John Hardy M-1 Specifications

Mail: P.O. Box AA631

Evanston, IL 60204 USA

Ship: 1728 Brummel St.

Evanston, IL 60202 USA

THE JOHN HARDY COMPANY

Phone: [phone]

Toll-free: 866-379-1450

Fax: [phone]

www.johnhardyco.com

M-1 Mic Preamp

October 6, 2003

M-2 Mic Preamp

M-1 Personal Mic Preamp

The M-1, M-2 and M-1 Personal mic preamps are among the finest mic preamps in the world. They provide the accuracy
and transparency that is missing in other mic preamps. No matter what your application, they will provide superior
results. The world's best input transformer (Jensen JT-16-B), best op-amp (990C discrete class-A op-amp) and the
elimination of all coupling capacitors from the signal path combine to provide the highest performance.

The M-1 and M-2 have a 19” wide rack-mount chassis (1.75”H x 19”W x 8”D) and can be ordered with one, two, three or
four channels. The M-1 Personal mic preamp has an 8” wide chassis with a capacity of one channel. There are two meter
options, and the best Jensen output transformer (JT-11-BMQ) is available as an option. These options and basic channels
can be easily added later.

The M-1 was introduced in 1987. The M-2, introduced in 1996, is a variation of the M-1. The first difference is the gain
controls: The M-1 has a two-section gain-pot providing continuously variable adjustment in two overlapping ranges of 12
to 40dB and 32 to 60dB. The “HIGH GAIN” switch changes ranges. The M-2 has a 16-position gain-switch with 1%
metal-film resistors, providing accurate and repeatable gain-settings from 15 to 60dB in steps of 3dB.

Further differences involve the push-button switch to the right of the gain-pot or gain-switch. The M-1 has a “HIGH
GAIN” switch as mentioned above. Since this switch is not required in the M-2, the p.c. board layout was modified to
allow that switch to be used in the M-2 as either a “20Ω MIC” switch, or a “20dB PAD” switch, depending on how the
board is assembled. The 20Ω MIC switch provides optimum matching of microphones with extremely low output
impedances. The 20dB PAD switch attenuates the input signal by 20dB prior to the JT-16-B input transformer, providing
a maximum input level of +29dBu.

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Highlights

The Jensen JT-16-B Input Transformer is
Jensen's best mic-input model. Jensen is
known worldwide for their superior au­dio transformers. If you thought trans­formers were a compromise, you haven't
heard the JT-16-B!

The JT-16-B is a large, low impedance
ratio (150:600Ω) transformer made with
a proprietary 80% nickel (nickel-iron­molybdenum) core material. The large
size allows it to handle extremely high
signal levels of +12dBu at 30Hz and
above, +8dBu at 20Hz. The low ratio
provides less distortion, flatter frequency
response and more linear phase response
than more typical high-ratio transformers
(150:15kΩ). The proprietary 80% nickel
core material is far superior to, and much
more expensive than the steel often
found in other transformers.

The JT-16-B outperforms transformer­less mic preamps because it eliminates
the input coupling capacitors that are re­quired with transformerless designs. Ca­pacitors degrade the audio signal be­cause they have a property known as di­electric absorption, where some of the
signal passing through the capacitor is

absorbed by the dielectric of the capaci­tor, then released a short time later. This
smears the signal. Transformerless de­signs require these capacitors to keep the
phantom supply voltage from reaching
the circuitry of the preamp. Transform­ers inherently block DC voltages, elimi­nating the need for the capacitors.

The JT-16-B provides better common
mode rejection than transformerless de­signs, important in electrically noisy en­vironments. It handles common mode
voltages as high as ±300V peak. Trans­formerless designs are usually limited to
maximum voltages equal to their power
supply voltages, typically ±15V to ±18V.

The 990 Discrete Op-Amp is faster, qui­eter, more powerful and better sounding
than the typical monolithic op-amps
found in other equipment. Each individ­ual (discrete) transistor, resistor, diode,
capacitor and inductor of the 990 has
been carefully chosen for its task. This
provides a level of performance that is
not possible in a monolithic op-amp
where all components are fabricated on
the same tiny chip of silicon. The 990
operates from ±24V power supplies, al-

lowing output levels of greater than
+24dBu. It can drive long cables and
loads as low as 75Ω, something mono­lithic op-amps cannot do. See the 990
data package for further information.

Elimination of All Coupling Capacitors
from the Signal Path results in less degra-

dation of the audio signal. Two superior
techniques are used to accomplish this:

1. Input bias current compensation cir­cuitry nulls out the small DC currents
(thus voltages) that flow from the inputs
of the 990 (or any op-amp), voltages that
could cause noise when operating the
gain controls. This circuitry also reduces
the DC offset voltage at the output of the

990. Most other mic preamps use cou­pling capacitors to block the input bias
currents, resulting in signal degradation.

2. DC servo circuitry nulls out the DC
offset voltage at the output of the 990,
eliminating the need for a traditional out­put coupling capacitor to block that volt­age. The signal degradation caused by
that capacitor is also eliminated. See the
schematic on page 7 for details.

