Tech Flashback: The Microcasette – Part 2: The Recorders

If I had just a bunch of tapes but nothing to use it with, it wouldn’t be that exciting. After all, the last thing I had (prior to this batch of donated gear) was a Computec branded single-tape answering machine that used microcassettes. Luckily for me, along with the cassettes were some recorders that I could play with.

Sony M-200MC

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The first recorder we will look at was donated by a uni colleague, and didn’t see much use to his knowledge. This unit seems a relatively recent unit, the M-200MC, featuring the “clear voice” moniker. It seems to be a relatively high-end unit, with zoom microphone (three pattern) and auto-reverse facility so that it could automatically continue playing/recording the other side without needing to flip the tape over manually.

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Despite this, it did seem the unit did have some use, and time hasn’t been too kind on it, as the auto-reverse occasionally jams up, and the fast-playback switch is intermittent and rarely functions. Oh well, lets take a look at the unit anyway.

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Here, we can see the unit as it appears from the front, with the mic stowed in the left, and fully extended in the right. The microphone is stowed by pushing it in, and extended by toggling the mic-mode lever on the front upwards. The front of the recorder has a speaker for replaying audio, the cassette door itself, a tape counter, and several LED indicators for recording, battery in use and battery depleted. A indicator is given for the direction the cassette is running. The cue marker feature allows you to record a low-frequency signal to the tape, turning into a tone when played back at high speed fast forward/rewind to add markers to the recording. A wrist-strap is also provided as standard.

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It seems like the designers have decided to make this unit a little complicated in terms of its controls. A slider controls the direction of tape travel, with the left button stopping the operation of the deck and engaging eject on a second push. The middle button plays the cassette (and can go in both directions due to the auto-reverse mechanism), with the right-most button engaging record. A toggle slider forwards/rewinds the cassette, and changes its wind direction based on the state of the auto-reverse lever.

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Pause is available by engaging a lever at the rear, with fast playback and voice operated recording also available by small switches on the rear.

20150808-1159-8832 20150808-1200-8833Confusingly, the volume control is placed on the front of the recorder, along with a 3.5mm stereo output jack that outputs monoaural audio. On the other end of the deck, we find the tape speed selector, and an external DC input.

It seems whoever designed this deck decided to put as many controls in strange locations as possible, as it seems hardly standard or intuitive to me.

But wait, there’s more!

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On the underside of the unit is a slider which allows you to extend and retract the legs to keep the unit stabilized. The battery door is also at the bottom and accepts two AAA’s.

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20150808-1157-8827The door and the guides are made of plastic, as is most of the body itself, contributing to a somewhat cheap feel. It was Made in China after all. It seems to be typical of the later Sony products. It also came with a large folded map-like manual, which was copyright dated 2001. This is relatively late in the magnetic media age, where most people had already discontinued using magnetic tape by the late 1990’s, and early 2000’s.

As it’s the only unit of this sort, and it’s still working, I have decided to keep this one in its present condition rather than tearing it down.

Olympus Pearlcorder L150

The second unit we will look at is the Olympus Pearlcorder L150 – a sleek, premium quality unit featuring a metal front chassis. I was informed that this unit was purchased as a spare and was never used aside from testing, thus makes a good specimen to keep. It’s Made in Japan and the quality definitely shows.

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Inside, there is a cardboard tray. Sliding the tray out reveals a pristine unit, along with a still-sealed XB15 sample cassette. Despite this, batteries are not included.

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The unit could not be more intuitive to operate, featuring the normal deck-push-button style interface, with no fancy auto-reverse features or sliders like the Sony. A tape counter was present on the front of the unit. As was usual on these units, cue/review operation whereby fast audio during fast-forward and rewind was available to aid in seeking to a particular spot on the tape, and an integrated speaker allowed for reviewing without headphones.

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The top of the unit featured a potentiometer volume control, a mode switch that could be turned off (no special mode), to pause and to fast play (for playback) or variable control voice activated recording (where the recording threshold volume was set by the volume control) in order to save tape and review time. The microphone is integrated in the end, as well as a red recording LED that doubled as a battery indicator.

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The underside featured the speed control switch, where 2.4cm/s (standard) and 1.2cm/s (half-speed) could be selected. Two 2.5mm mono jacks provided earphone out and microphone in connections. An external power jack was also provided.

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20150808-1149-8816The rear of this recorder had a plastic back, in stark contrast to the nice metallic front. Inside the recorder, the deck was lined with shiny metal with metal guides, and batteries sound be inserted easily through a sliding door near the speaker.

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It came complete with a manual and colour product guide leaflet, where various lengths of cassette and earphone/microphone accessories are shown.

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It wasn’t the only unit I got though. I actually got given a second identical unit, sans packaging, with the exception that this unit was the one seeing regular usage, and was a little worse for wear with scratches and a few missing screws. However, this unit will come in handy, as we’ll see later.

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The size advantage of microcassettes is somewhat obvious when placed side by side with a Compact Cassette recorder.

