Coda 1 User manual
TECHNOLOGIES INC.
ADDRESS
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SAFETY PRECAUTIONS
INSTALLATION CONNECTIONS
INTRODUCTION
DETAILED INSTALLATION
DESIGN PHILOSOPHY
TECHNICAL DATA
CARE and HANDLING
WARRANTY
WARRANTY REGISTRATION
OPERATION MANUAL
FET PREAMPLIFIER 01
!
CAUTION
CAUTION
WARNING
WARNING !
SERVICING TO QUALIFIED SERVICE
CAUTION: TO PREVENT ELECTRIC SHOCK,
DO NOT REMOVE COVER. NO USER
SERVICEABLE PARTS INSIDE, REFER
PERSONNEL.
THIS SYMBOL IS INTENDED TO ALERT
YOU OF THE PRESENCE OF IMPORTANT
OPERATING AND MAINTENANCE
INSTRUCTIONS IN THE LITERATURE
ACCOMPANYING THE UNIT.
THIS SYMBOL IS TO ALERT YOU OF THE
PRESENCE OF UNINSULATED DANGER-
OUS VOLTAGE WITHIN THE UNIT'S
ENCLOSURE THAT MAY BE OF SUFFI-
CIENT MAGNITUDE TO CONSTITUTE A
RISK OF ELECTRIC SHOCK.
1
SAFETY PRECAUTIONS
WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT
EXPOSE THIS UNIT TO RAIN OR MOISTURE. TO
AVOID ELECTRICAL SHOCK, DO NOT OPEN THE
UNIT. REFER SERVICING TO QUALIFIED PERSONNEL.
Never install or remove the power cord from the chassis
unless it has been disconnected from the AC power source
first.
Never pull on the power cord when removing it from an AC
power source. Grasp it by the plug.
Do not leave the power cord connected to an AC power
source unless it is connected to the unit.
It is recommend that during extended periods of nonuse
that the units power cord be unpluged from its AC power
source.
Route the AC power cord so that it will not be damaged or
walked on.
CAUTION -
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This preamplifier is a precision device, designed in an effort to provide the listener with
unmatchedsoundquality,design,andconstruction. Inordertooperateyourpreamplifier
properly and to realize all of the capabilities of the FET PREAMPLIFIER 01, we recommend
that you read this entire manual carefully.
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INTRODUCTION
AC LINE INPUT (SEE BOTTOM) GROUND
LEFT
PHONO / LINE
RIGHTRIGHTRIGHTRIGHTRIGHTRIGHTRIGHTRIGHT LEFTLEFTLEFTLEFTLEFTLEFTLEFTLEFT RIGHT
COMPACTDISCTUNERVIDEOINRECORD ONEOUTINRECORD TWOOUTOUTPUT
LEFT RIGHT
BALANCED OUTPUT
RECORDER TWO
The first section of the installation instructions for the FET PREAMPLIFIER 01 is a diagram of
the basic configuration required to bring the preamplifier into an operating mode. These
brief steps will allow you to begin operating your system. Make sure during installation
that the level control is turned fully counter clockwise, all other components are off, and
AC power connections are interrupted to the preamplifier. While the diagram may be
self explanatory, we strongly recommend that you read the detailed instructions
following this introductory section.
POWER AMP
POWER AMP
INPUT OUTPUT INPUT OUTPUT
PHONO / LINE
COMPACT DISC
TUNER
RECORDER ONE VIDEO
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INSTALLATION CONNECTIONS
Ω
Ω
Ω
ΩΩ
Ω
Ω
Ω
22 22
47 47
100 100
1000 1000
1000 PF 1000 PF
200 PF 200 PF
100 PF 100 PF
50 PF 50 PF
ON
ON
I. Set up and Installation
1. If the phono stage has been incorporated in the preamplifier it will be necessary to set
the gain as well as the loading for each channel prior to installing the unit. With the unit
unplugged,remove the coverusing the suppliedAllen key. The defaultvalue for thegain
is “Low", such as would be used with a high output Moving Coil or a Moving Magnet
cartridge. The “High” setting will provide an additional 20dB of gain, if necessary, for
lower output cartridges.
2. In order to set the input loading, it will be necessary to toggle the DIP switches which
are located on the main board of the preamplifier. Each one of these switches connects
a resistor or capacitor in parallel with the input and so adjusts the load value. The default
values are 47k Ohms and 50pF. Refer to the diagram below, which is repeated inside
the unit, to determine the values which need to be switched in for your cartridge.
Replace the cover after setting the switches.
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DETAILED INSTALLATION
LOW
HIGH
LOW
HIGH
PHONO STAGE
WARNING: NEVER OPERATE THIS UNIT WITH THE TOP COVER REMOVED. NEVER MAKE ANY
INTERNAL ADJUSTMENTS WHILE THIS UNIT IS CONNECTED TO AN AC POWER SOURCE.
