Operating Manual
Mark Levinson®
Nº25
Dual Monaural
Phono Preamplifier
Madrigal Audio Laboratories, Inc.
1
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK,
DO NOT EXPOSE THIS APPLIANCE TO RAIN OR MOISTURE.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
CAUTION: TO REDUCE THE RISK OF ELECTRICAL SHOCK,
DO NOT REMOVE COVER. NO USER-SERVICEABLE PARTS
INSIDE. REFER SERVICING TO QUALIFIED PERSONNEL.
The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to alert the
user to the presence of uninsulated “dangerous voltage” within the product’s enclosure that may
be of sufficient magnitude to constitute a risk of electric shock to persons.
The exclamation point within an equilateral triangle is intended to alert the user to the presence of
important operating and maintenance (servicing) instructions in the literature accompanying the
appliance.
2
Important safety instructions
Please read all instructions and precautions carefully and completely before operating your Nº 25
Dual Monaural Phono Preamplifier.
1. ALWAYS disconnect your entire system from the AC mains before connecting or disconnecting
any cables, or when cleaning any component.
2. This product is equipped with a three-conductor AC mains power cord which includes an earth
ground connection. To prevent shock hazard, all three connections must ALWAYS be used. If
your electrical outlets will not accept this type of plug, an adapter may be purchased. If an
adapter is necessary, be sure it is an approved type and is used properly, supplying an earth
ground. If you are not sure of the integrity of your home electrical system, contact a licensed
electrician for assistance.
3. AC extension cords are not recommended for use with this product. If an extension cord must
be used, be sure it is an approved type and has sufficient current-carrying capacity to power
this product.
4. NEVER use flammable or combustible chemicals for cleaning audio components.
5. NEVER operate this product with any covers removed.
6. NEVER wet the inside of this product with any liquid.
7. NEVER pour or spill liquids directly onto this unit.
8. NEVER block air flow through ventilation slots or heatsinks.
9. NEVER bypass any fuse.
10. NEVER replace any fuse with a value or type other than those specified.
11. NEVER attempt to repair this product. If a problem occurs, contact your Mark Levinson® retailer.
12. NEVER expose this product to extremely high or low temperatures.
13. NEVER operate this product in an explosive atmosphere.
14. ALWAYS keep electrical equipment out of the reach of children.
3
From all of us at Madrigal Audio Laboratories, thank you for choosing the Mark Levinson® Nº25 Dual
Monaural Phono Preamplifier.
A great deal of effort went into the design and construction of this precision device. Used properly, it
will give you many years of enjoyment.
4
Table of contents
Rear panel ................................................................................................... 7
Unpacking and placement ....................................................................... 8
Unpacking .............................................................................................. 8
Placement ............................................................................................. 8
Ventilation .............................................................................................. 8
Voltage selection ........................................................................................ 9
PLS-226 bottom-panel label .......................................................... 9
Set-up and installation .............................................................................. 10
Connectors and cables ..................................................................... 10
Internal adjustments: phono gain ..................................................... 10
Phono gain settings (high-gain option) ..................................... 10
Phono gain settings (low-gain option) ....................................... 10
Internal adjustments: cartridge loading ........................................... 11
Cartridge loading settings (high-gain option) .......................... 11
Cartridge loading settings (low-gain option) ............................ 11
Internal adjustments: optional load terminals ................................. 11
Terminating the optional load .................................................... 11
Internal adjustments: varying the input capacitance .................... 12
Internal adjustments: varying the ground impedance .................. 12
Output ground impedance settings .......................................... 12
Making the internal adjustments ....................................................... 13
Nº25, internal adjustments ........................................................... 13
Power connection and system activation ....................................... 14
AC power cord polarity ............................................................... 14
Care and maintenance ........................................................................... 15
Specifications ............................................................................................ 16
Dimensions ................................................................................................. 17
Dimensions, Nº25, top view .......................................................... 17
Dimensions, Nº25, side view ......................................................... 17
Dimensions, PLS-226, top view ..................................................... 17
Dimensions, PLS-226, side view .................................................... 17
5
6
DUAL MONAURAL
PHONO
PREAMPLIFIER
Nº 25
POWER
SUPPLY
INPUT
S/N:
RIGHT CHANNEL
OUT
1
DESIGNED AND MANUFACTURED
IN U.S.A. BY
MADRIGAL
AUDIO LABORATORIES INC.
