The Stax Thread III

[TheAbyss2022]

Need an Energizer recommendation for the STAX SR-007A.


This is my bedroom setup.

I started with the STAX L-300 which were considerably easier to drive than this SR-007A.

Volume is not the problem: It is missing impact especially in the mid bass. Sub bass sounds fuzzy and incomplete, like it's not in focus. It sounds like a demanding planar magnetic headphone being driven by a decent amp which doesn't have enough power.

The soundstage is flat, and dynamics are lacking.

This is not consistent with reviews of the 007A. It is a supposed to be quite impactful and dynamic sounding, but may need a better energizer than the TOPPING EHA-5.

I'm from India, importing an energizer from Mjolnir Audio might incur significant import duties and customs. The higher end Stax energizers are also an option, but offerings from Mjolnir and LTE audio are generally considered superior.

What are my options?

EHA5 is basically a starter amp, a teaser of what the 007 is capable of.

Your options if you don't go the Stax route is Carbon/CC for the best solid state option. Birgir is flexible with the declared value so it won't cost that much to import. Tube route is BHSE for a warmer midrange and a more airy presentation but less impactful sound to Carbon. You can just run a tube pre through the Carbon so you get the best of both worlds.

 

[ericj]

You cannot measure after the 4.7meg ballast resistor generally as the impedance of your measurement device is dragging down the voltage with such little current flow. You’re likely measuring differences in the impedance / ballast resistor values (I think STAX used 2.2meg at some point also? I always take my measurements before the ballast (carefully). Differential probe possibly could do it but I haven’t tried as I always got dead accurate measurements from my DC-DC bias sources before the ballast, measuring across the bulk storage capacitor.

STAX bias has been pretty archaic for me and they did some questionable stuff which is why I abandoned it for newer tech which measures way lower for noise and it can be dialled in accurately.

In my experience it’s pretty important the bias is running near correct to prevent overdriving the stators, chasing that missing volume.

See above wrt 1000:1 probe. The impedance of my measurement device is 1010 megohms total. Admittedly i bought it because my 10mohm DMM was loaing down the SRD style voltage multiplier somewhat, and dramatically loading down the self-biased version. How this works is, if i connect it to a 600vdc source, the DMM reads 600mv. It's rated to 40kv and is the size of a turkey baster so i should really figure out a smaller version.

It wasn't immediately obvious where to probe for normal-bias on the srm-1/mk-2 board. It kind of looks like it's just a string of resistors and a capacitor hung off of the main power supply. If there's a schematic (for the late "B" version) I haven't seen it, though i know someone traced out the early "B" version.

Dug around some more and found one - looks like i would measure it at the junction of R002, R003, and R004.

Edit: Kinda understanding arguments for more complicated, adjustable bias supplies. But I'm trying to keep my design cheap as chips.