PassLabs XVR-1 Owners manual

PASS LABORATORIES XVR1 ELECTRONIC CROSSOVER NETWORK

OWNERS MANUAL

4/24/02

INTRODUCTION

Some audio products are designed for anybody who can put batteries in a flashlight. This
product is not like that.

Some audio products are designed so that you don’t have to study the manual. This
product is not like that, either.

Some audio products are designed so that you plug them in and you don’t have to fool
around with them for a year before the system is greatly improved….

Some Basics:

As you may already know, most loudspeaker drivers have specialized tasks and are
designed to operate over only a portion of the audio spectrum. They do not perform well
outside their given range, and are not usually designed to be driven outside this range
without bad results.

A filter system called a crossover network divides the audio spectrum into frequency bands
appropriate for the drivers. There are passive networks, usually found inside the speaker,
which are placed between the amplifier and the loudspeaker driver to create this effect.

Alternatively, there are active electronic crossover filters placed in the signal path before
multiple power amplifiers. Each amplifier then amplifies only a portion of the audio band
and powers the speakers associated with that frequency range.

There are many performance advantages offered by active crossover networks. They give
better performance in the following ways:

Higher power. Typically two amplifiers driving a speaker with an electronic crossover will
deliver peak wattages almost 4 times the peak (8 times the rms) wattage rating of a single
amplifier of the same power rating. This is because the voltage waveforms coming of the
high and low pass filters are not mixed, and the high pass voltage does not ride on top of
the low pass voltages. When the waveform of a low frequency approaches the limit of the
amplifier, there is no voltage left over for the high frequency. With an electronic crossover,
the available voltage is nearly doubled, and power is quadrupled.

Better use of power. Passive crossover networks divide down the power output of the
amplifiers, both in adjusting the efficiency of a driver against the other drivers used, but also
by dividing down the output signal as the frequency leaves the bandpass frequency range.
Very often this means that only a fraction of the power available from the amplifier can get to
the loudspeaker driver. It also means that the least efficient driver sets the efficiency
standard for all the drivers. Active crossovers do not suffer from this effect.

Higher damping factor. Many loudspeaker drivers depend on a low source impedance from
the amplifier to deliver their best performance. Even moderately good amplifiers have a
quite low source impedance, also known as high damping factor, and this quality helps the
loudspeaker driver to start and stop its motion more quickly and also evens out the
frequency response. Any passive crossover introduces significant impedance between the
amplifier and the amplifier, and can reduce damping factor from 1,000 to as low as 1.

Lower distortion. In addition to lowering the distortion of individual drivers and eliminating
the linear and nonlinear distortions of high power passive filter components, active filters
dramatically lower the intermodulation distortion of the amplifiers. Since the high
frequencies share the same amplifier as the low frequencies, the low frequencies can
modulate, or change the amplitude, of the high frequencies, particularly under high power
conditions.

More control and flexibility. It is difficult and time consuming to adjus t the characteristics of
a passive crossover filter. It is easy with an electronic crossover to adjust the crossover
frequencies, the filter cutoff rate (slope), the “Q” or sharpness of the cutoff knee, and the
volume level of the loudspeaker driver. Unlike a passive crossover, these characteristics do
not depend on the driver’s impedance which varies considerably at different frequencies.
The XVR1 is probably the most flexible electronic crossover in existence. It has literally
millions of possible settings, most of which you will never want, but they are available just in
case.

Tailoring amplifiers to speakers. Some amplifiers are more appropriate for powering
different frequencies and loudspeaker drivers. As an example, you might prefer to drive
your woofer with a big powerful solid state amplifier which will deliver the maximum dampin g
and control and drive your midrange and tweeter with a tube amplifier chosen for its
ambience and the sweet character if its high frequencies.

In any case, for those seeking the utmost performance from acoustic transducers (that’s
loudspeakers), an active filter system carries the most promise, and is particularly
necessary for those doing custom work and design.

Using an electronic crossover is not necessarily easy. Getting what you truly want requires
effort and patience and the ability to tell what you want when you hear it (or measure it).
While this crossover can execute a “canned” setting recommended by a speaker driver
manufacturer or a system designer, its true value lies in being able to do anything you want
to try.

