 KP> automobiles.  
I've actually experimented with them as guitar pickups.  Got some interesting 
quirks to work out, but they certainly provide a DIFFERENT sound...
MI>> narrow the gap in the playback head, the higher the frequency that
MI>> c reproduced. However, the wider the gap in the record head (to a
MI>> certain practical point, of course), the stronger the signal that
MI>> can be applied the tape.  This is why "professional" decks have
MI>> separate record and play heads.
 KP> I've seen test reports that show 3-5 khz wider frequency response
 KP> from cassettes.  Some mount the separate heads in a single housing
 KP> so there's less to adjust.
Also important to proper operation is that record and playback heads be 
aligned to each other; if a tape is played back on a head that's aligned 
differently from the head that recorded it, phase will be affected.  
Enclosing both in the same casing ensures they stay aligned, at least to each 
other.
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Love, luck, and lollipops...
Matt


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