View of inside of modded Phase Linear 400.
Extra high capacity capacitors seen installed in place of originals.
Added ground wires and discreet sheilded input wiring can be seen.
The oversized capacitors can be seen on the left. The size of the capacitors is less than that of the originals because of improvements of capacitor design.
View of the underside of circuit board shows resistor+capacitor decoupling of Left and Right channels. Ground traces of Left and Right channels are isolated and each given a home run ground wire to central grounding point. Sheilded wiring can be seen delivering signal from input connectors to Left and Right inputs of the circuitry.
The Phase LInear 400 and 700 amplifiers are among the best ever transistor amplifiers ever sold. The circuit is an excellent example of both simplicity and sophistication. A huge, high quality power transformer backs of the need for transient handling typically needed to reproduce music. The large number of output transistors allows for music to to spend more time in the more linear part of the transistor. Opinions as to the excellence of the circuit may vary, but the experience of the sound and music reproducing capabilities of this is hard to dispute. For one thing, it just sounds louder and more powerful than most other amps rated at 200 watts per channel. Often a 200 watt per channel amp seems barely adequate to power medium-small sized speakers, but the Phase Linear 400 seems more than adequate for such speakers.
This Mod came about as a result of poking around and tinkering after making a repair to a Phase Linear 400 and from fulfilling a customer’s request to install larger power supply capacitors.
Power supply sag during loud musical passages was causing slight but noticable compression of the soundfield.
Stereo imaging was slightly impaired by crosstalk between left and right channels.
Power supply capacitors are replaced with capacitors having 3 times the capacity. Power supply decoupling networks are spliced into the the printed circuit board wherein low and medium level circuitry resides.
The left and right channels were found to share a common ground over several inches on the printed circuit board. The ground for the left and right channels are separated from the input connectors forwards, with each channel getting it’s own ground wire to the power supply ground creating proper Y grounding.
See Details (below) for more info.