IN
LEFT CHANNEL
OUT
2
IN
2
3
4
3
Rear panel
PRECAUTION
Disconnect all associated equipment from the AC mains BEFORE
making signal connections and applying power to the Nº25/PLS-226.
1
POWER SUPPLY INPUT
This nine-pin connector accepts one end of the DC cable that
connects the Nº25 to the PLS-226 Power Supply.
2
OUT
Connect these outputs to any of your preamplifier's line-level
inputs.
PRECAUTION
NEVER connect the Nº25's outputs to your preamplifier's
PHONO inputs. The output of the Nº25 is at line level, and is
equalized per the RIAA standard.
3
IN
Connect your turntable's right-channel and left-channel signal
leads to these inputs.
4
Ground binding post
Connect your turntable's tonearm ground lead to this binding post.
7
Unpacking and placement
Unpacking
Unpack your Nº25 Dual Monaural Phono Preamplifier and PLS-226
Power Supply, and remove all accessories from the cartons. Keep all
packing materials for future transport.
Carefully inspect the product for damage and flaws. If you find any,
see your Mark Levinson retailer immediately.
Placement
To keep the cable between the tonearm and the Nº25 as short as
possible, place your Nº25 as close to the turntable as practical. This is
particularly important considering the extremely low signal levels
produced by a phono cartridge.
A two-meter-long DC cable is provided to connect the PLS-226 to the
Nº25. This allows you to place the PLS-226 so that it won't induce hum
in the Nº25 and other sensitive components. You should also place
other associated equipment so that it doesn't induce hum in the Nº25
and other components.
Ventilation
You may place the Nº25 on a shelf or in a cabinet where it's
convenient to operate. Be sure to allow 3 to 4 inches of clearance
above the unit to allow heat dissipation through air circulation.
Drawings are included in this manual to facilitate special installations
and custom cabinetry (see "Dimensions").
PRECAUTION
8
For your protection, review "Important safety instructions" before you
install your Nº25.
Voltage selection
The PLS-226 is factory-set (internally) for 100V, 120V, 200V, 220V or 240V
AC mains operation @ 50 or 60Hz. Make sure that the label on the
bottom of the PLS-226 indicates the correct AC operating voltage for
your location.
PLS-226 bottom-panel
label
PLS-226 POWER SUPPLY
DC OUTPUTS
AC INPUT
WARNING: BEFORE ATTEMPTING TO
Voltage
indication
OPERATE THIS DEVICE, REFER TO
OWNER'S MANUAL FOR PROPER
OPERATING INSTRUCTIONS AND SAFETY
PRECAUTIONS. HAZARDOUS VOLTAGE
AVAILABLE INSIDE; DISCONNECT AC~
MAINS CABLE BEFORE REMOVING COVER.
OPERATING VOLTAGE:
90 – 110VAC~
210 – 240VAC~
105 – 125VAC~
230 – 250VAC~
~50 – 60HZ
180 – 220VAC~
100 – 120VAC~
MAINS 2A SLO–BLO 250VAC 3AB
FUSES: 200 – 240VAC~
1A SLO–BLO 250VAC 3AB
SERIAL NO.
DESIGNED AND MANUFACTURED IN U.S.A. BY
MADRIGAL AUDIO LABORATORIES INC.
If the voltage indicated is incorrect, see your Mark Levinson dealer.
If you wish to change the AC operating voltage of the Nº25/PLS-226,
see your Mark Levinson dealer.
The Nº25/PLS-226 can be powered by a normal 15-ampere AC mains
line. If other devices are also powered from the same AC line, their
additional power consumption must be taken into account.
9
Set-up and installation
Connectors and cables
The Nº25 incorporates RCA-type connectors for audio signal input and
output.
The Madrigal-designed RCA-type connectors used for single-ended
audio interconnection are a great improvement over ordinary RCAtype connectors.
When connecting the Nº25 to your turntable and preamplifier, we
recommend Madrigal Audio Laboratories HPC Interconnect Cable.
HPC is available in various lengths, terminated with RCA, XLR, and
Camac connectors. See your Mark Levinson dealer for more
information.
Internal adjustments:
phono gain
The Nº25 is available with either a high-gain or low-gain phono option.
Each option offers two internally adjustable gain settings via two twopole miniature rocker switches, one for each channel. The high-gain
and low-gain phono options have been factory-adjusted at the lowest
gain settings (58dB and 38dB, respectively).
