Tape Guide (Q and A) (Apr. 1975)

Open Reel or Dolbyized Cassette?

Q. Would you recommend a Dolby cassette recorder over an open reel recorder at this time. Also, which machine would you consider to be superior to the others available?

-Joe Szalajko, Los Angeles, California

A. While cassette machines incorporating the Dolby B system are considered to be a substantial improvement over former cassette machines, it appears that a high quality open reel tape recorder operating at 3-3/4 ips is still better. And open-reel recorders operating at 7 1/2 ips are even better. The quality difference between cassette and open-reel machines is less than formerly, but there is still some difference. The policy of Audio magazine is not to recommend specific items of equipment.

8-Track Head Adjustment

Q. I would like to purchase an 8 track cartridge player for my car, and want one with an adjustment so that the tape head can be moved up and down for proper tracking. Who wants to hear two different selections at the same time? Not me!

-David E. Vogel; Tucson, Arizona

A. I do not know of any cartridge player with the head adjustment feature you are seeking. Even if you find such a machine it is unwise for anyone but a person equipped with the required knowledge and instruments to adjust the position of the tape head. In moving the head vertically, care must be taken not to disturb the azimuth alignment (90 degree angle between the tape head gaps and the long dimension of the tape). You should purchase a machine on the basis of its general quality consistent with what you wish to pay, and then have the position of the head checked by a competent technician, preferably one authorized by the maker of the machine.

Adding Erase-Defeat

Q. Can you explain how to add an erase-defeat switch to one's tape recorder? Is it safe just to open up the connection to the erase head, or would shorting the erase head be better?

-Donald A. Potts; Independence, Mo.

A. A substitute load is used when the erase head is defeated, so that the amount of bias to the record head is unaffected. That is, the erase head is disconnected from the bias supply and a resistor is connected in its place.

The value of the substitute load is determined by trial and error. It must draw the same amount of bias current as the erase head. The proper resistance and wattage rating of a substitute load resistor might be obtained from the manufacturer of your tape machine. Sometimes the specifications of one's tape machine state the impedance of the erase head at the bias frequency. This would indicate the appropriate ohmic value of the resistor. You can also measure the current drawn by the erase head with a wide band vacuum tube voltmeter (VTVM) across a small resistance in series with the erase head. Compute the current according to Ohm's law, then the resistance can be figured.

Control Button Pops

Q. I have a Signal Corps Telectro tape recorder, obtained through a government surplus house. This machine is solenoid controlled, much the same as an Ampex 354. It works fine except for one thing. Anytime I depress one of the motion control push buttons, a very loud pop is heard at the audio output. This is quite annoying, and I would like to know how I can eliminate this noise.

-John W. Schuerman; Richmond, Indiana

A. Quite likely you can eliminate the annoying pop by mounting a 400 to 600 volt capacitor across the switch actuated by the control button. A value in the range of 0.01 to 0.1 µF should do it. You may also need a resistance of about 100 ohms, 1/4 watt, in series with the capacitor.

(Audio magazine, Apr. 1975; Herman Burstein)

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