Herron Audio HL-1 User manual

Vacuum Tube
Stereo Preamplifier
HL-1
HL-1
Owner’s Manual
Solid-State
Stereo Preamplifier

Table of Contents
Introduction 1
Features 2
Design Considerations 5
Front Panel Features 6
Remote Control 8
Rear Panel Features 9
Installation and Operation 11
Technical Specifications 13
Herron Audio Solid State Stereo Preamplifier Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
Welcome!
Welcome!
Thank you for your investment in the Herron Audio HL-1 Solid State Stereo
Preamplifier, a milestone in high-precision audio playback equipment. The
HL-1 is a new design, benefiting from insights gained during continuous
refinement of the highly-praised and award-winning VTSP-1A vacuum tube
preamplifier. The HL-1 employs the latest advancements in semiconductor
technology incorporated in a way that produces totally natural and trans-
parent sound.
The care in engineering and manufacturing of this product anticipates a
lifetime of musical enjoyment. Years of research into circuit design and
component performance were applied to the development of the HL-1, and
new implementations of components have led to a breakthrough in perfor-
mance while maintaining conservative operation. As with all Herron Audio
products, the HL-1 is engineered to be reliable and user friendly.
Manufacturing of the HL-1 is performed under the tightest of quality
controls. Its limited production permits hand matching of components to
the most exacting standards in the industry. The units are burned in, bench
tested, and matched to extremely tight tolerances to ensure unprecedented
performance and lack of unit-to-unit variation.
one
©2004 Herron Audio
Division of Herron Engineering, Inc.
12685 Dorsett Road
# 138
Maryland Heights, MO 63043 (St. Louis area)
314.434.5416
314.434.6629 fax
www.herronaudio.com

The HL-1 incorporates an infrared
remote control for convenient opera-
tion of many of the preamplifier’s
front-panel functions. This remote
uses 38kHz modulation and detec-
tion of this signal initiates the HL-1’s
decoder circuitry, which is otherwise
dormant in order to prevent the
unwanted noise usually associated
with remote control circuitry. A flash-
ing red light in the display window
indicates the initiation of the remote
control decoding process in the HL-1.
When the red light is off, this cir-
cuitry goes to “sleep” mode.
The HL-1 utilizes two extremely
low distortion precision electronic
stepped attenuators (one for each
channel) in a fashion similar to the
VTSP-1A/166, with downshifting
starting at step 40 (a slight pause may
be detected as the unit changes
modes between steps 39 and 40). The
HL-1 has a total of 100 volume steps,
and the precise volume level is shown
as three digits in the front-panel dis-
play window. The use of electronic
stepped attenuators ensures contin-
ued high-quality performance
without any of the oxidation and cor-
Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
rosion that degrades conventional
mechanical stepped attenuators and
volume control potentiometer wiper
contacts.
At startup, the display on the HL-1
goes through a lamp test, and then
successively displays the model of
the unit “HL1,” phono stage option
“PH1” (if present), the revision of the
unit, “r01,” and the time in seconds
from 30 until the unit automatically
unmutes. The input display will
show the last input in use from the
last time the unit was on. When the
countdown is complete, the mute
will be disengaged (if it was not on
the last time the unit was shut
down), the function displays will
indicate the last state of use, and the
volume will be ramped up to a rela-
tively low level of 10. At this point
the user will be able to change the
settings.
The HL-1 incorporates circuitry to
switch the phase of the audio signal
by 180 degrees for absolute polarity
control. The amber “Invert” light
on the front panel will indicate if the
phase is being inverted. The phase
switching circuitry of the HL-1 is
designed so that no coloration is
added in either mode, and the true
effects of recorded phase polarity are
audible in either mode. The invert
mode can be controlled from both
the front panel and the remote
control.
NOTE: When the invert mode of
the HL-1 is switched, the unit auto-
matically mutes before changing
modes in order to prevent any
unwanted “pops” during switching.
The unit unmutes after the invert
mode is changed. The process takes
0.5 seconds.
The display brightness of the HL-1
can be dimmed from both the remote
and the front panel by pushing the
“Display” button. Operating the
“Display” button again will return the
brightness to its previous setting. The
blue “Display” indicator on the front
panel indicates dim-display mode.
Source input selection in the HL-1
incorporates gold-contact sealed relays
located at the input connectors, keep-
ing the signal path length to an
absolute minimum. This innovative
configuration eliminates the
distortion-generating wipers of con-
ventional selectors and long runs of
wire from the rear panel to the switch.
An additional benefit of using sealed
relays, the contacts are not prone to
corrosion, dirt, or the same kind of
wear as conventional selector
switches.
The HL-1 has a power-polarity
switch on the back panel for reversing
the power line polarity connection to
the primary of the power transformer.
This can be used to minimize the
capacitive reactance effects from the
power line on the audio circuitry of the
unit. This switch can be operated while
listening in order to determine the
best-sounding power polarity setting.
The “Video” input of the HL-1
can be placed in unity-gain mode by
pressing and holding the “Video” but-
ton on the front panel for a few
seconds. The volume display will indi-
cate “PAS” on the display when the
pass-through mode is initiated; only
the video input will be at unity gain.
Selecting any other input will shut off
the pass-through mode, and the vol-
ume will return to 10.
NOTE: The pass-through mode
cannot be selected from the
remote control.
All of the front panel display
lamps are driven from individual dis-
play latches for each element and are
Features
Features
two three
Herron Audio Solid State Stereo Preamplifier

