Rerurn to Romy the Cat's Site
In the Forum: Melquiades Amplifier
In the Thread: Staxquiades project
Post Subject: Staxquiades projectPosted by N-set on: 9/22/2012
fiogf49gjkf0d
This is something I've been chewing on for quite some time and finally decided
to make it happen: a serious Stax headphone amplifier.
I hope I can use this space as a sort of a blog-report on the progress...if not feel free to remove.
I've been "forced" to listen on headphones due to real estate constraints and it
seems those constraints will stay for few more years. At the moment
I'm using Stax Omega 2 MkI powered by a solid state amp Stax 717. I've always felt
it's barely up to the task of driving those little monsters and, apart from many other factors,
it sounds anemic. Adding Romy's EAR834 down the chain openned the whole new universe
(I could not listen to EMT155st for more than 10min...even after heroically changing Elko's to Elna's)
and 717 is now the weakest link.
I'm also mounting a second combo on my EMT930--SME3012R+whatever interesting cart I find,
which, if successfull, would too demand
more advanced amplification up the chain. Hence the need for a new amp. The most praised (at least by some groups
on head-fi.org and head-case.com) amp comes from a certain Stax mafia and is called Blue Hawaii.
I've never heard it, but for $5000 and 2yrs waiting time I can cook something myself...apart from that
looking at BH's schematics makes my eyes bleed...so I tried to design myself.
I must admit I have no idea how to properly power electrostatic headphones. I'm improvising from a few obvious facts:
*el-stats are capacitive loads (O2 is 110pF), very current hungry
*this current is better delivered fast: high slew rate
The very nature of el-stats forces the design to be Pi-Pi,avoiding the transformers. Another
axiom was to make it DC coupled so that there is nothing but tubes in the chain.
The inspiration comes from Milq, Axiom and Lynn Olsons Karna (reading Olson on PiPi amps has been very educative).
I want it to be flexible to some extent to try
different output tubes: EL34 (std. "Stax tube"), 2A3, 300B, 842, 801A
After endless hours of simulations here is the v1 design:
Milq's driver with it's bias but PiPi'ed, DC coupled with stacked PS (inspired by Chimeralabs' Axiom), the simplicity of the
signal chain...but a complicated PS. The most cruicial is the biasing of the driver as it sets the operaiting point of the output.
Hence I want to be able to change this bias and for each tube individually.
I ended up with a design which is a monster, a mastodont. Might be the most ridiculous amp to
power...mere headphones...well, maybe...one never knows until one
tries. A good point is that changing the output chokes to PP transformers would make it a medium-power speaker amp,
which may be usefull...somehere.
I'm slowly starting to get the parts: Lundahl chokes, PSU transormers, big caps, etc.
Cheers,
N-set
Rerurn to Romy the Cat's Site