Octave RE 280 MK2 User manual

RE 280 MK2

2
INTRODUCTION
Congratulations and thank you for choosing the OCTAVE
RE 280 MK2
You are about to enjoy the benefits of one of the world's most innovative and
reliable amplifiers. Take care of it, and your amplifier will provide you with many
years of listening pleasure.
You often hear people claim that there has been no real progress in tube amplifier
design for years. The operating principles of tubes have been documented
extensively and are well known to amplifier designers. The same can, of course, be
said for transistor amplifiers.
Nevertheless, there is still room for further development with both of these
technologies. This is both necessary and desirable. With tube amplifiers in
particular, a general reluctance to depart from the classic circuit designs has not
done the technology any favours. Today's loudspeakers and source equipment
provide better performance than ever before, but also make greater demands on
amplifiers. Modern sound reproduction equipment delivers a level of performance
at a price that simply would not have been possible 20 or even 10 years ago.
These advances have been achieved through the application of cutting edge
technology as it becomes available and affordable.
Integrating these technologies into amplifier design demands a detailed knowledge
of the inner workings of amplifiers and an appreciation of the sonic ramifications of
each modification.
We have specialized in tube amplification for the past 20 years, during which time
we have developed a number of innovative technologies that have earned us a
reputation as one of the leaders in the field.
We hope you will enjoy many hours of wonderful music with your OCTAVE
amplifier.
Andreas Hofmann

4
CONTENTS
Page
Introduction
1. OCTAVE technology ........................................................................... 6
1.1. OCTAVE amps in contrast to other tube amps ................................... 7
1.2. About the RE 280 MK2
2. Safety instructions................................................................................ 8
2.1. Before you begin.................................................................................. 8
2.2. Placement ............................................................................................ 9
2.3. Warranty............................................................................................... 9
3. Setting up............................................................................................. 10
3.1. Connecting the amplifier ...................................................................... 10
3.2. Burning in............................................................................................. 10
4. Operation: Front panel ........................................................................ 11
5. Connections: Rear panel ..................................................................... 12
6. Bias measurement facility.................................................................... 13
6.1. How it works......................................................................................... 13
6.2. Setting the bias .................................................................................... 14
7. Tubes
7.1. Tube layout .......................................................................................... 15
7.2. Tube service life................................................................................... 15
7.3. Removing the grille .............................................................................. 16
7.4. Replacing tubes.................................................................................... 16
8. Using the Black Box or Super Black Box ............................................ 17
8.1. Option: External Black Box .................................................................. 17
8.2. Option: External Super Black Box........................................................ 18
9. Troubleshooting.................................................................................... 19
10. Technical data and dimensions............................................................ 20
11. FAQ ..................................................................................................... 23

6
1. OCTAVE TECHNOLOGY
1.1. OCTAVE amps in contrast to other tube amplifiers
Sound 1. The design goal of OCTAVE amplifiers is honest, natural sound repro-
duction. The sound characteristics of an amplifier are derived from the
sum of all its parts. Tubes do not themselves guarantee high quality
sound.
Amplifier
Design
2. The limitations of classic tube designs are evident as soon as you con-
nect the speakers. These designs often only perform to their full poten-
tial when they are used with special loudspeakers. OCTAVE amplifica-
tion and power supply technology has largely overcome these well-
known problems. Thanks to their unique output stage design, they will
maintain their optimum sound quality with virtually any loudspeaker, ir-
respective of its load.
Control +
Monitoring 3. OCTAVE employs the latest electronic circuit designs to create the
best possible operating conditions for the tubes, and thus for the ampli-
fier itself.
OCTAVE Tube Technology
Power-
Management
Power supply
and
other functions Amplifier +
Sound Quality
OCTAVE amplifiers are equipped with a proprietary control and moni-
toring system we call Power Management. This is an "electronic brain"
within the amp that regulates and controls all of the amplifier's func-
tions. It includes the Soft Start Electronics that gently ramp up the
heating and supply voltages to save wear and tear on the components.
In the event of a problem, the Power Management's protection sys-
tem will disconnect the unit from the power supply. Power Management
helps us to achieve a completely consistent sound while at the same
time ensuring the total reliability of our products.
Hand built
4. OCTAVE amplifiers are hand built and individually tested. They are
designed and developed by Andreas Hofmann. The company has its
own winding department, in which all transformers are specially custom
wound for each amplifier.
made in
Germany
5. OCTAVE amplifiers are 100% built in Germany. Our employees are
highly qualified and committed. We collaborate closely with local spe-
cialist subcontracting companies. The hardware components are all
manufactured on modern CNC machines.

