I have found a collection of tapes that I used with my HB-8000 MSX computer. Among the commercial games and applications there are some that I have coded in BASIC, Assembly or both.

First tried to read the tapes on the real machine and save them on the SD card of my SDMapper, but I the success rate was low.

I tried to record the sound to decode on PC using one of the tools available (SofaCas, Castools) but the hum as quite high due to ground loop between the PC and the tape recorder.

I looked all over my parts for a landline phone transformer with 1:1 without success. The best transformer that I could find was a transformer with 150 Ohms (measured with multimeter) at one of the windings and 2 ohms at the other salvaged from surplus PCBs.

I have tried out the transformer connected to the tape recorder at either side and measured the amplitude with the oscilloscope to determine the turns ratio.

After some measurements I did the math and found a turns ratio of 15:1. It is worth to mention that such figure will turn the 7.5Volts pk-pk produced by the cassette player can produce a voltage of hundreds of Volts at the secondary of the transformer, depending upon which side of the transformer the cassette is connected. When in doubt connect the cassette side to the transformer side with the highest DC resistance.

At the end this is how I have connected the transformer. I have used an stereo plug at the PC side because my sound card did not liked to have one of the channels short-circuited to ground. A couple of jumpers to allow me to select to record in any of the channels or in both at the same time.

I wish I had a transformer with smaller turns ratio, because the 500 mVpp produced were not enough to achieve full scale of the recording, but I could record and decode some programs.

Here are some screenshots of recording using audacity.

And a screenshot of SofaCas running

Some pictures of the device assembled.

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And a screenshot of one game that I have successfully recovered: "Resta 1" or Peg Solitaire.