This is my first post. I’ve owned my PS Audio 4.6 pre amp since the late 80s. Aside from some scratchy pots over the years it’s been trouble-free (no cap job or any other interventions) and of course the phono stage sounds great. Til now, that is.
Today I noticed some hash/distortion on the left channel. The ol’ scientific revealed that the left phono input is compromised. This is true for Straightwire, High Gain, or Mono modes. Short of full cap job, any suggestions on where to start just to get it up and running? Other inputs are fine. Thanks! Happy Thanksgiving! - Winslow
That’s an oldie buit goodie and I would guess caps are not happy. Start with replacing all the power supply caps and see if it doesn’t help. All in you’re probably looking at less than $20.
Resurrecting this thread since I just finished my 4.6 restoration. I also had distortion in the left channel of the phono stage. After replacing all of the electrolytics on my unit, the issue was still there, so my next step was to replace the BJTs. I found a supply of NOS Motorola MPS 8099/8599 for a dollar each, so I went ahead and refreshed them all. I found 4 bad transistors, including one in the phono stage left channel with an hFE of “2” - this was totally worth doing!
I have pretty accurate schematics of the amplifier gain stages and am happy to share my experience restoring this classic pre. It’s totally worth the effort!
