Acoustat X Owners Manual

Page 1

_corporal:ion

HCOU>THT

3101 Southwest Furs! Tetrace. Fon Lauderdale, Florida 33315
Phone: 305/462~6700

The ACOUSTAT SERVO-CHARGE AMPLIFIER

Service and Owner's Manual

Page 2

ACOUSTAT
SERVO-CHARGE AMPLIFIER
SERVICE MANUAL

Con fen rs:

lntroducfion
Sysrem Sef-Up lnstrucfions
Shielding and Grounding of Audio Systems
Descriprion of the Servo-Charge Amplifier
Block Diagram
Theory of Operation
Constant Charge Electrostufic Panels
lnpu? and Equalization Amplifier
Phase inverter
Recrifier Amplifier
Trigger Amplifier
Panel Bias
Output Amplifier
Power Supplies
Infernal Grounding
Drawings
Overall Schematic
Chassis Assembly
lnpuf Area Assembly
Primed Circuit Assembly
Parts Lisl-
Componenr Changes
Troubleshoofing

Page 4

SET-UP INSTRUCTIONS FOR
ACOUSTAT ELECTROSTATIC
SPEAKER SYSTEMS

The set-up procedure, exclusive of assembly, is the same for all Acoustat
electrostatic speaker systems. We have been able to make the Monitor series
speaker systems more tolerant than the Acoustat X systems for small aberotions
in the set-up and room tuning; but we still advise that the preferred procedure
should be followed fully to obtain the best possible performance from the

system .

Some of the principal considerations which will determine the performance
potential of the speaker system as installed are:
The Wall Behind the Speakers:
This wall should be hard, reflective, and sufficiently rigid that
it will not rattle-~sliding glass doors are a No-No".
The Orientation of the Speaker System Within the Room:
Unless there is an overriding consideration to the contrary, the
speakers should proiect sound along the longer axis of the room.
This can be considered a universal rule of stereo speaker systems
and is in no way peculiar to Acoustat products.
The Grounding of the System:
It is essential that the power supply ground be connected to prevent
any buildup of charges in the Servo-Charge amplifier power supplies.
THE THIRD WIRE GROUND MUST BE CONNECTED.

While the system may function reasonably well with only the
power supply ground, this leaves the main signal ground floating.
THERE MUST BE ONLY ONE SIGNAL GROUND IN THE SYSTEM
and this should normally be provided at the inr v of the preamplifier.

Electric Feedback:
Electrostatic loudspeakers produce a strong electric field which can
influence the operation of any low level electronic circuitry in
close proximity and can result in feedback at frequencies well above
the audio spectrum--this has the effect of high power dissapation and
decreased headroom in the systen The tone arm of the turntable
and the input of the preamplifier should be kept at least six to eigh
feet from the nearest speaker to ensure that no feedback can occur.

Phasing:
Acoustat speaker systems are designed to preserve correct absolute
phase throughout the system including the final coupling of the
signa' to the air. This ensures that vocalists and instruments will
sound as natural as possible. Therefore, make sure that the
connections from the speakers to the amplifiers are correctly oriented:
the wires should enter the three prong Pomono plug from above.

Page 9

THEORY OF OPERATION

in order to understand the operation of the Servo-Charge amplifier, it is very
usefull to have at least a rudimentary understanding of the load which it was

designed to drive,
Acoustat uses what are referred to as constant charge electrostatic transducer
panels in which the electrostatic "plates" are driven in a push-pull format and

the driven diaphram is biased in such a manner that its electrostatic charge
remains constant despite the application of high voltage audio signals to the

electrostatic plates .

l C =q/V

I 1 J =CV2/2
e E is _
s l l1 l w ' F =_Eq

I l
o _

l I Where: C capacitance in fared:
* . + 41 ' V voltage in volt:
l + l ' J energy in ioules
. * V F Force in newton;
4 l ' l _ E electric field in

I | newton: per coulomb '
I * " q charge in coulomb:

I t

i

measure at e lectvic
field

newtons per coulomb
and volts per meter
[ are alternate units at
l
I

While we admit that the physics is not "obvious at a glance" we will, for the
purposes of this amplifier service manual, simply state the electrical requirements
to drive the electrostatic loudspeaker panels that we use at Acoustat Corporation
and not dwell on the physics of electrostatic loudspeaker design.

Page 27

SYMPTOMS

Unit shuts down
to standby, but
comes back on
immediately .

of

Unit will not

shut down to

standby mode.
or

Unit will not
turn on from

CAUSE

Defective LC.
or Arcing tube

Detective LC. ,
Q5 Transistor or

CURE

A detective integrated

circuit can cause this problem.
The OP-ll device was found

to be particularly prone to this
rare problem. An arcing tube
can also affect proper operation
of the turn on circuitry.

The attending tube will

usually arc at the shutdown

to standby point and bring
back the amplifier to the

full 0n condition. This tube
can sometimes be spotted in a
darkened room. The simplest

standby. bad Relay solution is to replace all
four tubes.

White noise in Leaky 2N3440 Be sure the noise isnt

background below (Ql,Q3) originating Upline in the

level of music

preamp or elsewhere by removing
the input to the servo charge
amplifier. It noise persists

replace QI or Q3.

Amp distorts ,
weakened output

sometimes accompanied
by a low level hum.

Detective 02,04,
Ql or Q3 transistor

Check/Repiace detective
transistor.

Intermittent drop

in volume, about
50%, accompanied
by low level hum.

Intermittently open
iunction mm4003
transistor(2N5416 on
later units)

Replace Q2 and Q4

Unit turns on from standby

due to AC line surges-

sometimes induced by an
air conditioner,ilourescent

lights etc.

Earlier production amplifiers
are sometimes found to do this.
Eliminate the problem by
installing a 680 ohm resistor

in series with the cathode
(banded end) of CRI4. This
resistor is factory installed
_-eginning with s/n I700.