Another short one. There’s not too much more I want to do before I get home from uni next week. Everything will get much easier to do once I can leave everything out on my desk and do some hardware modifications. The last thing I wanted to do to be sure that everything fitted the theory was to try writing to tape.
As I said in a previous post, it is necessary to bias the signal that is written on to the tape. The tape player from which I took the recording head used to use DC bias. It would add 50mV to the signal. Supposedly, so I read, AC biasing is much more effective. Adding a ~2V AC sine wave to the signal should result in higher fidelity sound. So I tried both, and what I found disagrees with this theory.
The method which achieves the best sound quality – according to my tests – is to DC bias the signal by 50mV DC… exactly what the original tape player did. AC biasing resulted in crackly sound that faded in and out. Perhaps it is no surprise then that this is what the original designers used, but I can’t find a way to explain it. Maybe this particular head is not suited to AC biasing? So for now at least, I will use DC biasing.