Tape Guide (July 1977)

Cassette Monitoring

Q. I want to re-record some cassette tapes, using two machines. But I want to be able to monitor the material through a speaker while the signal is going from one recorder to the other. Please tell me how this is done.

Why doesn't using a patch cord from the external speaker jack of one recorder to the Aux In jack of the other recorder work?

A. Most receivers, and integrated amplifiers and preamplifiers that rate as high fidelity equipment, permit you to monitor the incoming sound and at the same time feed it to a tape recorder. You would play your cassette into such equipment, listen to the sound through your amplifier and speaker equipment, and simultaneously feed the amplifier output (via the jack usually marked Tape Out) into another cassette for recording.

It seems that your connection from External Speaker to Aux In should work, and I don't know why it doesn't work in your case. Perhaps the signal voltage available at the External Speaker jack is too low, perhaps the jack is defective, or perhaps you are putting the wrong kind of plug, or a defective plug into this jack. Another possibility is that the Aux In jack is defective, or the cable might be defective. You should check all of these.

Impedance Mismatch

Q. How important is microphone tape recorder impedance matching? I am interested in using a 600-ohm microphone for a tape deck with an input impedance of 10 kilohms.

A. Microphone impedance is important from the viewpoint of avoiding treble loss, possibly hum, and other noise pickup owing to cable length between the microphone and the tape deck. If you have a cable run of more than 15 feet, a mike with low impedance is desirable. Ordinarily, an upward mismatch will have no adverse effects in terms of treble response and distortion, thus a 600-ohm mike could be fed into a 10-kilohm input. However, there remains a question as to whether the 600-ohm mike will deliver sufficient signal for a satisfactory signal-to-noise ratio. If not, then you require a step-up transformer mounted on the tape deck side of the cable whose output should approximately match the impedance of the deck's mike input.

8-Track to Open-Reel

Q. I have an extensive collection of 8-track cartridges which I am planning to transfer to open -reel tape. I would like to know what speed to use on the open-reel deck, 7 1/2 or 3 3/4 ips? I would also like to know the frequency response of an average 8-track tape and if there will be any improvement if I use a Dolby unit?

A. With an open -reel deck of moderate or better quality, the 3 3/4 ips speed should be quite adequate for copying your 8-track cartridges. These cartridges tend to have little response above 10,000 Hz, while good open reel machines should go well beyond that at 3 3/4 ips. These open -reel machines have quite high signal-to-noise ratios, so they add very little noise compared with the noise already on an 8 -track cartridge. Therefore, doubt that the use of a Dolby unit in the copying process would make any significant difference.

Tape Preservation

Q. I have a large collection of recorded tapes that I want to save intact. I am designing my own storage cabinets and would like to know if there is any way I can shield my tapes against magnetic fields.

A. Tapes are pretty safe if you keep them at least a foot or so from strong magnetic fields. However, you might consider lining your storage cabinets with magnetic shielding material, which is rather expensive. You can get information about such material from Magnetic Shield Division, Perfection Mica Co., 1322 N. Elston Ave., Chicago, Ill.

Deck Modification

Q. I have an old tape deck and would like to know if you recommend having it adjusted to take advantage of the low noise, high output tapes. If so, please explain how this should be done.

A. As low noise tapes are pretty much universally used now, it seems like a good idea to adjust your machine for them. These adjustments apply only to recording, and they entail approximately a 15 percent increase in bias, about a 3-dB reduction in treble boost at 15 kHz, and about a 2-dB increase in record drive current.

It would be best to make these adjustments when using the specific brand of tape you plan to use in the future.

When these adjustments are properly made, you should be able to get flat response within about 2 dB out to at least 15 kHz, and when recording a 400-Hz signal at a level that produces one percent harmonic distortion, the VU meter should read zero. If your machine has a magic eye tube, the recording reference level should be three percent harmonic distortion.

Stereo from Mono

Q. I have a mono cassette recorder. I can't afford a stereo system, so could I use two microphones, two level meters, and a microphone mixer to get stereo?

A. Inasmuch as yours is a mono machine, the use of several mikes and a mixer will not enable you to stimulate a stereo effect. However, several mikes and a mixer would enable you to obtain better sound coverage and thereby a much more pleasing effect.

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

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