Where was I? Right, back to the workshop and cue the music.
Sorry in advance for my photos. They get the job done, but some of them look pretty bad now. I'd retake them but the amp has long since been returned to it's owner.
Once both channels were running happily with their new parts on the benchtop power supply I turned my limited attention to the chassis. The phenolic insulators sandwiching the RCA jacks in place were starting to crumble so, some shiny new jacks were fitted courtesy of ApexJr.com for 99 cents. The input wiring was done with 22AWG shielded wire.
The pro Hafler models like the P125 and the P230 have a solid aluminum bracket for the ground connections between the main power supply caps. The DH200 and DH220 models only got some tinned wire which isn't very convenient or nice looking. I fashioned up a new bracket with some scrap...
Posted 16th April 2013 at 01:18 AM byrjm Updated 16th April 2013 at 12:23 PM byrjm
Over the last couple of years most of my interest in audio has been with transistors. I've been slowly teaching myself to read and understand the circuits.
Circuits like this one for example. Not hard, but still a bit too complicated for me to understand without the helpful wikipedia markup attached.
Instead I've looked at primarily at the schematics I have for discrete audio preamplfiers, 1970's vintage typically. Based on what I've learnt so far, I've done up a "test mule" in LTSPICE, shown below.
It's not a circuit you should build. It's for pedagogical purposes, though it does actually work reasonably well - in simulation anyway. Its just a simple starting point to observe how the different parts interact under simulation.