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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 condition


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 DMM's.
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 a human 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.
 
Testing 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 is boosted.
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.
 
Testing 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 the preamp.
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 equally.
 
Testing 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.
 
Testing 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.