PassLabs XONO Owners manual

Pass Laboratories

Xono Owner's Manual

Rev. 2.0 - 03/12/2002

Introduction:

The Xono is a high performance phono preamplifier for use
with moving magnet and moving coil cartridges. It features
extremely low noise and distortion, very high adjustable gain,
very high output swing, variable cartridge loading, and
balanced output.

The Xono uses three stages of circuitry. An ultra-low noise
non-inverting pre-preamplifier circuit is used to boost the low
output of moving coil (MC) cartridges by a selectable 16, 20,
26 or 30 dB without equalization. This drives the primary non­inverting gain stage, which also amplifies the high output of
moving magnet (MM) cartridges, and provides RIAA
equalization. Gain for moving magnet cartridges is a fixed
40dB and may not be adjusted. Output of the primary gain
stage is also applied to an inverting unity gain stage to provide
the negative polarity for the balanced output.

The main gain stage uses low noise matched JFETs for the
input circuit and power MOSFETs elsewhere in the gain path.
Voltage gain devices are operated cascode mode, and the
single-ended circuitry is biased by constant current sources.

The main gain stage uses a combination of active and
passive equalization to achieve the RIAA characteristic. The
active equalization works in the mid-band of the audio range
and the passive equalization determines the characteristic
and the highest and lowest frequencies. This stage has a
fixed gain value of 40 dB at 1 KHz single-ended and 46 dB
balanced.

The pre-preamplifier circuit uses four matched ultra-low noise
JFETs operated in parallel to provide an input random noise
floor less than 500 picovolts (-186 dBV). The cascoded output
of these JFETs drives another JFET to deliver a selectable 16,
20, 26 or 30 dB of un-equalized non-inverting gain. There is
no feedback employed.

Cartridge loading of the Xono is very fexible. Moving Magnet
cartridges can be loaded with capacitance from 0 to 650 pF in
increments of about 100 pF. There is provision for two load
positions for any additional value that the user may choose to
insert. Moving Coil cartridge loading ranges from 5 to 1000
ohms to 47 Kohms using eight switches with binary weighting
and providing 256 different values. The moving magnet
loading default is 47K ohms.

The balanced and unbalanced output connections of the
preamplifier have an output impedance of 300 ohms, which
will drive a 1000 pF cable load flat to about 1 megahertz.

The Xono has a very accurate RIAA equalization
characteristic, varying plus or minus 1/10 of a decibel from 20
to 20 KHz. This accuracy does not vary with gain or loading.

The preamplifier has extremely low noise. The Moving
Magnet noise floor at more than -100 dB below a 10 millivolt
input, which gives it an unweighted total noise of -90 dB. The
Moving Coil noise floor is better than -90 dB referenced to 1
millivolt input, giving a -81 dB unweighted audio band noise
figure.

and reduce the length of connecting wires. Sonically critical
parts have been optimized and upgraded through continued
extensive listening tests.

The Xono like the ono design was based on listening and not
measurements. Considering this, it is perhaps remarkable that
the final product displays such spectacular objective qualities.
However, we view the specifications as a secondary source of
pride in this product.

The measurements only hint at the listening experience with
the Xono. The sound is lush and smooth, with a wide sound
stage, fine detail and spectacular layering, and a nice firm
bottom. The preamplifier will allow you to renew your
acquaintance with your vinyl collection and appreciate the
essential character of the finest analog recordings.

Wayne Colburn

The Xono is adjustable to very high gain, 76 dB @ 1 KHz,
which makes it capable of delivering .5 V line level output for
cartridges with 80 microvolts output. This appears to be the
best figure in the audio industry.

The preamplifier has very low distortion and very high output.
Maximum harmonic distortion is less than .05% (1 KHz) at
outputs of 20 volts RMS. or less. This figure holds for MM
operation and highest gain MC.

The power supply for the Xono is contained in a separate
chassis and consists of an oversized, shielded toroidal power
transformer delivering an unregulated 85 volts peak to peak
DC through separate rectifiers and capacitors for each
channel which is then passively RC filtered before being sent
to the main Xono chassis. A custom manufactured shielded
cable carries the DC power from the supply to the main Xono
chassis. The main chassis of the Xono has separate stages
of active regulation for each channel followed by passive
filtering and then feeding the constant current sources which
bias the various gain stages. There is a total of 120, 000 mfd
of filter capacitance and five stages of filtering and regulation.

