Funk Tonstudiotechnik SAM-1C User manual

OPERATING MANUAL
BALANCING, DISTRIBUTION AND MATCHING AMPLIFIER

2
CONTENTS
___________________________________________________ ____________________________________
CONTENT INFORMATION page 2
FOR YOUR SPECIAL ATTENTION page 3
INTRODUCTION page 4..5
SIGNAL PATH AMPLIFIER MODULES page 6
CONFIGURATION KEY page 7
CONFIGURATION E AMPLES page 8..12
HUM LOOPS page 13
BLOCK DIAGRAM INPUT/OUTPUT MODULES page 14
AMPLIFIER MODULES SSOM-04Mc / SSIM-04Mc page 15..16
AUDIO SIGNAL QUALITY page 17 18
LEVEL ADJUSTMENT page 19
POWER SUPPLY page 20
CONVERSIONS / MODULE INSTALLATION AND REMOVAL page 21
MEASUREMENT DIAGRAMS page 22..24
TECHNICAL DATA page 25
NOTES ON IMMUNITY TO INTERFERENCE page 26
MAINTENANCE AND REPAIR page 27
CE - DECLARATION OF CONFORMITY page 28

3
FOR YOUR SPECIAL ATTENTION
______________________________________________________________________________________
These operating instructions apply in principle to all versions of the SAM-1C, as long
as no differences are pointed out.
ATTENTION :
Mains connection only to AC voltage 90..260 Volt/50 - 60 Hz !
To avoid fire and electric shock, do not expose the unit to rain or moisture!
If any liquid enters the interior of the unit, switch it off immediately and have it
checked by the manufacturer or a specialist workshop before continuing to use it!
NOTES ON THE LINE UP :
Never place the unit near heat sources such as radiators or hot air outlets, or in places
subject to a lot of dust, mechanical vibrations or shocks..
FOR CONDENSATION ACCUMULATION :
If the unit is moved immediately from a cold to a warm place, condensation may form
inside and there is a risk that the unit will not work properly. In this case, leave the
unit switched off for half an hour after transport.
CLEANING :
Clean the cabinet and front panel with a soft cloth lightly moistened with a mild soap
solution. Abrasive sponges, scouring powders and solvents such as alcohol or petrol
must not be used as they may damage the surface of the cabinet.
WARRANTY :
The warranty period is 3 years. Defects that are due to manufacture or faulty material
will be repaired free of charge during this period. The warranty claim expires after
external intervention !

4
INTRODUCTION SAM-1C
_____________________________________________________________________________________________________________
Balancing and matching amplifier
1. DESCRIPTION :
The SAM-1C is a universal, professional 4-channel matching and balancing differential amplifier
(instrumentation amplifier) in ironless circuit technology for use with the highest demands on sound quality.
Asymmetrical "home recording" and PC inputs and outputs and hi-fi equipment signals can be matched to
professional balanced or unbalanced studio equipment inputs outputs. Level adjustments from -10 dBv to +6
dBu and vice versa as well as signal distribution is also possible, depending on the configuration.
The SAM-1C is the successor of the SAM-1B SAM-1B with the additional possibility to mix signals. The audio
signal quality, such as common-mode rejection (unbalance attenuation), THD distortion, headroom and
overall dynamic range, has been further improved.
Compared to the SAM-1B, the SAM-1C version also has a precision switching power supply for operation with
all mains supplies worldwide with operating voltages of 80..260 V and frequencies between 45..440 Hz. The
mains cable of the SAM-1C is detachable.
The SAM-1C can enable the following functions simultaneously :
1. a high-impedance signal becomes low-impedance (impedance conversion).
2. an input signal can be amplifieda balanced signal becomes asymmetrical attenuated
3. a balanced signal becomes asymmetrical
4. an asymmetrical signal becomes symmetrical
5. 2 balanced signals can be summed (mixed) (stereo > mono)
6. "hum loops" between unbalanced units can be eliminated
7. switch-on or switch-off crackles of a sound system can be eliminated ("power-down" mute)
8. configurations as balancing and distribution amplifier internally possible
1.1 Mode of action :
To ensure that the interference voltages induced or influenced on a line cause as little interference as possible
in an input of an audio control system connected to this line, this input must be "symmetrical to earth", i.e.
the two resistances measured between each of the input terminals and earth must be equal in magnitude and
phase. The induced interference voltages, which are equal in magnitude and phase on both conductors, then
cancel each other out in their effect with a symmetrical input and have no influence. If the symmetry is not
exact, however, the induced voltage is not completely cancelled out and a residual interference voltage
remains in the subsequent transmission path.
The balanced input stages SSIM-04Mc of the SAM-1C achieve a typical suppression of balanced interferences
at 1 kHz in the ratio 1 000 000 1 approx. - 120 dB ! This extremely high symmetry also makes it possible to
optimally suppress interference due to different ground potentials. This also applies to applications with
otherwise asymmetrical cabling.
Auto-Mute :
The outputs of the amplifiers in the SAM-1C have a "power-down" mute relay in the output. This ensures a
largely crack-free switching on and off of the unit even after a sudden drop or failure of the supply voltage.

