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I returned to DIY electronics in 2009 after a 20 year pause by building a few kits to get in shape. This blog is for me to keep track of my progress.
Headphone amps

Krell KSA-5 clone

Posted 9th April 2016 at 01:27 PM by alexcp (My DIY projects)
Updated 11th April 2016 at 08:14 PM by alexcp

When I saw the discussions of KSA-5 headphone amplifier on 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.
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CMoy and PPA

Posted 13th August 2010 at 09:37 PM by alexcp (My DIY projects)
Updated 6th April 2011 at 01:35 PM by alexcp (Added pictures)

Of course I built the ubiquitous CMoy. It was a big improvement over various built-in headphone amps (e.g. in a TV) and added headphone capability to where it did not exist (e.g. to a Playstation).

Encouraged, I built the PPA project with a Young-Jung power supply. The enclosures for both the amplifier and its power supply are from modushop.

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 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.
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