not multiplexed or flashed at high
speed, as is usually done to save parts
and cost. The continuous lighting of
each selected element of the display
of the HL-1 prevents the electrical
noise that would be generated by
sequenced displays.
The HL-1 has an instant shutdown
circuit that mutes the output upon
loss of full line voltage (power loss).
This feature provides protection from
loud “pops” or noises from input
Herron Audio Solid State Stereo Preamplifier Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
equipment that may damage speakers.
With a power loss of more than a few
seconds, the unit will totally shut
down, and go through the full start-
up sequence when power is restored.
If the power outage is brief, the unit
will mute and wait 10 to 15 seconds
to unmute when the power is
restored. This delay will allow DC sig-
nals from input components enough
time to normalize so that loud “pops”
will be minimized.
• Multifunction remote control
• Volume level display (0 - 100)
• Unity gain pass-through function—initiated by holding video button
• Optional phono stage with switchable MM/MC modes
• Non-multiplexed display, eliminating radio and audio interference
• Switchable absolute polarity
• 100-step electronic volume control system with precision tracking and low
distortion
• Full-range, infinite-resolution indirect signal path balance control
• Stereo/mono switch
• Mute control
• Display brightness control
• Tape out/in loop
• Low noise design
• High input-signal capacity without overload
• Automatic muting at startup and shutdown
• Gold plated, Teflon-insulated RCA connectors
• Handpicked components for accurate response and consistent unit-to-unit
quality
• Reversing power line (AC) polarity switch for minimizing line-to-chassis
reactive currents and noise pickup
• Each unit is given an extensive burn-in, including rigorous bench and
listening tests
Design Considerations
Design Considerations
fivefour

Three-digit volume level display in the
display window at the center of the
front panel indicates the volume level
(0 to 100) and the parameters of the
unit during start-up. It also indicates
“PAS” during pass-through mode and
the gain state of the optional phono
stage “coil” (moving coil) or “MM”
(moving magnet) if present.
The selected input is indicated by
the blue lights on the left side of the
front panel.
These inputs are:
• Phono
• Aux
• CD
• Tuner
• Video
Units with the optional phono stage:
The MM/MC mode can be changed by
holding the phono button on the front
panel in for a few seconds. The unit will
mute and the display will show the mode
that has been selected for 10 seconds and
then count down for 20 seconds before
un-muting. The MM/MC mode cannot be
changed from the remote control.
Herron Audio Solid State Stereo Preamplifier Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
The tape input (loop) indicator is
on the right side of the front panel.
These inputs can be selected from
either the front panel or the remote
control after the unit has gone
through the start-up sequence.
The balance control provides a
full range of adjustment for relative
balance between the right and left
channels. In the centered position,
each channel is equal in signal sen-
sitivity. Rotating the balance
control in the clockwise direction
(to the right) decreases the volume
in the left channel relative to the
right channel. Rotating the balance
control in a counter-clockwise
direction (to the left) decreases the
volume in the right channel relative
to the left. In the fully clockwise or
counter-clockwise position, the left
or right channel respectively will be
muted. Normal operation is pro-
vided when the balance control is
in the centered position. The “Bal-
ance” knob operates an infinitely
variable control that is barely in the
circuit at center position.
NOTE: The balance control can-
not be operated from the remote.
The “Volume” knob operates a
stepped encoder. Rotating the volume
knob to the right increases the vol-
ume level, or to the left to decrease
the volume level. The level is dis-
played from 0 to 100 in the display
window. The volume can also be con-
trolled from the remote control.
NOTE: Since the volume control is
a stepped attenuator the individual
steps of the volume control as it is
raised or lowered may produce “clicks”
for a short period after the unit, or
input device has been turned on. This
will be most noticeable between steps
39 and 40. These “clicks” are the result
of a D.C. voltage at the input of the
unit causing instantaneous D.C. level
shifts as the volume control steps up
or down. This condition will usually
subside after a few minutes as the D.C.
level at the input from the source
component dissipates.
The red “Mute” light indi-
cates that the preamplifier is in
mute mode and no signal will pass
through the unit. During mute, the
stepped attenuators are set to zero
level and the output is shorted by a
relay. The mute mode can be initi-
ated or disengaged from the front
panel or the remote control.
The orange “Mono” light indi-
cates that the preamplifier is in
monaural mode. In mono mode, the
unit mixes the left and right signals to
monaural so that the signals coming
from the left and right channels are
the same. Mono mode can be initiated
or disengaged from the front panel or
the remote control.
The amber “Invert” light indi-
cates that the preamplifier is in
phase-inverting mode. The invert
mode reverses the absolute phase of
both channels. The invert mode can
be initiated or disengaged from the
front panel or the remote control.
The amber “Tape” light indi-
cates that the tape input has been
selected. The tape input allows the
user to loop the selected input
(source) signal out from the tape out-
put through a tape machine or other
processor, and listen to the signal
coming back into the tape input. The
tape input mode can be initiated or
disengaged from the front panel or
the remote control.
The blue “Display” light indi-
cates that the front panel displays are
in dim mode. The display mode can
be initiated or disengaged from the
front panel or the remote control.
Front Panel Features
Front Panel Features
six seven

