A normal (type I) Fuji DR60 cassette was used.
A portion of Side A had been passed from the permanent magnet erase head of Sanyo TRC-2500 portable cassette recorder with the recording AC head bias either not operating or at a very low level due to malfunction.
Another portion of Side B had passed through the Sony TC-D5 Pro II with REC levels at 0 and pad at -20dB, so in practice there is no recorded sound.
The increase of noise of Side A, Side B was compared with adjacent virgin parts of side A or Side B as vergin tape being degaussed? from the factory.
Playback of both sides were compared on the Sony TC-D5 Pro II with Sennheiser HD580 headphones.
The subjective noise impression was as follows.
The virgin tape of course is the most quiet. How different are side A or side B to this reference?
In fact this was not the reference. The reference set was the amplifier noise when the Sony was in pause mode.
By comparison to pause mode noise:
Vigin tape sounded 4 times louder.
AC bias noise impressed to tape from Sony TC-D5 sounded 8 times louder.
DC bias noise to tape from Sanyo permanent magnet DC erase head sounded 16 times louder. The main difference was that the noise was not only HF hiss but it was a broadband noise containing bass components too.
DC noise was large but perhaps not as much as expected. This type of DC bias can be equivalent to 8mA passing from an erase head. See yesterday's post on JVC erasing DC current as shown in the service manual.
Would a recording bias of a few hundred microamperes or less be adequate for nice recording including sound on sound and of a much lower noise?
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