Tape Guide (Jul. 1982)

Using a Master Tape

Q. I have a 10 1/2-in. reel of tape that I use for recording material off the radio; this material is then transferred to cassette. How many times can I use the tape reel before poor reproduction occurs?

-Michael Conner, St. Louis, Mo.

A. As a very rough guess, your master tape should be good for 100 to 1,000 plays before its performance begins to drop noticeably. So much depends on the quality of the tape, on how gently it is treated by the deck, on the tape speed (the faster the speed, the greater the wear for a given recording time), on temperature and humidity conditions, etc. that it is difficult to be specific.

Scratchy Tapes

Q. For some reason, my cassette tapes have scratches. Please tell me what causes this and how I can prevent it.

-Violet Hurdle, Brooklyn, N.Y.

A. I am not sure what you mean by scratches. If you refer to the fine striations that run the length of the tape, these are normal and due to friction between the tape and the heads. If you refer to audible scratchy sounds, the cause would seem to lie in the electronics of your deck.

Capstan Encapsulated

Q. I am trying to choose between two open-reel tape decks, one having dual-capstan drive and the other a single capstan. Is dual-capstan drive that much better than single?

-Arthur Aframe; Waltham, Mass.

A. There are usually several engineering approaches to a stated objective, and one is not necessarily better than the other--what counts is how well the approach is executed. Hence, a deck with dual-capstan drive may be better in terms of motion performance, but not necessarily. There are single capstan decks which deliver very fine performance.

Circuit Trap

Q. I am rebuilding the electronics of my tape deck. The circuit that I intend to use for the record preamp has a parallel resonant trap connected between the output of the record amplifier and the record head. I am not sure what this part of the circuit does.

-Earl Blackman Jr.; Florence, S.C.

A. The purpose is to prevent the bias current, which is fed to the record head along with the audio signal, from getting back to the signal amplification section and interfering with its proper operation. The trap has maximum impedance at the bias frequency (to which the trap is tuned), but at audio frequencies, the trap presents minimal impedance so that the audio signal can pass from the audio amplification section to the record head.

Reel Standardization

Q. I am curious as to why open-reel tape on 10 1/2-in. reels is usually available in the United States only on standard NAB reels. Assuming that one does not expect to use the tape on a studio deck that only accepts NAB reels, is there any advantage to using them?

-Mark Goldfield; Brooklyn, N.Y.

A. The reasons for standardizing an item such as a tape reel are to achieve optimum performance and to assure compatibility with the decks for which it is intended.

Inasmuch as the demand for 10 1/2 in. reels in this country is largely by those using professional decks which take the standard reel, tape manufacturers have not elected to serve the much smaller market which would like other types of 10 1/2-in. reels. In any event, adaptors are available to permit the NAB reel to be used on home decks which operate at 15 ips but which cannot accommodate the standard reel.

Blown Speakers

Q. While recording a phono disc, with the "input volume" sliders of my cassette deck set at about the "4" position, I blew my speaker's fuses. The preamp's volume control was not more than 1/4 of the way up. After turning the disc over in order to tape the second side, I may have changed the preamp's selector setting from Phono to Tape.

-Joseph Cuifo; Utica, N.Y.

A. The blown fuses are likely due to your accidentally turning the preamp's selector switch from Phono to Tape.

This could cause feedback oscillation, resulting in a signal powerful enough to blow the fuses. To avoid a recurrence, set the volume control of your audio system at a very low level--nearly off--when making your settings for tape recording, and then gradually turn up the volume of your preamp. If you hear a squeal or other loud sound, quickly turn down the volume and check all your switch settings.

Ratios Revisited

Q. In reference to your Tape Guide column in a past issue, I would like to point out that a ratio of 1,000 to 1 is 30 dB, not 60 dB as stated.

-Michael Carlin; Malvern, Pa.

A. The Tape Guide stated that a 1,000 to 1 ratio between two voltages is 60 dB. That is a correct statement. If I had referred to a 1,000 to 1 ratio between two amounts of power, that would be 30 dB. Each multiplication of power by 10 is represented by 10 dB. Each multiplication of voltage by 10 is represented by 20 dB (assuming that the load resistance is unchanged).

Power = E^2/R, where E is voltage and R is resistance. Accordingly, power rises with the square of the voltage. Thus, a 1,000 to 1 voltage ratio results in a 1,000,000 to 1 power ratio, which is represented by 60 dB.

High Bias Tapes

Q. Recently a company came out with a high bias tape which I thought might give better results than the one I've been using. The first time I used the new tape, the reproduced sound was very close to the original. But when I recorded on a second cassette of the new brand, the playback level was low, with a lot of distortion and fuzziness. This never happened with my old tapes. What's wrong?

-Eugene Bolabek Jr., Linden, N. J.

A. My guess is the tape. But in all fairness, it should be recognized that occasionally one finds certain combinations of tape brand and tape deck which work well individually but not together. In other words, the new tape you tried might work perfectly well with other decks, even though it doesn't do so with yours. This situation, however, sounds like variation between batches of the new tape.

(adapted from Audio magazine, Jul. 1982; HERMAN BURSTEIN)

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