Instruction Manual

OPERATIONAL NOTES
SWITCHING ON
The power switch is located on the right hand corner of the front panel. Flip the switch up to turn on the
preamplifier and down to turn off the preamplifier. Do not flip the power on and off rapidly or you may damage the
bridge rectifiers in the power supply.
RUNNING
It is not recommended that you leave your preamplifier permanently switched on. This only wastes electricity and
tube life. Your preamplifier has solid state rectification and reaches peak operating condition in approximately 30
minutes.
RACK MOUNTING
Most owners of this unit will choose to mount the unit in a rack. There are several major concerns. First is
ventilation. You should allow clearance above and below the unit. Do not mount the MIC EQ-500 COMBO in a
2U flight case as this will not have enough ventilation. The result will be a short working life of the unit. Another
good reason for clearance above and below is minimizing hum. Some gear radiates hum fields and it is possible for
this unit to pick up the hum and amplify it. Grounding can also be a concern. Other gear screwed to the metal rack
rails serves as another ground path. The ground terminals on the back panel may help. Lastly if the unit will be
portable then you may want a shock mounted rack. The 1/4" aluminum front panel is about as good as it gets for
strength and the unit is not too heavy in back but the tubes are can become microphonic as a result of vibration.
TUBE LIFE
As with all tubes, their quality degrades with age. This is due to cathode emission, a natural process found in all
tubes. We recommend that you have your preamplifier checked every 4-5 years, depending on usage. An excessive
increase in noise level can indicate the need to replace a tube. The most likely candidate for a noisy tube will be the
shorter ones as they are used as first stage preamps and have the most gain.
HUM
This unit is meant to use the third pin of the mains as the ground reference. The GROUND TERMINALS are one
method to reduce hum. Verify that the two terminals are connected with the ground strap or that the hum is less
with the strap off one terminal. If all else fails try a three pin to two pin AC adapter rather than break off the AC
ground pin. More than likely it is the mic or mic cabling at fault.
Another source of hum can be equipment stacked on top of one another. This is not a good plan from the
ventilation standpoint generally and it is likely to introduce hum, buzz or noise into the system. Certain gear
radiates magnetic fields or high frequency noise around its chassis and other gear may be prone to receiving these
fields. Distance helps greatly.
Transformer isolated balanced inputs and outputs are most immune to ground problems. Cutting the shields at
either the source or destination may help but not on the MIC PRE INPUT. Here the shield is required for phantom
power and providing a shield for the microphone. These balanced inputs and outputs will interface to unbalanced
inputs and outputs automatically. This is a prime benefit with transformers. The internal meter may have to be
disregarded when feeding -10 dBu inputs.
Locating the MIC EQ-500 COMBO close to the mic is advisable in some situations. Most mics are not great at
driving long cables. Not only can noise and hum be reduced, but signal fidelity is often dramatically improved.
The downside is having to run out to the studio to adjust a control. One should not really have to be re-adjusting the
controls of this unit every few minutes. If a compressor is patched between the MIC EQ 500 COMBO and the tape
machine then the engineer has adjustment of level to tape at arms reach without resorting to patching the signal
through the console.