WAD 2A3 PSE Tweaks - Part 2

[FAQ Team]

There has been one reported instance of HF instability with the Global feedback modification when used with high capacitance speaker cables. This instability was in the audible frequency range and was heard as a high pitch whistle from the speakers. Adding a Zobel Network directly across the loudspeaker terminals of the amplifier effectively cured it. The network consists of a 2W 10R resistor in series with a .1uF 50v Polypropylene Film & Foil capacitor. The Network can be soldered directly onto the speaker terminals inside the amp or if it is wished for quick removal it can be added to the terminals externally.





5U4 replacement with PSU capacitor change

The quality of the 5U4G rectifier valve has a marked effect on the sound quality of the 2A3 and users may wish to change the supplied Edicron (branded Svetlana) valve for a better New Old Stock type. As standard the 2A3 uses a 100uF electrolytic capacitor directly after the rectifier (C13). The supplied Edicron 5U4G is capable of supplying current into C13 but many NOS rectifiers are not rated for a 100uF first capacitor. If changing the 5U4G C13 should be lowered in value to below 50uF. A quality Polypropylene Film and Foil Motor run cap would be suitable. There may be a slight increase in hum after this is done.


A users upgrade specification - updated Jan 2004

Reproduced with kind permission, thanks Tony/Greg.

All Part numbers are from RS unless otherwise stated. <http://rswww.com>

Opinion

"............... For me, this spec represents the best I've achieved so far in terms of improved sound quality and dynamics over the standard kit. Tony has developed this further with Sowter O/P Tx's and of course his famous power supply capacitor bank made up of lots of motor run caps all in a seperate box that sits under the amp. For various reasons, I'm not prepared to go there. For me the cost of the Sowters were not justified in terms of the percentage of sound improvement achieved, and the additional space the cap bank took up was for me inpractical, although I acknowledge there is a minimal improvement to sound quality. To be speculative, the other potential improvement is to invest in TJ Meshplate 2A3 valves, but again, for me, the price is prohibitive."