There are several sections to this owners manual: Introduction, Product Description, Quick
Installation, Some Real Basic Theory, Some Real Tips, Some Real Projects, and Some
Product Specs.

2

Cautions:
Remove the AC power cord from the XVR1 power supply before opening the

enclosure of the XVR1 in order to adjust the filter settings. When the power supply is
connected to the AC wall socket there are high voltages inside.

Do not open the enclosure to the XVR1 power supply. There are adjustable parts
inside the power supply, but there are dangerously high voltages inside.

It is fairly easy to set the crossover filters with characteristics which will damage
loudspeaker drivers. Follow the instructions closely and double check the settings
before powering up the amplifiers.

Please read the Quick Install section before attempting to operate the XVR1. Even if you
are a big time expert in audio, you will probably need this information if you need to adjust
any characteristic of the filters.

Unless you are provided with a document indicating otherwise, the following are the default
settings of the filters that ship with the XVR1:

Low Pass: 1060 Hz, 12 dB/oct, Q = MEDIUM AS SEEN ON PAGE 9

High Pass: 1060 Hz, 12 dB/oct, Q = MEDIUM AS SEEN ON PAGE 13

Thank you for purchasing this product. It was created over a period of several years for our
own loudspeaker design efforts, and it is the design that ultimately performed with the most
flexibility and quality, and gave us the most satisfaction with the end result. Many of the
practical things we learned about what makes an effective active crossover are described in
the Theory of Operation section of this manual. Remember that it takes patience and
persistence to get the absolute best out of an active system, bu t the results will be worth it.

You will may have additional questions not covered in this manual. Please feel free to
contact us at WWW.PASSLABS.COM

Nelson Pass
Copyright 2002
Pass Laboratories, PO Box 219, 24449 Foresthill Rd, Foresthill, CA, 95631, USA

Tel [phone], Fax [phone], WWW.PASSLABS.COM

3

PRODUCT DESCRIPTION

The XVR1 is a two channel crossover filter for bi-amplification. It offers two channels of
either balanced (XLR) or single-ended (RCA) input, and divides the input signal of each
channel into two frequency bands, the low pass band and the high pass band. These
filtered signals can be adjusted for loudness on four knobs on the front panel, one each for
two channels of low pass, and one each for two channels of high pass. The low pass and
high pass signal outputs are presented both as balanced (XLR) and unbalanced (RCA).

The characteristics of each of the crossover filters is extremely flexible and adjustable,
offering approximately 20 million possibilities. Each filter offers 1,2,3 or 4 poles for 6, 12,
18, or 24 deciBels per octave (dB/oct) slopes at 39 frequencies ranging from 22 Hz to
18,000 Hz. The 4 poles are independently adjustable, meaning that they can each be at 39
different frequency values, and are not required to have the same value as with
conventional crossover networks. This is of particular value in fine adjustment of crossover
points and custom equalization of loudspeaker drivers and phase compensation. In
addition, the sharpness of the frequency curve or “Q” is available in low, medium, or high
characteristic. These filters are adjustable through clearly marked jumpers on the main
board of the XVR1.

The XVR1 circuitry is completely discrete single-ended Class A, using matched JFET input
devices and bipolar current sources. The input circuit features a high input impedance and,
when used balanced, a very high rejection of common mode noise. The distortion and
noise imposed on a signal running through all possible circuits in the system is typically less
than .05% at 30 volts balanced output from 10 Hz to 20 KHz, and less than .005% at 3 volts
output. Provision has been made to completely bypass unused 3 and 4 pole portions of the
filters so as to absolutely minimize distortion and noise.

The outputs of the XVR1 are designed to drive balanced (XLR) or single-ended (RCA)
cables and will drive ordinary amplifier impedances to 45 volts peak balanced, or 22 volts
single-ended. The outputs of the XVR1 are muted to ground through relays to prevent turn­on noise through the speakers when the unit is initially powered up. When power is
interrupted or when AC line voltage is too low to support supply regulation, the relays mute
again, preventing turn-off transient noise.