7
1. OCTAVE TECHNOLOGY
1.2. About the RE 280 MK2
The RE 280 MK2 stereo amplifier is a push-pull power amplifier in ultralinear
configuration. Power output is approx.2 x 70W at 2% THD.
OCTAVE power amplifiers have always set new standards in sound and
reliability.
POWER
MANAGEMENT
With the introduction of his RE 280 stereo power amplifier, Andreas Hof-
mann left traditional power amp technologies far behind. It goes without
saying that this amplifier - like all OCTAVE products - included OCTAVE's
proprietary Power Management and protection electronics.
The Power Management system monitors and controls the heating and
supply voltages at switch-on. This is tremendously important in extending
the service life of the tubes and maintaining a consistent sound. It also re-
lieves the power supply components of the strain of handling huge surge
currents at turn-on.
PROTECTION
SYSTEM Many manufacturers neglect to include electronic or even passive protection
systems in their tube amps, which means that the life - and indeed the op-
erational safety - of these amplifiers is greatly dependent on factors over
which the user has no control. OCTAVE fits its power amplifiers with an
electronic protection system as a matter of course.
LOAD STABIL-
ITY The technical breakthroughs that set the original RE 280 apart were its op-
timized input gain section and power supply. Indeed, it used a totally new
power supply design, featuring double star-earthing and supply voltage iso-
lation. The optimization of the input stage provided absolute immunity from
influences such as the loudspeaker load, together with excellent phase sta-
bility for highly accurate push-pull operation and an extension of the usable
frequency range up to 80kHz. From a sound quality point of view, these
enhancements delivered a consistent tonal performance that remains inde-
pendent of the impedance response and efficiency level of the speakers.
BIAS
A further effective feature is the Bias measurement facility.
Unlike the simpler class-A power amplifier type, AB amplifiers
require adjustment of the negative grid bias to optimize the idle current for
the power tubes. The setting can change as the tubes age and it must also
be adjusted whenever tubes are replaced. Normally, this requires test
equipment and a knowledge of what and where to measure, but with the RE
280 MK2, you can check and adjust the bias any time the amp is on.
This adjustment has a huge influence on the sound quality and performance
characteristics of an amplifier (see diagram 1 under Technical Data).

8
2. SAFETY INSTRUCTIONS
2.1. Before you begin
Before using your RE 280 MK2, please remove the protective grille and install the output tubes
supplied with your amplifier in the appropriate sockets (see Removing the Grille and Tube Layout).
Replace the grille before switching on.
Operating the amplifier without its protective grille is dangerous and not recommended.
In case of emergency: disconnect the plug from the mains supply
Never use an amplifier that is damaged or faulty. Make sure that it cannot be used until it has been
repaired by a qualified service engineer.
Make sure that there is easy access to the IEC socket and power cord.
Do not open the case
There are dangerously high voltages and hot tubes inside this equipment. To avoid a burn or the
risk of electric shock, never allow anyone except qualified personnel to open the case or remove
the grille.
Servicing and maintenance
For reasons of safety, please ensure that servicing, repairs and other modifications to OCTAVE
equipment are carried out only by a qualified technician. Fuses should also only be changed by a
qualified technician. Always replace fuses with ones of the same type and rating. If your amplifier
requires servicing, please ship or take your equipment directly to OCTAVE or to one of our author-
ized service centres.
Explanation of the warning symbols:
The exclamation point within an equilateral triangle is intended to alert the
user to important operating and maintenance instructions.
The lightning flash with arrowhead symbol within an equilateral triangle is
intended to alert the user to the presence of uninsulated 'dangerous volt-
ages' within the product's enclosure that may be sufficient to constitute a
risk of electric shock to persons.
Before connecting
Make sure that the voltage of your amplifier matches your electricity supply voltage.
Grounding
This amplifier is a protection class 1 device (with an earth conductor). To exclude the risk of electric
shock in the event of a fault, the unit must be grounded. Use a three-core mains cable with a three-
pin plug (supplied).
Safety warning: hot tubes!
Warning: Remove the protective grille at your own risk. OCTAVE accepts no responsibility for inju-
ries caused by the removal of this grille.

