Stereo High Resolution Portable Cassette Player

Found this dirt cheap cassette player and decided to buy it just out of sheer curiosity to see how simple it is inside.

It looked bad. Case was not fitting properly, the window detached from the case (glue dried out) and had no accessories .. It looked both new and old at the same time.

Table of Contents

• Overview
• Repairs
  • Cracked motor pulley
  • Broken headphones jack
  • Changing the belts
• Wow and Flutter
• Gluing the Window

Overview

Doing a little test, nothing worked. No play, not even engine noise…

I decided to take it apart to see what I’m up against – and, to save you time – the following problems were encountered:

• “Stereo” in the name, but Mono in reality
• Motor stuck – I had to give it a hard turn
• Belts were kinda loose, but not yet too loose
• Pulley too close to the motor – belt rubbed against the outer casing of the motor
• Cracked motor pulley
• Huge noise coming from the motor
• Unusable headphone jack – no jack would fit in

Repairs

I took the player apart and had a look inside:

When applying power, the motor made a small sign of life and then stopped. It felt something was gripped. I gave it a turn by hand and somehow, it was able to set itself in motion afterwards. I decided to oil it a bit (sewing machine oil) and also grease the two belt pulleys.

Cracked motor pulley

Then I spotted that the motor pulley was cracked. Surprisingly, I have an identical motor with identical pulley that I recuperated from a CD drive unit at one moment …

I considered swapping the motor with the one I have recuperated from the CD player, but this player looked so cheap that I said … neah.

Broken headphones jack

I was not able to fit any headphone jack – pushing any harder and I would have definitively break something else.

But I still wanted to hear the thing playing, thus, I took out the signal tracer (AF mode) and started tracking the signal. Everything seemed fine up until the final amplifier transistor where there was no signal on the emitter.

The transistor didn’t measure shorted, thus I had to trace a bit around to understand what is going on. I hate de-soldering parts just to test them. And two surprises: the Left and Right channels are shorted together (so it is not a Stereo, but a Mono player), and the headphones are the Emitter Load. Without headphones plugged in, Emitter is just floating. Duuuh, obviously. Power of habit after checking the other transistors ?

Ok, so I need to fix the output jack or bodge a resistor ?

The transistor was an ITT 9014C, a small signal transistor rated at 100mA. So 3V battery, 100mA maximum output .. 32Ω headphones would be at the limit given that Left and Right are shorted, so the load resistor would appear like a 16Ω.

I decided to swap the headphone plug, as I found one that I salvaged from some other device, and was matching exactly.

I could finally hear it – but it was awful. A lot of noise coming from the motor – an annoying buzzing. Louder volume covers the buzzing but I can still hear it.

Changing the belts

Since the belts were a little loose, I chose similar one from a set I have:

The small white pulley next to the motor is so close to the metallic case of the motor, that the belt sometimes rubs onto the case. In fact, the case of the motor seems to peel off, it is held in place by the paper label. I decided to rotate the motor just to see, and it did make some room:

Wow and Flutter

The playback sounded too fast .. so I needed to calibrate a bit the speed.

I do have a DIY test tape with a 3Khz signal (the seller was bragging about recording it on a high end tape recorder). With WFGui, a 100Ω resistor bodged as Load, I was able to bring it down to approx 3kHz (it was running closer to 3.5kHz).

The worst W&F is at 0.6%, but it was wondering around +/- 20Hz of the 3000Hz reference.

I was also curious to characterize the noise it produces (at 3kHz). Here it is, using Behringer UCA222 and REW:

The most “impressive” is THD+N which hovers at around 75% (it is this lower due to averaging, I’ve seen it at 90% too).

Case is made of cheap plastic, the screws came out having a lot of chewed plastic on them – so if I open it once or twice more, the plastic threads will be stripped.

Gluing the Window

The last step was to use SuperGlu for the window:

I decided to keep it for its … red color. And maybe because it is part of the history of portable cassette players, very recognizable shape.