Manley MIC EQ 500 COMBO - Manual (Page 7)

HINTS, notes, etc
The MIC EQ-500 COMBO preamp section and make-up gain stage use a similar circuit to
several of our most expensive yet most popular circuits. The MANLEY VARIABLE MU
LIMITER COMPRESSOR uses a similar topology. It would be described as a transformer input,
fully differential tube amplifier, transformer output.
The "optimum" setting of the MIC GAIN control is simple - Describing technically what to
do is difficult. If a microphone is plugged in to the MIC IN and the MIC PRE OUTPUT is
connected to a digital tape recorder then look at the recorder's meters to set the level. If the LINE
OUTPUT is used because EQ is wanted then still use the digital recorder's meters. Then why
include a VU meter ? The key phrase is "digital (tape) recorder". They use peak meters rather than
VU meters and the readings will probably be different. VU meters are the standard for "analog"
tape machines and many consoles. You can still use the internal VU meter to get an optimum
setting for the MIC GAIN. You should have the EQ INPUT set to MIC PRE OP, the EQ in
BYPASS and the LINE GAIN around "12:00" or straight up. Set the MIC GAIN so that the needle
rarely gets into the "red". Once you add a bit of EQ then you may want to adjust the LINE GAIN
by watching the internal meter or by watching the tape machine or console meters.
You can "insert" your favorite compressor and gate two ways. The first way is to go from
the MIC PRE OUTPUT to the compressor's input and then from the compressor's output to the
LINE IN. Switch to LINE IN to "hear" the compressor or switch to MIC PRE OP to bypass the
compressor. The second way is to patch the compressor between the LINE OP and the tape
machine. The first way the compressor is before the EQ and the second way puts the compressor
after the EQ.
The EQ is a passive circuit meaning that the entire EQ uses only inductors, capacitors and
resistors to give cut and boost at various frequencies. These types of circuits often have a tendency
to sound better than op-amp based circuits. This seems to be yet another proof that less is more
when it comes to recording.
This EQ uses stepped CUT & BOOST controls. This is pretty rare in studios but very
common in mastering. Mastering engineers prefer stepped controls because it allows returning to
exact settings and quality stepped controls are known to sound better than pots. Stepped
FREQUENCY controls are pretty much the only choice in a passive EQ's. The EQ frequency is
determined by switching in different capacitors and inductors. There is no bandwith or " Q"
control but the PEAK / SHELF switch is a close cousin in this unit. The SHELF mode is a lower
Q or wider bandwidth than PEAK. In boost modes the SHELF setting is actually part PEAK and
part SHELF. Take a look at the curves on the next page. In CUT settings the SHELF mode is a
true shelf. The other thing to notice is that in SHELF the actual cut and boost is less than the in
PEAK mode. The numbers marked around the EQ knobs are pretty accurate in PEAK but not in
SHELF. To the ear the difference between PEAK and SHELF may be subtle. This is especially
true at 40 Hz and 15 Khz because the differences are so close to the edge of the spectrum. The
3Khz and 5Khz show the differences most clearly.
The LINE IN input impedance is 1000 ohms which may be difficult for some semi-pro IC
gear. The symtom would be distortion at high levels. Vintage gear is typically 600 ohms - tougher.
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