M-1: Dual Range Gain Control and “HIGH
GAIN” Switch. The overall gain adjust-

ment range is 12 to 60dB, a span of
48dB. Rather than cover the entire 48dB
in one revolution of the gain pot, there
are two smaller, overlapping ranges se­lected by the “HIGH GAIN” switch. The
low gain range provides adjustment of
12 to 40dB, the high gain range 32 to
60dB. This provides 28dB of adjustment
per range, with 8dB of overlap. The rela­tively small 28dB of adjustment per
range provides great feel and resolution,
with sufficient overlap to keep you “in
range” at all times.

There are two reasons for the great feel:
First, with fewer dB of adjustment per
revolution, it is easier to adjust the pot to
the desired gain setting. The second rea­son is a more technical one, and very im­portant. A single 10kΩ pot covering the
entire 48dB range in a single revolution
could get a bit “touchy” as it approached
the maximum gain point (minimum re­sistance), due to contact resistance varia­tion (CRV). The gain pot of the M-1 is
actually a two section pot having a 10kΩ
section and a 500Ω section. In high gain

Standard Features

applications where CRV would be a
problem with a 10kΩ pot, the 500Ω sec­tion of the pot is used. CRV is reduced
by a factor of twenty, virtually eliminat­ing any touchiness. See page 5 for de­tails.

The unusually low minimum gain of
12dB allows the M-1 to handle input lev­els as high as +12dBu before the output
is driven past its +24dBu maximum out­put level. The JT-16-B input transformer
can handle input levels of +12dBu at
30Hz and above, and +8dBu at 20Hz.

If you need infinite resolution so you can
set the mic preamp to any gain, or have
the ability to “ride gain” during a perfor­mance, the gain controls of the M-1 are
ideal.

M-2: 16-Position Rotary Gain-Switch with
1% metal-film resistors provides accurate

and resetable gain control from 15 to
60dB in steps of 3dB. For situations
where quick and exact gain-matching of
channels or exact resettability is re­quired, the gain controls of the M-2 are
ideal.

M-2: “20Ω MIC” Switch provides optimum
matching with microphones that have a
20Ω output impedance. Note that the
Jensen JT-16-B mic-input transformer
does exceptionally well with just about
any low-impedance microphone, includ­ing those with a 20Ω output impedance,
but this switch provides further refine­ment. The switch takes the place of the
“HIGH GAIN” switch of the M-1.

M-2: “20dB PAD” Switch provides a 20dB
resistive pad before the input trans­former. This increases the maximum in­put level to +29dBu for situations where
excessively high input levels are encoun­tered. Most applications won't need a
pad, but for those that do, this option
provides it. This switch takes the place
of the “HIGH GAIN” switch of the M-1.

Note that you can get an M-2 channel
built with the “20Ω MIC” option or the
“20dB PAD” option, but not both. These
options take advantage of the fact that
the “HIGH GAIN” switch of the M-1 is
not needed in the M-2, and the p.c. board
was modified to allow that switch to be
used one of three ways.

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M-1 and M-2 Common Features:

Polarity Reverse Switch (“POL REV”) re-

verses the signal polarity at a point im­mediately before the input transformer.

48V ON/OFF Switch (“+48V”) for phantom
power. The phantom supply has more
than enough current to handle any con­denser microphone.

All Front Panel Switches are LED Illumi­nated. A custom clear plastic push button

was developed for the M-1 and M-2.
Each button's function is marked on the
front surface and is illuminated dimly
when off, brightly when on, each button
with its own LED color. The HIGH
GAIN switch of the M-1 (20Ω MIC or
20dB PAD for the M-2) uses a red LED,
the POL REV switch uses an amber
LED and the +48V switch uses a green
LED. No guessing about these switches!

Gold Plated XLRs for maximum reliabili­ty. Gold does not tarnish or oxidize. Sil­ver plated XLRs are available on special
order.

Ground Lift Switch on Each Channel al­lows disconnection of the shield (pin 1)
of the output XLR. This can be helpful
in eliminating ground loops. This mini­toggle switch is on the rear panel.

Toroidal Power Transformer with addi­tional silicon-iron shielding eliminates
hum problems caused by stray magnetic
fields. Some manufacturers use a sepa­rate power supply chassis and umbilical
cord to keep the power transformer's
stray magnetic fields from interfering
with the audio circuitry. In the M-1 and
M-2, the stray magnetic fields are con­trolled at the transformer. Each trans­former is carefully tested for stray mag­netic fields under worst-case full-load
conditions. The optimum rotational posi­tion is determined, then the silicon-iron
shielding is added to assure hum-free
performance. Thanks to these extra de­tails, the transformer can be built into the
M-1 or M-2 chassis. No separate chassis
and umbilical cord to deal with.