Remote control functions:
• Input Selection
• Absolute Polarity
• Display Brightness
• Volume, Mute, and Mono/Stereo
The remote control is laid out in a
fashion similar to the front panel of
the HL-1.
The input controls are on the left
side (top to bottom) in the following
order:
• Phono
• Aux
• CD
• Tuner
• Video
The volume is controlled with the
two white buttons at the top center of
the remote. The Vbutton on the
left decreases the volume. The V
button on the right increases the
volume.
The controls on the right side of
the remote (top to bottom) are in the
same order as the front panel:
• Mute
• Mono
• Invert
• Tape
• Display
Herron Audio Solid State Stereo Preamplifier Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
NOTE: The balance control can-
not be operated from the remote
control.
The remote control will only con-
trol the unit if the top of the remote is
pointed toward the display window of
the HL-1. The remote control uses 2
CR2025 3-volt lithium batteries.
The rear panel was designed for flexi-
bility and ease of access to
less-frequently used functions. The
high-precision RCA input jacks are
gold-plated to minimize signal-
degrading corrosion. The special
Teflon insulation material in the
RCA connectors maintains purity of
the signal from the input cable into
the unit.
Power Connection
An IEC power cord connector is
provided for attaching either the
factory-provided power cord or
another chosen by the user.
Power Switch
When the unit’s POWER switch is
placed in the on (“1”) position, the
unit is powered up. At power up, the
unit is automatically muted until full
operational capabilities are reached
and the voltages are stable at the
tubes. When switch is moved to the
off position, the unit is automatically
muted and powered down.
Power Line Polarity Switch
This switch selects the power-line
polarity. AC line polarity may affect
performance. The following is the rec-
ommended procedure for determining
the best operation:
• With the mute engaged set the
power line polarity switch to the
"A" position then disengage the
mute.
• Set the volume control to the
desired level and listen closely to
the quality of the reproduction.
This will be used as a baseline for
determining AC polarity.
• Engage the mute function and
change the AC polarity of the
preamplifier by switching the
Rear Panel Features
Rear Panel Features
NOTE: the indicator on
the batteries must be fac-
ing the back side of the
remote. Installing the
batteries in the wrong
direction may damage the
remote control.
eight nine
The Remote Control
The Remote Control