5
XLR-FEMALE
3
21
XLR-MALE
-
+
-
+
INTRODUCTION SAM-1C
___________________________________________________________________________________________________________
The SAM-1C has a modular design and can therefore be offered in different versions. Due to the service-
friendly design, the amplifier modules including all sockets can be exchanged or extended subsequently in
a few minutes without soldering.
All inputs outputs have spindle trimmers on the rear panel of the unit, with which the amplification can be
adjusted very precisely for each channel separately from the outside.
During the development of the SAM-1C, special attention was paid to lowest noise (dynamic range at
amplification 1 : typ. 136 dB !) and minimal distortion with a very broadband design of all amplifier stages.
The THD distortions in the important mid-range are typically below - 130 dB at signal levels between
-10 dB...+12 dB! This could only be achieved by using several operational amplifiers per balanced input
and "instrumentation amplifier technology". An excellent phase response of typ. less than 1° in the range
of 10 Hz...20 kHz and a large signal bandwidth of more than 100 kHz guarantee excellent impulse
processing (see also chapter AUDIO SIGNAL QUALITY).
The SAM-1C can also be used for matching time code signals due to its exceptional bandwidth of over 200
kHz. The excellent crosstalk attenuation of over 125 dB at 1 kHz and 120 dB at 10 kHz between the two
channels also allows the use of both signal paths for different mono signal sources simultaneously.
Due to the very high common-mode rejection of the balanced input amplifiers of typ. 120 dB at 1 kHz,
interferences interfering with the balanced line are almost completely eliminated.
The prerequisite for the exceptionally high common-mode rejection or symmetry of the amplifiers used is
our laser-trimmed precision networks on ceramic carriers.
The balanced inputs of the SAM-1C can also be operated asymmetrically at the input without any
problems, e.g. for use as an asymmetrical catch-up amplifier impedance converter, phase reversing stage
or for "hum loop elimination" see also chapter HUMBLE ELEMENTS.
Once the output level has been set, it remains constant due to servo balancing with balanced and
asymmetrical wiring of the XLR outputs. In contrast to many other balanced amplifier circuits, the
maximum achievable output voltage (headroom) of the SAM-1C does not decrease with asymmetrical
wiring of the balanced output! This results in a further improvement of the dynamic range compared to
comparable balancing amplifiers of typ. 4..6 dB when the outputs are operated in unbalanced mode.
Flawless operation is guaranteed at all balanced outputs up to 300 Ohm output load.
The unbalanced inputs outputs are connected via gold-plated cinch sockets. The balanced inputs outputs
are connected to XLR sockets with gold-plated contacts.
1.2 Pin assignment of t e XLR sockets :
Pin 1 is audio ground
Pin 2 is the +in output of the amplifiers
Pin 3 is the -input output of the amplifiers
All balanced inputs and outputs are
equipped with NEUTRIK XLR sockets. The
pin assignment is as usual in professional
technology (see picture). Circuit zero
(ground) and earth (enclosure) are
separated from each other to achieve
greater freedom when installing in different
systems.
1.3 Rear view SAM-1C :
Compared to the predecessor models SAM-
1A and SAM-1B, the SAM-1C is equipped
with a standard mains socket for mains
cables. The power switch is also located on
the back of the unit.

6
EINGANG LINKS
VERSTÄRKUNG LINKS 0..-20 dB
VERSTÄRKUNG RECHTS 0..-20 dB
XLR-FEM ALE
OUT L
OUT R
CINCH
SYMMETRISCHE EINGANGSSTUFE
LINE AUSGANGSSTUFE
MASSE
SYMMETRISCH
EINGANG RECHTS
SYMMETRISCH
J1
J3
VERSTÄRKUNG 0 (+6) dB
MASSECHASSIS
J8A
J9A
J8B
J9B
SUMMIERUNG
R24
R25
J10
J11
321
321
J2
J3
MASSE CHASSIS
AUSGANG LINKS
SYMMETRISCHE AUSGANGSSTUFEEINGANGSVERSTÄRKER
J2/J3 VERSTÄRKUNG FIX 0 dB
VERSTÄRKUNG 0..24 dB
XLR -M ALE
AUSGANG RECHTS
CINCH
SYMMETRISCH
SYMMETRISCH
J4
J5
DÄMPFUNG
DÄMPFUNG 0...-X dB
MASSE
R1
R2
R1b
R2b
22kO m
22 kO m
EINGANG 1R
EINGANG 1L
J6A
J7
SIGNAL PATH AMPLIFIER MODULES SAM-1C
_____________________________________________________________________________________________________
2-CHANNEL DIFFERENTIAL AMPLIFIER MODULE SSIM-04Mc
On analogue balanced audio lines, the signal level is often higher than on unbalanced cabling. When
converting from balanced to unbalanced technology, an adjustable level reduction is therefore usually
desired. The differential amplifiers (desymmetrical amplifiers) of the SAM-1C normally allow an
attenuation in the range of -20...0dB, depending on the setting of the spindle trimmers. For special
cases, however, amplification of the audio signal is also possible. For this purpose, solder jumpers J1 for
the left and J3 for the right channel are provided on the SSIM-04Mc modules. If these are closed, the
corresponding channel works with +6 dB amplification in the input stage. The gain adjustment range is
then approx. -14..+6 dB. The max. permissible input voltage decreases by 6 dB to approx. +18 dBu
when the jumpers are closed. Jumpers 8..11 allow summation or distribution of the input signals within
the module.
Circuit zero and chassis are separated from each other in the SAM-1C. Pin 1 of the XLR socket is
connected to circuit zero and the ground connection (shown in black in the diagram) of the
corresponding RCA socket, the XLR housing is connected to the chassis (protective earth connection
green).
2-CHANNEL BALANCING AMPLIFIER MODULE SSOM-04Mc
On unbalanced audio lines, the signal level is often lower than on analogue balanced cabling. When
converting from asymmetrical to symmetrical technology, an adjustable gain will therefore usually be
required. The SAM-1C's balancing amplifiers normally allow a gain in the range of 0...+24 dB,
depending on the setting of the spindle trimmers.
For special cases, attenuation of the audio signal is also possible. For this purpose, solder jumpers J4
for the left and J5 for the right channel are provided on the SSOM-04c modules. When these are closed,
the resistors R1 and R1b (R2 and R2b) work as voltage dividers of the corresponding channel. The
attenuation achieved depends on the resistance ratio of these two resistors and must be calculated
accordingly. The resistors R1b R2b are 22 kΩ. For an input attenuation of 6 dB, for example, R1 R2
must also be changed to 22 kΩ. R1 and R2 have a resistance of 330 Ohm in the standard version.
Suitable resistors of the type "Micromelf" or SMD-0204 can be requested if required. After setting the
damping jumpers, the input impedance of the corresponding channels is reduced to values between
22...220 kΩ, depending on the dimensioning of the resistors R1 or R2. Jumpers 6 and 7 enable the
distribution of an input signal to both amplifier trains.

