I have a Kenwood 6340 quad receiver with a plug-in CD-4 demodulator. I recently purchased a four-channel Teac open-reel recorder in order to tape all my CD-4 records. As yet I have been unable to make acceptable recordings due to excessive distortion and the presence of a high-frequency tone in the recording. If the same disc is copied in stereo, the recording comes out beautifully.
I have been able to eliminate the problem in two ways, both of which produce unacceptable recordings: 1) by adjusting the carrier signal level to a point where all separation between front and rear channels is lost; 2) by recording at such low volume on the Teac that playback is plagued with lots of noise. Can you help me out?
-John Steigleder, Tarzana, Calif.
We would guess that the carrier frequency from the disc is leaking into the quad output and inter-modulating both with the recorder's AC bias and with the audio. If so, the four quad outputs could each go through a high-cut filter before being fed to the tape recorder. If you have access to four channels of Dolby-B noise reduction with FM filtering (which cuts out everything above about 17 kHz to prevent interference between the 19-kHz pilot or the 38-kHz subcarrier and the Dolby circuit), that should eliminate un wanted by-products created by the inter action of the demodulator and the recorder: if these by-products remain, it probably indicates malfunction in the demodulator.
I am very critical of sound quality from a disc. Some discs are so warped that the finest tone arm couldn't possibly track them, and some have pits and mountains on their surfaces. My audio equipment totals $3,000 but what good does all this do when discs that should never have made it past the quality inspectors (if any) are put on my turntable? I use some of the top quality disc cleaning equipment (Discwasher record cleaner d-U and the Zero stat), but it has been a big disappointment. I have been thinking of installing some noise-reduction equipment, but I wonder if this would be just a waste of money also.
-R. A. O'Briant, F.P.O., Seattle, Wash.
Take heart, help is on the way-a little, at least. We know of some new noise-reduction products in the works and plan to report on them as soon as possible. Generally the record companies insist that they are not receiving many complaints about their products. If you and all other dissatisfied record buyers direct complaints to the offending companies, that might help. And you can't expect products like Discwasher and Zerostat to cure manufacturing defects in records. They are intended for cleaning and static reduction, respectively.
I own a Marantz 4300 four-channel receiver. According to specs, it delivers 100 watts [23 dBW] per channel with two, or 40 watts [15 dBW] with four, into 8-ohm loads. Eventually I would like to install a larger power amp in the pre-out section of the Marantz, retaining its preamp section. The rated preamp output is only 1 volt. Is this voltage enough to drive, say, a power amp rated at 100 to 150 watts [20 to 21 1/4 dBW] to full output? I plan to use one power amp for the front channels and one for the back.
-Tom Fiore, Brooklyn, N.Y.
It depends on the amp. Quite a few in that range can be driven to rated output power by 1 volt, and you really don't need to be too fussy about this since the difference between 1 volt and, say, 1.2 volts at the input is less than 1.6 dB at the output. Most people are hard-pressed to hear a difference that small under normal listening conditions.
I have been using a Citation 12 amp (and Citation 11 preamp) to drive JBL 100s. I have now upgraded my speakers to Ohm Fs. I feel the amp is inadequate and want to buy a higher-powered one. I play mostly chamber music, solo piano, o' small jazz groups, in a room of about 2,000 cubic feet. Although some of the music has a wide dynamic range, I don't play loud rock o' loud symphonies very often. Will a Phase Linear 400 function well at such a low level' Will an Ampzilla or a BGW? I have heard that some of the superamps have to work at a certain level before they "wake up." Which amp would you buy to play such mu sic in such a room with Ohm Fs? Assume an $800 or $900 limit.
-Dick Wellstood, Sea Girt, N.J.
Any "super-amp" that needs an alarm clock to "wake up" is not worth buying. Certainly the Phase Linear, Ampzilla, and BGW work perfectly well at low levels. Why in the world do you want a more powerful amplifier any way, if you listen at low levels? The principal difference between your Citation 12 and the superamps you are considering is that the latter can drive your speakers about 5 dB louder. The differences at low levels will be even less apparent with the highly inefficient Ohm Fs than with most other speakers.
I have a Pioneer SX-737 receiver and a good outdoor FM antenna with 75-ohm lead-in. My problem is that multipath distortion occurs when the television set in my living room is on NBC and my receiver is tuned to 101.1 FM. This television is in no way hooked up to my FM antenna, since it has its own antenna. The strange thing is I have a portable set in the same room with my stereo, also hooked up to the TV antenna, and I get no interference from it whatsoever! How do I get rid of this frustrating problem?
-Terry West brook, Texas City, Tex.
What you have is probably not multipath though the effect may be similar-but parasitic radiation from the TV set. (The portable set doesn't radiate.) There are several possible remedies:
1) If the FM antenna is directional and has a rotator and if the station comes from a direction that allows it, point the FM antenna away from the TV antenna.
2) Install an FM trap in the TV antenna lead.
3) Enjoy another channel.
4) Keep the TV turned off.
5) Get the TV checked for excessive radiation.
6) Get a new TV set.
A section of a recent JBL ad focused exactly on what interests me the most about loud speakers: "Take the volume to the edge of silence, then come back a little. Can you hear every part of the music? Are all the textures and detail and harmonics of the music still there, or is only the melody lingering on?" As an apartment dweller on the verge of component buying, I can't think of a more important aspect of speaker performance. Yet all loudspeaker test reports I've read focus al most exclusively on how well speakers per form loud and super loud. Why don't you include low-volume listening evaluation as well?
- Martin Abraham, New York, N.Y.
We do include low-level evaluation in our loudspeaker reviews, although perhaps not in an obvious way. We are concerned with the dynamic range of the speaker, the difference between the loudest and the softest sounds it can reproduce. A range of 65 dB or so will take care of just about anything that can be recorded on disc, but an orchestral performance on a DBX-encoded tape, for example, could demand 80 dB or more range from the speaker. The limiting factor is usually how loud the speaker can play without excessive distortion. The low end is normally not a problem; in fact many speakers do an excellent job of reproducing the residual noise from the power amps driving them. Another probability is that the ambient noise in the room will overwhelm the speaker output while it is still clear as a bell. In any case, it is difficult to see how a loudspeaker could suffer from a disabling low-level aberration without betraying itself at higher levels as well. Therefore, in our opinion, program material of wide dynamic range-from pianissimo to fortissimo-is necessary for evaluation of all aspects of loudspeaker performance. We would suggest, incidentally, that you switch on the loudness (or contour) control if you perform the test outlined in the JBL ad; otherwise the strange frequency response that results may be blamed on the speaker rather than on the nonlinear response of the ear.
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(High Fidelity, Mar. 1977)
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