If you wish to increase the gain, see "Making the internal adjustments;"
refer to the tables below for the proper switch positions for each gain
setting.
Phono gain settings
(high-gain option)
Phono gain settings
(low-gain option)
10
Switch
#1
#2
On
Off
Off
On
Gain
58dB
64dB
Nominal Cartridge Output (3.54 cm/sec)
.2mV - .6mV
.2mV and Lower
Switch
#1
#2
On
Off
Off
On
Gain
38dB
44dB
Nominal Cartridge Output (3.54 cm/sec)
Greater than 2.0mV
2.0mV and Lower
Internal adjustments:
cartridge loading
The high-gain and low-gain phono options offer internally selectable
cartridge loading via two four-pole miniature rocker switches, one for
each channel. The high-gain and low-gain options have been factoryadjusted at 825Ω and 47KΩ, respectively.
If you wish to change the factory-adjusted cartridge loading, see
"Making the internal adjustments;" refer to the table below for the
proper switch positions for each load setting.
Cartridge loading settings
(high-gain option)
Cartridge loading settings
(low-gain option)
Internal adjustments:
optional load terminals
Terminating the
optional load
Switch
#1
#2
#3
#4
30Ω
Off
Off
On
Off
100Ω
Off
On
Off
Off
825Ω
On
Off
Off
Off
10KΩ
Off
Off
Off
Off
Optional
Off
Off
Off
On
Switch
#1
#2
#3
#4
825Ω
Off
Off
On
Off
10KΩ
Off
On
Off
Off
22KΩ
On
Off
Off
Off
47KΩ
Off
Off
Off
Off
Optional
Off
Off
Off
On
Resistance values other than those listed above can be
accommodated via the optional load terminals. Load resistors can be
inserted into these terminals, allowing virtually any load desired.
Solder
Optional load
component
Solder
PC board
See "Making the internal adjustments;" refer to the "Cartridge loading
settings" tables for the proper switch positions for the optional load.
Because the inherent input resistance (all switches off) is in parallel with
the optional load terminals, use this formula to calculate the actual
resistor needed:
R = 1/ (1/RD - X)
RD = Desired resistance in ohms
X = 0.00002 for Low-gain Phono Option,
0.0001 for High-gain Phono Option
Note: We recommend precision metal-film resistors; see your
Mark Levinson dealer.
11
Internal adjustments:
varying the input
capacitance
If you wish to vary the input capacitance of the phono option to
obtain the optimal value for a particular cartridge, a capacitor may
also be inserted into the optional load terminals (see "Terminating the
optional load" and "Making the internal adjustments").
Because the inherent input capacitance (all switches off) is in parallel
with the optional load terminals, use the following formula to calculate
the actual capacitor needed.
C = CR - CT - CP
C = The capacitor value
CR = Recommended capacitance value
CT = Tonearm capacitance including leads
CP = Preamplifier inherent shunt capacitance
(Low-gain phono option - 100pf; high-gain phono option - 1000pf)
Note: We recommend high-quality polypropylene, polystyrene
or Teflon capacitors; see your Mark Levinson dealer.
Internal adjustments:
varying the ground
impedance
The Nº25 offers internally selectable ground impedance via two twopole miniature rocker switches, one for each channel. These switches
have been factory-adjusted to 0Ω.
If you encounter a phono hum problem caused by a ground loop
when connecting the Nº25 to your preamplifier, changing the factoryset output ground impedance may alleviate the problem. see
"Making the internal adjustments;" refer to the table below for the
proper switch positions for each impedance setting.
Output ground
impedance settings
12
Switch
#1
#2
Off
Off
On
On
Output Ground Impedance
1Ω
0Ω
Making the internal
adjustments
1. Make sure all associated equipment is disconnected from the AC
mains, and that the PLS-226 is disconnected from the AC mains.
2. Using a 3/32" Allen key, remove the eight 4-40 socket-head cap
screws securing the end caps on the rear of the Nº25's chassis.
3. USing a Phillips screwdriver, remove the four 4-40 screws securing
the Nº25's top plate. Carefully slide the top plate to the rear and
remove it.
1
2
3
4
OFF
Nº25, internal adjustments
Output ground
impedance
(right channel)
Optional
load pins
Cartridge loading
(right channel)
Phono gain
(right channel)
Optional
load pins
Cartridge loading
(left channel)
Phono gain
(left channel)
Output ground
impedance
(left channel)
O 1
N
2
O
F
F
4. Adjust the gain switches (using a ballpoint pen or similar
instrument) and install optional loads as desired.
