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F5 HA   2015

 

The F5 headphone amplifier is a downscaled version of the "legendary" F5 power amplifier by Nelson Pass designed for headphone duty. Patrick aka EUVL (XEN Audio) came up with the schematic more as a mental jogging exercise (as he puts it himself) but eventually realized it P2P with a very compact layout on simple veroboard. This is an all FET amplifier schematic based on the Toshiba 2SK170BL and 2SJ74BL complementary pair as front end, that, with proper device matching, requires no DC offset servo and will deliver very low distortion and very high bandwidth. Output devices are either the popular IRF9610/610 or better Fairchild FQP3P20/FQP3N30.

  

I consider myself lucky that the prototype amplifier was given to me permanently for testing and to eventually case it up with a proper power supply of my own choice.

 

 

basic schematicbasic schematic

 

 

During testing I tried various power supply topologies from a standard 7815/7915 bipolar supply to shunt regs. I eventually settled on a 'simple' cap multiplier supply inspired by Rod Elliot's schematic but improved by EUVL. The cap multiplier was easy to build and is working exceptionally well, both in terms of noise performance and sonic properties. I learned my lesson here that not everything has to be powered by shunt regs (that failed in this case because of severe oscillations). The chosen power supply just carries on the theme of a 'simple' but very effective design.

Yet another psu schematic I tried is the so-called 'Nazar'-reg, named after the smart russian fellow who invented it. I actually choose this variant of a simple LM317/337 suppy for my final build of the F5 HA, see the images below. The F5 sure shows its entire beauty with this supply so I can wholeheartedly recommend it.

 

cap multipliercap multiplier

 

Nazar regNazar reg

 

 

For the case of the F5 HA I choose an all aluminum case that I designed in Alias. At the time I had a rare opportunity to have the aluminum parts professionally milled on a CNC machine, and I happily accepted the offer. The case is based on readily available Fischer heat sinks and sports a solid 25mm front and a 10mm back panel. The divider that holds the Xfeed board and it's supply (Didden regs) was also cut on the milling machine, bottom and top panel were custom made at Schaeffer Apparatebau. Despite the smallish appearance this sure is my heaviest case. :)

 

 

For those interested in the F5 headphone amplifier and more in-depth information please refer to the thread on DIYaudio 

http://www.diyaudio.com/forums/pass-labs/271926-f5-headamp.html

 

 

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