Pioneer SG-9800

Twelve octaves of control, and an overload lamp that tells you when you've gone too far.

High-Fidelity (May 1980, p.8) opened its coverage by saying not all stereo equalizers are created equal. Listeners who assumed otherwise, it suggested, probably hadn't heard Pioneer's new SG-9800.

Overview

The SG-9800 is a twelve-band graphic equalizer. It divides the audio spectrum into octaves instead of the broader bands on most consumer EQ units of the period. Pioneer's own documentation gives the center frequencies: 16Hz, 32Hz, 64Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz, 16kHz, and 32kHz. That's a wide spread. The bottom band sits below what most speakers can reproduce, and the top band sits above what most adults can hear. Each band gives ±10dB of level variation. So if there's a room mode at 125Hz or a shrill tweeter at 8kHz, there's a dedicated fader for each.

Internally, the circuit is a conventional graphic-EQ topology, carefully done. The signal goes through a buffer amplifier, then a summing amplifier, then into a bank of twelve band-pass filters. A second summing stage handles the output. Each filter is built around the same basic circuit. Only the resistor and capacitor constants change to set the center frequency, and the R and C values that set the Q are adjusted per band. The level control for each band decides whether that band's output is fed back to the first summing amp or passed forward to the second. That's how the boost or cut is achieved.

The front panel is laid out for the practical business of using twelve bands. There's a power switch with an indicator lamp and, more usefully, an overload indicator. That lamp lights when the octave control is set too high and peaks appear in only part of the frequency range, or when a strong signal is fed in directly from the preamplifier. Pioneer's manual is specific about what to do when it lights: back off the attenuator and the octave control until it goes dark. The attenuator switches offer 0dB, -3dB, and -6dB positions. The guidance is to run at 0dB under normal conditions, and to drop to -3 or -6 only when the program has wide dynamic range or the overload lamp comes on.

The switching logic trips people up, so it's worth understanding before you buy one. There are three coupled switches: Equalizer On, Equalizer On Recording, and Equalizer Off. They are interlocked in behavior. Pressing one requires that the others be released, and the manual explicitly warns against pressing more than one at a time. Equalizer On processes signals from the Equalizer Input jacks and sends equalized signal to the Output jacks. Equalizer On Recording does the same but also routes the equalized signal to the Tape Rec jacks, so you can print the EQ to tape. Equalizer Off bypasses the whole thing. There's also a tape monitor switch with its own indicator, for listening to a deck connected to the Tape jacks during recording or playback. None of it is self-evident from the front panel alone.

The SG-9800 was sold in six versions, split by voltage and market. The KU type is the U.S.A. model at 120V. The KC is the Canada model, also 120V, drawing 30VA and carrying CSA approval. The R is the general export model, switchable between 110V-120V and 220V-240V at 50/60Hz, drawing 25W. The R/G is the U.S. Military model with the same switchable voltage and the same 25W draw. The WE is the Europe model at 220V and 240V, and the WB is the United Kingdom model, also 220V and 240V. The service manual for the KU type covers the core machine, with additional sections for the KC, R, and R/G types. A separate service manual (ART-364) covers the WE and WB. In North America, the KU or KC will almost always be the one that turns up. The export and European versions are less common on this side of the Atlantic.

A service bulletin dated January 27, 1981 documents a production-line change to the slide volume controls with LEDs. The terminal length went from 16mm to 20mm, and the old part number ACX-005 was superseded. The bulletin says only the new control is available as a replacement. When it goes in place of an old one, the terminal should be trimmed by 4mm. The affected serial number ranges are recorded by type: for the SG-9800/R/G, serials from 4820101 onward; for the KC, from 3401201; for the KU, from 3610601; for the WB, from 9900501; for the WE, from 9803801; and for the R, from 4711401. All of these are dated June 1980. That helps with dating a unit and with knowing whether a replacement part will drop in cleanly.

The SG-9800 is a period piece in the best sense: a time when graphic equalizers were taken seriously as system tools rather than as tone-control toys, and when a manufacturer would build twelve discrete octave bands with proper filter topology and a genuine overload warning system to keep users out of trouble. Units that have survived forty-plus years are worth checking carefully before purchase — the slide potentiometers are the wear item, and a unit with scratchy or dead faders will need attention. The coupled switch logic is also worth verifying, since a stuck or misbehaving switch will defeat the bypass function entirely. But a clean SG-9800 remains one of the more capable graphic equalizers of its era, and the octave-band layout gives it a precision that most of its contemporaries simply didn't offer.