5. Reassemble the Nº25.
13
Power connection and
system activation
Be sure all associated equipment is disconnected from the AC mains.
After making all signal connections and internal adjustments, connect
the DC cable to either of the nine-pin female connectors on the rear
panel of the PLS-226. Connect the other end of the DC cable to the
nine-pin connector on the rear panel of the Nº25.
Connect the AC cord to the male IEC connector on the rear panel of
the PLS-226, then connect the AC cord to the AC mains.
To PLS-226
To AC mains
AC power cord polarity
1
2
3
2
1
1 = Line (hot)
2 = Neutral
3 = Earth ground
3
The LEDs on the PLS-226 and Nº25 will light. Allow the preamplifier
circuitry to stabilize for 1 to 2 minutes, then connect all associated
equipment to the AC mains and activate it.
For optimal sonic performance and longevity, the Nº25/PLS-226 is
designed to remain powered at all times (a power-on/power-off
switch is not provided).
14
Care and maintenance
To remove dust from the cabinet of the Nº25, use a feather duster. To
remove dirt and fingerprints, we recommend isopropyl alcohol and a
soft cloth.
15
Specifications
The correlation between published specifications and sonic quality is
unreliable. A list of numbers reveals virtually nothing. All technical
measurements must be subject to qualitative as well as quantitative
interpretation.
Measurements of the Nº25 yield excellent results by any standards.
However, only those specifications that apply to its actual operation
are included here.
■ Power consumption: 20W maximum, depending on options
■ Mains voltage: 100V, 120V, 200V, 220V, 240V AC @ 50-60Hz
■ Overall dimensions: See "Dimensions"
■ Shipping weight: Nº25: 10 lbs. (4.6kg)
PLS-226: 12 lbs. (5.5kg)
■ Connector complement: 4 RCA-type connectors
1 nine-pin connector
1 binding post (turntable ground)
■ Gain: Selectable (see "Set-up and installation")
■ Low-gain phono option: 38dB, 44dB
■ High-gain phono option: 58dB, 64dB
■ Input impedance: Selectable (see "Set-up and installation")
■ Maximum output: 6V
■ Recommended load: 10KΩ or greater
For more information, see your Mark Levinson dealer, or contact:
Madrigal Audio Laboratories, Inc.
2081 South Main Street (Route 17), P.O. Box 781
Middletown, Connecticut 06457 USA
Telephone (203) 346-0896
(FAX (203) 346-1540
If purchased in North America, this Mark Levinson product’s warranty is owner-transferable.
Warranty conditions are valid only in the country where the product was originally purchased.
For warranty information and conditions on products purchased outside of North America,
contact your local dealer or regional distributor.
16
Dimensions
3/8"
(9.5)
7/64"
(2.5)
Dimensions, Nº25, top view
1-1/8"
(26.7)
3/4" dia.
(19.1)
5-5/16"
(134.9)
8-1/2"
(215.9)
6-3/16"
(157.2)
10-1/2"
(266.7)
1"
(25.4)
13-1/8"
(333.4)
1/2"
(12.7)
7/8"
(22.3)
7/64"
(2.5)
Dimensions, Nº25, side view
2-9/16"
(65.1)
2-3/4"
(69.9)
7/16"
(11.1)
1-21/32"
(42.1)
3/8"
(9.5)
7/64"
(2.5)
Dimensions, PLS-226,
top view
1-1/8"
(26.7)
3/4" dia.
(19.1)
7-13/32"
(187.9)
7-39/64"
(193.0)
5-9/64"
(130.6)
1-1/4"
(31.8)
10-1/2"
(266.7)
13-1/8"
(333.4)
Dimensions, PLS-226,
side view
2-35/64"
(64.8)
2-3/4"
(69.9)
7/16"
(11.1)
7/64"
(2.5)
17
MADRIGAL AUDIO LABORATORIES
2081 South Main Street, P.O. Box 781
Middletown, Connecticut 06457 USA
Telephone: (203) 346-0896
Fax: (203) 346-1540
®
is a registered trademark of Madrigal Audio Laboratories, Inc.
18
630034-1
©1993 Madrigal Audio Laboratories, Inc. All rights reserved.
Printed in U.S.A.
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