3. The balanced outputs are equipped with switchable phasing due to differences in the
USA/EUROPEAN standards. The default setting is EUROPEAN, but may be switched
according to the following diagram.
Note: These switches may also be used for selecting absolute phase .
XLR BOARD XLR BOARD
4. Position the FET PREAMPLIFIER 01 in the space which you have chosen, leaving enough
space to connect the ancillary components of your audio system, and the AC power
cord for the preamplifier. Although the FET PREAMPLIFIER 01 has the ability to reject
external fields that produce system noise, it is recommended that the unit not be placed
near any sources of strong electromagnetic energy.
5. Before installation, make sure all of the power switches of any associated components
are switched off. If any of your other audio components do not have power switches,
make sure they are unplugged from their AC power source.
LEFT RIGHT
BALANCED OUTPUT
LEFT RIGHT
BALANCED OUTPUT
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+
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+
_
+
_
1
2
3
1
2
3
1
2
3
1
2
31
2
3
1
2
3
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5
DETAILED INSTALLATION
USA EUROPEAN
Note: The Operating Voltage of the FET PREAMPLIFIER 01 is convertible
in order that it may be used worldwide. Contact your dealer to
arrange altering the operating voltage.
AC LINE INPUT (SEE BOTTOM) GROUND
LEFT
PHONO / LINE
RIGHTRIGHTRIGHTRIGHTRIGHTRIGHTRIGHTRIGHT LEFTLEFTLEFTLEFTLEFTLEFTLEFTLEFT RIGHT
COMPACT DISCTUNERVIDEOINRECORD ONEOUTINRECORD TWOOUTOUTPUT
LEFT RIGHT
BALANCED OUTPUT
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DETAILED INSTALLATION
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6545321
II. Source-Output, and Power Connections
The input and output connectors are clearly marked on the rear lip of the top cover. It
is important to remember the correct left or right channel orientation. The function and
channel markings on the rear panel correspond to the front panel controls and their
signal paths.
1. The GROUND post should be attached to the ground wire from a turntable.
2. The PHONO/LINE inputs should be attached to either the outputs of a turntable, or
if using the bypass option, may be treated as another line level.
3. The CD, TUNER, and VIDEO input connections are all line level inputs, requiring only the
insertion of the RCA plugs.
4. The RECORD ONE and TWO inputs should be attached to the OUTPUTS of the
corresponding recording device; alternately, they may be used as additional line inputs.
5. The RECORD ONE and TWO outputs should be attached to the INPUTS of the
corresponding recording device.
6. The OUTPUTS (unbalanced) should be attached to the amplifier inputs either directly,
or through a crossover or processor, as appropriate to the application.
7. The BALANCED OUTPUTS should be attached to the balanced inputs of the amplifier,
either directly or through a crossover or processor, as appropriate to the application.
8. The AC LINE INPUT should be attached to the power cable provided with the pre-
amplifier. After making the appropriate connections and rotating the level control fully
counter clockwise, insert the three prong safety plug into an appropriate AC power
source. Once properly connected, the LED on the front panel will light. At this point, you
may switch on your chosen ancillary components including the power amplifier.
III. Front Panel Control Functions
1. The INPUT SELECTOR control selects the source which will be presented to the
unbalanced OUTPUTS and BALANCED OUTPUTS.
2. The RECORD SELECTOR control selects the source which will be presented to both of
therecordoutputs. Because of the independentcontrols,one source may bemonitored
while a second, different source is being recorded.
Caution: Do not attempt to activate the record mode of a recording device when it is
selected as a recording source. This is an illogical state and may cause oscillation of the
recording device. If the monitor control is set for this device, the oscillation may produce
damaging levels at the unbalanced outputs and balanced outputs.
3. The MODE control allows selection of stereo and reversed stereo, as well as mono
(summed) output.
4. TheBALANCE control works byattenuatingtheright channel when being rotatedfrom
the detent in the counterclockwise direction, and conversely, the left channel for
clockwise rotation.
The element is conductive plastic. Adjustment is continuously adjustable allowing for
infinitesimal adjustments to match channel gain, which is impossible with stepped
controls.
5. The OUTPUT LEVEL control is a precision tracking, audio taper, conductive plastic
potentiometer used to adjust the voltage level at the outputs and balanced outputs.
Clockwise rotation, of course, increases output.
Select a source with the INPUT SELECTOR switch and advance the OUTPUT LEVEL control
to the level you wish. Keep in mind that your input sources will vary in level which can,
when switching from one input to another, abruptly yield uncomfortable sound pressure.
Note: Ifapower interruption occurs to thesystem,reduce the OUTPUT LEVEL controlgain.
The resumption of power will cause no noise pulses in the FET PREAMPLIFIER 01. However,
some sources may produce high output voltages on turn on, which may cause damage
to an amplifier or speakers .
