Audioclinic (Q and A) (May 1973)

by Joseph Giovanelli

Low Front-Channel Gain

Q. I recently converted my stereo system (which includes a McIntosh 1700) to quad by adding an EV decoder and a Dynaco SCA-80. I have noticed that, when using the decoder, there is a tremendous loss of gain in the front amplifier, as opposed to its stereo performance. Is this expected? If not, what can I do to receive more gain?

-Ed Willner, Clarksville, Indiana

A. The EV decoder has no insertion loss. This means that the front channel performance of your equipment should be substantially the same as it was before the conversion to four-channel.

To determine what is wrong, temporarily connect your front channel amplifier for conventional stereo by bypassing the decoder. Note if gain has been restored. If it has, you will know that restored. If it has, you will know that nothing has gone wrong with the front channel amplifier.

Recheck your wiring to the decoder to be sure that all cables are in their proper places. Check that all cables are in good condition.

It is possible that something is wrong with your particular decoder. If all other checks have proved negative, this becomes a likely possibility. To determine that you do have a problem in the decoder, feed a I kHz audio signal into the two inputs of the decoder.

Measure the resulting output voltage appearing at the two output terminals. If this measurement does not yield substantially the same voltage as does the input from the oscillator, the decoder is defective.

Be sure to check the tape switches of the decoder and receiver to see that they are in their correct positions.

Groove Echo

Q. I recently put together a system consisting of a Marantz 2270, Dual 1229 with a Pickering V-15/750E cartridge. When played at full listening volume, I have noted what appears to be an echo for one revolution of the disc prior to the onset of any loud music. This occurs both at the beginning of the record and in appropriate spots within a recording.

I presume this may be due to some irregularity in the first groove because of the side impressions of the subsequent groove.

I would appreciate your opinion on the cause of this and what, if anything, can be done to prevent it. I am also interested in knowing why I do not hear this on records which are transmitted on FM.

-Jack R. Harnes, M.D., New York, New York.

A. When playing a phonograph record, it is not at all unusual for a slight echo to be heard either before or after a given passage is heard.

(When the echo precedes the actual signal, we often call this a "ghost"; when it follows the music, we call this an "echo".) There are a number of contributing factors. The modulation being impressed on a given groove during the cutting process can cause the sufficient deformation of the surrounding area of the disc so that this information will be "printed" on either the groove preceding or the groove following the actual modulation. The degree of audibility of the "echo" depends on the level of modulation, the spacing between grooves, the level of the modulation in the adjacent grooves, and the evenness of the deposition of metal during the plating process involved with producing the scampers used to press phonograph records.

While I have not tested this theory, it does appear that some types of styli bring out more of this unwanted signal than do others.

If you have a record on which groove echo is heard, and if this same disc is played on an FM station, you should hear this same groove echo unless it is masked by the noise generated within the tuner or by man-made interference.

Check to see that your stylus is clean. In addition, check for proper tracking force. Excessive tracking force can deform the surface of a disc, thus causing an increase in unwanted echo.

(Audio magazine, May 1973)

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