Funk Tonstudiotechnik Balancing and Matching Amplifier SAM-1C
The telephone conversation with Thomas Funk, the boss of the Berlin company Funk Tonstudiotechnik, was very enlightening for me. No voodoo, but pure measured values, completely in my sense: numbers, data and facts, as it is appropriate for studio equipment. The SAM 1-C professional four-channel matching and balancing or differential or instrumentation amplifier, equipped with active electronics, transfers an audio signal between the balanced and unbalanced worlds. It acts as a link of output and input impedances of connected devices. This creates clear electrical conditions and achieves the best possible matching.
Output and input impedances that are mismatched between hi-fi devices, the mixing of balanced connectors (XLR or Tuchel) and unbalanced connectors (RCA or Cinch), and cable types with different capacitances and conductor lengths make it difficult for the user to connect devices if one does not know the exact electrical conditions or is unable to adjust to them. We know the cable discussions with all the advertisements of still better conductor material, dielectric, better insulation or conductor braiding, etc. I consider these to be exaggerated, because in most cases a mismatch can be traced back to values such as cable capacitance per meter and/or the ohmic resistance of a connection. For this reason one reads again and again that RCA cables should not exceed a certain length (2 m? 3 m? 5 m?). In unfavorable constellations of impedances between amplifier inputs and outputs, the often suboptimal "inner values" of cables come into play, no matter what price range they come from. When connected, the user generates electronic filters that can influence the frequency response. In technical jargon, this is called a low-pass or high-pass filter. Since different cables each have different values, the sound character of the music listened to can change when comparing due to these properties.
I came across the SAM-1C when I had operated my Telefunken M15 tape recorder in the next room of my listening room because of the high mechanical running noise and had to handle long balanced audio cables, which I connected directly to my amplifier via the connection of the "cold" conductor with ground because of the lack of a balanced input. This way caused unclear conditions because of the different impedance and matching ratios between the outputs and inputs as well as the cable length. It is possible to measure these parameters and work on matching, but this would only ever be an "island solution" for the current requirement.
An interconnected SAM-1C with its extremely high impedance inputs provides a relief of the signal outputs of source devices and thus prevents a too low impedance load of inputs of subsequent devices and/or influences by audio cables with high capacitive values. By this measure an improvement of the low bass behavior including reduced phase deviation, also in the high frequency range, can be achieved. In the above application, the best solution is to connect the SAM-1C at the end of the long balanced line and then go to the amplifier with a short RCA cable.
A transformer would also be suitable for this type of matching, but the inputs and outputs to be connected would each have to have the optimum impedance values for this transformer. This would be difficult to realize in practice. If one were to ignore an optimal matching when using a transformer, this could result in a level reduction or a level increase at higher frequencies. Sonically, therefore, this would not always have to be the best solution, and again, each application would have to be considered individually. A high quality would be indispensable with a transformer, which could be reflected sensitively in the price.
For use with a tape recorder, the SAM-1C is indeed "shooting with cannons at sparrows" with regard to the measured values, if you consider that the signal-to-noise ratio of a tape recorder is about 60 dB and the SAM-1C has a dynamic range of 136 dB (gain = 1, CCIR unweighted) at 0 dB gain. However, I have not found a comparable unit in the price/performance segment that carries a price tag with the budget-friendly amount of €487.90. The functionally identical in-house SAM-1B is 4 dB worse with a dynamic range of 132 dB (CCIR unweighted) at 0 dB gain and the price of 445.06 € and would also be perfectly adequate for my intended use. The decision for the better signal converter was due to the fact that it was in stock in a black case, which I really wanted.
Four screwdriver slots labeled "GAIN" are found on the audio connection side. Level adjustments can be made here using spindle trimmers. Thus, unbalanced outputs of PCs or hi-fi equipment such as CD players or phono stages can be optimally adapted to professional balanced inputs of studio equipment or active speakers. Then, as in my case, signals can be fed directly into the recording input of a tape recorder without an interconnected mixer console. In another application, the balanced outputs of studio equipment can be converted asymmetrically to RCA jacks and the level lowered to hi-fi equipment level. For the exact adjustment of the levels measuring instruments are necessary. The Minirator MR-PRO and the Minilyzer ML1, both from NTI Audio, are very well suited for this purpose. Or you can have the device adjusted for your requirements directly from the factory during the order process.