The XVR1 comes with a physically separate power supply which carries provision for
powering two XVR1 chassis for tri-amp filter configurations. Each XVR1 chassis draws
approximately 15 watts, and is designed to operate continuously. Additional XVR1’s and
supplies are used in cascade to create crossover filters for 4 amplifier and 5 amplifier
systems.

4

INSTALLATION AND SETUP

You can put the XVR1 and its power supply anywhere you like, but keep in mind that they
should be close enough so that the power cord will reach from the XVR1 to the power
supply. You can place the XVR1 on top of the supply if you like.

You may occasionally want to adjust the filter characteristics of the XVR1 (see sections
below) and to do so it will be necessary to have access through the top cover, and so you
might want to consider placing the XVR1 so that you can easily access the top cover.

The XVR1 power supply is designed to power one or two XVR1 filter networks. Each XVR1
is provided with a 25 pin cable for connection from the XVR1 to the power supply. Attach
the cable to the appropriate 25 pin connector on the back of the XVR1 and connect the
other end to either of the two 25 pin connectors on the back of the power supply. Do not
plug in the AC power line yet.

There are two sets of input connectors for the Left and Right channels; single ended RCA
audio connectors and balanced XLR connectors. On the XLR connector, pin 1 is grounded,
pin 2 is positive signal, and pin 3 is negative signal. Pin 2 of the XLR connector is the same
as the “tip” or “hot” pin of the RCA connector. If you are using the RCA input connection,
you will obtain best results with pins 1 and 3 of the XLR connector shorted together with the
jumper provided. The XVR1 will work without the jumper when you use the RCA input, but
the jumper gives lower noise and is preferred. If you remove this jumper when using the
XLR connection, save it for future use. If you lose it, contact Pass Labs for a replacement,
which we cheerfully send.

By the way, the input impedance for RCA connection is 44.2 K ohms, and is 66.3 K ohms
for balanced connection.

Each of the four filters, two Low Pass and two High Pass, has a set of output jacks on the
back of the XVR1. Each set of output connections has a single-ended RCA jack with which
you are probably familiar, design to accept an ordinary audio cable which connects the
output of the filter to the input of a power amplifier. Also included is an XLR balanced output
connector for driving balanced lines and intended to connect to a similar connector on the
input of a power amplifier. On the XLR connector, pin 1 is grounded, pin 2 is positive signal,
and pin 3 is negative signal. Both pin 2 and 3 are driven actively with an output impedance
of 100 ohms.

You may use either or both RCA and XLR output jacks without adjusting anything, keeping
in mind that they share a common ground and also have the positive output in common, so
that pin 2 output of the XLR is the same connection as the “tip” of the RCA connector.

Ground noise is a common problem with active crossovers as there is more opportunity for
ground loops when you have multiple amplifiers. Use of balanced operation commonly
avoids these problems, but you may find that you have to break the earth ground
connection of one or more components in order to eliminate the ground loop. If you do this,
it is advisable to leave at least one component, preferably the XVR1, earth grounded
through the AC power connection so that electrical safety can be assured.

5

Setting Up the Filters

The XVR1 is shipped with a hex or “allen” wrench for the purpose of opening the top cover
of the XVR1 for adjustment of the filters.

DO NOT OPERATE THE XVR1 WITH THE COVER REMOVED. THERE ARE HIGH
VOLTAGES INSIDE WHICH ARE HAZARDOUS. ALWAYS UNPLUG THE AC LINE
CORD OF THE XVR1 POWER SUPPLY WHEN THE COVER IS OPEN.

If you have any hesitation about your expertise or ability to perform the internal
adjustments to the XVR1 filters, then get a qualified technician to do the work.

This section assumes that you are planning a filter with medium “Q”, or corner sharpness,
and that all poles for each high or low pass filter are at the same frequency. For information
on using different Q values or different pole frequencies, refer to the MORE OPERATION
DETAILS section of this manual.

This section also assumes that you know what frequency and slope you want each filter to
have. The choices are 22, 25, 29, 36, 48, 53, 59, 66, 75, 88, 106, 133, and 180 Hz. Each
of the four poles available has a labeled spot for a shorting plug to set the frequency of that
pole. Each pole also has three sets of pins for shorting plugs to set the frequency multiplier,

X1, X10

, and

X100

.

