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THE GREEN LED ON MY P-251 DOES NOT LIGHT UP (BUT THE AMBER LAMP DOES).

 

The LED lights slowly when a mic is connected, after the amber lens, as is indicates heater voltage to the tube, and the amber incandescent illuminated immediately upon the application of AC power, as it indicates rectified AC voltage before the heater regulator circuit. If the LED does not illuminate after 1 minute, either the tube is shorted (unlikely), there is a short in the multipin cable, or the wrong supply is being used with the mic (most common situation).

 

 

ARE YOUR POWER SUPPLIES INTERCHANGEABLE?

 

No, each supply is adjusted to the mic. Specifically, the heater voltage each tube requires is unique and factory adjusted. Interchanging supplies could lead to heater under or over voltage conditions, which in turn leads to either less than ideal noise performance of degraded  (shorter) tube life. Different tubes have different current requirements so an adjustment for one tube might not even power up another tube, and the same adjustment could overheat another tube.

 

 

I OWN 2 BOCK 251's, CAN I MIX & MATCH THE SUPPLIES?

 

No, and it's a good idea to somehow mark the mics and supplies so that they don't get mixed up.

 

 

I OWN A BOCK 251 & A BOCK 241, CAN I SWAP THE SUPPLIES?

 

No they use very different tube types so the adjustments are very different.

 

 

HOW DO I CHANGE THE FUSE ON MY P-251 or N470 PSU?

 

At the rear of the unit is the IEC 320 power input module, there is a small drawer that pulls out with assistance from a screwdriver, provided that no AC power cord is connected to the unit.

 

 

WHAT VOLTAGES DO YOUR POWER SUPPLY PRODUCE?

 

The B+ is 120v and the heater is 5.9v, though the heater can generally be adjusted from .5v to 7v. Adjusting the heater over 6.3v will shorten the life of the tube, and adjusting it to under 4v will yield unacceptable noise.

 

 

WILL PHANTOM POWER DAMAGE MY MICROPHONE PSU (POWER SUPPLY UNIT)?

 

No, all current production mics are built so that this will not damage the equipment.

 

 

MY MICROPHONE DOESN'T REQUIRE PHANTOM POWER. WILL PHANTOM POWER DAMAGE MY MICROPHONE IF IT IS LEFT ON?

 

No, all current production mics are built so that this will not damage the equipment.

 

 

I HAD NOISE IN MY MIC SO I RESET THE POWER SUPPLY. WHAT DID I DO?

 

Your mic is not a computer there is no '”resetting”. “Reset” is a term more appropriate for digital or other complex systems. There is no internal “on/off” switch in the mic and that switch is not controlled by the power supply.

 

 

WHY YOUR MICROPHONE POWER SUPPLY IS NOT A COMPUTER:

 

Your microphone is a completely analog transducer system which converts acoustic pressure and pressure gradients to electronic signals. The power supplies for these mics are fully linear and  high voltage. The power supplies for computers are low voltage switching switching power supplies.

 

 

WHAT IS PHANTOM POWER?

 

"Phantom power" and is  covered by DIN spec 45596. The positive terminal of a power  supply is connected through resistors to both signal leads of a  balanced microphone, and the negative terminal is connected to  ground. 48 volts is the preferred value, with 6800 ohm resistors  in each leg of the circuit, but lower voltages and lower resistor  values are also used. The precise value of the resistors is not  too critical, but the two resistors must be matched within 0.4%.  Phantom power has the advantage that a tube condenser, dynamic or ribbon mic may  be plugged in to a phantom powered microphone input and operate  without damage, and a phantom powered mic can be plugged in to  the same input and receive power. The only hazard is that in case  of a shorted microphone cable, or certain old microphones having  a grounded center tap output, current can flow through the microphone, damaging it. It's a good idea anyway to check cables  regularly to see that there are no shorts between any of the  pins, and the few ribbon or dynamic microphones with any circuit  connection to ground can be identified and not used with phantom  power. One old studio trick is to change the old cable out on a P48 mic with a new, known good cable to improve performance.

 

 

WHAT IS THE MINIMUM POWER SUPPLY FOR YOUR PHANTOM POWER MICROPHONES AND HOW WILL THE PERFORMANCE OF THE MIC CHANGE WITH E.G. A 12V POWER SUPPLY?

 

Current production Bock Audio P48 mics will function in a range from 38 to 52vdc, 48-52v being the ideal range. Voltages below 38v ensure compromised performance. If your Bock  mic works on 12v please call Ripley's Believe it or Not,right away! As there are no internal switching power supplies or oscillators, both the amplifiers and capsule polarization networks  are linear and require stated voltages to function.

 

 

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