This folder has been printed to give you an idea of F M A C O U S T I C S ' philosophy, their products, the differences in stan­
dards and the way of manufacturing.
S o m e steps in the making of an F M 600A power amplifier are shown below.
Selecting power transistors: The reliability of a product stands or falls
with the quality of its components. Have a look inside an F M Acoustics
and you will immediately realise the difference. Only the best components
from the world's leading manufacturers are used despite the higher c o s t
E a c h and every component is c h e c k e d at the supplier's factory, then
c h e c k e d again a s soon a s it arrives at the F M factory. After this all active
devices g o through a test set where different parameters are measured
and the components are matched and colour c o d e d .
Mounting power transistors on cooling fins: Power transistors are
pecially manufactured for F M Acoustics a s there is no «standard» tran­
sistor available that handles the extreme requirements of voltage, current,
nnearity and speed. All power transistors are additionally c h e c k e d on a
, :urve tracer at low a n d high temperature and different voltage and current
levels. After this and other selections the transistors are carefully mounted
>y hand on the custom extruded cooling fins with torque-sensitive tools.
: .ater the transistors a s well a s the insulation between e a c h transistor a n d
Hie cooling fin are measured with a specially built testing machine.
Hand-soldered audio circuit: The individual parts are assembled and
--ach section like control print, peak reading led display, power supply,
• udio stages etc. undergoes a function test. Then the different sections
re mounted together a n d the product g o e s to a first calibration test.
Calibrating an F M 6 0 0 A : The assembled amplifier is then transferred
to the test b e n c h where e a c h amplifier is individually calibrated and c o m ­
pensated. D o z e n s of different parameters have to be measured by means
of the most a d v a n c e d testing facilities a n d specially built testing machines.
The typical final testing time of a power amplifier amounts to five hours.
After everything is o.k. the amplifier is moved into the specially built burn-in
Amplifiers in the fully automated burn-in r o o m : A specially built burnin machine controls up to 12 amplifiers at the s a m e time. The amplifiers are
thermally cycled by varying power levels, cycle times etc. Temperature in
the burn-in room is usually around 40°C, so that the amplifiers are strained
harder than in any practical application. Every 5,10 or 20 minutes the
amplifiers are allowed to run on their quiescent current for a few minutes
s o that there are continuous temperature differences in all components.
The amplifiers are burnt-in for at least 50 hours continuously with a
minimum of 200 thermal cycles. After this the amplifiers are placed on a
vibration table for 2 hours, so that all mechanical and electronic parts are
also stressed to levels far a b o v e any normal operation mode.
T h e s e are s o m e of the reasons that the failure rate of F M products
is between 3 a n d 10 times lower than those of the world's other leading
Final Test: The amplifiers are m o v e d b a c k to the test bench where
the final test is performed. All parameters that have been; measured at
the calibration test are c h e c k e d again a n d hand-entered in the instruc­
tion manual that is delivered with e a c h product. After this final test the
amplifiers are again inspected mechanically a n d then carefully p a c k e d .
B e c a u s e every product is fully h a n d m a d e the quantities that c a n
be built are extremely limited (e.g. the maximum quantity of F M 800's
that c a n be manufactured in one year is 4 0 0 pieces!). This of course is
another reinsurance that quality is unmatched, a s other manufacturers
have to divide their care to ten-thousands a n d hundred-thousands of
units. The difference c a n be seen, felt a n d heard.
N e w product development: There are different ways of planning
and introducing a new product. Most of todays c o n s u m e r a n d c o m ­
mercial products are 3-month developments, the reasons for this being
time-pressure a n d a fashion that is constantly changing.
