The Tascam Porta 03 was used as transport with direct connection to its head.
Signal path:
On recording:
the song Is it OK if I Call you mine? from Fame soundtrack CD - Sony Portable CD Player line out - Pleiades 2N3053 one transistor amplifier - magnetic head side A, L channel, biased at 1mA DC - TDK SAX 60 new cassette
On reproduction:
Is it OK if I call you mine? TDK SAX - Sony TC-D5 Pro II - Sennheiser HD580
Before connecting the head to Pleiades 2N3053 output, the Sennheiser HD580 headphones were connected to check sound quality. It was very good but the amplifier was slightly overdriven by line out. It operated at just 1.3V. (Always use a fuse in series with a battery for safety).
Then the headphones unplugged, the head was connected and play was pressed to move the tape.
DC bias current is 1mA.
Then the cassette was taken to Sony TC-D5 Pro II for reproduction.
It worked. Sound came just from the left headphone. It did not sound like chewing sand. This is because there was DC bias from the 2N3053 collector. Ie direct coupling to collector and battery, the head inbetween the two (with fuse for safety).
The sound was not good.
It was like a bass midrange telephone.
The vocal reminded of someone singing to a mic without an R,L Pleiades filter in parallel with the mic.
There was lack of high pass filtering.
The Sony TC-D5 VU meter showed up to -5dB.
There was some bass hiss noise. Mostly apparent when the song was paused while recoding. As it seems noise comes from the DC bias.
After this single take, another one was recorded but this time on top of it was recorded again the same song. It worked, both sounds could be heard together but distortion was much worse. And it sounded as if the bias was much less. The output was much less than when the head records at one pass.
A possible cause for the bad sound is that the output impedance of the 2N3053 transistor is about 300Ω or less. So there is impedance match with the head. And the head is driven at constant voltage with respect to frequency rather than constant current wrt frequency.
The much higher output impedance of an electron tube amplifier, eg Pleiades V6, should be tried or a series resistor at the output of transistor etc. All precautions for voltages of any magnitude and safety should be strictly followed. Even if it a battery powered amplifier such a the Pleiades V6. And a series fuse with any battery must be used for current warming up safety or fire hazard in case of a short circuit.
Looking through at a JVC cassette recorder and the Uher 4200 portable reel to reel schematics a 22K or 10K resitor respectively can be seen in series feeding the recording head. The resitor has a few nanofarads (nF) shunt capacitance possibly making an additional high turn over gentle slope high pass, RL Pleiades filter. The resistor in itself with the shunt inducstnce of the head form a 6dB per octave high pass filter, a 6dB per octave Pleiades L filter. This slope is then reversed in a playback amplifier until a some turnover frequency, defined by the μS time constant. For example 70μs for IEC 7.5ips. (μ ie micro comes from the Hellenic word μικρο pronounced mecro with short e sound meaning little or tiny). So after some frequency we stop reducing the treble at playback to compensate for head gap compared to recorded wavelength losses etc.
It is not known yet what is the optimum DC bias current.
If memory is correct sound on sound on reel to reel recorders with erase head disabled sounds a lot better, at 7.5ips.
For better news on quality of sound see part 2:
https://euroelectron.blogspot.com/2018/10/connecting-directly-tape-recording-head.html
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