Sanders Sound Systems Electrostatic Amplifier User manual

Sanders Sound Systems
Electrostatic Amplifier
OWNERS MANUAL
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Table of Contents
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INSTALLATION........................................................................................................................................................................... 3
LOCATION....................................................................................................................................................................3
INPUT CONNECTIONS ............................................................................................................................................ 3
OUTPUT CONNECTIONS........................................................................................................................................3
POWER CONNECTIONS..........................................................................................................................................3
ELECTRICAL PROTECTION AND FUSES ..........................................................................................................3
OPERATION .................................................................................................................................................................................4
OUTPUT FUSE REPLACEMENT ...........................................................................................................................4
LINE FUSE AND VOLTAGE SELECTOR................................................................................................................................. 5
DESIGN PHILOSOPHY...............................................................................................................................................................7
BACKGROUND............................................................................................................................................................7
PROBLEMS and SOLUTIONS.................................................................................................................................7
Current limitations...................................................................................................................................................7
Voltage limitations....................................................................................................................................................8
Protective circuitry................................................................................................................................................... 8
Power............................................................................................................................................................................. 8
Efficiency......................................................................................................................................................................9
Stability......................................................................................................................................................................... 9
Size and Weight .........................................................................................................................................................9
DESCRIPTION.......................................................................................................................................................... 10
SPECIFICATIONS.................................................................................................................................................... 11
Rated Power............................................................................................................................................................. 11
Bandwidth ................................................................................................................................................................ 11
Distortion.................................................................................................................................................................. 11
Gain.............................................................................................................................................................................. 11
Slew Rate................................................................................................................................................................... 11
Input Impedance.................................................................................................................................................... 11
Noise ........................................................................................................................................................................... 11
Output impedance ................................................................................................................................................. 11
Dimensions............................................................................................................................................................... 11
Weight........................................................................................................................................................................ 11

Page 3
INSTALLATION
LOCATION
To provide for adequate ventilation, you should
allow at least two inches of unobstructed space
above and a couple of inches on each side of the
amplifier. Because of its large power supply, the
amplifier produces a small local magnetic field
that may be picked up by low-level circuitry such
as preamplifiers, turntables, and the like. For
this reason, you should also provide at least four
inches of space between the amplifier and these
low-level components.
INPUT CONNECTIONS
Signal input is made through two rhodium-
plated RCA (unbalanced) or two XLR (balanced)
type connectors. Use one or the other. Do not
use both RCA and XLR connectors at the same
time as they will load each other improperly.
OUTPUT CONNECTIONS
The output to your speakers is made through
heavy-duty, gold-plated, five-way binding posts.
Be sure of the correct speaker phasing by
connecting the speaker cables to the same color
posts for each channel.
Check and double-check that the speaker
terminals are not shorted together by any loose
strands of wire. Check at both the amplifier and
speaker connections. Shorting the output
terminals together will blow the output fuses
and can damage the amplifier.
POWER CONNECTIONS
Be certain all associated equipment is turned off
before making any connections. Insert the
power cord into the AC LINE INPUT on the back
panel and then connect it to an appropriate
power source. This is a powerful amplifier. If
you use a power conditioner or generator, it
must be able to deliver at least 1800 watts of
power to the amplifier.
ELECTRICAL PROTECTION AND
FUSES
Although not essential, it is a good idea to use a
surge protector to prevent damage to the
amplifier in the event of an electrical storm or
other causes of abnormally high mains voltage.
These are inexpensive and can be obtained from
any hardware store. You do not need to use an
expensive line conditioner, but if you do, these
normally will have surge protection built-in so
you do not need to use additional surge
protection.
The amplifier has two status lights on the front
panel. These indicate that the left and right
channels are getting power. If the power switch
is "on" and either or both lights go out, it
indicates that their respective channel has a
problem.
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Page 4
OPERATION
THE ESL AMPLIFIER IS DESIGNED
TO BE LEFT "ON" CONTINUALLY.
It is extremely efficient. It only draws six watts
at idle (less than most preamps), so feels cool
and does not waste electricity. Although there is
a power switch on the back panel, the amplifier
is designed to be left on continually. Electronics
last longer when they are left on, as repeatedly
switching them on and off is stressful to them.
You can expect an indefinite life-span if you just
leave it on.