A new F M A c o u s t i c s product d o e s take a long time (most c u s t o m ­
ers say it's m u c h too long) until it is introduced. However this philosophy
guarantees that the product provides a top performance right from the
beginning. Furthermore s u c h a product remains on top over many
years (the F M 8 0 0 A introduced in 1976 has not yet b e e n rivalled by
any other power amplifier) a n d should be regarded more a s a long term
investment (the average lifetime e x p e c t a n c y is over 20 years) than a
typical c o n s u m e r product. This philosophy is also manifested by the
people who p o s s e s s an F M A c o u s t i c s product, people who d o not
need fancy k n o b s a n d frontpanels, people w h o work professionally with
the product or have a serious dedication, people who believe in the old
tradition of hand craftmanship rather than «fast a n d efficient a s s e m b l y
There is no n e e d to explain that s u c h a way of production must be
considerably more expensive than usual w a y s a n d this is the reason
that an F M A c o u s t i c s will cost more at the initial stage than products
with similar specification. But nothing c a n be c o m p a r e d to the enthu­
siasm, pride a n d involvement that g o into e a c h product that carries the
name F M Acoustics.
- isureras
Today there are many high-power amplifiers available that
have certain advantages and certain drawbacks. Almost all are
designed for a price or for certain specifications but the
engineers at FM ACOUSTICS did not have such pressures and
took great care that in the design of the FM 600A andFM 800A
power amplifiers no detail was overlooked nor were com­
promises accepted. The amplifiers advantages lie not just in
superb specifications but in the way they reproduce sound with
an unmatched naturality, the exclusive components that are
used, the extreme care during assembly tuning and final test,
the rugged mechanical design and their long-term stability.
They have been in production since 1976 With little modification
and when used with appropriate high-quality equipment have
outperformed any other known power amplifier in the most
critical applications providing superb natural sound and un­
matched reliability.
To further reduce the size and weight of the transformer FM
ACOUSTICS are using a new type of transformer winding.
Figure 1 shows a cross-section of a conventionally wound trans­
former. Figure 2 shows the special rectangular foil which is
used to decrease space requirements and increase stability at
high current levels. Because of this transformer stability, the
amplifiers will provide much higher output levels under music
conditions than their rated power might suggest and, in fact,
the amplifiers have considerably more dynamics and sound
tighter than competing amplifiers with similar and even higher
power ratings.
Both amplifiers have the same features, same printed cir­
cuit boards and components. The only difference is that the
FM 800A has a larger power transformer, more output devices
and a low-noise dual-speed fan.
FM 600A: Sophisticated convection cooling:
The FM 600A uses large black anodized aluminium extru­
sions as heat-sinks that are directly mounted on the rear-panel
and tightly connected to the whole chassis cover and frontpanel which altogether radiate heat very efficiently. This
guarantees that the power amplifier stands up well to con­
tinuous long-term use in heavy-duty professional applications.
FM 800A: Duai-speed forced-air cooling system:
The higher output capacity of the FM 800A requires
increased air-flow. The heart of the FM 800A is its rubber-sus­
pended direct-blowing dual-speed forced-air cooling system.
This exclusive design achieves superb thermal stability and
extremely low thermal stress, which results in a tremendous
increase in long-term reliability. At continuous full power
operation into 8 Ohms for 24 hours the FM 800A reaches 39°C
only. (All other designs will either not stand this or operate at
around 1 0 0 ° C )
Temperature Stability:
Sensors on power transistors, forced-air cooling system
and power transformer individually measure temperature and
automatically control the dual-speed fan on the FM 800A. The
highest temperature before the sensors activate is a con­
servative 80° C and not 100° C or 120°C which other manufac­
turers allow. Therefore the transistors work in a safe area with
plenty of reserve. Unlike amplifiers using power Mosfets the
transistors in the FM 600A and FM 800A do not reduce the
current capability with increasing temperature. They deliver the
same output current at all temperatures from —25° C to
+ 80° C which guarantees that no dynamic compression and
power limiting occur at high temperatures, a weakness of many
other designs.
Delayed turn-on:
A special delayed turn-on circuit is used to protect the load
from thumps and transients. Within 5 seconds after switch-on
the amplifier has completely stabilised and the speakers are
connected without transients.
Overdesigned Power supply:
Extremely powerful mains transformers with a continuous
rating of 1000 W (FM 600A) and 2500 W (FM 800A) made of
special high-efficiency steel are used to reduce the weight of
the amplifiers and to guarantee continuous full power capacity
with extremely low distortion. Three (3) individual bridge rec­
tifiers with a current rating of 50 A are used for absolute
accuracy and dependability. Furthermore the transformers are
designed to work noiseless on 50 Hz and 60 Hz supplies. In­
stead of one smaller standard power transformer per channel
(which would be cheaper) FM ACOUSTICS are using one overdesigned power transformer for both channels while crosstalk
is minimised by special techniques. This results in better
dynamics with music material.
