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Old 14th June 2007, 09:51 PM   #1
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Default Tape players/adapters

Hi guy's, quick question if I may chaps...
I have one of those tape to 3.5mm audio jobbies for playing MP3's (and using as a hands free kit!). and I was wondering if I could hard wire a 3.5mm jack into the board on the tape players magnetic head?
OK, I know I have to have a tape in there anyway to get the thing to 'imagine' its playing a tape but I wondered if I could bypass the 'head-to-head' interface and feed my audio directly into the next stage...whatever it is...

Thanks for looking guy's
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Old 15th June 2007, 05:54 AM   #2
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The tape head will be connected to a preamp IC. You would need to remove the IC and connect your signal source to the points that were previously the output of the preamp IC. Since most of the head units use DC biasing for the preamp section, you may need to bias the circuit at ~1/2 of the regulated voltage in the head unit. Generally, the regulator operates at ~10v. You'd need to isolate the signal source from the DC bias with a capacitor. To determine the actual bias voltage, you could measure the DC voltage on the output of the preamp IC before removing it from the circuit.

If your signal source is powered by batteries and not, in any way, connected to the vehicle (except through the signal cables), it may work well enough. If you are going to power it via a regulated power supply that is connected to the chassis ground of the vehicle, you may run into ground loop problems (noise). A ground loop isolator could be used to break the ground connection and should get rid of the noise.
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Old 15th June 2007, 06:30 AM   #3
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Quote:
Originally posted by Perry Babin
The tape head will be connected to a preamp IC. You would need to remove the IC and connect your signal source to the points that were previously the output of the preamp IC. Since most of the head units use DC biasing for the preamp section, you may need to bias the circuit at ~1/2 of the regulated voltage in the head unit. Generally, the regulator operates at ~10v. You'd need to isolate the signal source from the DC bias with a capacitor. To determine the actual bias voltage, you could measure the DC voltage on the output of the preamp IC before removing it from the circuit.

If your signal source is powered by batteries and not, in any way, connected to the vehicle (except through the signal cables), it may work well enough. If you are going to power it via a regulated power supply that is connected to the chassis ground of the vehicle, you may run into ground loop problems (noise). A ground loop isolator could be used to break the ground connection and should get rid of the noise.
Excellent reply Perry, thank you very much for the insight
Looks like I'm hotwiring the car at the weekend then

Thanks again
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Old 18th June 2007, 08:58 PM   #4
dangus is offline dangus  Canada
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I'm reasonably sure there is EQ in the preamplifier after the tape head. So, if you patch in there you'd either need to disable the equalization components or use an inverse-EQ network or use the tone controls to make things sound OK.

Considering what new decks cost these days, it might be smarter to just pick up another deck that already has an input jack. If there some compelling reason to keep the original tape deck, I'd think about wiring an input jack someplace upstream of the volume control, since that should be line-level and un-EQ'd.
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Old 18th June 2007, 09:37 PM   #5
lgreen is offline lgreen  United States
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I agree with the last post, the tape head cannot simply be removed with a wire to take its place because the tape head signal will go to a preamp/equalizer. You gotta either go upsteam of this or remove/bypass it.

If you are going through the trouble to open up your head unit, why don't you just figure out where the line level signal lives (I'd probe around the volume control) and bring this out to a 1/8" minijack and a DPDT switch so you can easily connect and disconnect your source. You could even mount the switch and jack on some plastic or metal flush to the tape door if you choose to not use the tape player anymore.
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Old 18th June 2007, 10:10 PM   #6
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He was told that he would have to remove the preamp IC. Generally, the equalization for the tape head will be in the preamp circuit. When the IC is removed, the equalization should be removed.
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Old 19th June 2007, 07:18 PM   #7
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Default Buy a cassette adapter

I have a Panasonic cassette adapter than came with an MP3 player. To tell you the truth it sounds great. While it may not be quite as good as a direct connection, it is still darn good. And you can use it right away.

Even my other one from Radio Shack is decent.
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Old 22nd June 2007, 03:47 AM   #8
dangus is offline dangus  Canada
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Quote:
Originally posted by Perry Babin
He was told that he would have to remove the preamp IC. Generally, the equalization for the tape head will be in the preamp circuit. When the IC is removed, the equalization should be removed.

D'oh! How'd I miss that? Ripping out the preamp IC is a little drastic, unless the cassette mechanism is already broken. But then if it is broken you've got to fool the sensors so it doesn't automatically stop. If you patched in just before the volume control, then you could leave it on radio instead which would be much simpler. Not running the cassette motor should make for less electrical and mechanical noise too.

I used a Sony cassette adapter that came with a Discman for a long time; it was a great deal better than nothing. Would an FM modulator be any better? They're both kluges... and maybe both are "good enough" for car use.
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