Herron Audio M1A User manual

Owner’s Manual
M1A
Power
Amplifier

M1A Power Amplifier Owners Manual
Table of Contents
General Safety, Installation, 1
and Operation Instructions
Important Safety Instructions 2
Warning 4
Important (UK only) Instructions 5
The Amplifier 6
Front Panel Features 7
Rear Panel Features 8
Installation 10
Troubleshooting 11
Technical Specifications 12
FCC Notice 13
Re-cycling 14
RoHS Compliance 14
©2013 Herron Audio
Division of Herron Engineering, Inc.
12685 Dorsett Road
# 138
Maryland Heights, MO 63043 (St. Louis area)
314.434.5416
www.herronaudio.com

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
1
General Safety, Installation,
and Operation Instructions
It is important to read this document before attempting to use this product.
Pay close attention to safety instructions.
Appears on the component to indicate the presence of
uninsulated, dangerous voltages inside the enclosure – volt-
ages that may be sufficient to constitute a risk of shock.
Appears on the component to indicate important operation
and maintenance instructions included in the accompany-
ing documentation.
Appears on the component to indicate compliance of with
the EMC (Electromagnetic Compatibility) and LVD (Low-
voltage Directive) standards of the European Community.
WARNING Calls attention to a procedure, practice, condi-
tion, or the like that, if not correctly performed or adhered
to, could result in personal injuries or death.
CAUTION Calls attention to a procedure, practice, condi-
tion, or the like that, if not correctly performed or adhered
to, could result in damage or destruction to part or all of
the component.
Note Calls attention to information that is essential to
highlight.
WARNING
CAUTION
Note

M1A Power Amplifier Owners Manual
2
Important Safety Instructions
1. Read these instructions
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a dry cloth. Great care and attention has gone
into the materials chosen to produce the product. A gentle wipe with
a dry, clean cloth is all that is required to remove any dust. Treat it as
you would a fine piece of furniture because that is how they have been
designed.
7. Do not block ventilation openings. Install in accordance with the
manufacturer’s instructions.
8. Do not install near any heat sources such as radiators, heat regis-
ters, stoves, or another apparatus that produces heat.
9. Do not defeat the safety purpose of the polarized or ground-
ing-type plug. A polarized plug has two blades with one wider than
the other. A grounding-type plug has two blades and a third grounding
prong. The wide blade or third prong is provided for safety. If the pro-
vided plug does not fit into the outlet, consult an electrician for replace-
ment of the obsolete outlet.
10. Protect the power cord from being walked on or pinched,
particularly at plugs, convenience receptacles, or the point where it exits
from the apparatus.
11. Only use attachments and accessories specified by the
manufacturer.

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
3
12. Use only with the cart, stand, tripod, bracket, or table
specified by the manufacturer or sold with the apparatus.
When a cart is used, use caution when moving the cart/
apparatus combination to avoid injury or tip over.
13. Unplug this apparatus during lightning storms or when unused
for long periods of time.
14. Refer all servicing to qualified service personnel. Servicing is re-
quired when the apparatus has been damaged in any way, such as when
the power cord or plug has been damaged; liquid has been spilled or ob-
jects have fallen into the apparatus; or the apparatus has been exposed
to rain or moisture, does not operate normally, or has been dropped.
15. No naked flame sources, such as candles, should be placed on the
apparatus.
16. The appliance coupler is used as the disconnect
device, the disconnect device shall remain readily oper-
able.
17. Terminals marked with this symbol may be considered HAZARDOUS
LIVE and the external wiring connected to these terminals requires in-
stallation by an INSTRUCTED PERSON or the use of ready-made
leads or cords.
18. This exclamation point within an equilateral
triangle is intended to alert the user to the presence of
important maintenance (servicing) instructions in the
literature accompanying the appliance.
Warning! To reduce the risk of fire or electric shock, do not
expose the apparatus to rain or moisture. Do not place objects
containing liquid, such as vases, on this apparatus.