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Despite having the same overall length, it is not as wide and almost half as thick.

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This made it much more convenient, and made it possible to slip it into your shirt pocket.

Olympus Pearlcorder L150 Teardown

Seeing as I had a second unit which was well worn, it wouldn’t be a big loss if it was broken apart. After all, half the screws were already missing, which made taking it apart easier. The front fascia can be removed by undoing the three Philips #0 screws along the spine of the recorder, opening the battery compartment, and levering the metal plate off.

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Here, we can see the front speaker, and we can see through to the motor that is tucked behind. The pinch-roller and head is visible, and the “hole” in the cover can be seen to adjust the head azimuth. Undoing three screws on the rear allows us to remove the rear plastic panel.

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Here, we can see the rear of the speaker – rated at 4 ohms at 0.15w. We can also see the main PCB, with curved traces that seem to be somewhat hand-designed. Wire connections are made to the speaker (green), batteries (red and black), motor (red and black), microphone (red and black) and head (brown and black) using solder. Some wires are secured to the PCB by using double-sided sticky tape. Unfortunately, the wires were not long enough to let the board go free, so I had to desolder the wires to flip the board over.

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The PCB is a double-sided unit, and has plenty of capacitors. Two adjustment pots, visible through the rear of the casing, have 2.4 and 1.2 marked next to them, so they’re likely to be tape speed adjustments for the two tape speeds. The whole unit seems to be governed by a monolithic IC, a Sanyo LA4165. Near the top, the surface mount tape switch sensor, and to the right, the volume potentiometer can be seen. Interestingly, two contact switches are visible as well near the top, which interface with the mechanism itself. Towards the middle bottom, it appears there is an infrared optical sensor.

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The reason for this is clear once we look at the mechanism – this is used with the stroboscopic pattern on the wheel to regulate the speed of the motor. After all, the battery voltage varies under different states of charge, so relying on the batteries and DC motor to regulate speed is not going to work well. I’m not sure, but I suspect other units may take different approaches to speed regulation.

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Looking at the transport as a whole, we can see it is belt driven from the motor, driving a weighty brass flywheel (to keep the speed somewhat constant despite small variations through inertia). An array of different levers, springs and gears make up the rest of the deck, which I didn’t take apart any further, as if I did, I would never be able to reassemble it!

In the end, the unit was reassembled in functioning condition, and instead, I decided to do a bit of a Frankenstein modification to it, by desoldering the 2.5mm mono jacks which were lint-filled, oxidised and unreliable, and replacing it with direct connections to 3.5mm stereo plugs. This was then plugged into a USB sound card which was pulled from a (poor quality) Logitech headset, so I now have a microcassette to USB interface that could capture from microcassette as well as record from computer to microcassettes.

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In case you were wondering, that was how I managed to test the frequency response of the microcassettes – adapting old things into the “modern” world.

Tape Counters

Before we leave the subject of microcassettes, it’s rather interesting to note that microcassettes had two speeds as standard – 2.4cm/s and 1.2cm/s, whereas Compact Cassettes only had just one. This allowed you to squeeze twice as much from your tape, if you didn’t mind a slight reduction in quality. There were also other play modes, with some featuring variable speed playback, and both these units featuring a “boosted” speed playback.

Another interesting feature is the mechanical tape counter. Similar to an old fashioned odometer in a car, this counts the total number of revolutions of something inside the recorder itself. It’s not actually standardized nor normalized to any unit of time whatsoever. As a result, you might make notes about your tape recording at a given counter “time” and this would not be easily translatable if played back on another deck. It also needed to be manually reset to measure counts from a certain “zero” point (nominally, the beginning of the tape). I suspect it may be related to the number of turns of the cassette hub itself, in which case, the time unit it represents changes slightly depending on whether the hub is empty or full (as the circumference changes).

In order to see what these two units did, I decided to try and use the various lengths of cassette that I have to see what the counters would show when fully winding them to their ends.

                Olympus Pearlcorder L150   Sony M-200MC
Olympus XB15    240                        120
Sanyo MC-60     732                        367
Olympus XB80    1014                       508

Surprisingly, there was a straightforward correlation between the two readings – namely that the Sony read about 1/2 the value of the Olympus, plus or minus several counts due to mechanical tolerances (and probably tape stretch and packing differences). That was rather surprising! I was expecting a more complicated scaling factor, given the mechanical nature of the devices.

By the way, if you were wondering just how I found out the approximate length of the cassette I wound from the C-120 Compact Cassette was – I found out with the help of the tape counter!

Conclusion

The size and weight advantages of the microcassette for portable recording purposes are clear once compared side by side with a regular Compact Cassette recorder. The microcassette recorders are a rather precision unit, given the small size, with the Olympus featuring optical speed feedback control of the tape speed. The Pearlcorder L170 could be seen to use a monolithic integrated circuit to perform most of its functions, despite having a PCB that looks more like it was hand-drawn. It was interesting to see that the counters on the two units were related by a division by two.

About lui_gough

I’m a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!

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