Cross-section wire
Cross-section wire giving
considerably higher efficiency
The amplifiers contain ten (10) different protection sys­
tems per channel, six of which are electronic and four of which
are by fuses. These protect the amplifier and the load against all
possible damages:
Delayed turn-on circuit to protect loudspeakers.
2. Short-time and continuous open-circuit protection (this
protection will not shut down amplifier).
3. Short-time and continuous short-circuit protection (this
protection will not shut down amplifier).
4. Special first stage circuit acts as input protection (this
protection will not shut down amplifier).
5. Protection against thermal overload and failure of forcedair cooling system (protection will shut down amplifier
temporarily and reset automatically).
Protection of loudspeakers and amplifier against DC-off­
set with separate systems for + and — DC-offset (pro­
tection will shut down amplifier. Manual resetting re­
7. Special superfast acting fuses against extreme high-fre­
quency overloads and/or instability of preceeding equip­
ment (protection will shut down amplifier. Fuse must be
replaced before resetting.)
8. Separate fuse for fan on FM 800A. (Fuse must be replaced
before resetting.)
9. Separate fuse for electronic protection systems. (Fuse
must be replaced before resetting.)
Primary side mains power fuse. (Fuse will shut down am­
plifier completely. Return amplifier for service.)
These protection systems guarantee that in real-world
fault situations the amplifier will not be damaged by misuse and
that it will protect the loudspeakers from dangerous DC vol­
tages and HF oscillations that could damage them within se­
conds. The protection systems are not just simple crowbar cir­
cuits that short-circuit the power supply as this results in greatly
reduced capacitor and rectifier life and always requires manual
resetting. They are either complex individual circuits or easy to
replace fuses and each one of them is designed specificly for
its special application.
Error Indicator:
The Error indicator on the frontpanel will light should the
temperature rise above 80° C and the amplifier will reset au­
tomatically after about 1 minute. The Error indicator will also
light if a DC voltage appears on the output or if any of the fuses
of other protection circuits blew. If the Error indicator lights the
loudspeakers are immediately disconnected from the amplifier
for protection.
Stereo or mono operation:
A stereo-mono switch on the rear-panel of the FM 800A
converts the amplifier instantly from a two-channel stereo am­
plifier to two mono amplifiers which are ideally suited to drive
large arrays of loudspeakers. The amplifiers cannot be connec­
ted in bridge mode as - despite the contrary claims of many
other manufacturers - neither these nor any other amplifiers
can be made absolutely stable in a bridged mode when working
into real-world impedances. Bridging an amplifier always results
in a degrading of sound quality and this is not acceptable for
Led level indicators:
Studio-type high speed led-arrays are used as level indi­
cators instead of fragile VU meters which are much too easily
damaged. Every led has its own precision comparator for
accurate peak level indication. Unlike other led-arrays the leds
in the FM ACOUSTICS are undamped and have an extremely
fast attack and decay time. This allows one to see system diffi­
culties like instabilities, oscillations, excessive tonearm
resonances etc. that cannot be seen on other led indicators.
The amplifiers are able to drive all currently available loud­
speakers, even highly reactive electrostatic systems while
remaining stable. They are also capable of driving inductive
loads such as servo motors, shake tables etc. They are designed
for 4 - 1 0 0 Ohm systems, but can drive down to 2 Ohms and
above 100 Ohms without difficulties. For lower impedances
than 2 Ohms there are special versions available.