9
2. SAFETY INSTRUCTIONS
2.2. Placement
1. Location
OCTAVE equipment is designed strictly for use in a dry domestic environment. Do not use it in the
open air or in damp environments!
Never place plants or liquid filled containers on your OCTAVE equipment. Take care that objects
do not fall or liquids are not spilled into the enclosure. Should this happen, remove the mains plug
immediately and have your amplifier checked by a qualified service technician.
Condensation may form if the amplifier is taken from a cold environment into a warm one. If you do
this, wait until the amplifier has reached room temperature and is dry before switching it on.
Avoid installing the unit close to sources of heat such as radiators or anywhere that it may be in
direct sunlight.
Do not operate the unit near flammable materials, gases or vapours. Avoid areas where there may
be heavy accumulations of dust or where the unit may be subject to mechanical vibration.
Place your OCTAVE amplifier on a stable, even surface.
2. Grille
Never operate the amplifier without the protective grille.
3. Ventilation
Make sure that your amplifier has a good flow of air around it. If you intend to install your equip-
ment in a cupboard or a shelf unit, ensure that there is at least a ten centimetre gap between the
ventilation slots and the walls all around the amplifier. The rear panel of cupboards should have
ventilation holes to prevent heat build up. Do not rest the equipment on a soft surface such as car-
pet or foam sheeting.
2.3. Warranty
OCTAVE can only guarantee the safety, reliability and performance of this unit if modifications and
repairs are carried out by specialized personnel and if the amplifier is operated in accordance with
the instructions contained in this manual.

10
3. SETTING UP
3.1. Connecting the amplifier
1. In your own interest, please observe the Safety Precautions and positioning advice
(Chapter 2)
2. Before connecting your OCTAVE amplifier up, switch off all the other equipment that you intend
to connect to it. This will avoid a source of possible problems when you plug these components
in.
3. Connect the outputs from your preamplifier to the appropriate inputs on the RE 280 MK2 ampli-
fier. Make sure that switch 2 (on the rear panel next to the power amplifier inputs) is in the cor-
rect position.
4. Connect your loudspeakers to your RE 280 MK2 amplifier, making sure that you observe the
correct polarity (positive on the amplifier to positive on the speakers).
5. Check that the amplifier is switched off before connecting the power cable to the
wall socket.
Before connecting the optional outboard Black Box, ensure that it is switched off.
(see Chapter 8, Black Box)
6. The power switch for the RE 280 MK2 is located on the front panel (see Chapter 4, Operation)
There is no muting or standby facility.
When you switch on, the warm-up LED next to the power switch illuminates. The unit is ready
for use after about two minutes.
7. Check that the volume control is not set at maximum before playing music through the amplifier.
8. Switch the other components on in any order.
3.2. Running in
All OCTAVE equipment is subject to a 48-hour soak test at the factory to burn in the tubes. The
tubes are preselected for use in each particular model.
The sound quality of tube equipment improves throughout the initial running-in period of up
to three months.
During this time, daily use is beneficial (even at high levels) but not a requirement. Continuous
operation does very little to help reduce the running-in time and is therefore not recommended.
Power amplifiers should not be left in burn in mode for longer than 4 to 5 hours. The burn in facility
is intended for use only to burn in new output tubes. (See ‘Replacing the tubes’). OCTAVE tubes
fitted to our amplifiers or supplied as replacements do not need to be burned in.

11
4. OPERATION - Front panel
Power switch
To switch the amplifier on, push the knob in; the LED next to the knob lights up gradu-
ally.
Important! Do not pull on the knob when it has been pushed in, as this could damage
the retaining mechanism.
Make sure that access to the power switch is never obstructed.
Bias measurement selector switch
Off position: The measurement facility is disabled
Position V1 - V4: The measurement facility is connected to the relevant tubes. To
ensure the accuracy of any adjustments, be sure to set the volume control to 0.
NOTE:
The RE 280 MK2 is equipped with a soft-start circuit and a power-up delay timer.
The amplifier is ready for use after a delay of approximately 3 minutes.
Because there are no relays in the signal path, a low-level, slightly distorted signal
from your source equipment may be heard through your loudspeakers during warm-
up.
This circuitry extends tube service life and also protects the power section from voltage
spikes.

