[sci.electronics] Hissing from tape recorders ?

anthony@batserver.cs.uq.oz.au (Anthony Lee) (04/06/90)

Just want to ask a simple question.  I notice that my tape recorder when
played without a tape hisses.  I just want to know why and how I can
get rid of the hiss.  Is this because the head have been magnetised one
way and need demagnetising ?

Thanks in advane 
--
Anthony Lee (Humble PhD student) (Alias Time Lord Doctor) 
ACSnet:	anthony@batserver.cs.uq.oz	TEL:+(61)-7-371-2651
Internet: anthony@batserver.cs.uq.oz.au	    +(61)-7-377-4139 (w)
SNAIL: Dept Comp. Science, University of Qld, St Lucia, Qld 4072, Australia

berryh@udel.edu (John Berryhill) (04/06/90)

In article <3190@moondance.cs.uq.oz.au> anthony@batserver.cs.uq.oz.au writes:

>Just want to ask a simple question.  I notice that my tape recorder when
>played without a tape hisses.  I just want to know why and how I can
>get rid of the hiss.

Put in a tape.

> Is this because the head have been magnetised one
>way and need demagnetising ?
>SNAIL: Dept Comp. Science, University of Qld, St Lucia, Qld 4072, Australia

It is obvious from your signature that you probably have heads that
are polarized for the northern hemisphere instead of the southern
hemisphere where magnetic fields point the other way.  Short of going
to the electronics store to get what are usually callled "aussie heads,"
you might try operating your tape deck upside down.  You may also need
to adjust the tape speed to compensate for the coriolis effect which
is probably making your tapes run slightly faster than normal since
motors calibrated for the northern hemisphere have to turn the other
way.

--
							      John Berryhill
					   143 King William, Newark DE 19711

wb8foz@mthvax.cs.miami.edu (David Lesher) (04/06/90)

In <16020@nigel.udel.EDU> berryh@udel.edu (John Berryhill) writes:


>>Just want to ask a simple question.  I notice that my tape recorder when
>>played without a tape hisses.  I just want to know why and how I can
>>get rid of the hiss.


>It is obvious from your signature that you probably have heads that
>are polarized for the northern hemisphere instead of the southern
>hemisphere where magnetic fields point the other way.  

No!
The problem is your power line is the incorrect phase for
the recorder. Run an extension cord from the Northern Hemisphere
to plug it into, and your problem will go away. Be sure and get
the cable with insulation rated for underwater use.

-- 
A host is a host from coast to coast.....wb8foz@mthvax.cs.miami.edu 
& no one will talk to a host that's close............(305) 255-RTFM
Unless the host (that isn't close)......................pob 570-335
is busy, hung or dead....................................33257-0335

elliott@optilink.UUCP (Paul Elliott x225) (04/06/90)

In article <16020@nigel.udel.EDU>, berryh@udel.edu (John Berryhill) writes:
> It is obvious from your signature that you probably have heads that
> are polarized for the northern hemisphere instead of the southern
> hemisphere where magnetic fields point the other way.  Short of going
> to the electronics store to get what are usually callled "aussie heads,"
> you might try operating your tape deck upside down.  You may also need

GIVE US A BREAK!

Any fool knows that this problem can be easily solved by turning the 
cassette tape (or reel) over; swapping side A and side B.  

Pre-recorded tapes are a problem, however...

-- 
      Paul M. Elliott      Optilink Corporation     (707) 795-9444
            {uunet, pyramid, pixar, tekbspa}!optilink!elliott
   "Less than perfect, that's what I've been striving for all along."

thomas@mvac23.UUCP (Thomas Lapp) (04/07/90)

> Just want to ask a simple question.  I notice that my tape recorder when
> played without a tape hisses.  I just want to know why and how I can
> get rid of the hiss.  Is this because the head have been magnetised one
> way and need demagnetising ?

I can't believe some of the (joking) replies I've seen to this one.
If you are talking about the hiss which gets louder when you turn up the
volume, the reason is that you are hearing the amplification of noise
created by the components making up the amplification circuit.  Cheaper
machines have more hiss.  More expensive recorders have better quality
components which have less noise associated with them.  The hiss is white
noise which results (ultimately) from the brownian motion of the molecules
in the components.  The only way to get rid of this noise is to cool the
machine way down (like liquid gas temperatures).  Not worth the bother
in my opinion ;-)

> Anthony Lee (Humble PhD student) (Alias Time Lord Doctor) 
> ACSnet: anthony@batserver.cs.uq.oz    TEL:+(61)-7-371-2651
> Internet: anthony@batserver.cs.uq.oz.au        +(61)-7-377-4139 (w)
> SNAIL: Dept Comp. Science, University of Qld, St Lucia, Qld 4072, Australia
                         - tom

--
internet     : mvac23!thomas@udel.edu  or  thomas%mvac23@udel.edu
uucp         : {ucbvax,mcvax,psuvax1,uunet}!udel!mvac23!thomas
Europe Bitnet: THOMAS1@GRATHUN1
Location: Newark, DE, USA                          
Quote   : The only way to win thermonuclear war is not to play.

