audio research

Solid state stereo preamplifier.

The heart of the SP-7 preamplifier design is the Analogue Module amplification concept. The four AM-8 Analogue Modules are the result of a search for a solid-state approach that provides superior musically-accurate performance along with immunity from the sonic degradation of power supply and coupling functions.

These modules are highly linear with precise symmetry and balance, along with extremely wide bandwidth. The exceptional dynamic range results from a very low noise floor, careful choice of operating currents and a controlled overload characteristic. The accuracy of musical definition is enhanced by elimination of all audio coupling capacitors and all electrolytic bypass capacitors.

Four high-speed "zero-impedance" electronic regulators are used for total isolation between phono and hi-level amplification sections. These regulators are controlled by precision tracking reference voltage sources with controlled turn-on characteristics. Servo sensors for DC balancing are energized immediately at turn-on, so that safe and silent performance is insured even during final stabilization of the tracking reference voltages. The SP-7 is fully operational within 10 seconds and fully balanced in about 40 seconds. No warm-up muting circuitry is required.

Although the SP-7 has no coupling capacitors, it is technically not "DC-coupled" since it will not pass continuous DC signals. Servo correction circuits are used to maintain DC balance at all times. Sub-sonic response is extended below 0.1Hz to preserve integrity of attack.





MSRP (US new retail)
$995. Later increased to $1,195. Later increased to $1,295.


Frequency response High level section: ±.25 dB, 1 Hz to 50kHz. -3dB points below 0.1 Hz and above 400kHz.
Magnetic phono: ±.25 dB of RIAA, 10 Hz to 40 kHz.
Distortion (THD) Less than .002% at 2V RMS output, 20 Hz to 20 kHz (Typically less than .0005% in the midband).
Intermodulation distortion: Less than .002% at 2V RMS output.
Noise & hum High level: (1) 250 µV RMS maximum residual unweighted 100 kHz bandwidth noise at main output with gain control minimum (86 dB below 5V RMS output). (2) More than 90 dB below 1V RMS input (less than 20µV equivalent input noise.
  Magnetic phono: 2 µV equivalent input noise, wideband RMS (-74 dB reference 10 mV input) (Less than 1 µV above 200 Hz or -80 dB reference 10 mV input).
Gain Magnetic phono input to tape output: 28 dB.
Magnetic phono input to main output: 60 dB.
High level inputs to main output: 26 dB.
Input impedance 50 kOhm phono, 90 kOhm high level inputs. Also has provision to add to the 30pF phono input capacitance for matching certain magnetic cartridges.
Output impedance 250 Ohms main output, 1200 Ohms tape output. Recommended minimum load for best audio quality 600 Ohms and .01µF maximum capacitance main output, 10kOhms and 200pF maximum capacitance tape output.
Output polarity  
Maximum inputs Magnetic phono, 500 mV at 1 kHz (2.0V RMS, 10kHz).
High level inputs essentially overload proof.
Rated outputs 2V RMS 1 Hz to 50 kHz, 10 kOhm load (maximum main output capability is 14V RMS output at 1/2% THD at 1 Hz to 50 kHz into a 10 kOhm load, 10V RMS at 1/2% THD at 1 Hz to 50 kHz into a 600 Ohm load).
Power supplies Four electronically-regulated tracking solid-state supplies. Line regulation better than .01%.
Power requirements 100-130 VAC 60 Hz (190-250 VAC 50 Hz) 10 Watts.
Other Amplification: Four AM8 Analog Modules®. No coupling capacitors.
Dimensions 19" (48 cm) W x 3 1/2" (8.9 cm) H (standard rack panel) x 8 1/2" (21 cm) D. Handles extend 1 1/2" (3.8 cm) forward of front panel. Rear chassis fittings extend 3/4" (1.9 cm).
Weight 16 lbs. (7.3 kg) Net, 20 lbs. (9.1 kg) Shipping.