12/11/2023 0 Comments 8 track tape recordersLimitations again are the magnetic formulations used, as we should of stop using and making ferric oxide tapes in the 1990's, as it is not possible do much with higher audio frequencies, with tape speeds below 19cm/second. Another advantage is been able to use C type noise reduction, that was not about in the 1970's as tape hiss is a major issue with the 8 track format, far more so than with cassettes. As for 8 track performance this is well a head of all the other decks I have tested so far, I put this down to the end of developments in the 1980's for this format. With this version two design it would be a mid-range cassettes deck. This is what sets out a high-end tape deck from a standard ones, all comes down the EQ design used, this is why you only see low end cassettes recorders these days. Record equalization is just important as playback if not more so, as magnetic tape does not have a flat frequency response, so therefore this needs to be EQ out. With both 8 track and cassettes having very different record, erase and playback architecture, this is where this board layout came into it's own, providing the flexibility for these two formats. Another issue has been getting the integrated circuits, as there is not a single chip made for this recording technology, as it took months of waiting to get all the parts together with the current chip shortage. Only the top part of the board is required for the playback amplification, where the record processing uses the largest space, leaving what is left for the micro-controller. The printed circuit board layout was done in a way to keep the digital and analog sections isolated, to minimize unwanted noise from the digital side. Another improvement is how the high voltage bias power supply is driven from the FPGA, providing for a wider operating voltage range. The analog interface uses two phase pulse converter to sample the left and right audio inputs, where the FPGA converts this to a digital bias signal, based on my analog digital modulator (ADM), as used with class Q amplification. The field programmable gate array (FPGA) provides an AC waveform to analog bias and the erase heads, from common clock for the micro-controller and the FPGA. The big difference is how the record section works, where there are both AC and digital bias circuits used, making it possible to compare the performance between them. As it is important when using ferric oxide tape, as it make overall improvement with keeping noise levels low and to make best out of this tape formulation. The next stage is the noise reduction block, that is common to both record and play parts to provide an extra level noise rejection. Equalization (EQ) is must as the frequency response from the play heads and the tape need to be flattened out and with a low-pass filter to minimize the noise. As the signal level that comes in from the playback heads is at a very low level, it is important to minimize any unwanted noise at the low noise amplification (LNA) stage. Here is the block diagram of the working prototype, as a basic over view of both playback and record parts.
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