7
SAM-1C CONFIGURATION KEY
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2. CONFIGURATIONS :
2.1 Type designation :
The SAM-1C is available with 4 or only partially equipped with 2 independent amplifier trains. In the type
designation :
1st digit after slash = number of balancing channels,
2nd digit = number of differential channels (de-symmetrizer).
Example: SAM-1C 0-4 means: 0 balancing and 4 differential amplifier channels. The hyphen (-) between
the digits means: no connection between the amplifier channels. If this hyphen is replaced by a letter or a
combination of letters, all or some of the audio channels are internally interconnected (see following
diagrams).
Example: SAM-1C 4V0 means: 4 balancing amplifier channels and 0 differential amplifier; the V between
the digits means: the balancing channels are internally configured as distribution amplifiers.
The configuration of the input and output modules can be changed subsequently.
The 2-channel versions can also be subsequently expanded without soldering. The power supply and the
necessary internal wiring are already available for this purpose.
2.1.1 Type designation key :
Audio connections between the channels
= no connections between the channels (standard version)
= connected as distribution amplifier
= Distribution amplifier fully balanced
-
V
SVS
= switched as mono distribution amplifierMV
= switched as mono mixing amplifierM
= connected as mono distribution amplifier fully balanced
SMVS
= switched as stereo mixing amplifierMS
S A M - 1 C / 2 - 2
Device type Unit series Number
Balancing
amplifiers
Number
Differential
amplifiers
with Switching power supply

8
SAM-1C CONFIGURATION EXAMPLES
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2.2 VARIANTS :
2.2.1 Configurations :
Available 2-channel versions :
SAM-1C/2-0 2x Cinch in > 2x XLR sym. out
SAM-1C/0-2 2x XLR sym. in > 2x Cinch out
SAM-1C/0M2 2x XLR sym. in > 2x Cinch mono out (Summing amplifier)
SAM-1C/2M2 2x XLR sym. in > 2x Cinch mono out + 2x sym mono out (Summing amplifier)
SAM-1C/2MV0 1x Cinch in > 1x Cinch direct out + 2x sym. out XLR (Distribution amplifier)
SAM-1C/2SMVS1 1x XLR in > 4x Cinch direct out + 2x sym. out XLR (Distribution amplifier)
SAM-1C/2SVS2 2x XLR sym. in > 2x XLR sym. out (Fully balanced matching amplifier)
Available 4-channel variants :
SAM-1C/2-2 2x Cinch in > 2x sym. out XLR + 2x XLR sym. in ⇒ Cinch out.
SAM-1C/4-0 4x Cinch in > 4x sym. out XLR
SAM-1C/0-4 4x XLR sym. in > 4x Cinch out
SAM-1C/0M4 2x XLR sym. stereo in > 2x [2x Cinch mono out] (Summing amplifier 2-way stereo)
SAM-1C/4V0 2x Cinch in > 2x Cinch direkt out + 2x 2 sym. out XLR (Distribution amplif.)
SAM-1C/4MV0 1x Cinch in > 3x Cinch direkt out + 4x sym. out XLR (Distribution amplifier)
In principle, up to 4 amplifier channels (2 modules) can be installed in the SAM-1C. Combinations of
distribution or summing amplifier configurations and additional individual modules are also possible,
depending on the space available. In this case, the functions of the modules can be specified individually,
separated by slash . Example :
SAM-1C/0M2/2-0 2x XLR sym. in > 2x Cinch mono out (Distribution amplifier, stereo > mono)
+ 2x Cinch in > 2x XLR sym. out
2.3 CONFIGURATION EXAMPLES :
2.3.1 2-c annel differential and 2-c annel balancing amplifier :
This configuration is used, for example, to adapt the recording and playback side of a stereo unit with RCA
jacks to professional studio equipment with sym. XLR inputs and outputs. It follows that, for example, a
professional unit with XLR connectors can also be matched to a system with RCA jacks. Level corrections
are possible simultaneously and independently on all lines.
Signal flow : SAM-1C/2-2 1 differential amplifier module and 1 balancing amplifier module
EINGANG
XLR-FEMALE
CINCH
SYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
DÄMPFUNG VARIABEL
MASSE
MASSE
CHASSIS
321
321
SYMMETRISCHE AUSGANGSSTUFEEINGANGSSTUFE XLR-MALECINCH
AUSGANG
MASSE
VERSTÄRKUNG VARIABEL
MASSE
CHASSIS

