1982 Preamplifier Schematics

Preamp ‘82, block 1 — phono stage Preamp ‘82, block 1 — phono stage

This is the phono stage, handling both MM (Moving Magnet) and MC (Moving Coil) pickups. The design uses active RIAA compensation, which was untraditional for the EC design — up to this time it used passive high-pass and active low-boost. The gain stages are designed to handle the active feedback, and note (!!!!!), the active RIAA compensation used shunt feedback. A tough job to calculate, but when that was done, it worked wonders!

Preamp ‘82, block 2 — line stage Preamp ‘82, block 2 — line stage

The line-stage section is more traditional, with a normal series-feedback line stage. Note the extra buffer on the output.

For both block schematics above, note the roman numbers inside the amplifiers, denoting the particular gain block used.

Gain stages 3 and 4, ‘82 Gain stages 3 and 4, ‘82

This drawing shows gain blocks 3 and 4. Note the completely symmetrical design. The other gain stages also used an ingenious method of utilizing all the current from the last differential stage. Also note the current generators — ever seen something like that? Well, it works!

Details on compensation and other design choices will be described further in a later write-up. Don’t try to build the gain stage as shown above without that context — smoke will arise. Be patient.