- Why
should I purchase a "Bob's Device"?
- Photos of some of Bob's Step-Up Devices
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- What about Grounding- FAQs
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What about Grounding?
Each
unit includes a grounding post that can be used to
connect your turntable ground and your preamplifier ground. It
also
includes a ground "lift" switch. In all modes, the
transformer cases and faraday shield internal to the transformers are
connected
to the ground screw. In the "ground in" mode, the phono system
ground is connected to the chassis ground. In the "ground out"
mode, the phono preamp system ground is connected to the chassis
ground.
In these modes, the minus sides (negative sides or shields) of the
output
cables are connected to the grounding lug. This configuration
works well
for those systems where the turntable ground is connected to the
negative leads
coming from the phono cartridge or where the negative inputs to the
preamp are
internally connected to ground. In the "lift" mode, none of the
conductors in the RCA jacks are connected to the case, ground, or
shield and
there is no electrical connection between channels. This design
avoids
any transformer induced ground loops regardless of the configuration of
your
other equipment.
So, you have the Step-Up Device and you want to properly install it into your system:
Step 1 - Connect the leads from your turntable to the input connectors on the Device.
Step 2 - Connect the ground lead from the turntable to the ground lug on the Device.
Step 3 - Use a short pair of interconnect cables to connect the output of the Device to the input of your Phono Preamplifier or Phono Inputs. For best results, this set of cables should be like the ones in this DIAGRAM .
Step 4 - Turn everything on and listen to the background noise. Move the ground / lift switch to whichever position is quietest. Then move the transformer around to find the quietest location.
If you are continuing to have problems, try connecting an ordinary piece of wire between the ground lug on the phono preamplifier and the device (in addition to the one from the turntable). Then try the ground / lift switch in both positions to see what sounds best. Then, if it still is not quiet enough, take a look at the following information:
Start from your cartridge and follow the wires, looking carefully for any places where the negative terminals of the cartridge (lets call them system ground) are connected to equipment grounds (let's call them chassis ground, sometimes referred to as drain wires) We only want one chassis ground connection between pieces of equipment. When there is more than one chassis ground connection, there is the possibility of a ground loop (it doesn't know which way to go, so it keeps on moving and generates noise.)
The next 2 paragraphs repeat the initial steps above, but written in narrative format, and in more detail:
If your turntable has a pigtail along with the RCA connectors, then that is the chassis ground from the turntable. Connect that pigtail to the ground lug on the step up transformer. Then connect everything else, without connecting the ground to the phono preamp. Try the ground / lift switch in both positions and see which is quietest. Then, additionally, connect a separate wire between the ground lug on the step up transformer and the ground screw on the phono preamp and see if that is quieter or noisier in either of the ground / lift switch positions. Then you can determine whether you need to ground the phono preamp to the step-up transformer or not. Regardless, you need the proper interconnect as shown in my DIAGRAM to go between the step up transformer and the phono preamp.
You only want them connected that way at one end, hence the ground / lift switch. So, here is the short answer. Remove the ground wire connecting the turntable from the phono preamp. Connect ONLY the ground from the turntable to the Box you got from me. Don't connect the wire from the box to the Phono Preamp just yet. Now, make sure that you use interconnect cable between the transformer and the Phono Preamp that have 2 wires inside (positive and negative) and the shield is connected to the outside (chassis ground of the cable) at only one end. (The cable will have the negative lead and the ground attached to the outside of the RCA connector at one end. The cable will only have the negative lead (Not the ground) attached at the other end.) Now, with everything hooked up, turn it on and listen to the hum. Then move the switch to whichever position offers less hum. Then touch the preamp ground wire to the ground lug and see if it is less or more noisy. Then remove the wire from the phono and see if it is quieter or not. Then touch the phono wire to the preamp wire and see if that is quieter.
Here is
another way of looking at the situation:
Your
cartridge has 4
connectors: + and – for each channel. None
of those is a
ground wire. After the wires leave the tone arm, there is usually
a block
or a connection point on the turntable where the tone arm wires are
connected
to the RCA cables.
Find
that point
and look to see electrically how that connection is made. Look to
see if the
connections go directly to RCA + and – on the cable and look to
see if there is
a ground connection. It may be hard to tell since the RCA
connectors may
or may not be insulated from the enclosure (you will see a Teflon or
other
insulated washer on both sides of the connector). If they are not
insulated, there is inherently a ground connection there, and the
– sides of
both cables are also inherently connected together at that point.
The
cables from the
turntable go to the SUT. The SUT is constructed so that in the
LIFT mode,
all 4 wires pass independently through the SUT without being connected
to
ground. The RCA output cables continue to the phono stage.
We
don’t know how the
wiring is set up inside the phono stage. Things we don’t
know are whether
the – sides are grounded to the chassis and whether the + and
– signals are
inverted. This is nearly impossible to determine without a
schematic and
there is no industry standard. The best
way to check for inversion is to switch the + and – wires on the
cartridge and
see if that fixes the problem or makes it worse.
To
top all that off,
the signal wires are all subject to stray electromagnetic (EM)
interference. That is the main reason why cables are shielded and
why we
twist the wires. If the wires are not twisted, they act like an
antenna
and pick up EM. If we twist them, it confuses the EM and makes it
a worse
antenna. So the best setup is one where the signal wires are
twisted and
there is a shield around them that is attached to a chassis ground, not
to any
of the signal cables.
Some
tone arm
manufacturers take one of the – wires from the cartridge and
connect it to
chassis ground. I don’t know why, but they sometimes
do.
I
try to take all this
into account with my design which when you move the switch from lift to
ground,
it connects all the – signal wires to the chassis ground.
That takes care
of a lot of problems with the inconsistencies in wiring both with tone
arms and
with phono stages.
You
need to understand
all of this and clearly look at your system. Take into account
that there
should only be one chassis ground connection at each unit. If
there are
multiple connections you get what is known as a ground loop where it
also acts
like an antenna but the EM signal keeps looping and gets
amplified. So
you are better off without a ground than with an extra ground.
One of the main
challenges is with the interconnect cables. RCA connectors only
have a +
and – and the – is sometimes connected to chassis
ground. So it is
important to use cables that have 2 conductors and a shield, with the
shield
connected to the – conductor on one end only.