FAQ - Metering
Testing the Meter's Resistance Modes
Testing the resistance of a Pickup Coil
Testing for Coil Isolation Failure
Testing for Grounded Pole Pieces
Testing the Meter's Voltage Modes
Testing the voltage on the Pole Pieces, Strings and Pickup Shield Wire
Testing the voltage on the Pickup Wires
The Audere preamp uses a DC connection to the pickups. This design
lowers the distortion level compared to other common
preamps and is different than the typical connections most Luthiers
and Repair shops use. So it is important to follow our instructions.
This FAQ is design to explain how to use a Low Cost DMM (digital voltage
meter) to find the common wiring problems.
To make these tests you only need a volt meter of modest quality. All
of these tests use either the Ohms or DC voltage measurement modes.
First insert the probes into the DMM input connections. In all
the tests the Red probe will be connected to the volt/ohm input and
the Black probe will be connected to the meter common.
- Testing the Meter's Resistance Modes
- If you have not use a volt meter in a while then it is best to
verify it is working correct.
Actually every experienced user always
does the following 2 simple test in Ohms mode.
1) Verify the meter reads correctly under the open
The Next test is to verify the meter works under a short condition
Depending on your leads you might not be able to get down under 0.5
ohms. This will be fine for all the tests you need to make.
If you have any reason to suspect a meter is not working correctly
in Ohms mode you can test it by measuring known good 100, 1K, 10K,
100K and 1Meg ohm resistors. This will cover 95% of all
failure modes in most
- Testing the
resistance of a Pickup Coil
- Testing the resistance of a coil in a pickup will immediately
detect broken wires. Since the wires on the coil are thinner than
strand of hair they can be easily damaged, most likely by someone
poorly installing a pickup cover. Pickups will differ in their resistance
level but if you get < 5K or > than 20K you
should be suspect a major problem. Most pickup manufacture publish
the approximate resistance of their pickups.
for Coil Isolation Failure
- The pickup coils should be insolated from the shielding
and from the pole pieces.
The most common reason for these problems is a pickup
winder will short the shielding to the common side of the coil on
purpose. This is not a great idea from a noise prospective even
in a passive only system and will cause lots of problems for our
preamp (for example popping when the Z-Mode switch is moved). Luckily
when a pickup maker connects these 2 points on purpose
the undesired connection is most often done at the end of the wires
in the cavity.
Look carefully at the end of the pickup wires - you probably only
need to disconnect the the shielding wire from the pickup common
wire to fix the problems. Retest
Less commonly the connection was made on the bottom of the pickups.
In this case, pull up the pickup and cut or unsolder the undesired
connection. Now solder a new wire to the exposed shielding or terminals
so you have a separated ground. Retest
The non fixable case is where the insulation has broken down on
the pickup coil wire. This is much more likely
to occur on a vintage pickup especially if the coils were
wired directly on top of the magnets or pole pieces. Some times a
player will hit the magnets hard enough to move the magnets which
could easily cause the insulation to fail as the coil is fixed -
the magnet is sliding relatively and the insulation is in between.
It is easy to test with a meter. If you read a short of close to
it with one
or the other end of the coils on your meter - then
you probably do not have a internal failure. But if
you have a mid reading X ohms to one side of the coil leads and Y
to the other side
where X+Y is a reasonable resistance for the pickup then
you probably have an internal coil failure. You need to send the
pickup to be rewound.
In general, If the pickup coil is connected to
the pickup magnet then this is a big problem with an
Audere preamp because we have put
a voltage on the pickup common. The 2 common side effects are:
1) If you have correctly connected the magnets to ground (as we instruct) and
you have connected the pickup coil to the magnets in error, then
you are now, draining off some extra battery current and you have
a distorted output potential, the Z-Mode switch will pop LOUDly when
you change modes and the preamp might shut down as the bass control
2) If the magnets do not have a separately connected ground but the
strings are grounded (which is typically true) then when grounded
strings contact the pole pieces
you will short an internal node in the preamp. The output will slew
like crazy creating a LOUD pop. This pop is present even when the
volume control is turned down.
The meter tests above will detect the source of both of these problems.
for Grounded Pole Pieces
- We would really like everyone to ground their pole pieces and we
have a FAQ about how to do it.
With a meter it is simple to test that the pole pieces are well grounded
The reading should be very small (normally it will not reach 0 Ohms)
but if it is more than 20 ohms then your
connections might not be very good. Sometimes the ground
connections are made with conductive adhesive and if you do not
keep pressure on these adhesives then they will often slowly increase
their resistance till failure.
This test can be preformed before or after the pickup is wired to
If the pickup is already connected to the preamp then you can move
the black wire to the pickup connector as will be show below.
- Testing the
Meter's Voltage Modes
- Just like for ohms there are some simple tests to verify the meter's
DC voltage measurement system.
If the reading is not zero then the meter has a significant problem...
Next test the voltage of a battery - this will verify the meter
is good and the battery is also...
You can also invert the 2 leads and verify you get the correct negative
voltage. Sometimes when a meter has been abused and an internal
diodes is blown out then positive or negative volts will not work
the voltage on the Pole Pieces, Strings and Pickup Shield Wire
- For the following tests (3 tests in 1 drawing), the preamp
must get powered up so insert a cable into the bass. The common side
of the meter (black lead) will get connected to the cable's metal
plug. If you do not have a metal plug then you can use the internal
Gray/White wire or anything connected to that wire.
If the magnets and strings are both at 0 volts then they can not make
any extra noise when they contact each other.
the voltage on the Pickup Wires
- By looking at the voltage on the pickup wires after they are connected
to the preamp we can verify that no pickup connections are incorrectly
shorted to ground. It is good to do these measurements in Mid Z-Mode
with all coil configurations if you are using a pickup coil tapping
or selection switches etc.