Since the balanced inputs and outputs can also be operated asymmetrically, the SAM-1C can also be used as an impedance converter for long RCA cables.
A special feature is the flexibility in the configuration of the SAM-1C. Audio modules can be exchanged quickly and without soldering. Up to four amplifier channels or two modules can be installed in the SAM-1C. Here are the examples of the available 4-channel variants. A "configuration key" can be downloaded from Funk Tonstudiotechnik:
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 direct out + 2x 2 sym. out XLR (distribution amplifier)
SAM-1C/4MV0 1x Cinch in -> 3x Cinch direct out + 4x sym. out XLR (distribution amplifier)
In the course of our telephone conversation we came to the excellent measured values that can be written with the SAM-1C. With my Audio Precision measuring station, which has excellent key data regarding the inherent noise, I come with the SAM-1C to the measurement limit, so I leave the collection of data to the developer. Since I can assess the measuring equipment used, the test environment and the meticulousness, the company Funk Tonstudiotechnik enjoys my full confidence. In this house, they know how to do things like this. Thomas Funk has been developing his equipment with heart and soul for more than 40 years and can draw on a huge wealth of experience.
These measured values are impressive:
Phase response of less than 1° in the range of 10 Hz...20 kHz
Wide signal bandwidth of over 100 kHz for excellent pulse processing
Bandwidth of over 500 kHz, thus applicable for matching time code signals
Crosstalk attenuation of over 125 dB at 1 kHz and 120 dB at 10 kHz between the two channels, allowing the use of both signal paths for mono signal sources
Common-mode rejection of the balanced input amplifiers of typ. >115 dB at 1 kHz for the almost complete elimination of interference that can leak into balanced lines
The balanced inputs and outputs can be operated asymmetrically, e.g. for use as an asymmetrical catch-up amplifier, impedance converter, phase rotation stage or for "hum loop elimination
Once set, the output level remains constant due to servo-balancing with balanced and unbalanced wiring of the XLR outputs. The maximum achievable output voltage (headroom) with asymmetrical wiring of the balanced output does not decrease! This results in a further improvement of the dynamic range of 4 - 6 dB compared to comparable balanced amplifiers when the outputs are operated in unbalanced mode.
Operation up to 300 Ω output load is guaranteed
Circuit zero (ground) and ground (housing) are separated from each other for greater flexibility when installing in different systems
Modular design for different variants. Service-friendly design: The amplifier modules including all sockets can be exchanged or extended subsequently in a few minutes without soldering work
The SAM-1C can provide the following functions simultaneously:
High impedance signals become low impedance (impedance converter)
Input signals can be amplified or attenuated
Symmetrical signals become asymmetrical
Asymmetrical signals become symmetrical
Two balanced signals can be summed (mixed) without feedback (from stereo to mono)
Hum loops can be eliminated between unbalanced devices
Eliminate power-on or power-off clicks in a sound system ("power-down" mute)
Internal configurations as balancing and distribution amplifier possible
I like the fact that the SAM-1C is small and does not come with an imposing, "milled from the solid" housing, which would ultimately only make it more expensive. So it can do its job unobtrusively and can also move to the back if needed. The power jack and power switch are on one side, and the audio inputs and outputs are on the other. Form follows function.
I can't report about a sound character of the SAM 1-C, because the device doesn't change the audio signals. But it does eliminate sound changes that can be caused by mismatching "from the outside". Impedance and hum problems as well as level adjustments can also be handled with the SAM-1C. It works phase-linear, broadband, very low noise and therefore interference-free. This device is the perfect link for all tasks when it comes to adjusting audio signals. Try it out. It could well be that the search for the most suitable cables will then come to an end.
On the homepage of Funk Tonstudiotechnik you can find further interesting developments like a highly linear headphone amplifier or the preamplifier MTX-Monitor.
Contact via the homepage http://www.funk-tonstudiotechnik.de/, by phone: +49 30 / 611 51 23 or via e-mail (sales / customer service): funk@funk-tonstudiotechnik.de.
Text and photos: Claus Müller