M1A Power Amplifier Owners Manual
4
Warning
• TO PREVENT FIRE OR SHOCK HAZARD, DO NOT USE THIS PLUG WITH
AN EXTENSION CORD, RECEPTACLE OR OTHER OUTLET UNLESS THE
BLADES CAN BE FULLY INSERTED TO PREVENT BLADE EXPOSURE
• TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS
APPLIANCE TO RAIN OR MOISTURE
• TO PREVENT ELECTRIC SHOCK, MATCH WIDE BLADE PLUG TO WIDE
SLOT AND FULLY INSERT
This lightning flash with an arrow head symbol, within
an equilateral triangle, is intended to alert the user to the
presence of un-insulated “dangerous voltage” within the
product’s enclosure that may be of sufficient magnitude
to constitute a risk of electric shock to the persons.
Warning: To reduce the risk of
electric shock, do not remove
cover (or back), no user-service-
able parts inside. Refer servicing
to qualified service personnel.
This exclamation point within an equilateral triangle is
intended to alert the user to presence of important mainte-
nance (servicing) instructions in the literature accompany-
ing the appliance.

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
5
IMPORTANT! (U.K. only)
This unit is supplied in the U.K. with mains lead fitted with a moulded 13
amp plug. If, for any reason, it is necessary to remove the plug, please remove
the fuse holder and dispose of the plug safely, out of reach of children.
It must not be plugged into a mains outlet.
The wires in the mains lead supplied with this appliance are coloured in ac-
cordance with the following code:
Green and yellow..............Earth
Blue................................Neutral
Brown.................................Live
WARNING - This appliance MUST be earthed
As the colours of the wires of the mains lead of this appliance may not cor-
respond with the coloured markings identifying the terminals in the plug,
proceed as follows:
The wire which is coloured green-and-yellow must be connected to the
terminal in the plug which is marked with the letter E or coloured green or
green-and-yellow, or by the earth symbol :
The wire which is coloured brown must be connected to the terminal
which is marked with the letter L or coloured red.
The wire which is coloured blue must be connected to the terminal
which is marked with the letter N or coloured black.
If connecting to a BS1363 plug, a 13 amp fuse must be used.
WARNING:
ANY MODIFICATIONS TO THIS PRODUCT NOT EXPRESSLY
APPROVED BY HERRON AUDIO WHO IS THE PARTY RESPON-
SIBLE FOR STANDARDS COMPLIANCE COULD VOID THE USER'S
AUTHORITY TO OPERATE THIS EQUIPMENT.

M1A Power Amplifier Owners Manual
6
nance free and remains stable even
with a 1 micro-Farad capacitor con-
nected across the output terminals.
The M1A engenders the fine resolu-
tion and liquidity normally associ-
ated with tube amplification plus the
power and bass control of solid state.
Individual voices remain distinct
and clear amidst the crescendo full
orchestra and chorus. The sound
of the M1A is pure and true to the
source.
It has the clarity, focus in time, and
natural sound inherent in all Herron
Audio products.
DC Response
The M1A incorporates automatic
low level d.c. offset cancellation plus
high level d.c. shutdown speaker
protection circuits. The effects of
continuous low level d.c. at the
input of the M1A will be nulled out
over time and higher levels of d.c. at
the input will engage the shutdown
protection.
The Amplifier
The M1A is a full complementary
symmetry bipolar implementation
and contains no coupling capacitors
in the forward direction. It employs
the latest technology in wide band
output devices with enhanced low
level linearity. Proper stage-to-stage
impedance matching insures extraor-
dinarily low distortion and unique
successive stage to output confluence
provides a seamless combination of
micro/nano-resolution from forward
stages and robust controlled power
and authority from successive stages.
This unified current summation
drive stage network eliminates the
crossover notch problems common
in many solid state amplifier designs.
High idle current or class A bias
output stage operation is not neces-
sary! The M1A runs cool under most
listening conditions and provides a
live presentation with none of the
hardness normally associated with
solid state amplifiers. The output
network of this amplifier is reso-
The Amplifier

