Tape Guide (May 1977)

Bias Adjustment

Q. In using low-noise tape, can there be an improvement even though the bias is set for conventional tape? If the bias is set for low-noise tape, how does this affect the playback of tapes recorded with the bias for conventional tapes? Can a switch for changing bias from low-noise to conventional tapes be built into an older tape deck? Does the bias differ among various brands of low-noise tape?

-Ronald Slakie, Tacoma, Wash.

A. There can be some improvement when using low-noise tape with conventional bias, but the best overall performance requires an increase in bias. Bias does not enter into play back, so properly recorded tapes will still play properly on a machine with the bias set for low-noise tape.

Yes, a switch for changing the bias from low-noise to conventional tape could be built into an older deck by a competent person. What such a switch does is to increase the bias for low-noise tape. This increase can be achieved by using different values of capacitors or resistors in the circuit from the bias oscillator to the record head. Bias for low-noise tape is about 15 percent more than conventional tape which you can determine experimentally by varying the bias until you get the flattest possible treble response using low-noise tape.

While the optimum amount of bias differs among particular brands of tape, usually the differences are slight enough not to have a pronounced effect upon the recording. For one seeking the best possible performance, it is advisable to adjust the bias for the particular tape used.

Deck Dilemma

Q. I own a Sony 651 tape deck purchased overseas and have found that the only tape I can use is Sony. If I use another brand, I get distortion in the left channel during recording. However, I can play tapes recorded on other machines regardless of brand. I took the machine to an authorized Sony dealer; all he could tell me was that the unit is biased for Sony tape and I can't record on other tapes without having the deck re-biased.

Since the Sony 651 isn't available in the U.S., I don't believe him because even less expensive units than this one can play all brands and record on them also. I've made inquiries at the regional Superscope center and they stated that they have no service information on this machine at all. Now I don't know where to turn and I trust that you may be able to find the answer to my problem.

-Kenneth Kinney, East Detroit, Mich.

A. Yours is a strange problem made all the more peculiar by the fact that the distortion appears only on the left channel. If Sony tapes were much different than competitive tapes, and therefore required an appreciably different bias, then your difficulty would appear on both channels. Perhaps the left channel is somewhat under biased. If this channel also sounds overbright in recording, this would confirm the possibility of under biasing. It may also be that the VU meter is improperly calibrated for the left channel, so that you are over-recording and, hence, getting distortion on most tapes. It would be well to have the bias and VU meter calibration carefully checked by an authorized service station using whatever tape you customarily record on.

Recording Squeal

Q. I have a small recording business and have been using Scotch 175 tape.

Recently some of these tapes have developed a high frequency chatter or squeal which is mechanical and can be stopped by rubbing the tape with a light coating of talcum powder. The squeal occurs only on the Scotch 175 tape even when used with several different brands of tape machine. Have you heard of anyone else having this problem with the Scotch 175 tape?

-Robert Coe, Manchester, Conn.

A. Yes, I've heard other complaints about squeal, sometimes involving Scotch tape which is not surprising in view of 3M's large share of the market, but yours is the first complaint about the 175 tape. Another professional I know complained about a different Scotch tape and indicated that all the trouble lay in one particular batch. He returned the number of reels, got new ones in exchange, and hasn't had any problems since. You, too, may have been unlucky enough to have gotten a number of reels from a defective batch. You should contact a 3M dealer about your difficulty.

Discount Dilemma

Q. I have seen an ad in various audio magazines for a stereo tape transport...it says: "Stereo tape transport.

Made for leading manufacturer, two speed, pause control, seven-inch reel, 50-15,000 Hz, 0.25 percent wow and flutter, with record/play and erase heads. Without case, $19.50." Can this transport be used for copying tape from one deck to another? Can it be worthwhile for so low a price?

-A.H. Raynor, Hillcrest Hts., Md.

A. Note that the item in the ad is only a transport, and you would have to supply the electronics for recording and/or playback. I am rather doubtful about the quality of anything selling for this advertised price as a good head alone costs more, and the wow-and-flutter specification is not very good.

(Source: Audio magazine, May 1977; Herman Burstein)

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