power line polarity switch to the
"B" position then disengage the
mute for listening. Repeat the
process, listening to the same
source.
• Place the AC polarity switch in
the position that sounds best. It
may be necessary to change the
AC polarity if you make other
equipment or power connection
changes in your audio system.
Note: The AC polarity switch should
only be operated with the unit muted
Inputs
The inputs are grouped by channel:
the upper bank contains the left-
channel inputs, the lower contains
the right-channel inputs. The
left/right input pairs are arranged ver-
tically. The input pairs are arranged
on the back in the same order as on
the front panel and remote (with the
exception of the tape loop input).
Herron Audio Solid State Stereo Preamplifier Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
RCA input plugs should be inserted
firmly into the input jacks while the
unit is powered down. Any individual
ground-bleed connections should be
connected to the gold ground lug
located near the end of the banks of
input jacks.
Outputs
There are two types of outputs in the
HL-1. The main outputs are intended
for connection to high-quality power
amplifiers or a multi-channel elec-
tronic crossover. Two pairs of main
outputs are provided so that users
may distribute the audio signal to
multiple amplifiers.
The tape outputs are provided to
allow monitoring of the selected
audio signal after the input relays.
The signal from the tape output corre-
sponds to the input chosen by the
user and displayed on the front panel.
Operation of the Herron HL-1 stereo
preamplifier is straightforward. As
with any fine audio component, care-
ful setup and integration into one’s
system is important for optimum per-
formance, safety, and reliability. Please
read through the following setup
instructions completely prior to oper-
ating the unit.
Procedure
1. Position the unit in a well-
ventilated area on a firm,
stable surface, away from
equipment that generates
alternating magnetic fields
such as motors, transformers,
etc. Magnetic fields of this
type can introduce hum into
the signal path.
Good ventilation is
important in order to
prevent overheating of
the unit. Excess heat will
shorten the life of the
unit.
2. Connect the signal cables
from the source components
(CD, turntable, VCR, tuner,
etc.) to the HL-1’s rear panel
jacks, left-to-left and right-to-
right. Connect any ground
bleed wires to the ground con-
nector of the turntable.
3. Plug the amplifier and tape
recorder input cables into the
corresponding outputs, left-to-
left and right-to-right.
4. Plug the power cord into the
IEC socket. Make sure it is
firmly seated prior to inserting
the plug into an AC outlet.
5. Plug the power cord into a
115-volt (U.S. spec units)
AC outlet.
6. Power up the source
components.
7. Power up the HL-1 by switch-
ing on the power switch.
8. Once the HL-1 is powered
up and operating, power up
the downstream amplifier(s)
and crossover, if any, as
recommended by their
manufacturers.
9. With the Volume control in the
lowest position, gradually
increase the gain until the
desired level is reached.
10. When the listening session is
complete, it is suggested, but
not required, that the HL-1 be
Installation and Operation
Installation and Operation
eleventen

Frequency response: 1 Hz to beyond 100 kHz,
20 Hz to 20 kHz +/- 0.1 dB
Output Impedance: 250 ohms nominal at 1 kHz (predominantly
complex/imaginary-passive)
Input impedance: 100,000 Ohms
Gain: 14 db
Volume Control: 100-position electronic stepped attenuator,
maximum differential 0.1 dB channel to
channel
Absolute Polarity: Switchable
Front Panel: Available in black or clear anodized
aluminum
Dimensions: 18” wide x 3.5” high x 10.5” deep
Optional Phono Stage:
Gain: MM 44dB, MC 64dB
Input Impedance: MM 47K Ohms, MC 47K Ohms
Warranty: 3 years, parts and labor
Owner’s Manual
Please read the Owner’s Manual completely BEFORE operating the unit.
Technical Specifications
Technical Specifications
powered down after the
crossover, amplifiers, and tape
recorder, and before the source
components.
Power Requirements
It is recommended that the HL-1
stereo preamplifier be connected to
the same power source (dedicated cir-
cuit) as the other source components
(phono stage, turntable, CD player,
SACD player, etc.) and power ampli-
fiers in the audio system. This will
reduce the component-to-component
differential RFI (radio frequency inter-
ference) level that will be required to
be conducted by the audio intercon-
nects, which are a very important part
of the audio chain. RFI can add
brightness and lack of clarity to an
audio system.
With the higher definition and
detail available through the HL-1,
Herron Audio Solid State Stereo Preamplifier
careful attention to the setup of other
components will yield significant ben-
efits. There may also be considerable
gains from the upgrade of existing
electronics.
We recommend the use of high-
quality interconnecting cables
between the source components and
the HL-1, and between the HL-1 and
components downstream of it (the
power amplifiers and speakers).
Due to the increased definition of
detail, it may be necessary to make
minor adjustments in speaker position
or active crossover settings to opti-
mize their performance. We have
determined that minor time align-
ment changes in a setup can produce
major advances in the overall quality
of the reproduced signal, bringing the
listener closer to the original
performance.
twelve thirteen