Posted 9th April 2016 at 02:27 PM byalexcp (My DIY projects)
Updated 11th April 2016 at 09:14 PM byalexcp
When I saw the discussions of KSA-5 headphone amplifier on head-case.org and on this forum, I thought it may be a nice use for the bag of 1000uF capacitors I had at the time. This was the main motivation for putting this Krell KSA-5 clone together.
The main challenge was to drill the front panel. The 10mm aluminum panel that came with the enclosure is easy to work with, but I wanted it to be pretty and asked the people at Modushop to CNC it for me.
Although it works ok, I think it is not a very good power amplifier for loudspeakers. As a headphone amplifier, it is no match for my Musical Fidelity X-CANv8.
On first power-on the amp oscillated at 12 MHz when connected to headphones. The oscillation was inaudible but clearly visible on a scope. A quick look at head-fi.org showed that PPA instability is not a new problem. I reduced the value of R11 (see PPA's schematic), which eliminated the oscillation and improved the sound. I replaced the recommended OPA627 with LME49710.
PPA is positioned as a high-end DIY headphone amp, and it is in this project that I felt how subjective "high-end" is. PPA is a nice amp, but a true high-end device like Musical Fidelity X-CANv8 simply blows it away.