Check that the cables are properly phased (that
the cables are connected to the red and black
terminals on the speakers and amplifier
identically for both channels). Out-of-phase
connections will result in an image that is diffuse
and directionless rather than having pin-point
precision.
Some preamplifiers produce large turn-on and
turn-off DC voltages, which you will hear as a
“thump.” If your preamplifier does this, be aware
that these surges probably will briefly drive the
amplifier to full output. When an amplifier has
as much power as the ESL Amp, such voltage
surges can damage speakers and/or blow fuses.
Well-designed preamps won't do this, but it is
surprising how many expensive preamplifiers
have this problem.
To avoid such problems, turn on your
preamplifier first. Within five seconds, solid
state preamplifiers will have stabilized so you
can safely turn on the ESL amplifier. If your
preamplifier uses vacuum tubes, you should wait
a full minute before turning on the amplifier.
When turning off the system, turn off the
amplifier first, wait about a half minute for the
power supply capacitors to mostly discharge,
then turn off the preamplifier. An excellent way
to avoid this cumbersome start-up and turn-off
procedure is to always leave your preamplifier
and amplifier on.
OUTPUT FUSE REPLACEMENT
The amplifier has an 8-amp, fast-blow, output
fuse for each channel. These are located on the
back panel near the red speaker binding posts.
The amplifier will deliver over 600
watts/channel on music when using these fuses.
If you have relatively delicate speakers, you may
wish to replace these fuses with 2 amp, fast-blow
fuses to protect your tweeters. These fuses are
American AGC types, which are standard fuses
that measure 1 /
4" diameter by 1-1
/
4" long. Two
spare fuses are supplied with the amplifier.
If you should blow a fuse, you may access the
fuse by pressing firmly inward on the cap and
turning it 1 /
4turn counter-clockwise (bayonet
type). The cap will then spring out and can be
removed, the fuse replaced, and the cap
reinstalled.
You should never blow a fuse. If this occurs, you
should find the problem and correct it. Note that
by far the most common cause of blown fuses is
changing speaker cables while leaving the
amplifier on. It is hard to avoid touching the two
cable ends together when changing cables, and
shorting the cables will usually blow the fuse. So
always turn the amplifier off and wait 30 seconds
for the capacitors to discharge before changing
cables.
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Page 5
LINE FUSE AND VOLTAGE
SELECTOR
There are a pair of line fuses inside the fuse
drawer that is located on the back of the
amplifier. This drawer also has a window in it
that shows the mains voltage that the amplifier
uses.
To change the fuses or the mains voltage you
must open the drawer. The drawer is spring
loaded and will pop out if you release the latch
that holds it.
To release the latch, you will need a small tool
such as a small screwdriver or ball point pen.
Put the tool in the notch as shown in the draw-
ing, and push the latch towards the voltage
window. The drawer will release and you can
gently grasp it and pull it out of the amplifier.
With the drawer in your hand, you will see the
fuses. You can simply pull them out of their
spring clips and replace them.
A fuse blows to protect the amplifier for a reason.
You should identify the cause and correct it
before replacing the fuses.
The correct fuse size is 5mm x 20mm. For 200
volt circuits, a 5 amp, slow-blow type should be
used. For 100 volt circuits, a 10 amp, slow-blow
type should be used.
The mains voltage can be selected so that the
amplifier can be used anywhere in the world. To
do so, remove the fuse drawer and look inside
where the drawer fits. You will see a white
plastic "star" that shows the voltage on it.
Remove this star by pulling it straight out of the
amplifier. You can do this by putting your little
finger or a ball point pen or small screwdriver
into the recess on the left side of the star and
pulling it out.
With the star in your hand, you will see that it
has four sides and each side has a different
voltage printed on it. These are 100, 120, 220,
and 240. Pick the one that best matches the
mains voltage in your location. If your mains
voltage is 230, use 240 volts on the star.
Orient the star so that your voltage will face
outward from the amplifier and show through
the window in the drawer, then push it back into
the amplifier. You can now slide the drawer back
into place and press firmly against its spring until
it is flush and the latch "snaps" and holds the
drawer in place.
