getting to know your read/write heads

Re: getting to know your read/write heads

Postby mitcho » Fri Sep 09, 2011 7:33 pm

Wow! Thanks for such replies. I should buy you a drink :D
I'm trying to connect the r/w head to a tape head preamp and again found 5 wires connected to it :D It's from a walkman with autoreverse. Did you just pick 2 out of them and everything worked fine? I tried all combinations but not one worked.
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Re: getting to know your read/write heads

Postby guest » Sat Sep 10, 2011 11:24 pm

did you check that the tape deck worked
before doing the mod

the 5 wires are probably as follows
2 for left channel
2 for right channel
1 for case ground

the two channels will probably be
in seperate shielded pairs

make sure to disconnect the wires
from the tape deck head first
then take one of the shielded pairs
and connect them to the floppy head
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Re: getting to know your read/write heads

Postby mitcho » Wed Sep 14, 2011 8:12 am

Finally, I got rid of the buzz. I connected the FDD heads to the tape head preamp of a walkman. Now I've got a stereo signal. Each channel is on his side of the floppy disk. The signal is still low but can be heard.
Shall we open another thread for the circuit that connects the three FD drives to the arduino?

edit: basically what I did to get rid of the buzz is that I used short wires. as short as possible.
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Re: getting to know your read/write heads

Postby guest » Thu Sep 15, 2011 12:20 pm

congratulations

another thread would be good
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Re: getting to know your read/write heads

Postby mitcho » Fri Sep 16, 2011 8:33 am

Thank you! :D
Just one more thing. I'm trying to add bias (DC) to the input signal (AC). How did you put them together? An inverting summing circuit like this (http://www.wiringdiagrams21.com/2009/12/03/audio-mixer-inverting-summing-circuit-diagram) wouldn't work because, if I'm not wrong, a capacitor can not pass DC signals. Do you have a diagram of what you did to add bias to the input signal or do you remember maybe how much bias did you add? Thanks a lot for your help.
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Re: getting to know your read/write heads

Postby guest » Fri Sep 16, 2011 11:34 am

you can use the summer amplifier
because the bias you want to add
is actually an AC bias

you need to put a 40kHz signal in
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Re: getting to know your read/write heads

Postby mcanulty » Sat Oct 01, 2011 5:25 pm

Hey, yeah, I tried running DC through one of the heads because one of the patents I read implied that they were using dc to erase, and that's how I burnt out one of my r/w heads (the only one I managed to burn out actually!). Those little coils don't like to see much current at all.

Guest is quite right, bias frequencies vary, but 40khz is a good start, just get it out of the audible frequency range and mix it with your audio signal. Technically, it helps to get the magnetic media moving around better, so that you can lay down a cleaner signal, but I found it was most especially useful for erasing audio. To make it work I played around until I found a frequency at a resonant peak of my r/w head, but it worked fine with heads that had a different resonant frequency range as well, so I don't think it's a huge deal.

To get a better idea of what's going on, take a look at this link on the GSU hyperphysics site:
http://hyperphysics.phy-astr.gsu.edu/hb ... /bias.html

You can also google "tape bias" for some helpful links.
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Re: getting to know your read/write heads

Postby Paleorama » Wed Oct 05, 2011 9:21 am

Using a high-frequency tone for erasing is an amazing idea! should it be a certain amplitude to overwrite the existing "data"?
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Re: getting to know your read/write heads

Postby mcanulty » Wed Oct 05, 2011 3:45 pm

You'll have to experiment with it, it will depend how loudly you wrote your audio data. I found that as I got more acquainted with my system I was able to back off the recording 'volume' or amplitude and which gave me a weaker signal that erased much more easily but didn't cost me in terms of audio quality.
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Re: getting to know your read/write heads

Postby kris_mcdougall » Thu Oct 13, 2011 1:25 pm

My tape deck actually has three conductors plus a shield/ground. It looks like they combined the negative signals of the two channels together and made: L+, R+, (L+R)- and ground.

EDIT: Looks like this is definitely the case. As other users may encounter the same wiring using cheap cassette decks (mine is a dual cassette Panasonic ghetto blaster from the 80's) I'll share my findings:

L+ = White
R+ = Red
LR- = Yellow
Braid = Ground

This isn't to say that yours will have the same colours, but I hope this will help somebody.
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