12
5. CONNECTIONS: Rear panel
RCA cinch input
Input from the preamplifier (using RCA phono interconnect)
Input muting switch
Muting switch for the input
Switch "cinch": RCA cinch input on
Switch "muting": both inputs muted.
This position is useful for connecting and disconnecting cables
without switching the power amplifier off.
+Speaker outputs
Loudspeaker connection terminals. When connecting the power amplifier to your
speakers, take care to connect the red terminals on your amplifier to the positive
terminal on your speakers. The blue (negative) terminals connect to the negative
terminals on your speakers.
Black Box and Super Black Box connection
The Black box and Super Black Box are outboard power supply upgrades for the
power amplifier (see p. 14, 15 ). The RE 280 MK2 must be switched off using the
power switch before connecting and disconnecting the Black Box!
Model identification plate
Model and serial number.
Power connection
AC input, IEC socket
Operating voltage
Details of the operating voltage and power consumption

13
6. THE BIAS MEASUREMENT SYSTEM
6.1 How it works
V1
V2 V3
V4
V7 V6 V5
ok
+ burn in off
Trimmer + LED
for tube V3
Trimmer + LED
for tube V1 Trimmer + LE
D
for tube V4
Trimmer + LED
for tube V2
BIAS-selector switch
The bias measurement system
The bias measurement facility makes it easy for you to check and adjust the idle current of the
output tubes. Getting the bias setting right for all four tubes is critical both for the sound of the
power amplifier and for the service life of the tubes. This is why we have incorporated a bias meas-
urement facility into the RE 280MKII that allows you to set the bias yourself without the need for
test equipment.
Service engineers may wish to remove the grille to set the bias, but the adjustment can also be
made through the grille using a long screwdriver. The trimmers are located next to their respective
tubes. Next to each trimmer you will see a pilot lamp, which shows which tubes have been selected
with the bias selector switch. A row of LEDs in front of the transformer cover assists you in setting
the bias correctly. It shows three conditions: bias too low, correct, and too high.
The LED display:
green LED (OK) Setting is correct
yellow "-" LED Setting is too low
yellow "+" LED Setting is too high
orange "burn in" LED Setting for burning in new tubes (see page 13)
red "off" LED Illuminates when the electronic protection has switched the
amplifier off (see pages 4 and 16)
The display is very accurate (2%). Fluctuations in the supply voltage may cause the green LED to
go out and the - or + LEDs to light up. This has no detrimental effect, and does not mean you have
to readjust the bias once you have set it correctly. The important thing is to adjust all four tubes at
the same time.

14
6. THE BIAS MEASUREMENT SYSTEM
6.2. Setting the bias
Make sure that no signal is playing through the amplifier when you are adjusting the bias. It is
sufficient to turn your preamp volume control to 0; there is no need to disconnect the speakers.
Procedure:
1) Turn the volume control on your preamp to 0.
2) Set the bias selector switch to V1. The green LED next to the trimmer for tube V1 will light up
to show that you have chosen to adjust the bias for tube V1.
3) The bias setting for this tube is correct when the green OK LED on the display illuminates.
If the yellow + LED illuminates, the bias is set too high.
turn the trimmer anti-clockwise until the OK LED illuminates.
If the yellow - LED illuminates, the bias is set too low.
turn the trimmer clockwise until the OK LED illuminates.
Repeat this procedure with the other three tubes
4) Switch the bias selector back to its "off" position.
Note:
If the orange burn-in LED lights up at the same time as the yellow LED when you are
adjusting the bias, it will be impossible to get the green LED to come on. This
combination of LEDs shows a defective tube, which you should replace.
It is not possible to adjust the bias if the amplifier's electronic protection has cut in (as
indicated by the red "off" LED in the display). When you activate the measuring facility
under these circumstances, the burn-in and - LEDs will illuminate for all tubes. You
must fix the fault before using the measuring facility. If a defective tube is causing the
problem, you should locate and replace it. (See Troubleshooting on page 16)

15
7. TUBES
7.1. Tube layout
V1
V2 V3
V4
V7 V6 V5
Output tubes: V1 - V4: 6550 or KT 88 fitted as standard
Driver tubes: V5 - V7 ECC82 (E82CC, 12AU7A, 5814, 6189)
7.2. Tube service life
Thanks to the protection circuits and soft start electronics, the output tubes used in your amplifier
should achieve an average service life of 3 to 5 years. Although this life expectancy figure is typi-
cal, it cannot, of course, be guaranteed absolutely, since it is dependent on the type and the manu-
facturer of the tubes themselves.
The internal protection and soft start circuits cannot prevent tube faults. They are designed to
minimize the stress on the amplifier and to protect it should a fault develop. You can select tubes
by measuring their characteristics, but this does not guarantee that they will last for a long time.
Indeed, it is impossible to predict how long output tubes will last. A well-made tube has a life expec-
tancy of between 3 and 5 years. However, it remains impossible to detect certain weaknesses in
the structure of a fully functional tube.
The protection circuits in the power amplifier will also protect the unit against the damage that a
defective output tube could cause.
Driver tubes can last for 10 years or longer.
Because tubes have different service lives, you will never have to renew the entire tube com-
plement at the same time.
Please note that some tubes need a long time (up to 300 hours) to achieve their optimum sound
quality.