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Page 6
CARE AND CLEANING
If you wish to clean your amplifier, use a diluted
ammonia-based cleaner. Window cleaners like
“Windex” also work well. Do not use any
abrasive cleaners or chemical solvents like
“Ajax”, acetone, or paint thinners.
Use particular care not to damage the aluminum
faceplate. Aluminum is a medium harness metal
and although it is anodized, it can be easily
scratched by the careless use of tools during
installation.
The amplifier may overheat and the finish may
fade if exposed to direct, unfiltered sunlight or
intense heat for prolonged periods.
Save your box and packing materials. They will
be very helpful for moving or if you need to ship
the unit for servicing by the factory.
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Page 7
DESIGN PHILOSOPHY
Conventional amplifiers have serious problems
when forced to drive electrostatic loudspeakers.
Roger Sanders has developed the first amplifier
specifically designed to drive these unusual
speakers:
BACKGROUND
Electrostatic loudspeakers (ESLs) are very differ-
ent from conventional magnetic speakers and
place unusual and difficult demands on the way
amplifiers deliver power to them. A magnetic
speaker presents a resistive/inductive load to an
amplifier, while an ESL appears mostly as a
capacitor.
Resistors dissipate power as heat. So the voice
coils of magnetic speakers get hot as they use up
the current the amplifier sends to them. A
capacitor stores an amplifier's electrical energy
instead of dissipating it as heat. Therefore an
ESL doesn't actually “use” power like magnetic
speakers. ESLs are sometimes called “wattless”
speakers because of this. But their behavior is
highly reactive, which means that they send the
electrical current back to the amplifier when the
musical signal reverses polarity. Amplifiers tend
to be unstable with reactive loads.
A watt is a measurement of power. It is the
product of volts times amps. Volts is a measure-
ment of the pressure or “push” behind the elec-
trons flowing along a conductor. Amps (a short
form of “ampere”) is a measurement of the flow
of electrons along a conductor.
Amplifier power is measured in watts, which is
fine when working with magnetic speakers. But
an ESL doesn't operate on watts, it operates on
voltage. Therefore, an amplifier's wattage rating
can be very deceptive when evaluating its ability
to drive an ESL.
To take an extreme example, let's look at two
amplifiers, both rated at 100 watts. One has a 10
volt power supply that delivers 10 amps of
current. The other produces 100 volts at 1 amp.
Although both amplifiers generate 100 watts, the
one with the higher voltage will drive an ESL to
much louder levels than will the low voltage one.
Resistance in AC (alternating current) circuits is
called impedance, because it often varies with
frequency. The impedance of a magnetic speaker
will be essentially constant.
In a capacitor, the impedance is inversely
proportional to frequency. So an ESL will have a
high impedance at low frequencies, and a very
low impedance at high frequencies —typically
2Ωor lower.
PROBLEMS and SOLUTIONS
Current limitations
An amplifier must deliver more current as the
impedance of the speaker decreases. This
requires a larger power supply and output devic-
es that can pass large amounts of current. Such
parts are costly, so modestly-priced amplifiers
are only designed to drive relatively high imped-
ance loads —like 8Ωspeakers. Better amps use
superior parts and can handle 4Ωloads.
But few of even the best amplifiers can handle
the very low impedance 2Ωloads of an ESL well.
Many otherwise fine amplifiers find themselves
unable to pass sufficient current through their
output stages to drive an ESL at high frequencies.
This is known as “current clipping”, and results
in poor high frequency performance.
The Electrostatic Amplifier (“ESL amplifier”)
solves this problem by using a massive output
stage. Each output transistor is capable of
delivering 250 watts —and there are eighteen of
these per channel. As a result, it can deliver a
staggering 135 amps of current with a combined
power rating of 4500 watts per channel!
The output impedance of an amplifier must be
lower than the impedance of the speaker, or
current clipping will result. With so many output
devices, the output impedance of the ESL
amplifier is nearly zero. Current clipping simply
is no longer an issue.

Page 8
Voltage limitations
ESLs are voltage operated devices. The higher an
amplifier's power supply voltage, the louder it
will be able to play an ESL (assuming it can also
deliver sufficient current).
Because high voltages are not needed for
magnetic speakers, and because high voltage
parts are expensive, conventional amplifiers
often lack sufficient voltage to drive ESLs to truly
loud levels.
