Last Updated on Sunday, 12 December 2010 02:09 Written by Tom Krehbiel Sunday, 12 December 2010 00:41
For years I've been insisting that a proper phono stage must include a mono switch for paralleling the channels when playing a pre-stereo LP, 45, or 78. Remember there were about 75 years of commercial recording before stereo discs hit in 1957. Recordings made during that time can still be played on modern equipment, but benefit greatly from single channel rather than stereo playback. Since CDs hit, phono preamplification and equalization have largely disappeared from home audio gear and the stereo/mono selector (sometimes with reverse stereo or variable blend features) also disappeared.
External phono stages became the way to put preamplification back into a home audio system. Unfortunately the obvious step of including a mono function was almost universally overlooked.
For those who did not come of age during the mono-to-stereo transition, here's why combining the right and left channels when playing a monaural recording matters.
When listening to a mono recording, the sound naturally emanates from a single phantom channel midway between the left and right speakers. But a stereo phono cartridge still sends out independent left and right signals that go to the left and right speakers. The sound signal that is common to both channels, the mono signal, forms that centered phantom sound image.
Those left and right signals should be absolutely identical but in practice often are not. There is inevitably a bit of surface noise, for instance, possibly other noises. Any bits of noise are uncorrelated with regard to left and right channels and will form an extraneous and unwelcome stereo soundstage around the mono music that's nailed in the center (or should be).
Electrically combining the left and right channels at some point in the audio chain will collapse the noise spread into the phantom center channel where it will be largely masked by the music. Since the monoing is most beneficial for phono playback, the logical place for a mono switch is on the accessory phono stage.
I've taken every possible opportunity to point out to equipment designers the need for a mono switch on a phono stage. Many looked at me with uncomprehending eyes. Some said "Well putting a switch into the signal path will degrade the sound and our customers would object." Others said, "Yes. It would be a good idea but there's not really any call for it."
As of this week, all that has changed and Parasound and John Curl get the credit.
Parasound's new Halo JC 3 phono preamplifier sports a monoing switch on its front panel. And what's even more important, it is by all accounts a meticulously designed and engineered product in every way.
The JC 3 offers:
dual mono design in the audio channels
unbalanced inputs and outputs using Vampire RCA jacks
balanced outputs using Neutrik XLR jacks
a custom-made three-position input impedance switch for 47 k ohm MM cartridges, 100 ohm MC cartridges, and 47 k ohm MC
direct-coupled amplification circuits with DC servos rather than coupling caps and FET followers on each channel's board
dual mono power supplies with an R-core transformer
an integrated AC line conditioner
83 dB s/n ratio on the MM input and 73 dB on the MC
RIAA equalization accurate to within 0.2 dB
auto turn-on via a 12V trigger input (as well as a manual power switch)
AC line polarity reverse switch to eliminate hum in many systems
and a switchable 115V-60Hz/240V-50Hz AC power input allowing use around the world.
The new Halo JC 3 is likely to meet with similar acceptance to John Curl's Vendetta Research SCP2B, a preeminent phono preamp for going on 20 years. My wishful thinking is that if a widely respected Halo JC 3 has a mono switch, such switches will start to show up on other phono stages.
By the way, if you wish the mono switch weren't there, it appears to be an easy job to open up the case of the JC 3 and pull off one connector to unhook it totally. To me that would be a terrible step backwards however.
As you go down the list of features above, you'll see that fighting noise on every front seems to have been a priority as the Halo JC 3 went through its development. Parasound's president and founder, Richard Schram tells some of the story. "After working with John Curl and circuit board designer Carl Thompson, we are convinced that one of the most important elements of phono preamp design is to use the smallest possible amplifier circuit with the least amount of copper to act as an antenna for noise. To keep the background black and silent I insisted on housing each channel in its own extruded aluminum enclosure, each further isolated from the power supply with 3/8-inch thick low-carbon mild steel partitions."
The Parasound Halo JC 3 is available now with a suggested retail price of $2,350.
For more information, visit Parasound's website.