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

Tape Thickness

Dear Mr. Burstein, I am writing in reference to the first item "Tape Length" which appeared in your Tape Guide section of the April, 1973 issue of AUDIO. Perhaps by now you have received all sorts of comments to your statement, "For anything like good results, 1/2 mil tape is generally not recommended." It has been the experience of cassette manufacturers that 1/2 mil (C-60) cassettes are preferred by knowledgeable audiophiles for two reasons. (1)

The magnetic oxide coating is thicker on C-60 tapes than on C-120 and some C-90 tapes. Consequently, saturation and distortion is less of a problem and dynamic range is improved with C-60 tapes. (2) C-60 1/2 mil base film is less likely to cause physical and mechanical problems. Usually it winds up better so there is less edge damage and consequently less edge program distortion or dropouts. Statistically, the mechanical jamming rate among cassette manufacturers is far less with C-60 than with C-120 cassettes.

With reliable cassette transports that are properly maintained, "name brand" cassettes rarely cause the tape speed slow down or excessive wow and flutter problems that Mr. Thurwachter mentioned. However, if the torque required to drive a cassette is at the upper limits of the IEC specification and if the transport batteries are not at full strength, these mechanical problems will occur.

-John E. Jackson, Manager, BASF Systems

You are completely correct. The state of the art has changed so that, at least for cassette, 1/2 mil tape, which is used in the C-60 cassettes, does a fine job. In fact, I have found that at least one manufacturer's C-90 and C-120 cassettes, which use tapes even thinner than 1/2 mil, do a surprisingly good job. My comments about 1/2 mil tape do not apply to cassettes, where 1/2 mil and thinner tapes are giving very good performance.

The Tape Guide did not mean to imply that 1/2 mil tape (C-60) is worse than thinner tapes (C-90 and C-120). It meant that 1 1/2 mil and 1 mil tapes are better than 1/2 mil tapes.

Matching Microphone Impedances

Q. I recently bought a Sony Mx-12 mixer. The manufacturer suggests that I use low impedance mikes to feed it.

I have been using high Z mics with it.

Am I doing wrong? Is it important to match the impedance?

-Louis Hone, Montreal, Canada

A. I have noticed that transistors do not seem to care what kind of mikes drive them, within reason, of course.

However, the use of high Z microphones with circuits designed for low impedance units will result in more mixer noise because its inputs are not properly terminated. I suggest, therefore, that if you are using dynamic microphones, you also use matching transformers to lower their impedance. If your microphones are crystal units, you will lose low frequencies by feeding them into this mixer. This will be the case even when you use a transformer with them.

No transformer can help because there is none which can work into the high impedance needed by crystal microphones.

Cassette Head Longevity

Q. What is the usual life expectancy of the record-playback head in a cassette deck? My cassette operates an average of seven hours a day and about 12 hours on weekend days. I have noticed a notch on the face of the head, but I'm not sure if it is a machined notch or due to wear. From the information I have given you, do I have a lot more life left in the head?

-Dennis G. Mueller, APO San Francisco

A. In the case of open reel machines, a good conventional head is considered capable of giving 1,000 to 2,000 hours of service. I don't think that a cassette head would give more. So you can judge whether the head in your cassette machine is coming close to the time of replacement. I doubt that the notch you see in the head is a machined notch.

(Audio magazine, Nov. 1973; Herman Burstein)

= = = =