I found an old post from 11/08 on the diyAudio Forum, from mightydub, with part numbers and a schematic for the PS Audio 4.6 pre-amp.
Mightydub supplied me with fantastic information, enabling me to fix my PS Audio 4.5 pre-amp. It had the 4.5/4.6 common problem, worn out selector switches. They are Lorlin switches, and contrary to information on the PS Audio Forum, the parts are still made, and readily available.
mightydub’s info was specific to the 4.6 pre-amp, but the 4.5 and 4.6 pre-amps shared many parts. The switch part numbers are the same, and worked on my 4.5 pre-amp.
I love the sound of the PS Audio 4.5 pre-amp using the Straightwire setting, which bypasses the line level amp. If your source has a high enough output, you can select Straightwire, which bypasses the entire pre-amp, using only the volume potentiometer. Thus you are only listening to your CD or digital source output, and not the pre-amp. For vinyl records, you can choose to use only the PS Audio phono section, bypassing the line level amp. That assumes the use of a moving coil cartridge with a moderate or high output level. Pretty neat design.
I ordered the switches from Allied Electronics:
MANY thanks to mightydub!
Here’s the information mightydub sent me:
Here's the schematic and data sheet on the switches. The switches are a modular system, you start with the basic switch then you can add additional wafers to it. The output, tape feed, and source switches are 2 pole, 5 way though only the input selector uses all 5. The output and tape feed have a stop pin that limits it to 4 positions. The balance switch is two 12 pole wafers. The schematic is hard to follow but it all makes sense once you take the preamp apart and study it a bit.
I found the switches at Allied Electronics, you could also try Farnell in the UK. I just did a google search and see availability at a variety of places.
1 Lorlin SWITCH + 1P 12W Mfr's Part#: PT6434
3 Lorlin PCB SWITCH MECHANISM Mfr's Part#: PT6422
2 Lorlin PCB 2 POLE 5 WAY Mfr's Part#: PT602-003
2 Lorlin PCB 1 POLE 12 WAY Mfr's Part#: PT602-001