Tape Guide (Q and A) (Apr. 1972)

Trouble with S-O-S

Q. I have discovered, at my expense, that the well-advertised features of sound-on-sound and sound-with-sound are impossible to achieve. Because of the physical distance between the, record and playback heads, there will always he approximately a one second delay between the two signals being recorded.

Therefore the signals cannot be synchronized. Does this difficulty exist in all moderately priced decks? If so, can synchronization of several musical parts be accomplished with a mixer and two tape decks?

-Herbert N. Foerstel, Philadelphia, Pa.

A. So far as sound-with-sound is concerned, where signal 1 is recorded on track A, while signal 2 is recorded on track B, you are correct in that there is a distinct problem of synchronization when separate record and playback heads are used. However, in the case of sound-on-sound, signals 1 and 2 are both recorded on the same track, and there should be no problem in achieving synchronization with a tape machine that has separate heads and proper sound-on-sound facilities.

Such a machine permits you to listen (through earphones or speakers) to signal 1 at the very instant it is being played on track A and recorded on track B. Simultaneously, through the mixing facility of the machine, you can also record signal 2 on track B. The displacement between the record and playback heads is of no consequence.

Yes, if you wish, you can achieve sound-on-sound synchronization by using two tape decks and a mixer. This would enable you to produce stereo sound-on-sound.

Four-Channel Conversion

Q. I have a Revox A77 tape deck which I would like to modify so as to be able to play four-channel stereo tapes, such as the Vanguard Surround Stereo series. I plan to replace the present playback head with a four-track one from Nortronics and add two Revox playback amplifier circuit boards. Is this modification feasible? Will the conventional record/playback facilities and/or qualities be affected?

-Dennis J. Penner, Pinawa, Manitoba, Can.

A. I think that this modification is feasible, assuming that the Nortronics head is specifically designed for mount ing on your transport. You will of course have to align the head carefully with respect to azimuth and vertical height.

Keep the cables from the head to the new playback amplifiers as short as possible and of low capacitance per foot in order to minimize treble loss.

Assuming that the Nortronics replacement head is of a quality comparable with the original, I don't see why the record/playback facilities in your machine should be adversely affected.

Speed Changing and Fade Outs

Q. Apart from spending $400 on a commercial product, how is one to vary the speed of a tape machine, with about 15% range of adjustment or even more. Some of the tapes I wish to copy are as much as a minor third off. Is there a practical way of arranging things so that, on a previously recorded tape, a fade erase can be made after recording?

- Matthew Notkins, New York, N.Y.

A. To vary the tape speed you might construct a power supply with variable frequency. Such supplies have been described in the audio literature, and a little research on your part should turn up something suitable to your needs.

To accomplish fade erase, you might try installing a variable resistance or variable capacitance between the audio oscillator and the erase head.

(Audio magazine, Apr. 1972; Herman Burstein)

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