Toroidal power transformers inherently
have lower stray magnetic fields than

conventional EI-core transformers. They
are also smaller and lighter. They are
also much more expensive!

Universal Power Supply. An internal
switch provides six primary voltage
choices: 100, 120, 140, 200, 220 and 240
volts. The power cord is detachable, with
a line filter included in the input connec­tor. These features allow the preamps to
be easily adapted for use anywhere in the
world. The supply accommodates
over/under voltage situations easily.

Chassis Ground Isolation Switch allows
the chassis ground to be isolated from
the signal ground, or tied to it. This can
be helpful in eliminating ground loops in
certain situations. This mini-toggle
switch is on the rear panel.

Built to Order, the way YOU want it. Start
with only one basic channel if you wish.
Additional channels, meters and output
transformers can be easily field-installed.
The mainframe is ready for all four
channels, with blank panels provided for
unused channels. Have it your way!

VU-1 Meter Card is a very accurate and in­formative meter that directly monitors the
output level of the MPC-1 mic preamp
card. There is no need to monitor the input
level of the MPC-1 because the output will
clip before the input transformer saturates.

The VU-1 provides a 20 segment LED bar­graph display and separate "peak" LED (la­beled “PK” on the front panel) to indicate
extremely high signal levels. An LED-illu­minated front panel switch (green LED)
gives a choice of “Peak” or “VU” meter
ballistics. The “Peak” ballistic provides a
fast attack time for the bargraph so that
transients are fully indicated. The “VU”
ballistic provides a slower attack time, sim­ilar to a standard mechanical VU meter.
The meter scale accurately covers -28 to
+10dB in linear steps of 2dB (15 yellow
LEDs, 5 red LEDs). Easy calibration of the
meter's 0VU operating level is accom­plished by moving an internal plug-in
jumper to one of four positions: 0dBu,
+4dBu, +8dBu or Adjustable (the ad­justable position covers -10 to +12dBu via
a 25-turn trim pot). Standard setting is
“+4” (0VU on the meter scale equals a
+4dBu output level).

The firing point of the separate peak (PK)
LED is calibrated via a 25-turn trim pot for
output levels of 0 to +22dBu. The standard

Options

setting of +22dBu provides at least 2dB of
warning prior to clipping. Jumpers are pro­vided to choose BAR mode (cumulative
LEDs) or DOT mode (one LED at a time)
for the display.

Circuitry includes a full-wave rectifier,
peak detector, Peak and VU ballistics, and
a temperature compensated log/linear con­verter. The circuitry is DC coupled and
uses high-speed, precision op-amps with
extremely low DC offset voltage and drift
(better op-amps than you find in the signal
path of many consoles!). All of these fea­tures guarantee accurate performance over
a wide temperature range, and for years to
come. On-card voltage regulation for the
op-amp power supplies, and isolated
grounding for the 5 volt LED power supply
assure that the VU-1 will not interfere with
the mic preamp circuitry.

PK-1 Meter Card provides a peak LED func­tion only. It uses the same full-wave rectifi­er, peak detector, 25-turn trim pot for firing
point calibration, on-card voltage regula­tion and isolated grounding for the 5 volt
LED power supply that is used on the VU­1 card.

JT-11-BMQ Output Transformer is the best
Jensen line-output transformer. It compli­ments the outstanding line driving capabili-

ty of the 990 by providing a balanced,
floating, isolated output. Ground loop
problems are eliminated because the signal
is coupled magnetically rather than direct­ly, something that transformerless circuits
cannot do. Your application may not re­quire an output transformer, but if you need
one, the JT-11-BMQ is the best.

PIN 2 or PIN 3 HIGH? There are two polarity
standards in use today for XLR connectors.
The official IEC, SMPTE and AES stan­dards state that pin 2 is high (relative to pin

3), while the unofficial standard states that
pin 3 is high (relative to pin 2). The M-1
and M-2 make it very easy to deal with
this. A pair of plug-in jumpers is located
next to each XLR, allowing you to quickly
change from “PIN 2 HIGH” to “PIN 3
HIGH”, or vice-versa. It is very important
to verify the polarity of the equipment that
will be used with the mic preamp, and to
maintain correct polarity when connecting
the mic preamp. Possible problems range
from an audible change due to an inadver­tent reversal of polarity, to slight degrada­tion of the signal if a transformer-coupled
output is driving an unbalanced input of
the opposite polarity, to possible damage to
the 990 in a direct-output configuration
driving an unbalanced input of the opposite
polarity (driving a short-circuit!). Please
specify PIN 2 HIGH or PIN 3 HIGH!

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