The Technical Stuff
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26
Impedance Matching
Depending upon their design, different microphones provide different output impedances. Typical mic
impedances range from as low as 50 ohms (the symbol for ohms is
) to thousands of ohms (K
ohms). The 6176 Mic input can be set to either 500 ohms or 2.0K ohms, allowing it to accommodate
virtually every kind of microphone. Switching between these two positions while listening to a
connected mic may reveal different tonal qualities and/or gain differences. Generally speaking, a
microphone preamplifier should have an input impedance roughly equal to about ten times the
microphone output impedance. For example, if your microphone has an output impedance of
approximately 200 ohms, the switch should be set to the 2.0K position. However, making music is not
necessarily about adhering to technical specifications, so feel free to experiment with the settings to
attain the desired sound: doing so will not result in harm to either your microphone or the 6176. (
see #2
on page 4
)
The 6176’s Hi-Z input is intended for electric guitar, electric bass, or any instrument with a magnetic
or acoustic transducer pickup. It can be set to either 47K ohms or 2.2M (million) ohms. The 47K ohms
setting is best suited for the -10 dBv level signals typically provided by active basses and guitars,
while the 2.2M ohms setting is more suitable for instruments with passive pickup systems. Since a
particular instrument’s output impedance may actually be somewhere between the active and passive
levels, feel free to experiment to achieve the best sound at the desired level. Again, changing the
input impedance will not harm your instrument or the 6176.
Phantom Power
Most modern condenser microphones r48 volts of power to operate. When delivered over a
standard microphone cable (as opposed to coming from a dedicated power supply), this is known as
“phantom” power. The 6176 provides such power when the Phantom switch is in the on (up) position
(
see #11 on page 5),
applying
48 volts to pins 2 and 3 of the mic’s output connector.
While, in theory, this should result in no harm to the connected microphone even if it does not require
phantom power (since pins 2 and 3 are out of phase and therefore cancel one another at the
microphone), problems can occur if the shield (pin 1) is broken or if the connection is made such that
both signal pins do not make simultaneous contact. Even if all is good, the application of phantom
power can often result in a loud pop (transient). For these reasons, we strongly recommend that the
the 6176 Phantom switch be left in its off (down) position when connecting and disconnecting
microphones.
Only turn the Phantom switch on if you are certain that the connected microphone
requires 48 volts of phantom power
. If in doubt, consult the manufacturer’s owners manual for that
microphone.