9
DÄMPFUNG VARIABEL
MO NO OUT 1
MONO OUT 2
MASSE
MASSE
CHASSIS
STEREO-EINGAN G
XLR-FEM ALE CINCHSYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
MISCHSTUFE
SAM-1C CONFIGURATION EXAMPLES
_______________________________________________________________________________________________
2.3.2 2-c annel differential amplifier :
This version enables the connection of 2 balanced audio signal sources to unbalanced inputs. Two
independent amplifier channels are realised by using a differential amplifier module SSIM-04Mc. The gain
of each output can be adjusted separately in the range of -20..0 dB, with jumpers J1 and J3 it is also
possible to switch on gains of up to 6 dB.
Signal flow : SAM-1C/0-2 with 1 differential amplifier module SSIM-04Mc
2.3.3 2-c annel balancing amplifier :
This version enables the connection of 2 unbalanced audio signal sources to balanced inputs. Two
independent amplifier channels are realised by using a balancing amplifier module SSOM-04Mc. The gain
of each output can be adjusted separately in the range of 0..+24 dB, level reductions can also be
achieved with jumpers J4 and J5.
Signal flow : SAM-1C/2-0 with 1 balancing amplifier module SSOM-04Mb
2.3.4 2-c annel summing amplifier wit balanced input :
This version enables the connection of 2 balanced audio signal sources which are mixed and available as
an unbalanced mono signal at 2 unbalanced cinch outputs. The gain of each output can be adjusted
independently in the range of -22..-2 dB. Versions with maximum amplification of -10 ..+10 dB are also
available.
Signal flow : SAM-1C/0M2 with an asymmetric amplifier module SSIM-04Mc
3
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFE
EINGANGSSTUFE
XLR-MALE
CINCH
AUSGANG
MASSE
VERSTÄRKUNG VARIABEL
MASSE
CHASSIS
EINGANG
XLR-FEMALE
CINCH
SYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
DÄMPFUNG VARIABEL
MASSE
MASSE
CHASSIS

10
SAM-1C CONFIGURATION EXAMPLES
_____________________________________________________________________________________________
2.3.5 4-c annel distribution and balancing amplifier :
The balancing amplifier modules SSOM-04Mc of the SAM-1C can also be configured internally as stereo
distribution amplifiers (1 unbalanced RCA input to 2 balanced XLR outputs each). In this case, the input
signals are applied in parallel to the involved RCA sockets of one channel, so that the second RCA socket
can be used as a loop-through output (see diagram below). The gain of each balanced output can be
adjusted separately. The following example shows a configuration 2x 1 to 2; inputs unbalanced, outputs
balanced.
Signal flow : SAM-1C/4V0 2 stereo output modules as balancing and distribution amplifiers
2.3.6 4-c annel balancing amplifier :
This version allows the connection of up to 4 unbalanced audio signal sources to balanced inputs. Four
independent amplifier channels are realised by using 2 balancing amplifier modules SSOM-04Mc. The gain
of each output can be adjusted separately in the range of 0..+24 dB, level reductions can also be
achieved with jumpers J4 and J5.
Signal flow : SAM-1C/4-0 2 stereo output modules SSOM-04Mc as balancing amplifier
2.3.7 2-c annel summing amplifier fully balanced :
This version allows the connection of 2 balanced audio signal sources which are mixed and available as
an unbalanced mono signal at 2x 2 unbalanced cinch outputs and additionally balanced mono at two XLR
connectors. The gain for the balanced outputs can be adjusted independently of each other in the range
of -22..+18 dB.
Signal flow : SAM-1C/2M2
3
AUSGANG 1 L SYMMETRISCH
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFEEINGANGSVERSTÄRKER
XLR-MALE
AUSGANG 1 R SYMMETRISCH
3
AUSGANG 2 L SYMMETRISCH
2
1
3
2
1
VERSTÄRKUNG 0..24 dB
AUSGANG 2 R SYMMETRISCH
MASSE
CHASSIS
MASSE
CINCH
3
2
1
3
2
1
MASSE
VERSTÄRKUNG VARIABEL
MASSE
CHASSIS
321
321
SYMMETRISCHE AUSGANGSSTUFEEINGANGSSTUFE XLR-MALECINCH
AUSGANG
SYMMETRISCH
MASSE
VERSTÄRKUNG VARIABEL
MASSE
CHASSIS
SYMMETRISCHE AUSGANGSSTUFE
EINGANGSSTUFE XLR-MALECINCH
AUSGANG
SYMMETRISCH
321
321
SYMMETRISCHE AUSGANGSSTUFEEING ANGSST UFE XLR-MALECINC H
DÄMPFUNG VARIABEL
BUS 1 MONO
BUS 2 MONO
MASSE
MASSE
CHASSIS
BUS 1 MONO
BUS 2 MONO
MASSE
VERSTÄRKUNG VARIABEL
STEREO-EIN GANG
XLR -FEMALE CINCHSYMMETRISCHE EIN GANGSSTUFE BUFFERSTUFE
SYMMETRISC H
AU SGANG MONO
2x SYMMETRISCH
MASSE
CHASSIS
MISCHSTUFE

