Phase Linear 400 mod

Phase Linear 400 Mod:

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.  

The Drawbacks   :

1. Power supply sag during loud musical passages was causing slight but noticable compression of the soundfield.  
2. Stereo imaging was slightly impaired by crosstalk between left and right channels.

The Solution  :

1. Power supply capacitors are replaced with capacitors having twice the capacity.  Power supply decoupling networks are spliced into the the printed circuit board wherein low and medium level circuitry resides.  
2. If not recently replaced all electrolytic capacitors are replaced.
3. 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.

(Price is for modification labor and parts.  Does not include unit to be modified.)

(Repairs not included)