When an amplifier runs out of voltage, it clips
(more correctly called “voltage clipping”). This
results in distortion and compressed dynamic
range. Depending on the amplifier and its
behavior when clipping, the music will take on a
wide variety of non-musical qualities. Note that if
an amplifier is clipping, it really doesn't matter
how well-built the amplifier is, or how
impressive its design philosophy is —it simply
won't sound as good as an amplifier that isn't
clipping. Therefore, the most important
amplifier specification is its power rating.
When observed on an oscilloscope, most
audiophiles are amazed at how often their
favorite amplifier is clipping when playing music
moderately loudly.
ESLs have a legendary reputation being able to
produce effortless and crystal-clear sound, with
magnificent resolution of subtle inner-detail. A
clipping amplifier will destroy these qualities.
The ESL amplifier operates at very high voltages.
The power supply can deliver 90 volts to an ESL.
This will drive most ESLs to “ear-bleeding”
levels with voltage to spare. The result is
electrostatic sound that retains its totally
effortless and clear qualities at any tolerable
listening level.
Protective circuitry
Most transistor amplifiers require protective
circuitry to prevent their output transistors from
being damaged when they attempt to drive low
impedance loads at high levels. In high quality
amplifiers, this circuitry switches the power on
and off to the output transistors very quickly.
This causes voids and voltage spikes to be added
to the sound which is one of the major causes of
the harsh sound often heard in overloaded solid-
state amplifiers. In fact, it is this and the
introduction of large amounts of odd-order
harmonic distortion from voltage clipping that is
the cause of the dreaded “transistor sound” —
not the use of transistors per se.
The ESL amplifier has such a massive output
section that it does not need any protective
circuitry. It can drive loads below 1Ωwithout
damaging its output transistors. Since it has so
much voltage and current capability that it
virtually never clips, it doesn't exhibit any
“transistor sound.”
Power
As previously mentioned, “power” in the usual
sense, does not apply to ESLs. But it is useful to
try to make comparisons to get an idea of what
can be expected for a purpose-built ESL
amplifier. Also, many of the features that make
the ESL amp so effective for ESLs also work
splendidly with magnetic speakers. So it is
worth rating an ESL amplifier using conventional
power measurements.
The term “volt-amps” is used instead of “watts”
when evaluating an amplifier's ability to drive
the capacitive load presented by an ESL. Volt-
amps is still the product of volts x amps (as is
watts) but the difference is that they are not
necessarily being delivered simultaneously.
Another way of saying this is that the voltage and
current are out-of-phase with each other.
When driving a resistor, the voltage and current
flow together (“in-phase”). In a capacitor, the
current leads the voltage by 90 .
The ESL amplifier can deliver more than 1000
volt-amps per channel into an ESL. That means it
will act like a conventional amp rated at 1000
watts per channel.
When driving magnetic speakers, the ESL
amplifier will deliver over 300 watts/channel
into an 8Ωload, and over 600 watts/channel into
a 4Ωload.

Page 9
Efficiency
Many modern amplifiers are extremely ineffi-
cient. Enormous amounts of their power, in fact
most of it, is wasted as heat.
Audiophiles who prefer to leave their amplifiers
on continually have discovered that a large,
inefficient power amplifier can add over $100
per month to their electric bill. In a ten-year
period, their amplifier will cost them $12,000 in
electricity! To produce so much waste heat,
some of these amplifiers even require special
mains wiring.
Roger Sanders believes that the use of such
amplifiers is absurd, unnecessary, and
environmentally irresponsible. Proponents of
these amplifiers claim that inefficiency is
necessary to keep distortion at very low levels.
At one time this may have been true. But with
modern technology, it is possible to make
amplifiers that are extremely efficient while still
maintaining vanishingly low distortion levels.
The ESL amplifier has less than 0.03% distortion
from 20 Hz to 20 kHz up to the onset of clipping.
It does this while dissipating only a few watts at
idle and actually runs cool to the touch. It may
be left on indefinitely without concern for
electricity usage.
Stability
The weird phase angles and high reactivity of
ESLs causes conventional amplifiers to become
unstable. The ESL amplifier solves this problem
by avoiding the use of global feedback, using
modest amounts of local feedback at the input
stage, and an output stage with so much capacity
that it is essentially unaffected by reactive loads.