It is extremely important that the preceeding equipment has
an output impedance according to the studio standard (600
Ohms or lower) as otherwise it is not possible to realise best
performance. The same applies to stability of preceeding equip­
ment. Before working with a system always check the com­
plete set-up with an oscilloscope for any instabilities or
Sound quality:
When auditioning the FM ACOUSTICS 600A & 800A you
should always compare to the original natural sound (attend
some concerts then ask your dealer to lend you an FM A C O U S ­
TICS for a few days to use at home in your set-up). To achieve
optimal results it is absolutely necessary to use the most natu­
ral sounding components available. The best performance will
be achieved when using the FM 240 reference preamplifier
and if necessary the FM 212A M C prepreamplifier. They have
absolute compatibility with all existing cartridges and can drive
any number of power amplifiers with absolute stability and
naturalness. Do not just make your decisions upon a few hours
listening and comparing in a dealers showroom as the reference
is live sound and not any other component. While realising that
words cannot describe sound quality satisfactorily and while
realising that the FM 600A's and the FM 800A's advantages
vary in strenght depending on the associated components
there are still some remarkable differences when comparing to
other power amplifiers. One immediately realises the accurate
depth reproduction while transients have superb dynamic
range and detail but lack the forward projection that many tran­
sistor amplifiers produce. The FM ACOUSTICS are devoid of
another weakness of currently available amplifiers, the ioss in
imaging and depth on quiet or loud passages. Middle frequency
reproduction is without equal and outperforms even today's
tube designs without having their inherent colouration. Low
bass is considerably extended and tightened up. A similar fre­
quency-range extension can be found in the top octaves.
The reason for these improvements lie partly in the circuitry
(the amplifiers work in class A most of the time) but one of the
most important reasons is that each transistor is tested and
selected for four different parameters into many colour-coded
groups and that only transistors with the same codes are used
in each stage. Furthermore each amplification stage is tuned
to optimum performance during the calibration test. This care
is very time consuming and expensive (sometimes 7 0 - 8 0 % of
the expensive high-voltage transistors must be rejected) but it
is the only way to guarantee this kind of sound quality, no unit
to unit variability and utmost reliability.
We encourage you to listen carefully under closely controlled
conditions for an extended period using the best and most
natural sounding components (only very few tube preamplifiers
will give satisfactory results). Then you will be able to realise
the potential of thejFM 600A and FM 800A.
For a product used in extreme professional applications
reliability is sometimes the most important parameter. Both
amplifiers are currently used in very demanding applications
from Norway to South Africa all over the world. Therefore the
parts used in the FM ACOUSTICS are extremely over-dimen­
sioned to guarantee long-term stability: you will find only 1%
tolerance precision metal-film resistors, the capacitors are ex­
pensive computer types, the audio circuitry uses only selected
special high-voltage, high-speed metal can transistors, the
power transistors (300 V, 30 A, 9 MHz) are specially manufac­
tured for FM ACOUSTICS, the long-life precision poten­
tiometers are dust- and waterproof, the frontpanel is not just
printed as usual but negatively anodised so that signs and num­
bers will never peel off etc. There is no other amplifier available
that is made out of such superb components. Have a look in­
side an FM ACOUSTICS and you will immediately realise the
Superb craftmanship:
Before the assembly starts every component is checked.
Then all hand-soldered P C boards are checked visually and
electronically. After this each FM ACOUSTICS amplifier is com­
pletely hand-assembled by experienced Swiss craftsmen. Then
each amplifier is tuned to optimum performance, is calibrated
and a first final test including all measurements is performed.
Led arrays, fan low- and high-speed operation, DC sensor
operation, all protection circuitry etc. are tested and power,
distortion, noise etc. are measured. Then every amplifier is
burnt-in for at least 50 hours under worst-case conditions. Then
each amplifier goes onto a shake table for two hours. When it
comes back to the test bench all curves and data must be exact­
ly the same as before. If they are the same the data are entered
in the instruction manual. If the data changed the amplifier is
left on the burn-in until it fails and then the reason for this dif­
ference and failure is analysed. This results in an unmatched
reliability and long-term stability.
Because of this extreme care the FM ACOUSTICS power am­
plifiers can only be made in small quantities.
Unfortunately specifications have been misused and misun­
derstood considerably during the last years. From unrealistic
power ratings to distortion ratings at 1 KHz only (the ear is
more sensitive to distortion at lowerfrequencies) specifications
were mainly used to sell a product. Many trustful customers
were disappointed when they realised that specifications were
misleading them.