When a pole is not used, th ere are two spots to place the shorting ju mpers, both marked

OUT

which disable that pole of the filter.

The poles of each filter are to be used in sequence, that is to say we use the bank of pins
labeled
frequency and multiplier settings of
the

A 12 dB/octave 2 pole filter uses the banks of pins labeled
An 18 dB/octave 3 pole filter uses the banks of pins of
A 24 dB/octave 4 pole filter uses the banks of pins of
Again, the two jumpers for each unused pole of any filter should be placed on the two sets

of
Under no circumstances should you use

should never use
but we make no guarantees that your loudspeaker will appreciate the result. Observe the
following cautions whenever adjusting the filter characteristics of the XVR1:

POLE 1

OUT

positions.

OUT

pins provided.

first, then

POLE 4

POLE 2

POLE 3

with

and so on. A 6 dB/octave single pole filter uses only the

POLE 1

POLE 2

in the

and the jumpers of

POLE 1, 2

POLE 1, 2, 3

POLE 1

with

OUT

setting. Doing so will not hurt the XVR1,

POLE 2, 3

POLE 1

and 3.

in the

POLE 2

and

, and 4.

OUT

, and 4 are set to

.

setting, and you

6

Remove the AC power cord from the XVR1 power supply before opening the
enclosure of the XVR1 in order to adjust the filter settings. When the power supply is
connected to the AC wall socket there are high voltages inside.

It is fairly easy to set the crossover filters with characteristics which will damage
loudspeaker drivers. The XVR1 is sufficiently flexible that it can be made into an
oscillator through some combinations of filter values. For this reason, set the front
panel level controls of the XVR1 to minimum and double check the settings before
powering up the amplifiers. After powering up both the XVR1 and the power
amplifiers, gently raise the level controls of the XVR1 while listening for any potential
noise.

Each filter of the XVR1 actually consists of two filters cascaded, each capable of 6 or 12
dB/octave slopes and each capable of its own “Q” setting. For this reason, you will see that
each filter has two sets of “Q” pin settings, L, M, and H (Low, Medium, and High). These
can be set independently, and in this section, it is assumed that the jumpers of both are in
the M (medium) or middle position.

As the two parts of each filter are cascaded, signal runs through both of them in series,
however when using only one or two poles for 6 or 12 dB/octave, it is not necessary to also
run the signal through the second part and pick up the extra noise and distortion that the
second part contributes. To enhance performance, each filter also offers a means of
bypassing the second part when you are using 6 or 12 dB/octave slopes. In the middle at
the top of each filter you will see a 3 pin jumpe r switch which allows selection of either

18/24

or
enables the second part also. It is not essential to bypass the second part of the filter
circuit; it will work fine on
a bit more noise and distortion.

. Selecting

6/12

bypasses the second part of the filter circuit, and selecting

18/24

even if you are only using a 6 dB/octave filter, but it will have

6/12

18/24

In the following pages we are going to show you four different setups each for high pass
and low pass filters, along with the resulting curves for each. Note the positions of the
jumpers in each of these examples, and we hope you will gain the proper insight as to how
these jumpers work. All of the examples assume a crossover frequency of 1060 Hz, which
has the frequency jumpers on

In each of these cases, we are going to show you a set of 4 response lines in each
frequency response graph. These are the characteristics for the 6, 12, 18, and 24
dB/octave settings. We do this so you can get a sense of the comparative response of
these four different slopes, and we will be indicating which of the four lines matches the filter
setting shown on that page.

Please note that only one channel of the crossover is shown here. You will need to set the
filters for both the LEFT and RIGHT sets of filters. The LEFT channels are in the front of the
XVR1 and the RIGHT channels are in the back, and both are labeled on the left of the main
board.

By the way, we provide some extra shorting plugs packed with the XVR1 in case you lose or
break any. If you come up short, contact Pass Labs, and we will provide you with some in
exchange for a smile.

106

and the multipliers on

X10

.

7

6 DB/OCT ( 1 POLE ) @ 1060 Hz

8

12 DB/OCT ( 2 POLE ) @ 1060 Hz

9

18 DB/OCT ( 3 POLE ) @ 1060 Hz

10

24 DB/OCT ( 4 POLE ) @ 1060 Hz

11