TAPE GUIDE (Jan. 1992)

Whatever Happened to Mike Inputs and dbx NR?

Q. Doesn't anyone record live sound anymore? I just went shopping for a new tape deck to replace my worn-out one. I really require only two features-dbx noise reduction, because I have over 200 tapes encoded in that fashion which I'd like to be able to play, and a pair of microphone inputs so that I can make recordings of my voice. There wasn't a single deck at any store in Seattle that would play dbx-encoded tapes-much less record from a microphone.

What's happening here? A few years ago, virtually every deck had inputs for microphones; now, none do. And, to make matters worse, there are no inexpensive microphone preamps available; the cheapest one I could find was $300-more than I intended to pay for the entire tape deck.

-Norm Strong; Seattle, Wash.

A. If you look at the Annual Equipment Directory in the October 1991 issue of Audio, you will find several cassette decks with a list price under $400 that are equipped with microphone inputs. Not many, and far fewer than in past years, but still some.

True, dbx noise reduction has nearly disappeared from home tape decks, having been largely supplanted by Dolby C NR. Therefore, a deck with both dbx and mike inputs is a rare bird. You will find only one, the Proton AD630HX, in the 1991 Directory, and its list price is $800.

If the deck you employed to make dbx-encoded tapes is still in working order or if it can be put into working order at modest cost, I suggest that you get a deck with mike inputs and Dolby NR (of which there's still a reasonably wide selection) and use your old deck to play your old tapes for copying onto your new deck as Dolby encoded recordings. (Editor's Note: As recording all 200 cassettes would be quite a job, you might want to copy only your favorite tapes and keep your old deck for occasional playback of the others. - I.B.) If your present deck is no longer operable, you might want to comb the second-hand market for a deck equipped with dbx NR.

Some audiophiles use mixers to feed microphones into tape decks. Radio, Shack has several at quite reasonable prices, and Audio readers have given me favorable reports on these. Also at moderate price, Radio Shack has some P.A. amplifiers with mike inputs that will accept low- or high-impedance mikes.

Optimizing Output Level

Q. I have a question concerning the output level setting of my tape deck. On playback, I have a choice between adjusting the deck's output level control or adjusting the volume control of my amp. Similarly, when dubbing from one deck to another, I have a choice between the output control of the playback deck and the input control of the dubbing deck. Is there an optimum output level for a tape deck?

- Harvey S. Lee; Arlington, Mass.

A. There is probably an optimum output level setting for a given tape deck in given circumstances, but this optimum is usually quite broad and seldom, if ever, critical.

Two factors should be taken into consideration. First, one wishes to drive the following equipment, say, a preamp, adequately. This is not simply a matter of ultimately achieving sufficient volume. If the preamp's volume control follows active electronic stages, a low setting of this control reduces noise of these early stages.

So a high setting of the tape deck's level control permits a low setting of the preamp's control for a desired volume. On the other hand, if there is a possibility of overdriving the preamp, resulting in distortion, the deck's control should not be set too high.

(If the deck's output control is turned all the way up or nearly so, one assumes--but should not be certain that the manufacturer has had the good sense to ensure that the deck electronics, if any, following the control will not be overdriven by peak signals.) The second factor is the possible effect of the volume control on treble response. The resistance of the control, together with circuit capacitance, may produce some high-frequency loss within the audio range. The loss tends to be greatest when the control is at electrical (not physical) mid-setting. Such loss can occur with both the deck's and preamp's level controls.

Therefore, it is advisable, if one can, to avoid electrical mid-setting. On the other hand, in today's well-designed equipment, one may well find that the possible treble loss is only of theoretical significance--that if it occurs at all, it may be too small to matter audibly.

Effects of Equalization Changes In the August 1989 "Tape Guide," Thomas L. Savio of Bloomington, Minn. stated that when using 70-uS equalization with Type II or IV tapes he gets "duller" sound than with 120-µS equalization. I replied, "Theoretically, unless you record at excessively high levels, your recordings should not sound duller with 70 µS...." Reader Dan Overman of Albany, Ore. responded: "I have another perspective.... Your response was very informative, but you did not offer any possible explanation for Mr. Savio's contention that 70-µS equalization makes his Type II and IV tapes sound duller than does 120 µS. Some cassette decks permit manual switching of equalization only when recording; they switch playback equalization automatically by reading the cassette shell notches.

(My own deck combines record equalization switching with bias switching and automatically selects playback equalization.) If this were the case with Mr. Savio's deck, manually selecting 120 µS for recording on Type II or IV tapes would result in an excessively bright sound when playing back at 70 µS (which could be done unknowingly if the deck's features are not clearly understood), making tapes recorded at the proper equalization sound duller by comparison."

Mr. Overman is correct in that I didn't do justice to Mr. Savio's question, but his last sentence is not correct. Operation at 120/70 µS (120 µS in recording, 70 µS in playback) causes dulling of the sound because 120 uS in recording produces less treble boost than does 70 µS; 70/70 µS nominally produces flat response. Thus, 70/70 µS is brighter than 120/70 µS. Brightest sound is provided by 70/120-µS operation. In comparison, 70/70 µS is relatively duller.

(Source: Audio magazine, Jan. 1992, HERMAN BURSTEIN)

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