--
The UUCP Mailer

myers@hpfcdj.HP.COM (Bob Myers) (04/10/90)

>....................The only way to get rid of this noise is to cool the
>machine way down (like liquid gas temperatures).  Not worth the bother
>in my opinion ;-)


And likely to void the warranty as well... :-)



Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.

irwin@m.cs.uiuc.edu (04/12/90)

/* Written  9:57 pm  Apr  5, 1990 by anthony@batserver.cs.uq.oz.au in m.cs.uiuc.edu:sci.electronics */
>/* ---------- "Hissing from tape recorders ?" ---------- */
>Just want to ask a simple question.  I notice that my tape recorder when
>played without a tape hisses.  I just want to know why and how I can
>get rid of the hiss.  Is this because the head have been magnetised one
>way and need demagnetising ?

>Thanks in advance 
--
>Anthony Lee (Humble PhD student) (Alias Time Lord Doctor) 
>ACSnet:	anthony@batserver.cs.uq.oz	TEL:+(61)-7-371-2651
>Internet: anthony@batserver.cs.uq.oz.au	    +(61)-7-377-4139 (w)
>SNAIL: Dept Comp. Science, University of Qld, St Lucia, Qld 4072, Australia
/* End of text from m.cs.uiuc.edu:sci.electronics */

I have been following this thread for a time and note the responses
that have been received. Most were in jest in one form or another.

I would like to offer a serious response. I worked part time at a
service bench for a local TV and audio service shop for a few years.
I have serviced a lot of tape recorders. One thing that I noted was
that most recorders make use of an automatic volume control circuit.
This is to take up part of the differences in record level from tape
to tape.

If one purchases several music tapes and plays them, they can not
assume that all are recorded at the exact same level. If you set
the volume of the recorder on play back to what you like, then play
tapes, you note that most music is about the same level. This is
because of the automatic level in the pre-amp stages of the unit.
It will take care of minor differences in levels from tape to tape.

Now, if you put the recorder into play mode, with no tape, the pre
amp stages are running WIDE OPEN, as there is no signal to cause
them to throttle back, hence, lots of noise. The stages would not
normally run at such high gain, if a tape were actually in place
as the signal being sampled would cut down the gain.

I am not sure just why you want to put it in play mode without tape,
just to use the audio stages or what, you might offer an answer to
this.

Al Irwin
Univ of ILL
Dept of Comp Sci
Urbana, IL
irwin@m.cs.uiuc.edu

craig@oakhill.UUCP (Craig Shaw) (04/12/90)

>that most recorders make use of an automatic volume control circuit.
>This is to take up part of the differences in record level from tape
>to tape.
>
  It has been my experience that automatic level control (ALC) is used
only to set RECORD level, not playback volume. This is a "feature" on the
cheap sets, and can cause tape saturation (when a sudden loud noise occurs)
and "breathing" (noise level modulation) when recording intermittent
conversation in a low backgroud-noise setting.

  If I'm wrong, I sure alert net-watchers will point this out [as I have :-) ].
-- 

I'M THE NRA.
Craig D. Shaw - MCU Systems Design (512)891-2245  Motorola Inc., Austin, TX.

elliott@optilink.UUCP (Paul Elliott x225) (04/12/90)

In article <21000070@m.cs.uiuc.edu>, irwin@m.cs.uiuc.edu writes:
> I have serviced a lot of tape recorders. One thing that I noted was
> that most recorders make use of an automatic volume control circuit.
> This is to take up part of the differences in record level from tape
> to tape. [... describes why with no input, AGC jacks up the gain...]

Correct me in I'm wrong, but isn't AGC only for recording?  I assume we're
not discussing Dolby or other companding modes, just the normal AGC used
in the cheaper tape recorders (like the ones I have).

Still no answer as to why a particular machine would be especially noisy...


-- 
      Paul M. Elliott      Optilink Corporation     (707) 795-9444
            {uunet, pyramid, pixar, tekbspa}!optilink!elliott
    "Less than perfect, that's what I've been aiming for all along."