Vice President, Design

The Xono is based on the design pioneered in the Aleph
Ono. The basic Ono design has not changed but been
extended and refined. The separate power supply combined
with the additional filtering and dual mono power supply
design contribute to the lower noise floor and sonic
improvements. The main circuit board layout has been
completely revised to reduce noise, shorten the signal path

Setup

The Xono consists of two chassis; powersupply and

preamplifier, linked by a power umbilical.

The preamplifier has two sets of input connections, and two
sets of output connections, and power conection through a
DB-25, D-Sub connector.

The output impedance of the single ended output connection
is 300 ohms. The output impedance of the balanced output
connection is 300/300 ohms. This value is low enough to
drive ten thousand picoFarads (10000 pF) of cable
capacitance flat to 100 KHz.

Selection of input, adjustments for gain and cartridge loading
are accomplished via switches on the interior of the Xono.

The powersupply chassis has an AC line power connection,
fuseholder and two Sub-D connectors. The amplifier's voltage
and current rating are indicated on the rear. It will be either
240 volts, 220 volts 120 volts, or 100 volts. A 0.5 amp 3AG
slow blow fuse is provided with 100-120 volt units, and a 0.25
amp slow blow fuse is provided with 220-240 volt units. The
frequency rating of the power supply is 50 to 60 Hz. The
preamplifier typically draws 20 watts during operation. The
powersupply has twin DB-25 connectors that povide power
and control functions to the preamplifier. This cable must be

installed before the unit is powered up.

The shielded DB-25 cable may be installed into either outlet,
but we suggest the outemost (right side, viewed from the rear)
as it was optimised specifically for the Xono. These cables
are designed to be a snug fit, but must never be forced.

We have provided a standard AC power cord which fits into
the IEC line receptacle at the rear of the powersupply. The
preamplifier is equipped for operation with an earth ground
provided by the AC outlet. Do not defeat this ground. The
chassis and circuit ground of the preamplifier is connected to
earth through a power thermistor, which gives a ground
connection but helps avoid ground loops.

The preamplifier has two sets of input connections on the
rear, which are pairs of RCA connectors with right and left
channels indicated. If your signal source is a low output
moving coil cartridge, you will use the moving coil input. If
your signal source is a high output moving magnet cartridge,
you will use the moving magnet input. A ground post is
provided for grounding the turntable.

The two sets of output connections on the rear are a pair of
RCA connectors with right and left channels indicated. These
connections provide a single ended output of the preamplifier.
A pair of XLR connectors provides a balanced output
connection. On these connectors, pin 1 is grounded, pin 2 is
the positive signal output, and pin 3 is the negative signal
output.

The output signal of the balanced connector is twice the level
of the unbalanced circuitry, by the virtue of having the same
amplitude signal plus its inverse.

To change these settings, it is necessary to take the top off

the preamp using a 5/32 hex wrench, which we supply.

It is very important that you always disconnect the AC

line power before opening the preamp.

If you do not feel capable of safely adjusting the settings

internally, please contact your dealer or the factory.

On the main board you will see a set of DIP switches which

are used to alter the input connections.

Two switches, S1 and S1A, are used to select moving coil
and moving magnet inputs. Positions 7 and 8 are labeled MC
and MM. Select one only by depressing the switch toward the
silk screened label, which is the ON position of the switch.

On these same switches, positions 1 through 3 are used to
select the capacitive loading of the moving magnet cartridge
input. You may select 100 pF, 220 pF, and 330 pF, or any
combination of these values, which are additive, for a
maximum of 650 pF, or no capacitance by simply leaving the
switches in the off position. Two additional blank positions
4/CX and 5/RX are available for you to solder your own
loading values onto the main board. Position 6 allows 1000
ohm loading of the moving magnet stage for use with some
cartridges.

Switches S2 and S2A are used to adjust the resistive loading
of the inputs for low output moving coil cartridges. Switch
positions 1 through 8 will load the input from 10 ohms up to
1000 ohms in roughly binary steps. The switches and
resistors are in parallel, so placing more than one switch in the
"on" position loads the cartridge with the two resistor values in
parallel. Placing all resistors "on" will give approximately 5
ohms loading.

The preamplifier is shipped with the moving coil stage
enabled, with the higher gain setting (69 dB single ended, 75
dB balanced) and a 100 ohm input load. To obtain 4 dB lower
gain, locate the jumper connectors for each channel next to
the two large capacitors. Please study the annotated
photograph before you attempt this. As an added reference,
they are midway between the two loading switches, but
several inches nearer the front. With the jumpers in place, the