11
SAM-1C CONFIGURATION EXAMPLES
_____________________________________________________________________________________________
2.3.8 4-c annel differential amplifier :
This version allows connecting up to 4 balanced audio signal sources to unbalanced inputs. Four
independent amplifier channels are realized by using 2 differential amplifier modules SSIM-04Mc. The
gain of each output can be adjusted separately in the range of -20..0 dB, with jumper J1 and J3 also
gains up to 6 dB can be switched on.
Signal flow : SAM-1C/0-4 with 2 stereo differential amplifier modules SSIM-04Mc
2.3.9 2-c annel matc ing amplifier fully balanced :
The SAM-1C is also available as a 2-channel fully balanced matching amplifier. In this configuration 2
balanced audio signals can be level corrected. In the input amplifiers a level reduction between 0...-21 dB
can be set. For each output a gain of 0...+23 dB can be adjusted independently via the spindle trimmers. A
short circuit at one output has no influence on other outputs.
In addition, an unbalanced signal can be taken from the RCA sockets. However, long cables should not be
connected here, as the capacity of the cables connected here can also have a slight influence on the
balanced outputs.
The following block diagram shows as an example a configuration 2x 1 on 1. The SSIM-04Mc module works
as a differential amplifier. The output signal of this amplifier is fed to both RCA sockets of the
corresponding channel and the input stages of the SSOM-04Mc module. The symmetry of the input signals
has no influence on the symmetry of the output signals and vice versa.
Fully balanced matching amplifier SAM-1C/2SVS2 with 1 each SSIM-04Mc and SSOM-04Mc
3
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFEEINGANGSSTUFE XLR-MALECINCH
DÄMPFUNG VARIABEL
MASSE
MASSE
CHASSIS
MASSE
VERSTÄRKUNG VARIABEL
EINGANG
XLR-FEMALE CINCHSYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
AUSGANG
SYMMETRISCH
MASSE
CHASSIS
EINGANG
XLR-FEMALE
CINCH
SYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
DÄMPFUNG VARIABEL
MASSE
MASSE
CHASSIS
EINGANG
XLR-FEMALE CINCHSYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
DÄMPFUNG VARIABEL
MASSE
MASSE
CHASSIS

12
SAM-1C CONFIGURATION EXAMPLES
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2.3.10 Mono distribution and balancing amplifier 1 on 2 :
The SSOM-04Mc balancing amplifier modules can also be configured internally as mono distribution
amplifiers (1 unbalanced RCA input to 2 balanced XLR outputs). In this case, the input signal is also
applied in parallel to the second RCA socket of a channel, so that this second RCA socket can be used as
a loop-through output "BUS-OUT". The gain of each balanced output can be adjusted separately. As the
following example a configuration 1x 1 on 2; inputs unbalanced, outputs balanced.
Signal flow : SAM-1C/2 MV 0 1 SSOM-04Mc module as distribution and balancing amplifier
2.3.11 Mono distribution amplifier 1 to 2 fully balanced :
Signal flow : SAM-1C/2 SMVS 1 with one module each SSOM-04Mc and SSIM-04Mc
2.3.12 4-c annel mono distribution and balancing amplifier :
The balancing amplifier modules SSOM-04Mc of the SAM-1C can also be configured internally as mono
distribution amplifiers (1 unbalanced RCA input to 4 balanced XLR outputs). In this case, the input signals
are applied in parallel to the involved RCA sockets of one channel, so that the second, third and fourth
RCA sockets can be used as loop-through outputs ("BUS-OUT" see diagram below). The gain of each
balanced output can be adjusted separately. The following is a configuration 1x 1 on 4; inputs
unbalanced, outputs balanced.
Signal flow : SAM-1C/4 MV 0 2 modules SSOM-04Mc as distribution and balancing amplifier
3
AUSGANG 1 SYMMETRISCH
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFEEINGANGSVERSTÄRKER
XLR-MALE
AUSGANG 2 SYMMETRISCH
3
AUSGANG 3 SYMMETRISCH
2
1
3
2
1
VERSTÄRKUNG 0..24 dB
AUSGANG 4 SYMMETRISCH
MASSE
CHASSIS
MASSE
CINCH
3
AUSGANG 1 SYMMETRISCH
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFEEINGANGSVERSTÄRKER XLR-MALE
AUSGANG 2 SYMMETRISCH
VERSTÄRKUNG 0..24 dB
MASSE
CHASSIS
MASSE
CINCH
3
2
1
3
2
1
SYMMETRISCHE AUSGANGSSTUFEEINGANGSSTUFE XLR-MALECINCH
DÄMPFUNG VARIABEL
MASSE
MASSE
VERSTÄRKUNG VARIABEL
EINGANG
XLR-FEMALE CINCHSYMMETRISCHE EINGANGSSTUFE BUFFERSTUFE
SYMMETRISCH
AUSGANG
SYMMETRISCH
MASSE
CHASSIS