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
7
The front panel has three indicator
lights for easily monitored opera-
tional readiness of the unit. The first
light is the “power” indicator. This
indicates that power has been turned
on. The “voltage” light indicates
that the amplifier circuitry has been
activated.
Upon shutdown the amplifier is
deactivated at the same instant that
the output relay is opened. This
prevents contact wear and contami-
nation from arcing which is com-
mon in conventional designs. The
approach used in the M1A prolongs
the life and sound quality of the
relay.
A blinking “voltage” light indicates
that there is d.c. present at the input
of the amplifier. The blue “output”
light indicates that the output relay
is engaged and the M1A is ready for
listening. If the M1A is overheated
(78 degrees Centigrade), the “out-
put” light and the “voltage” light
will turn off (amplifier deactivated)
until the heat sink cools 10 degrees
Centigrade. The normal start-up se-
quence of the unit is designed to run
a self check and accelerate the warm
up/break-in process.
Front Panel Features

M1A Power Amplifier Owners Manual
8
Output Terminals
The M1A has two gold-plated
speaker binding post terminals.
These terminals are labeled with the
designation “OUTPUTS” on the rear
panel of the unit.
The polarity is designated with red
and black insulating collars. The red
collar signifies the positive terminal.
The M1A is non inverting. Connec-
tion to the speaker binding post
terminals should only be made while
the unit is powered down.
The rear panel was designed for flexibility and ease of access to less frequent-
ly used functions. The high precision RCA input jack and output connectors
are gold plated to minimize signal degrading corrosion.
Rear Panel Features
Power Connection
An IEC power cord connector is
provided for attaching the Herron
Audio-provided power cord or an-
other chosen by the user.
Power Switch
When placed in the on position, the
unit is powered up. At power up, the
unit goes through a start-up se-
quence and remains muted until the
output light comes on. When the
switch is moved to the off position
the unit is automatically muted and
powered down.

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
9
Heat Sink
The heat sink on the back panel of
the M1A is designed to dissipate heat
generated by the output section of
the amplifier. For best performance
and long life the unit should be used
in a well ventilated area. Excessive
heating may occur under heavy load
conditions in a poorly ventilated
location and could cause the unit to
shut down.
Input Connector
The M1A has one gold-plated RCA
input connector. The RCA input
plugs (interconnect terminations)
should be inserted firmly into the
input jack while the unit is powered
down. It is not recommended that
the unit be powered on without an
input connection.
Connection to the speaker binding
post terminals should only be made
while the unit is powered down.
The RCA input plugs (interconnect
terminations) should be inserted
firmly into the input jack while the
unit is powered down. It is not rec-
ommended that the unit be powered
on without an input connection.

M1A Power Amplifier Owners Manual
10
Recommended Loading
We do not recommend using the
M1A with a 2 ohm load. As with
all audio amplifiers increasing the
load will increase the distortion and
defeat the purpose of having a really
clean amplifier such as the M1A. For
this reason we did not design the
M1A to drive a 2 ohm load to full
power. The over-current trip circuits
will engage under those operating
conditions.
Speaker Cable
Optimum performance from the
M1A will be obtained only with
careful selection of the appropri-
ate cables from the amplifier to the
speakers. Minimum capacitance and
inductance is preferred in order to
avoid over-shoot and ringing in the
cables. Here, simple high quality
cable is of utmost importance.
Installation
Placement
Although the M1A power amplifier
runs relatively cool, it is recom-
mended that these amplifiers are
used in an open area for best opera-
tion and prolonged life.
Each M1A contains an oversized
toroid transformer wound in a con-
figuration designed for minimum
magnetic field radiation. It is recom-
mended, however, that the M1As be
placed at least a few feet away from
sensitive front end equipment such
as a turntable or phono stage.
Power Connection
When possible, connect the same
power outlet used for the preamp,
phono stage, CD player, etc. This
configuration will minimize the
reactive currents from power line RF
that will be impinged on the inter-
connect cables between the audio
equipment in the system.
Zobel networks should not be added to the
speaker cable connections!
The M1A contains three highly tuned neutraliza-
tion networks in the output stage and adding
additional networks will degrade the sound.