16
7. TUBES
7.3. Removing the grille
Operating the amplifier without its protective grille is dangerous and not recommended.
To remove the grille:
1. For your own safety, switch the amplifier off using the on/off switch and disconnect the
power cord.
2. Pull the grille upward to remove.
7.4. Replacing tubes
Tubes should only be replaced by qualified personnel.
General procedure:
Switch the amplifier off and allow it to cool down for 10 minutes. Take off the pro-
tective grille. Remove the old tubes and fit the new ones.
New driver tubes
Replacement driver tubes require no adjustment.
New output tubes:
1. Before you switch the amplifier on after new output tubes have been fitted, turn all
bias adjustment controls (they look like little screws) counter clockwise as far as they
will go. These are ten-turn potentiometers, i.e. it takes ten revolutions to go from the
maximum to the minimum setting.
2. Switch the amplifier on. After the start-up period, both the minus the burn-in LEDs
should light up for each output tube. If the burn-in LED for one or other of the tubes is
dim, or does not light up at all, this is not necessarily a problem. If one of the tubes
shows green or plus, it is defective and you should replace it.
3. After a 30-minute warm-up period, you can adjust the bias of all the output tubes as
explained on page 11. When you have done this, your amplifier is ready for use. De-
pending on the type, age and manufacturer of the tubes, you may need to readjust
the settings in the first few weeks.
4. Replace the protective grille when you are done.

17
8. USING THE (SUPER) BLACK BOX
8.1. Option: External Black Box
OCTAVE, with the Black Box technology, offers an instrument to optimizing the OCTAVE amplifier
in respect to the speaker. This flexibility is a unique feature of the OCTAVE brand.
The dynamic and tonal stability of an amplifier is strongly dependent upon the stability and capacity
of the power supply, therefore the Black Box and Super Black Box were developed as external
upgrades to the OCTAVE amplifiers’ power supply storage capacitors by increasing their capaci-
tance by a factor of 4 (Black Box) or 10 (Super Black Box), respectively. This is a tremendous
benefit if the speaker is difficult to drive. Loudspeaker efficiency is made less critical, while the am-
plifier is enabled to handle speakers with minimum impedances as low as 2 Ohms.
The power supply capacitance increase realized via use of the Black Box or Super Black Box stabi-
lizes current delivery and reduces the impedance interaction of the load. This improves dynamic
range, separation, depth, soundstage size and articulation, rendering the musical reproduction
clearer throughout the entire frequency range. The amplifier remains unaffected by mains varia-
tions and interferences due to the noise filtering characteristics of the capacitors
Black-Box
ConnectorLED
The LED lights up continuously when the power amplifier is on. The LED goes out when the protec-
tion circuitry trips. This is normal, as the protection circuitry cuts the power to the amplifier.
Specifications:
Dimensions: Width x height x depth = 170 x 97 x 257 mm
Weight: 3.1 kg
Connection cable: 70 cm long. Longer lengths available upon request
Connecting to the amplifier
Warning!! Before connecting the Black Box, switch the unit off using the power
switch and wait for 1 minute.
When inserting the connector, guide the anti-rotation lug carefully into the mating
recess in the socket.
When you switch the amplifier on, the LED on the front panel of the Black Box will
illuminate.
Please note:
When the amplifier's electronic protection circuitry cuts in, this will cause the LED
on the Black Box to go out, as it interrupts the power to the amplifier.
Should you wish to disconnect the Black Box, switch the amplifier off first and wait
until the LED on the Black Box goes out before doing so.

18
8. USING THE (SUPER) BLACK BOX
8.2. Option: External Super Black Box
Blue Power LED:
The blue Power-on LED illuminates when the power amplifier (or integrated amplifier) is
switched on via the amplifier's power on/off switch.
Yellow Discharge LED:
When the power amplifier is switched off, the yellow Unload LED illuminates for about 2 sec-
onds. This indicates that the rapid discharge circuit is discharging the electrolytics in the SBB.
The discharge circuit also activates if the SBB connecting cable is removed accidentally. This
makes it impossible for an SBB to contain a dangerous charge while it is disconnected.
Dimensions and weight
Dimensions: (Width x height x depth) = 203 x 159 x 320 mm
Weight: Approx. 7.5kg
Connection cable: 80 cm long. Longer lengths available upon request
Connecting to the amplifier
see Black Box