13
HUM LOOPS SAM-1C
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3. Ripple loops :
Often, hum disturbances are not caused by electrical or magnetic interference fields alone. Ground
potential differences between the connected devices, e.g. due to double grounding, result in "hum loops",
which can sometimes cause considerable interference currents due to the low-impedance shields of the
cables of the wired devices. Depending on the circuit design, these currents also generate hum voltages
within the connected audio devices and add to the already disturbed audio signals. Balanced circuitry can
easily remedy this situation.
3.1 Ground loops wit asymmetrical circuitry :
A real remedy can only be achieved by disconnecting this ground connection and using a LF transformer
or differential amplifier.
The following diagram shows the effect of a ground loop separation within an asymmetrical cabling by
interposing a balanced amplifier input (differential amplifier SAM-1c).
A differential amplifier or a high-impedance "instrumentation amplifier" ideally takes into account only the
difference between its two inputs. If the two inputs are connected to each other and then modulated
together, no signal is produced at the output. If you now connect the -input to the ground or shield pin of
the transmitting device and the +input to the hot pin of the signal output, an in-phase modulation of both
inputs of the balanced receiver occurs; in our example with 100 mV noise signal. However, the output
signal remains at 0 Volt, since there is no difference between +and -input.
If now the output of the transmitting device is modulated with an audio signal of 1 V, there will be a
difference of 1 V at the balanced input of the SAM-1C as well. Consequently this audio signal will also be
present at the output of the SAM-1C, but freed from the ripple voltage. This principle also works if the
two wires (blue and red) would be swapped. Only the phase position for the useful signal would turn by
180°. This can also be used to compensate for "phase shifts".
No amplifier works ideally. Common circuits achieve a suppression of the interference signal to
1 100..1 10.000 (40..80 dB). Therefore, a small amount of noise residual will often be detectable in the
output signal of the differential amplifier. Due to careful development, laser-trimmed circuits and
instrumentation amplifier technology, suppressions of up to 1 1,000,000 (120 dB) can be expected with
the SAM-1C. So in our example still approx. 0.1µV (~ -140 dB compared to useful signal) and thus far
below the background noise of connected devices.
In the SAM-1C housing (ground or protective earth potential) and circuit zero (ground) are separated
from each other in order not to create additional risk of ground loops.
The drawing on the left explains the practical connection of the
unbalanced signal source to the balanced input of the SAM-1C.
Pin 1 remains open and pin 3 is connected to the shield.
XLR-FEMALE
CINCH
EINGANG
IN
SYMMETRISCH
SENDENDES GERÄT OUT EMPFANGENDES GERÄT
DIFFERENZ MASSEPOTENTIALE
100 mV
AUDIOSIGNAL 1V
STÖRSIGNAL 100mV
STÖRSIGNAL 100mV
SAM-1C
AUDIOSIGNAL 0V
AUDIOSIGNAL 1V
STÖRSIGNAL 0mV
STÖRSIGNAL 0mV
AUDIOSIGNAL 0V
AUDIOSIGNAL 1V
STÖRSIGNALFREIES
AUDIOSIGNAL
GESTÖRTES
AUDIOSIGNAL
AUDIOSIGNAL 1V
gleic p asig
gleic p asig
STÖRSIGNAL
DIFFERENZ MASSEPOTENTIALE
0 mV
STÖRENDES GERÄT

14
BLOCK DIAGRAM AMPLIFIER MODULES SAM-1C
______________________________________________________________________________________________
Block diagram Audio 2-c annel module SSIM-04Mc
balanced XLR inputs to unbalanced RCA outputs
Block diagram Audio 2-c annel module SSOM-04Mc
unbalanced RCA inputs to balanced XLR outputs

15
AMPLIFIER MODULE CONFIGURATION SAM-1C
_______________________________________________________________________________________________
DIFFERENTIAL AMPLIFIER SSIM-04Mc
P1 P2 P4 P6
CN1 J2 J6 J7 J5 J1 J3 J4
Function of the trimmers and jumpers : CN1 Pin assignment :
J1 additional gain +6 dB left channel Pin 1 Ground
J3 additional gain +6 dB right channel Pin 2 Output left channel unbalanced
J2 Gain left channel fixed 0 dB Pin 3 Ground
J4 Gain right channel fixed 0 dB Pin 4 Ground
J5 0-Ω-Bridge (0-volt power supply ground) Pin 5 Ground
J6 Control „Power-Down-Mute“ Pin 6 Output right channel unbalanced
J7 Control „Power-Down-Mute“ Pin 7 NC 8 (Not connected)
J8 Stereo mono mode L (J8 A = stereo, A+B = mono) Pin 8 Power supply +12,0...20,0 Volt
J9 Stereo mono mode R (J9 A = stereo, A+B = mono) Pin 9 Power supply 0 Volt
J10 Impedance L internal to 1.5 kΩ (for summation) Pin 10 Power supply -12,0...20,0 Volt
J11 Impedance R internal to 1.5 kΩ (for summation) Pin 11 Power supply Mute-Relais A +
J12 Mute relay always to ground (Circuit ground) Pin 12 Power supply Mute-Relais A -
J13 Mute relay always on +supply (+12..20V) Pin 13 Power supply Mute-Relais B +
P1 CMRR adjustment symmetry 1 kHz input left Pin 14 Power supply Mute-Relais B -
P2 CMRR adjustment symmetry 10 kHz input left
P4 CMRR adjustment symmetry 1 kHz input right
P5 CMRR adjustment symmetry 10 kHz input right

