Tape Guide (Jul. 1981)

Limited Limiter

Q. My cassette deck has a limiter switch for recording. Am I better off using this switch and not worrying about recording level (assuming that I set it higher than I would otherwise), or should I always take the time to set the recording level accurately and leave the limiter switch off? - Name withheld.

A. For best results in recording, it is usually desirable to avoid use of a limiter and to carefully set recording level so that you will get maximum signal without noticeable distortion. However, if you are recording live material with strong transients, such as a guitar, you might obtain better results, in terms of a high signal to-noise ratio without appreciable distortion, by using a good limiter. The real answer lies in experience. Try making recordings with and without the limiter.

Some limiters do a fine job, while others make their presence felt.

Ohm Mike Goodness

Q. The instructions for my cassette deck recommend the use of mikes rated at 600 ohms to 10 kilohms, but add that "low impedance mikes with impedance of 150 to 600 ohms will also work satisfactorily." I do not quite know what to make of "satisfactorily."

-Timothy Marlyn, Glen Rock, N.J.

A. I believe it means that the mike will supply sufficient signal to drive the deck to full recording level. Some decks have a lot of reserve gain for recording from a mike, while others tend to be marginal in this respect. Apparently your deck is one of the former.

Reely Magnetic

O. I have an open-reel tape deck.

With a magnetometer I found an area of magnetism on the deck that is in the path of tape travel, between the heads and the take-up reel; I measured about 1/2-Gauss there. I also measured about 1/2-Gauss at the heads and cannot re move this with a demagnetizer.

-Erwin Specht, Cudahy, Cal.

A. So far as I know, it is difficult or impossible by ordinary means to remove all vestiges of magnetism from the heads, guides, or other metallic parts of a tape deck. If nothing else, it is claimed that the earth's magnetic field will pro duce some magnetism. Accordingly, the measurements you obtained seem relatively low.

Not Up to S/Nuff

Q. I recently bought an open-reel deck which sounds good except for an abundance of hiss. I had the unit tested by the manufacturer's service department, and it did quite well except for the signal-to-noise ratio, which was only 42 dB. I taped a record on my friend's ma chine of the same model and then played the tape on my deck. It sounded great, with barely noticeable hiss. Can you suggest any ways in which I could improve the S/N ratio?

-Keith Bonn, Chappaqua, N.Y.

A. From your description it appears that the problem lies in the recording amplifier of your deck, for otherwise a tape recorded on another deck would not play quietly on yours. Inasmuch as your deck quite obviously does not come anywhere near the S/N ratio specified by the manufacturer, it seems your best and most direct course would be to have the company undertake whatever repair or replacement is required to bring it reasonably near to spec. If for some reason you cannot do this, consider checking the type and quality of transistors, the bias oscillator, the quality of resistors, and possibly the quality of capacitors.

If you are technically knowledgeable, you might try replacing the resistors in the early recording stages with good low-noise types, such as metallic film.

Try to find out if there are equivalent but quieter transistors that can be used in the early recording stages.

A quite likely source of noise is distortion in the bias current: this is one of the places where one finds a marked difference between standard and high-quality tape decks. Slight amounts of distortion, too small to be seen on an oscilloscope, become apparent as noise in recording.

This source of noise appears not only at the record head but also at the erase head, which is driven by the bias oscillator. A mismatch between resistors and/ or between capacitors in the oscillator circuit could be responsible for distortion and noise, the oscillator transformer may be defective, and one final possibility is that magnetized heads and/or guides are producing noise.

(Adapted from: Audio magazine, Jul. 1981; Herman Burstein )

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