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Old 28th January 2009, 12:46 PM   #1
mth5044 is offline mth5044  United States
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Default Circuit before a recording head

Hello.

This may or may not be a noobish question, but I figure a forum full of incredibly astute people could help me out.

I've got an application that requires a signal to pass into a recording head and onto a recording medium, then to be picked up by a playback head(s).

I worked out a layout to take the signal from the playback head, bring it back up to a normal level and equalize it based on the LA3161 chip, but I am not sure what needs to happen before the recording head. I'm assuming that signal needs to be boosted to get a good signal down on the recording medium, but I don't know how the best way to go about this would be. I'm guessing it needs to be boosted, like a preamp maybe, but it can't get distorted.

I was thinking something based upon the BS170 transistor, but something else would work also. The simpler, the better. It doesn't have to be anything high quality, but I don't want to much signal degradation.

Thanks for any ideas you guys have. I appreciate it.

Take care,
Matthew
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Old 28th January 2009, 01:30 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

If your talking tape your forgetting about / ignoring recording bias.

/sreten.
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Old 28th January 2009, 10:28 PM   #3
mth5044 is offline mth5044  United States
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Unfortuantly, I haven't been able to find much information on what comes before the recording head, so I just figured that you had to boost the signal enough.

I guess I have some more research to do... *sigh*

Is there anything I can look at for an example? Or any known layouts/schematics I can look at? It isn't going to be on tape, but it's a similar material.

Thanks for the heads up!
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Old 29th January 2009, 09:58 AM   #4
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As well as the requirement for bias, you need to provide a 'constant current' to the head - this is usually done very simply by feeding the head via a resistor.

I would suggest you check out old tape recorder circuits.
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Old 29th January 2009, 12:34 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

Surely there are some cassette recorders / playback on a chip ?

AFAIK DC to a tape recording or playback head is a very bad idea,
you may thinking of the erase head which I recall being DC current.

/sreten.
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Old 29th January 2009, 01:57 PM   #6
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Quote:
Originally posted by sreten
Hi,

Surely there are some cassette recorders / playback on a chip ?

AFAIK DC to a tape recording or playback head is a very bad idea,
you may thinking of the erase head which I recall being DC current.

No, it uses the same high frequency as the bias (the same oscillator), but at far higher power to erase.

Some really cheap and nasty cassettes use a permanent magnet to erase the tape, and a crude (and poor) DC bias.
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Old 30th January 2009, 12:25 PM   #7
mth5044 is offline mth5044  United States
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Thanks everybody, I will look around for some tape player schematics.

I'm going to have a running project consisting of different recording mediums and I wanted to start with a floppy disc. Trying different coatings, testing wear and tear. Then maybe try running tape around a drum like the echorecs. Possibly harddrive recording.

I know, it's not practical, but I'm not a practical person
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Old 31st January 2009, 01:56 AM   #8
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Here is some schematics

http://www.audioschematics.com/tapelist1.html#Studer



When recording on tape you also have an equalization curve, to get better s/n and dynamics. worth thinking about.


recording on discs.. I have an old Rex Rotary, which is a dictaphone, "phonograph" which is recording on magnetic discs.... its from the 60's... Pretty cool stuff :-)
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