16
AMPLIFIER MODULE CONFIGURATION SAM-1C
_______ ____ ______ ____ ______ ____ ______ ____ ______ ______ ____ ______ ___ _______ ____ ______ ____
BALANCING AMPLIFIER SSOM-04Mc
J5 J4 C13 P3 P5 C14 P4 P6
CN2 J6 J7 J1 J8..J11 J2 J3
Function of the trimmers and jumpers : CN2 Pin assignment :
J2 Gain left channel fixed 0 dB (J2 closed) Pin 1 Ground
J3 Gain right channel fixed 0 dB (J3 closed) Pin 2 Input left channel asymmetrical
J4 Input level attenuation left active (J4 closed) Pin 3 Ground
J5 Input level attenuation right active (J5 closed) Pin 4 Ground
J6 Inputs directly linked (J6 A+B closed, J7 open) Pin 5 Ground
J7 Ground to input bridge (J7 closed) Pin 6 Input right channel asymmetrical
J8 close when used outside SAM-1C (Mute-Relais) Pin 7 NC 8 (Not connected)
J9 close when used outside SAM-1C (Mute-Relais) Pin 8 Power supply +20,0 Volt
J10 close when used outside SAM-1C (Mute-Relais) Pin 9 Power supply 0 Volt
J11 close when used outside SAM-1C (Mute-Relais) Pin 10 Power supply -20,0 Volt
J1 0-Ω- Jumper (0-volt power supply ground) Pin 11 Power supply Mute-Relais links +
P3 CMRR adjustment Symmetry impedance left Pin 12 Power supply Mute-Relais links -
P5 CMRR adjustment Symmetry output voltage left Pin 13 Power supply Mute-Relais rechts +
C13 CMRR adjustment symmetry 10 kHz left Pin 14 Power supply Mute-Relais rechts -
P4 CMRR adjustment Symmetry impedance right
P6 CMRR adjustment Symmetry output voltage right
C14 CMRR adjustment symmetry 10 kHz right

17
AUDIO SIGNAL QUALITY
________________________________________________________________________________________________
4. AMPLIFIER PATHWAYS :
The SAM-1C is equipped with very broadband amplifier trains that ensure an exceptional, very phase-clean
signal transmission. This is impressively proven by the following measurement reports. The balancing
amplifier module SSOM-04Mc, set to 0 dB gain (input signal level = output signal level), was driven by
square wave signals from a fast pulse generator.
Test signal Fig. 1: 1 kHz at a level of approx. 1.5V RMS (corresponds to +6 dBu line level) at a usual load
resistor of 10 kΩ. The wide frequency and phase response in the bass range and the clean processing of
even the deepest bass impulses can be seen from the barely visible slope of the roof.
Test signal Fig. 2: 10 kHz at a level of approx. 1.5V RMS. Load resistance of the oscilloscope during this
measurement: 300 Ohm. The very steep edges show the wide frequency response of the balancing amplifier
in the high frequency range. Even the fastest pulses are reproduced exactly!

18
AUDIO SIGNAL QUALITY
_______________________________________________________________________________________
Amplifier pat s :
Test signal Fig. 3: Large signal bandwidth of the SAM-1C. Sine signal 100 kHz at a level of approx. 10 V RMS
or 30 Vpp (corresponds to approx. +22 dBu line level). Even largest audio signals with highest frequencies
far above the audible range can be transmitted cleanly by the amplifiers. This measurement curve shows
that the SAM-1C can also be ideally used for signal balancing of the latest digital audio sources, which today
operate at up to 384 kHz sampling rate.
4.1 THD- Distortions :
This measurement record shows the typical, extremely low non-linearities at different input levels at the
balancing amplifier module SSOM-04Mc. The measurement was performed with a signal of 1 kHz, at a set
gain of 1 (0 dB) at the SAM-1C (level trimmer at left stop). From -6 dBu to +11 dBu line level the THD
values of both channels are below 0.0001%! Even with signals around -60 dB (relative to the overall
dynamic range of the SAM-1C -84 dB), this corresponds e.g. to very quiet parts in a Symphony recording,
the total THD distortions from the 2nd-9th harmonic are less than 0.03%. Good CD players have distortions
of more than 100 times at this level! The minimum is in the order of 0.00005% or 126 dB below useful
signal at input signals of +6 dBu (approx. 1.55 volts).
The left diagram shows the measured values of the SAM-1C, the right diagram shows the self-measurement
of the used analyzer which already belongs to the best measuring devices for such audio measurements.
Especially at higher signal levels the THD distortions of the SAM-1C are close to the limits of what can be
measured today.
The fact that in the right measurement record of the analyzer's self-measurement the distortions at high
levels are higher than with SAM-1C interconnected is not a measurement error! It is interesting that the
balanced signals can be processed more cleanly by the balanced input stages of the analyzer than the
asymmetrical test signals connected directly from the analyzer output to the input. This clearly shows that
balanced inputs operate cleaner with balanced drive than with unbalanced drive. In principle, this is true for
all devices with electronically balanced inputs on the market and varies depending on the circuit technology.
Many microphone preamps are also affected by this! Unfortunately, this problem is little known today.
Analyzer and SAM-1C Self-measurement only Analyzer

