Tape Guide (Q and A) (Aug. 1973)

By Herman Burstein

Takeup Squeak Revisited

In the June, 1973, issue Mr. David Tishler asked how to get rid of the occasional squeak in the takeup reel of his Sony TC-255. The answer was unfortunately phrased to indicate that the problem is a peculiarity of this model or brand. It is not.

Possible solutions, Superscope informs us, include replacement of a warped reel, replacement of worn-out reel cap holders or insertion of a thin plastic, cardboard or felt shim on the reel turntable so as to keep the reel from scraping.

Matching Impedance

Q. I recently purchased an Electro Voice 635A microphone rated at 150 ohms impedance, for use with a Sony 800B recorder having a microphone input impedance of 600 ohms. Is it necessary for me to obtain a transformer which will match the 600 ohm impedance?

- Wilson Clark, Washington, D.C.

A. An output impedance of 150 ohms into an input impedance of 600 ohms is ordinarily not a serious mismatch, and should cause no problems. However, if your tape recorder has barely enough gain on its 600 ohm input, so that the 12 db voltage gain to be obtained from a correct match is important, then you would require a transformer. I suggest that you contact the microphone manufacturer, as well as audio houses, about a suitable step-up transformer.

Adjusting For Tape

Q. What adjustments must be made to a tape deck to realize the full potential of high output low-noise tapes? Would the front panel bias adjustment on the Dokorder 9020V be of value in this respect? What functions do the high output low-noise tape selectors on the Sony TC-651 and the Akai GX-365 D perform?

-T.S. Wulbrecht, APO San Francisco.

A. To realize the full potential of low-noise tape, it is necessary to increase bias somewhat above that used for conventional tape, to decrease treble boost somewhat, and to increase record drive current somewhat. I would assume that the tape machines equipped with tape selector switches perform one or more of the above changes. And the bias adjustment on the Dokorder would be similarly useful.

Recording Matrix Quad Material

Q. Is it possible to record a matrix four-channel disc (for example, a Columbia SQ record) onto a two-channel tape deck in the conventional, two channel mode and not lose any of the code, i.e., to be able to play it back on a tape deck through the decoder, and deliver the same four-channel separation originally found on the disc?

-Capt. Burton Silbersteen, APO S.F., Cal.

A. You definitely can use a two channel tape deck to make matrix recordings. You can play these recordings into your decoder with assurance of getting back all four channels without loss. This is one of the advantages of the matrixing system of producing four-channel sound.

Playback Equalization

Q. I understand that there is supposed to be no difference between 7 1/2 and 15 ips equalization. But somehow I think that there must be some difference as there is quite a speed differential.

-Richard McCleary, Jacksonville, Fla.

A. So far as playback equalization goes, there is no difference between 7 1/2 and 15 ips according to the NAB standard. However, in recording, there are more severe treble losses at 7 1/2 ips than at 15 ips. Hence, 7 1/2 ips entails more treble boost. The specific amount of treble boost is not stated by the NAB standard. Rather, the standard requires that equalization in recording shall be such that, in conjunction with standard playback equalization, overall record-playback response shall be flat (within given tolerances).

(Audio magazine, Aug. 1973; Herman Burstein)

= = = =