My Adcom 545II Mods

This amp is a 10+ year old, class AB design.  It is rated for 100W a channel into 8 ohms and 150W into 4 ohms.   While not as popular as its 555 brethren of the time, it was a respectable value amp, with nice clean symmetrical layout.  I have two of these units, which will allow me to listen to one, while modifying the other. :)   Please note that these mods are probably not cost effective, but I am also using this as a stepping stone to building my own amp.

Plans for amp 1 mods:

• New power supply, replacing the 500VA transformer with an Avel 625VA one, new bridge rectifiers w/cap snubbers, increase ps caps from 4 x 10Kmfd to 6 or 8 x 10Kmfd, probably have to improve inrush current limiter.
  

• Replace cheap bias pots with sealed multiturn units.
  

• Replace all 5 per board electrolytic caps.  Increase the +- one from 47mfd to 470mfd.
  

• Match and replace, if necessary, emitter resistors.
  

• Precision match components in signal path of input and voltage gain stages.
  

• Replace signal and power supply wiring with slightly larger gauge and better quality.
  

Plans for Amp 2:

• Using the two 500VA Adcom transformers, make a dual mono amp.  PS caps will 4 x 10Kmfd per channel.  It will be a rather tight fit!
  

• Power cord replacement, and inrush current protection per transformer
  

• Same mods as above
  

• Possibly replace and increase the number of current driver outputs.  It has 3 NPN-PNP pairs per channel, and heatsink may allow to squeeze 4 pair.
  

Stock Adcom 545II Internals

Reverse shot of internals

Stock 500VA 80VCT Toriod

Transformer Removed

Amp Modules and PS cap bank

Empty chassis except for two diode bridges and misc

Mock-up to see how much fun fitting to the available space will be :)