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audio.com DESCRIPTION The SUM100 Summing Amplifier is an inexpensive, high performance amplifier that is designed as a line level stereo to mono summing amplifier. It is also useful as a gain block, and as an impedance converter and summing for IHF (RCA type) signals. The inputs provide balanced 40Kohm bridging impedance for line levels up to +24dBm. The high input impedance allows the SUM100 inputs to also bridge 10dBu (hi-fi, RCA plug) lines without loading. Front panel, screwdriver adjust, full range gain controls provide 26dB gain at full clockwise rotation, unity gain at twelve o’clock and a smooth audio taper to full off. The output driver is a servo controlled, ground-sensing circuit, which will supply over +22dBm to 600 ohm balanced loads and +20dBu to high impedance, unbalanced loads. The SUM100 uses rugged XLR type input and output connectors. Loop-through DC connectors allow several NANOAMPS to share a single external 24VDC power supply. Battery packs and DC-DC converters for portable use are also available. Up to three amplifiers will mount side-by-side in only one rack unit using the available rack mounting kits. NANOAMPS may also be neatly stacked or mounted side by- side on your desk with the available angled desk mounting kits. CIRCUIT DESCRIPTION INPUT STAGES The balanced input stages of the SUM100 Line Amplifier utilize a FET input LF347 quad op-amp in a clean, quiet inverting instrumentation amplifier configuration. Input levels up to +24dBm will be handled without clipping, excess levels cause only clean clipping without hang-up or phase reversal. Equal -6dB gains from both HI and LO inputs allow unbalanced sources to be easily accommodated. Bridging impedance is a high 40Kohms with good CMR. Linear panel adjust trimpots for both left and right signals are designed to be operated at their 12 o’clock position for maximum resolution. SUMMING AMPLIFIER Left and right signals are combined in an active summing network (A1B) which yields unity gain for each individual signal, three dB gain (RMS summation) for program audio signals and six dB gain for correlated inputs. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | audio.com GAIN STAGE A low noise NE5532 section (A1A) provides 26dB maximum gain. A linear control is used in a unique circuit configuration to provide a wide range logarithmic MASTER gain control characteristic in a variable gain stage with optimum noise performance. Output noise at unity gain is low enough to allow performance to exceed 16-bit digital dynamic range even at -10dBu nominal output. Unity overall gain is achieved at approximately 12 o’clock pot position. LINE OUTPUT The balanced output stage of the SUM100 utilizes a unique active balanced output driver IC, the Analog Devices SSM2142, that senses whether the connected load is balanced and floating or is unbalanced due to either side being grounded. A balanced output load will be driven with equal and antiphase levels on the HI and LO output lines. An unbalanced (one side grounded) load will cause the driver IC to shut off the signal output to the grounded side of the load and double the output level applied to the other side, thus maintaining equal output to either type of load. The output stage provides 6dB gain and will drive loads of 600 ohms and higher. Nominal output is +4dBm with clipping at +22dBm (10Vrms) into 600 ohm balanced loads for 18dB nominal headroom. Maximum output is reduced to +20dBu (7.8Vrms) when driving an unbalanced load since the full output swing of only one driver is available. This still provides a very comfortable 30dB of headroom above the typical -10dBu nominal unbalanced signal. POWER SUPPLY The SUM100 requires 22 to 30VDC and are designed to share a common external 24VDC "Wall Wart" type power supply. A pair of loop-thru DC connectors on the rear of each module permits several units to be daisy-chained with P/N20602-1 DC power cables to a single power supply. The WA100-1 and WA100-2 (230VAC) are 400Ma supplies. The SUM100 draws 70mA. Any combination of amplifiers, which add up to less than the supply rating, can be powered by a single supply. INSTALLATION UNPACKING Inspect the equipment. If there is any visible damage to the unit or to the box it came in, contact the factory but do not return anything to ATI without prior authorization and shipping instructions. It may be necessary to have the shipping Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | audio.com company inspect the unit and the box at your location. Count the pieces! Don't throw out the boxes and packing material until you are sure you have everything that is coming to you. The amplifiers need either their own separately ordered WA100 power supply or a DC cable, P/N20602-1 to share the supply of another amplifier. Rack and desk mounting hardware may be packed in with the unit even thou...