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
11
Symptom
1. The output light is on (blue) and there is no sound.
A. Check speaker terminations
B. Check the interconnect terminations at the M1A and at
the preamplifier.
C. Check the source equipment.
2. The power light is on, but the voltage light goes on and off and the
output light does not come on. No Sound.
A. Check input source for d.c. at its output. Note: It is not uncommon
for preamplifiers and other audio source equipment to produce a d.c.
offset for a short period of time after being powered up. This condition
will normally clear up after a few minutes. It is recommended that the
M1As be powered up after the preamplifier, phono stage, CD player,
etc. have been turned on.
3. The amplifier trips off while the output light and voltage light periodically
go out (the sound is interrupted) when listening at high volume.
A. This condition occurs when the internal protection circuits detect
an over-current condition.
4. The amplifier trips off and the output and voltage lights turn off. This
condition indicates that the output section of the amplifier has over-
heated (78 degrees centigrade). Make sure that the unit is adequately
ventilated. The unit will turn back on automatically when the heat sink
has cooled to 68 degrees centigrade.
5. The power light comes on but the voltage light never comes on.
A. The M1A contains two AGC 6 amp internal rail fuses (F2 and F3)
located on the p.c. board for circuit protection. In the unlikely event
of a failure of one or both of these fuses, red indicator lights will be
visible through the vents in the top of the unit.
Troubleshooting

M1A Power Amplifier Owners Manual
12
Technical Specifications
Configuration Single-channel (monaural)
Frequency response 20 to 20kHz +/- 0.1dB
Output Power 150 Watts @ 8 ohms, 275 Watts
@ 4 ohms (measurements at 1 kHz)
Gain 24 dB
Input Impedance 220k Ohms
Absolute Polarity Non-inverting
Power Requirements 100, 120, 230, 240 VAC. 50/60 Hz.
Standard IEC power connector
Toroidal transformer taps internally
selected for appropriate voltage
Main(s) Fuse 120 VAC - MDL5
230 VAC - MDL3
Dimensions 17.6” wide 3 4” high (including rubber
feet) 3 11” deep
Warranty 3 years, parts and labor
Manufactured by Herron Audio Division of Herron Engineering, Inc.
St. Louis, Missouri

M1A Power Amplifier Owners Manual
Please read the Owner’s Manual Completely BEFORE operating the unit
13
FCC Notice
This equipment has been tested and found to comply with the limits
for a Class B digital device, pursuant to Part 15 of the FCC Rules. These
limits are designed to provide reasonable protection against harmful
interference in a residential installation. This equipment generates, uses
and can radiate radio frequency energy and, if not installed and used in
accordance with the instructions, may cause harmful interference to radio
communications. However, there is no guarantee that interference will
not occur in a particular installation. If this equipment does cause harm-
ful interference to radio or television reception, which can be determined
by turning the equipment off and on, the user is encouraged to try to cor-
rect the interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from
that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.
Caution!
Changes or modifications not expressly approved by the party
responsible for compliance could void the user’s authority to
operate the equipment.

M1A Power Amplifier Owners Manual
14
Re-cycling
Correct Disposal of Waste Electrical and Electronic Equipment (WEEE) by
User in Private Households in the EU.
This symbol on the product or accessories indicates that they must not be
disposed of with your household wastes throughout the EU. To prevent pos-
sible harm to the environment or human health from uncontrolled waste
disposal, recycle it responsibly to promote the sustainable
reuse of material resources. Instead it is your responsibil-
ity to dispose of your waste equipment by handing it over
to a designated WEEE collection point for recycling. The
separate collection and recycling of your waste equipment
will help conserve natural resources and ensure that it is
recycled in a manner that protects human health and the
environment.
For more specific information about where you can take your equipment
for recycling please contact your local city/council office, your local waste
disposal service or the outlet where you purchased your RadiusHD product.
RoHS Compliance
Directive 2002/95/EC of the European Parliament and of the Council on the
reduction of the use of certain hazardous substances in electrical and elec-
tronic equipment, January 2003.
Background
The RoHS directive restricts the use of Lead (Pb), Cadmium
(Cd), Mercury (Hg), hexavalent Chromium (CrVI), poly-
brominated biphenyl (PBB) compounds, and polybromi-
nated diphenyl ether (PBDE) compounds in electrical and
electronic equipment sold in the European Union.