19
LEVEL ADJUSTMENT / POWER SUPPLY SAM-1C
______________________________________________________________________________________________
5. LEVEL ADJUSTMENT :
By default the modules with sym. input are adjusted to a gain of 0 dB. Any values between -21 dB...+6
dB are adjustable (+6 dB only with set internal jumpers).
The modules with sym. output are preset to a gain of +10 dB. Any values between 0...+23 dB are
adjustable. Level reductions are also possible on the SSOM-04Mc module after activating the jumpers
J4 J5. Clockwise rotation of the spindle trimmer screw increases the gain. Use only slotted screwdrivers
with 2...2.5 mm blade width.
For special cases jumper 1 (left channel) and jumper 3 (right channel) of the modules SSIM-04Mc
activate an additional gain of 6 dB at the input of the differential amplifiers. This allows to achieve even
higher dynamics at usual signal levels of "HiFi devices". If jumper 2 4 is set, the max. input voltage at
the balanced input must not exceed + 18 dBu. Higher input signals will not damage the amplifier stages,
but will cause clipping of the output amplifiers. Jumper 1 3 are not set by default (solder bridge open).
Important : As with most analog input amplifiers, no higher level signals should be present at the inputs
when the unit is switched off. This is especially true for preamps with extremely low noise floor like the
SAM-1A SAM-1B SAM-1Bs. Input voltages greater than +12 dBu (approx.3V) to these units when
powered off can damage the 1st amplifier stage! In contrast, the SAM-1C series is now equipped with
protection circuits against overvoltages and phantom power voltages for microphone supplies. This
measure once again increases the operational safety of the SAM-1C series.
6. GROUND CONCEPT :
Protective earth and operating earth are separated from each other in the SAM-1C and only connected
via an RC element consisting of a 0.1µF capacitor and a 2.2kΩ resistor. This creates a low impedance
connection for high frequencies as an RF shield, on the other hand this way there is no ground loop for
the mains frequency and its harmonics. This means that the SAM-1C works properly even when touching
other metal housings with "unclean" ground reference and thus no "hum loop" is created. The housings of
the XLR connectors are directly connected to the chassis (mains ground) in the SAM-1C.
To avoid hum loops via circuit zero (pin 1), the shielding at the balanced inputs and outputs should only
be connected to the housing of the XLR connector. Otherwise, interference currents via pin 1 could
generate a voltage drop via the internal resistance of the ground wiring in the device, which under
unfavorable circumstances would become noticeable as an interference signal.
If the balanced inputs or outputs of the SAM-1C are used as converters balanced < > asymmetrical, it is
often useful to connect the shield to pin 1 and 3 of the XLR connectors. If a hum loop occurs with this
connection, the shield is only connected to pin 3. Pin 1 then remains open.
7. ELECTRICAL FUSES :
The SMPS-12T integrated precision switched-mode power supply is primarily equipped with an electronic
current limiter. The fuse for the primary circuit is located on the circuit board and may only be replaced
by qualified personnel. On the secondary side the power supply has no fuses. The internal supply
voltages are also protected against short circuit or overload by a current limiter.
If the LED for monitoring the supply voltage on the front panel does not light up in the event of a fault,
the mains power supply is probably either interrupted, the internal mains fuse on the power supply board
is defective or there is an overload due to a defective audio board. If you are sure that an overload is not
caused by the audio circuits, the power supply should be replaced by a specialist.
The device is designed in protection class 1.
7.1 POWER SUPPLY :
The SAM-1C is equipped with the SMPS-12T low drop switching power supply for operation on 80...265
Volt 50...400 Hz AC voltage. Operation on 110V AC mains is therefore guaranteed without conversion.
An LED on the front panel is used to monitor the supply voltage.

20
POWER SUPPLY SAM-1C
______________________________________________________________________________________________
7.2 Power supply unit :
The current versions of the SAM-1C are equipped with the "ultra-low-drop" precision power supply SMPS-
12. This modern switching power supply produces extremely stable and pure supply voltages with
minimized power consumption and lower heating compared to conventional power supplies. Magnetic
interference fields, which can lead to hum in neighboring devices, are reduced by approx. 90% in this
power supply compared to conventional power supplies. The power consumption and thus also the
heating is reduced by this switching power supply technology by typ. 30..40%, the life span of the
components is thereby increased. The SAM-1C with switching power supply has fully equipped with 4
channels only a typ. Power consumption of 4.0 W.
The output voltages can be loaded up to 250 mA. At higher currents, the current limitation becomes
active and lowers the supply voltages. At the same time this is indicated by the "Power" LED on the
front going out. The internal supply voltages of the amplifiers are + - 19.7 volts. Short-circuiting the
output voltages will not damage the power supply.
When the power supply is switched on, it is gently boosted to full
supply voltage in approx. 0.2 seconds. Switching on the power supply
does not cause any crackling noise on the mains side or in other audio
devices. The adjacent measurement chart shows the power
consumption during the switch-on process. No interference peaks can
be detected.
To prevent damage to amplifiers and loudspeakers in case of overload
or short-circuit of a supply voltage, the power supply has a monitoring
of the symmetry of the output voltages. If a defined limit value for the
symmetry is exceeded even minimally, the device switches off. The red
power LED goes out.
Timer:
the SMPS-12T power supply has a "Power-Down-Mute" circuit that controls relays on the audio board
outputs. This largely avoids "power-on crackles" when switching a sound system on and off, or eliminates
existing power-on noises. The switch-on time is about 6 seconds, the switch-off time a few milliseconds
after falling below the minimum bias voltage. These control voltages are applied to the 10-pin connector
pin 7..10.
Power supply SMPS-12T
CONNECTOR PIN ASSIGNMENT CN2 10-pol.
Pin 1 + 19,7V Power-On-LED +(Rv= 8k25)
Pin 2 GND LED
Pin 3 - 19,7V Power-On-LED - (Rv= 8k25)
Pin 4 + 19,7V Audio
Pin 5 GND Audio
Pin 6 - 19,7V Audio
Pin 7 + 19,7V Mute-Relais A
Pin 8 GND Mute-Relais A
Pin 9 GND Mute-Relais B
Pin 10 - 19,7V Mute-Relais B
TESTPUNKT +19,7V
TESTPUNKT GND
TESTPUNKT –19,7V