The result is an amplifier that is completely
stable under all conditions —even at turn-on
where no muting circuit needed or used. There
is no “pop” or “thump” at either turn-on or turn-
off and the amplifier switches on instantly.
Size and Weight
Many of today's best amplifiers are so large and
heavy (over 100 pounds) that one person cannot
lift them. They cannot be placed on a shelf or in
an equipment rack. Some are so big that they are
split in two parts —a “mono-block” for each
channel. It often is difficult to find a place on the
floor to put them. Many spouses are less-than-
pleased about having such large amplifiers
cluttering their living space.
To produce large amounts of power for driving
resistive loads in highly inefficient amplifiers, it is
necessary to use outrageously large and heavy
power supplies and huge heat sinks. So it is not
surprising that such amplifiers are immense.
Despite its vast output potential, the ESL
amplifier weighs just 51 pounds and is sized
scarcely larger than a full-sized preamp. Its
dimensions are 17" wide x 5.5" tall x 16" deep.
Roger Sanders has achieved this remarkable
compactness by using a chassis made mostly of
lightweight machined aluminum, and using the
power supply to drive speakers instead of having
its power converted to waste heat.
Because the ESL amplifier generates so little
heat, the heat-sink requirements are greatly
reduced. Additionally, high-efficiency heat-sinks
are used that make it possible to further lessen
the weight and size of the amplifier. Nor is this
compactness achieved at the cost of having a
noisy cooling fan. The amplifier is completely
silent.
Due to its very low idle current, the amplifier can
and should be left on continually. There is no
need to turn it off and on, which stresses internal
components with voltage surges.
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Page 10
Build quality
The quality of construction is typical of the finest
components made today.
All exterior and interior aluminum parts are
anodized. Steel parts are powder-coated.
Resistors are high reliability, precision metal
film, 1% tolerance.
Capacitors are of the highest quality, and none
are used in the signal path.
Connectors are either rhodium or gold plated.
Both balanced and unbalanced connectors are
standard.
Wire has been eliminated wherever possible by
using modular construction.
DESCRIPTION
The Electrostatic Amplifier is designed with the
same level of thoroughness usually reserved for
the finest amplifiers. Differential voltage gain
throughout provides exceptional rejection of
external noise and contributes to the inherent DC
stability of the circuit. This allows direct
coupling at the balanced inputs without servo
circuitry and virtually eliminates any DC offset
that could overload the step-up transformers
found in all electrostatic speakers.
The front end is designed to provide a slew rate
of 50 V/µS without entering Class B operation, as
is common in many other designs. This,
combined with excellent high frequency design,
insures linear operation at high speed. The
power supplies take a very direct approach to
high performance. A top-quality 1700VA
toroidal transformer with independent rectifiers
and capacitors are used with large amounts of
storage capacitance.
The current stage is capable of producing peak
currents in excess of 135 Amperes with a degree
of linearity and speed that is not matched by
other designs when producing only a fraction of
this current. This is achieved by the
implementation of several distinct circuit
features.
Each channel uses eighteen individual output
transistors with a combined power rating of
4500 watts and a bandwidth of 10 Mhz.
The bias section is designed to produce a
precision transition with no abrupt changes in
distortion or output impedance. This “Precision
Bias” technique allows for extremely high
efficiency operation and yields seamless
performance regardless of the complexity of the
load impedance.
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Page 11
SPECIFICATIONS
Rated Power
1700 VA/channel, 20Hz to 20kHz, both channels
driven into an electrostatic speaker of up to 4nF
capacity.
600 Watts/channel, 20Hz to 20kHz into a
resistive 4Ωload.
360 Watts/channel, 20Hz to 20kHz into a
resistive 8Ωload.
Bandwidth
-3dB at 5Hz through 100kHz
Distortion
Less than 0.01% from 20 Hz to 20 KHz at full
output
Typically 0.0081% at small signal levels
Gain
26dB
Slew Rate
500 Volts/microsecond
Input Impedance
47kΩunbalanced or balanced
Noise
More than 100dB below rated output
Output impedance
Less than 0.01Ωfrom 20Hz to 20kHz
Dimensions
17 inches wide by 5.5 inches tall by 14 inches
deep
(43 cm W x 14 cm T x 36 cm D)
Weight
54 pounds (23.2 kG)
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