Tape Recorder Head Output
Hey everybody! I'm brand new to this forum and pretty new to "diy audio" in general. This question might be a no brainer for most of you but it has be quite confused and to avoid tearing apart another cassette player, hopefully I can find an answer.
Reccently I've bought a combo radio/cassette/portable TV and for a project I'm working on an trying to extract just the cassette bit. I've figured out getting the motor running but all I need to do now is get the output going to some sort of amp but just can't seem to get it to work.
There is a cable labeled "head" on the circuit board that it goes to and I snipped the plug off it and it is two thin wires shielded by what appears to be a third wire as it is sodered to something at the other end attached to the tape player. I'm thinking this could be the ground and I though extracting the audio would be as easy as plugging the two wires into an amp, pressing play and voila! It did not work that way.
It might have been the crappy audio cable but am I right to think that the two outs are just a positive and a negitive signal coming out of the tape head?
I remind you guys that I am very new to this and I'm sure this is a stupid question for most but it is for a school project and I really appreciate any expertise you can throw my way.
You can tell something about the tape head with an ohmmeter. You should get maybe 100 ohm across the read head. If you have two hundred ohm wires to the third wire, one is probably the read head and the other is probably the record head. If you only have one, one wire is probably connected to the metal shell of the head and is the anti-noise ground.
My 1957 design PAS2 preamp has a tape head input as well as mag phono, and the tape head has got as much gain as the mag phono, just not the bass boost parts. So for a preamp stage, ahead of the headphone amp or whatever, you need a 50x amp. So you use an op amp with 4.7k input resistors, and maybe a 250 K feedback resistor. 4558 op amps are cheap and pretty stable. See all the disco mixer and "I need to build a xxx mixer" threads on here for op amp circuits. Also see this http://sound.westhost.com/projects-2.htm
Linear amplification will not be good. A playback tape head needs equalization, i.e. bass boost. Search for NAB or IEC equalization curve. Also, the amplifier needs to be close to the tape head, otherwise (due to the high gain and strong bass boost) it will pick up hum that is difficult to overcome.
Thanks guys. I ended up cracking open a differnt tape player because this project deadline is very close and i figured it would just be easier to use the already built in amp then trying to teach myself how to make one. That project will be for next time. The only trouble is now I can't figure out how to get the record to work on the new deck. I'm gonna post that question in a new thread, but thanks for the advice. I'm sure all be back to this post at some point.
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