REVERSE
STEREO
MONO
PHONO/LINE
COMPACT DISC
TUNER
VIDEO
RECORD ONE
RECORD TWO
INPUT SELECTOR RECORD SELECTOR BALANCE OUTPUT LEVELMODE
FET PREAMPLIFIER 01
DETAILED INSTALLATION 7
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DESIGN PHILOSOPHY
I. Design Philosophy and Approach
The circuitry utilized in your FET PREAMPLIFIER 01 is the result of an advanced and
complete design process combining innovation and proven fundamentals. This process
avoids both the limitations of total adherence to convention and the flaws resulting from
inappropriateapplicationofclevercircuitgimmicks. Ourapproachdemands painstaking
consideration of every facet of each design choice regardless of how small. Analytical,
as well as subjective techniques are all applied in an open-minded fashion with “no
compromise” musical perfection as the goal. The resulting refinement of the product
escapes simple explanation. With this in mind, we present here a few design highlights
and concepts.
All voltage gain is derived from FETs. While careful design can yield good results from any
device type, FETs consistently seem to have the edge in voltage gain and interface
applications. This is borne out by superior sonic qualities observed in subjective testing.
FETs are inherently transconductance devices, meaning that an input voltage controls
an output current. In other words, it “senses” the audio signal without drawing current
from the source to provide an output. This eliminates complex interactions with the
sourceallowingmaximumperformancefromeachsystem element and greatly reducing
the chance of cable characteristics altering the sound. The absence of input current in
FETsalsoallowshighbiascurrents forlinearityandspeedwithoutsacrificingDC parameters.
While excellent capacitors for coupling use exist, there can be no doubt that a signal
path free of coupling caps yields the best possible signal integrity. The DC stability of the
circuit eliminates the need for any questionable DC servo circuits or coupling capacitors.
We make no AC compromises for DC performance, however. Our key design choices
provide not only inherent DC stability, but also optimized AC performance throughout
the audio region and well beyond. These choices include the use of top quality dual FETS
in differential configurations for all voltage gain. Because the signal in these stages is
handled in a balanced manner, rejection of unwanted noise and modulation from
external sources is extremely high. This rejection extends even to noise which may
originate within the circuit from support circuity such as current sources. Stray RF signals
are also rejected well.
In the phono stage where the necessary equalization requires the use of capacitors, we
use only high grade film types. These and other equalization components were carefully
chosen to maintain response to within .2dB of RIAA standard. An additional subsonic
rolloff at 14 Hz serves to reduce IM Distortion.
Noise is kept low by paralleling input devices, careful selection of circuit impedances,
and pre-screening of devices.
The class A complimentary followers used to drive the preamp output are of such speed,
linearity,andlow output impedancethatno feedback correction isrequiredor used. The
advantage of this is that the circuit’s perfect stability and transient response are
preserved into a wide range of difficult and unpredictable loads. Variation in sound
which could occur through interactions with interconnect cables and other system
elements are thus avoided. A simple, very high performance inverter provides a fully
balanced output on the preamplifier which allows the user to take advantage of the
balanced inputs on many power amplifiers. The most commonly acknowledged
advantage of this is rejection of stray noise pickup, but improvements in distortion and
bandwidth may occur also.
While many manufacturers intentionally omit recording buffers on the grounds of signal
path simplification, the potential advantages of their use were worth an investigation.
The resulting experimentation ended with the development of a circuit of such simplicity
and performance that its transparency was guaranteed. The circuit is simply a direct
coupled, class A, FET follower. Because of the FETs inherent characteristics, the buffer
provides total isolation of the recording system from the main signal. In addition, it
provides a relatively high, purely resistive load to the source, and a relatively low, purely
resistive drive to the recording system. This assures consistent stability and freedom from
interactions, including cable effects.
DESIGN PHILOSOPHY 9
The requirements of a power supply for flawless audio reproduction are straightforward
but important. The supplies in the FET PREAMPLIFIER 01 take a very direct approach to
high performance. First, a top quality shielded toroid transformer with plenty of reserve
current capability is used. The shielding eliminates strong fields which could induce hum
intosensitive circuitry. About 20,000 uFofcapacitance with verylowESR and inductance
provides good passive filtering. A reference voltage is developed by delivering a
constant current to zener diodes. The resulting voltage is heavily filtered and delivered
to each stage through independent class A followers which completely decouples the
stages. The resulting non-reactive low impedance over an extremely wide bandwidth
yields a perfect power source for the individual circuits. The simplicity and absolute
stability of the supplies removes the chance of unpredictable interactions which may
occur with the more elaborate, high feedback circuity often used.
Most companies in the upper end of the audio industry use either sheet metal or formed
aluminum. Bycontrast,theFET PREAMPLIFIER 01 hasallstructuralpartsmade of machined
extruded aluminum. The advantage of this over an all stamped chassis is that the
machined metal can be worked more precisely allowing us to work on tighter tolerances
and use PC mounted parts more easily. Moreover such a design allows easier servicing
either for repair or for future upgrading. From the standpoint of appearance, a
machined surface can be contoured in a far more precise manner, giving the final
product a more seamless appearance.
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