For instance almost all manufacturers quote slew rates either
with no measurement details or at the unrealistic level of 1 W
into 8 Ohms or so and are therefore able to quote very impres­
sive slew rates. At FM ACOUSTICS we quote slew rate at full
power — 3 d B into any recommended load which is certainly
much harder and honest than the good-looking 1 W rating of
other manufacturers. Another example is power rating where
you will find differences of up to 3 0 0 % for similar power am­
plifiers. FM ACOUSTICS have decided to quote honest
minimum specifications instead of the much used «typical» spe­
cifications. Two power ratings are quoted: one for the output
power into a given impedance when both channels are driven
by a musical signal or tone bursts (the normal application) and
a second extremely conservative 100 hours power rating that
will provide data for worst-case operation using any continuous
sine-wave frequency in the audio band at low, medium or high
ambient temperature and at very low distortion.
Please observe sucfi differences if you want to compare to
other specification sheets. However specifications alone will
not tell you much about the true value for a certain component.
They are here to give you some idea of what the product can
be expected to do when used with some other component.
FM 600A FM 800A
Power output:
with mixed musical signal or tone
bursts 4:4 both channels driven,
per channel:
250 W RMS into 8 Ohms
350 W RMS into 4 Ohms
400 W RMS into 2 Ohms
(2 Ohms with special version)
400 W RMS into 8 Ohms
600 W RMS into 4 Ohms
850 W RMS into 2 Ohms
100 hours operation using con­
tinuous sine waves in the audio
band at low distortion both
channels driven:
150 W RMS into 8 Ohms
250 W RMS into 4 Ohms
300 W RMS into 8 Ohms
400 W RMS into 4 Ohms
typical distortion in mid-frequency
band at rated power:
0,008% THD
0,007% THD
somewhat higher at very low and very high frequencies
Slew Rate:
at rated power - 3 d B into
rated impedance:
25 V/usec
25 V/usec
Damping factor:
at middle frequencies:
greater than 500
greater than 800
Hum and Noise:
below full power typical:
minimal unweighted:
90 dB
Frequency response:
at levels up to 50 W RMS:
5Hz-300KHz - 3 d B
5Hz-300KHz - 3 d B
Input sensitivity:
into 4 Ohms at rated power:
0,9 V RMS
0,8 V RMS
Input Impedance:
at all level settings:
4 - 5 KOhm depending on level
4 - 5 KOhm depending on level
Load impedance:
designed for:
can drive down to:
special version for low impedance:
4 - 1 0 0 Ohm systems
2.5 Ohms
available down to 1 Ohm
2 - 1 0 0 Ohm systems
1 Ohm
stable with all loads including transformer coupled electrostatic loudspeakers
Average life
at 25° C ambient, medium power,
22 years
10 hours per day, 365 days per year:
AC Voltage selector:
28 years
110/120/220/230 V
110/120/130/220/230/240 V
Max. Owerwoltage:
short-term, not on switch-on:
long-term, including switch-on:
180% V nominal
135% V nominal
180% V nominal
125% V nominal
Power consumption:
at idle:
at 3 0 % power:
at full power:
700 W
250 W
900 W
2500 W
Led indicators:
undamped, peak-reading, calibrated
in dBVabove OdB (0,775V)
into 8 Ohms:
200 W RMS
70 W RMS
0,7W RMS
0,07 W RMS
AC line:
self-locking, 3-pin XLR type, Pin 1 = Ground, Pin 3 = Signal
5-way binding posts
3-wire (grounded) cable
+ 30dB
+ 10dB
300 W RMS
10 W RMS
0,1 W RMS
19 kgs net, 20 kgs packed
29 kgs net, 30 kgs packed
for standard 19" rack mount
483 mm wide, 177 mm high,
330 mm deep (incl. handles)
483 mm wide, 177 mm high,
360 mm deep (incl. handles)
recommended for uses such as:
studio monitoring, P.A.,
laboratory, industrial
studio monitoring, heavy-duty
P.A., laboratory, industrial
Continuous research is done by FM ACOUSTICS LTD and they will improve their products if possible.
Therefore specifications are subject to be changed from time to time.
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