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Sharp PC-1211 tape loading problems (TRS-80 PC-1)

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Its not a matter of impedance, its just a tape recorder that dates from the era of speaker level on headphone jacks.  You were assumed to be sensible so wouldn't turn it up loud enough to hurt.  A generation of teenagers with hearing loss as young adults proved that wrong so now headphone jacks are power limited.

There's no way I'd mod a working or reasonably reparable original piece of computing history like that, but each to their own, so I didn't dump that on you.  As I suggested, an external amplifier is the way to go for compatibility with modern devices, powered by USB if available or 3x AA alkaline if not.  Probably just a low voltage RRIO OPAMP, AC coupled, input biassed mid-rail with variable gain of x1 to x10.

2.5Vpp input for a proper working of the first inverter looks pretty much, frankly.
Your first deck perhaps keeps its output wired at the 4-8ohm speaker, therefore the output amplitude is lower.
You may try to do the same with it as the second deck's schematics shows - the 100ohm load of the output instead of the 8ohm speaker.

Or, do make yourself a single transistor stage and put it into the first deck as the special output for the Sharp (see below an example, set the R4 such you get aprox half of the Vcc at the collector, any npn transistor will do).

Thank you both for your thoughts.
I decided to leave the PC working as it is with the tape recorder from the same era. The system is way to nice to hack and it works fine now.
Will definitely use an external amplifier or record to tape to copy data to and from the modern PC sound card.


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