YOU EXPERIENCE HUM WHEN CONNECTION TWO TURNTABLES TO A
PREAMP USING THE LOW NOISE SWITCH
OR
YOU EXPERIENCE HUM WHEN CONNECTION JUST ABOUT ANY DEVICE TO ANOTHER
A few facts about the Low Noise Switch. There is no connection
between L & R shield (we call it ground) . The input (or Common) shield only
connects to the corresponding Source 1 or Source 2 to which it is switched. The
chassis or earth ground is not connected in any way to any of the shields. This
eliminates hum loops that usually occur when trying to use ordinary switches to
connect two turntables to a preamp input.
One must connect the appropriate earth or chassis ground of each turntable to
the switch box, and run another from the switch box to the preamp being fed by
the switchbox.
There are variations that might be tried, such as, connect the earth of each
turntable to the preamp earth and also the earth of the switchbox to the earth
of the preamp. Other last resorts may include reversing AC plug polarities.
When totally baffled, I suggest, trying one turntable at a time.
* Connect one turntable to Source 1.
* Connect Common to the preamp input.
* Connect the turntable earth to the SW earth and connect the SW earth to the
preamp earth.
Now, the above electrically represents almost no difference than connecting the
turntable directly to the preamp. The only circuit intervention is 4 electrical
contacts that connect the L, the R, the LG, and the RG. The earth connection of
the turntable directly connects to that of the Preamp. The chassis of the the SW
simply surrounds and shields the switches. There is no connection from the SW
earth to anything else. There should be no hum. If there is, something is
extremely bizarre.
RCA CONNECTOR COMPATIBILITY
Nowadays there are often mixtures of English and of Metric
connector parts. The simple RCA connectors can sometimes look connected, but are
not. To explain. Sometimes, the diameter of the shield connection of an RCA
connector may actually be a minute fraction of a mm larger than the ring of the
jack into which you are plugging. You will feel normal resistance when pushing
it in, but what you are feeling may simply be that of the center post
connecting. The shield may actually be held by that center post directly in the
middle and the shields are apart by that minute fraction of a mm. The fix is to
pull the plug out and squeeze the connector's shield. You may have to use pliers
to make that circle a tad oval. Then, when you plug it in, it will definitely
make a good ground connection.
A POSSIBLE LAST RESORT MOD FOR SOME SITUATIONS
This simple modification to the circuit board has proven to solve nasty hum problems. The situation has usually been when one or both of the turntables have the chassis ground connected to one of the signal cables' shield. Two short insulated wire leads of just about any gauge that is convenient can be used.
HOW ABOUT ONE TURNTABLE TO TWO AMPS?