Sony TC-158SD

The TC-158SD (also known as TC 158SD) was a 4-track 2-channel professional Stereo Cassette-Corder manufactured by Sony Corporation of Japan in approximately 1975. It had a ferrite record and playback head providing an extended frequency response to audio reproduction quality. This was a portable unit for recording in the field measuring 350 mm × 100 mm × 240 mm, and mass 4.8 kg with batteries. It also had a built-in 10 cm loudspeaker, which provided 700 mW output for monitoring.

I just love the electronic design of the TC-158SD, because apart from IC 601 in the motor servo amp board, there are no integrated circuits anywhere else. They achieve everything, including the Dolby circuitry using discrete transistors. They have optimised the circuit and kept the transistor count down in order to minimize its power consumption, which enables it to last longer on batteries.

Just as the TC-152SD and TC153SD versions, this one also has a DC-DC converter for the power supply, and they have simplified it this time as it generates only the ±15 V for the preamplifiers. The negative voltage is used mainly for the playback equalisation preamplifiers. The previous versions also had to generate 9 V for the speaker amplifier, however in this design the voltage after the bridge rectifier is 9 V which they regulate down to 6 V using a two transistor and zener diode circuit. This voltage then powers a speaker amplifier, which is a simple two-transistor push-pull stage. Although the circuitry is much simpler, it operates at a much lower voltage, and consequently the speaker output does not appear to be as loud as the previous versions.

Looking at the circuit diagram, I was wondering why they kept the design so simple, and one main reason must have been to keep the transistor count low. However, the real advantage with this design is that it does not make any unnecessary changes to the audio signal. It faithfully reproduces the recorded sound, without any alteration, which is very attractive if you are into mastering.

The previous versions had a pair of sliders for the input level control; however, in this one, they change it to concentric rotary controls.

I just love these large volume unit (VU) meters, which are very responsive. When I was recording extra low frequencies, the needle was jumping all over the dial.

I tested its recording capability by feeding audio with greatly boosted bass and treble, and was impressed with its performance. I was able to use a cheap ferric tape, and it reproduced the sound with the bass and treble I had set. On my walkman, it sounds even better due to better headphones and modern chipset.

This Article Continues...