Signal Transfer Company: Amplifiers, PCBs, Audio Projects.

The Load-Invariant Power Amplifier: 2.0

The Load-Invariant Power Amplifier PCB has been redesigned to use modern output transistors in either TO3P or MT-200 packages. There have been many other improvements; see below.

A Load-Invariant power amplifier is specially designed to give exceptional linearity into low impedances. The ultimate aim- for perfect Load Invariance- is a distortion performance that does not worsen at all as the load impedance falls from 8 Ohms to 4 Ohms and below. No amplifier currently exists that is perfectly Load Invariant, but in this design Douglas Self approaches close to the ideal.

Exceptionally low distortion into low impedance loads.
Very low noise, due to innovative feedback design.
Unique enhanced-tempco bias generator gives excellent control of the critical quiescent conditions.

PCB price: Ł33:00 each.

Optional input bootstrapping to raise input impedance.
No difficult-to-obtain components.
Board fixing holes and pads provided for easy mounting of TO3P output devices to a heatsink.
Full overload and short-circuit protection.
High-quality double-sided plated-through-hole PCB with gold-plated pads, solder mask both sides, and full screen print. Fully RoHS compliant.
Double-thickness 2-oz copper to minimise ground resistance and voltage drops.
Board size 215 by 100 mm overall.

NEW FEATURES

Output devices can be either TO3P or the larger MT200 package.
The form-factor of the PCB has been altered so that two will fit side by side in a 19" rack chassis.
All transistor positions have emitter, base and collector marked on the top-print to aid faultfinding. TO3 devices are also identified on the copper side.
Alternate positions are provided for the input transistors (Q1,Q2 or Q101,Q102) so that devices with differing pin-outs may be used without having to cross their legs.
The PCB is double-sided PTH, so wire links have been eliminated.
Component values are included on the silk screen to aid in assembly.
Tall components have been placed so as not to obstruct screwdriver access when mounting the output devices.
Pads and tracking for a heatsink-mounted thermistor have been included. This will connect directly to the forthcoming Signal Transfer Protection PCB.
Wire connection points can be either via connectors or by direct soldering.
Mechanical fixing arrangements improved.
Comprehensive project notes included. The overlay includes mechanical dimensions for machining from flat bar an aluminium block for mounting the output devices.