Quote:
Originally Posted by tapehiss  i'm trying to understand the 24v. rail option... |
There are some major advantages to having 24V rails, even for the simple 312 circuit. Like mentioned before, you can use one of the discrete opamps that have been designed to run on higher voltage rails. This equates to higher headroom.
This gives the user the opportunity to use an opamp from
Fred Forsell or maybe one from
JLM Audio. Of course there is also the famed 990 version from John Hardy. I think John will also tell you that the 990 is not the best DOA in a 312 type circuit with a 2622 input transformer.
Our friend Pier Paolo Abbate manufactures the APP2050E, which is the high class A version of his APP2050. The E version has a higher max output current (1A peak) than that of the normal version (250mA). The APP2050 has similar THD values to the JE-990. He has designed the E version to do even better. The APP2050E has a very high headroom if used with 24V rails and 1:2 output transformer configuration (like in the VP312). We are talking about
34dBu!! 
Pier's White Market thread can be found
here.
So, there are many new and exciting possibilities. If you have a standard 500 series rack, just cut off the unused pins (16-18) and jumper wire over the PCB switch. It is a permanent mod though.
Special care should
always be taken. Just like Volker says, 24V and a 2520 will not get along very well for long. Smoke and the nasty smell of burning silicon & epoxy will happen very quickly.
Cheers, Jeff