Hey there, I am trying to make a tape recorder from scratch. What I want to do is to erase, record and play a magnetic tape. (Now, for the purpose of learning, it does not matter what type of magnetic tape I will use, it can even be a small walkman cassette, but I am willing to make a big 30 IPS recorder/player at the end...)
I also want to make all the circuits myself, like the biasing circuit, op-amps...
Here is my start point, I have made a circuit. I have 2 signals here which are VG1 and VG2. VG1 is my audio input and VG2 is the 100kHz sine signal.
The circuit is simply adding these two signals together. (First op-amp is summing the signals, second op-amp is inverting the negative signal to positive) So my output is signal 1 + signal 2 simply...
I am wondering what is the voltage "play and record heads" use. Because this new signal which will go to the record head should not be more than ...... volts? Can you fill the gap 🙂 ?
I also would like to know how much amplification I need for the preamplifier of the play head? (The signal comes from the play head, and goes to the pre-amplifier. )
Thanks in advance...
I also want to make all the circuits myself, like the biasing circuit, op-amps...
Here is my start point, I have made a circuit. I have 2 signals here which are VG1 and VG2. VG1 is my audio input and VG2 is the 100kHz sine signal.
An externally hosted image should be here but it was not working when we last tested it.
The circuit is simply adding these two signals together. (First op-amp is summing the signals, second op-amp is inverting the negative signal to positive) So my output is signal 1 + signal 2 simply...
I am wondering what is the voltage "play and record heads" use. Because this new signal which will go to the record head should not be more than ...... volts? Can you fill the gap 🙂 ?
I also would like to know how much amplification I need for the preamplifier of the play head? (The signal comes from the play head, and goes to the pre-amplifier. )
Thanks in advance...
Hello emretelci,
Is this to be a professional machine with three motors and 10.5" reels?
I may have circuit drawings of the Scully 280 somewhere.
Sincerely,
Ralf
Is this to be a professional machine with three motors and 10.5" reels?
I may have circuit drawings of the Scully 280 somewhere.
Sincerely,
Ralf
Hi, what you sketched is wrong in principle. The record head is a low impedance coil driven by constant AC current, not voltage. The bias signal should be superposed on it right at the head coil, so that the bias current is a magnitude higher than the audio signal.
On the other hand, the playback head is high impedance, and the audio signal is in the order of millivolts. In addition, it is increasing with frequency (assuming a constant tap flux). Consequently, higher frequencies should be suppressed, but at a certain frequency (where wavelength on the tape is comparable with head gap width), this equalization should go to flat again.
There are also other factors, main concern is lowest possible noise of amplification at playback. Proper level adjustment at record and playback is also important.
I also recommend to study circuit diagrams of commercial tape recorders.
On the other hand, the playback head is high impedance, and the audio signal is in the order of millivolts. In addition, it is increasing with frequency (assuming a constant tap flux). Consequently, higher frequencies should be suppressed, but at a certain frequency (where wavelength on the tape is comparable with head gap width), this equalization should go to flat again.
There are also other factors, main concern is lowest possible noise of amplification at playback. Proper level adjustment at record and playback is also important.
I also recommend to study circuit diagrams of commercial tape recorders.
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Thank you Ralf, I am trying to make if from scratch. I am also learning electronics so my plan is to build something simple for now, maybe a little walkman cassette recorder/player 🙂
Thank you, here are my graphics for biasing. I think it somehow looks right.
I am not sure how I can make a constant AC current for the record head. Isn't an AC audio signal coming from a preamplifier enough?
You can use a transconductance amplifier circuit to produce a current output. Any feedback only really matters at audio frequencies as distortion of the bias signal is irrelevant, so the amp could be close to open-loop at 100kHz perhaps?
Probably better to chase down some real schematics and see what they do...
Probably better to chase down some real schematics and see what they do...
> Probably better to chase down some real schematics and see what they do...
Absolutely. We are not as brilliant as the engineers who cooked-up the first magnetic recorders. Stuff they saw clearly is lost to today's designers. PLAGIARIZE!! (Then change a few values so nobody can prove it.)
BTW, some types of distortion on the bias waveform raises the hiss horribly. You want 2nd as low as possible, and 3rd is generally not-large. This is normally done with Tuned Circuits (though there were exceptions).
Absolutely. We are not as brilliant as the engineers who cooked-up the first magnetic recorders. Stuff they saw clearly is lost to today's designers. PLAGIARIZE!! (Then change a few values so nobody can prove it.)
BTW, some types of distortion on the bias waveform raises the hiss horribly. You want 2nd as low as possible, and 3rd is generally not-large. This is normally done with Tuned Circuits (though there were exceptions).
It is usually done by simply passing the audio signal through a large resistor (4.7k ... 10k) to the REC head. The bias signal goes directly, controlled by a variable capacitor or resistor. Usually there is a trap LC circuit at the output of the REC amplifier, in order to prevent bias flowing back to the circuit.