19
9. TROUBLESHOOTING
Noise and hum
Hum in an audio system is often caused by several system components being grounded sepa-
rately. It is particularly common in systems containing tuners, VCRs or satellite receivers con-
nected to an aerial, where a hum loop may be introduced via the aerial input.
Although the RE 280 MK2 is also grounded, it is equipped with a special technology that reliably
prevents ground loops. Should an earth loop develop via a tuner or television aerial, we strongly
recommend that you use a signal isolating filter on the aerial connection. This will eliminate all
ground loops.
Switching interference
Older fridges and 12V halogen lamps can cause cracking through the loudspeakers when they
switch on and off.
Solution: the only solution is to run your system from a single distribution board - if possible,
one that incorporates a mains filter. Under certain circumstances, fitting an inexpen-
sive industrial filter in the power line of your refrigerator may a be more effective an-
swer.
The channels are unbalanced and/or there is distortion at certain frequencies
The problem of channel imbalance or distortion in one channel is unlikely to be caused by de-
fective tubes. The most frequent causes are cables and faulty recording devices.
Solution: Unplug all non-essential components/cables from your preamp. Swap channels to
check your speaker and interconnect cables. You will generally be able to locate the
fault if it changes channel or disappears altogether.
Tube faults
There are 3 different symptoms indicating a faulty tube:
1. Broken heater filament: the tube stops glowing.
2. Defective cathode layer: the tube glows, but no current can flow. You can confirm this fault
using the bias display LEDs - no amount of adjustment will be able to extinguish the minus
LED.
3. Internal short circuit: Normally, the electronic protection cuts in and the red "off" LED illumi-
nates, or the tube will not respond to bias adjustment (the display keeps jumping from plus
to minus or vice versa).
With faults 1 and 2, the amplifier will still operate, although the channel containing the faulty
tube will be quieter than normal. At low listening levels, the fault may not be obvious, but distor-
tion will become evident at higher listening levels.
If fault 3 occurs, the protection circuits will normally switch the amplifier off. You may also hear
loud background noises just before it switches off, although these will not harm the amplifier.
You can find the faulty tube by removing one tube at a time. Operating the power amplifier with
just a single output tube is allowed for test purposes and will not damage the power amplifier.
This test must only be carried out by a qualified technician.

20
10. TECHNICAL DATA AND DIMENSIONS
In- and Outputs
Inputs 1 x RCA
Outputs 1 x Loudspeaker output
Amplifier
Power output 2 x 70W / 4 ohms
Frequency response 10Hz - 80kHz / 0.5dB
Total harmonic distortion 0.1% at 10W into 4 ohms
Signal-to-noise ratio 100dB
Minimum load impedance 2 ohms
Construction
- double sided PCBs with plated-through holes using 130µm copper
- ceramic tube bases with silver contacts
- specially selected and burned-in longlife tubes
- professional, low inductance electrolytic capacitors, LH grade 105° C
- available in a range of anodized colours
General
Power consumption 160W minimum, 320W at full power
Weight 25 kg
Standard accessories Power cable, 3mm slotted screwdriver,
1 spare KT88/6550 tube
Dimensions Overall dimensions in mm
off
V1
V2
V3
V4
Power
4
85
mm
176 m
m
176 mm
ca. 493 mm
with Black Box connector
408 mm

21
10. SPECIFICATION
Distortion in % at 3W into 4 ohms between 30Hz and 20kHz
at a variety of bias settings
0.01
4
0.02
0.05
0.1
0.2
0.5
1
2
%
30 20k50 100 200 500 1k 2k 5k 10k
Hz
1
2
3
K
min
= 0,025%
Curve 1: Bias adjusted correctly
Curve 2: Bias 10% out
Curve 3: Bias 30% out
Frequency response
-6
+2
-5
-4
-3
-2
-1
+0
+1
d
B
r
A
10 80k20 50 100 200 500 1k 2k 5k 10k 20k 50k
Hz
Between 10Hz and 90kHz the frequency response tolerance is just 0.3dB

22
10. SPECIFICATION
THD between 30Hz and 20kHz
0.0001
100
0.001
0.01
0.1
1
10
50
%
30 20k50 100 200 500 1k 2k 5k 10k
Hz
The total harmonic distortion curve is very linear, increasing only slightly at the lowest
frequencies.
This performance is only possible using a highly specialist output transformer.