How about the specs on VM-1a?
I'm also curious about how the auto-bias is accomplished (as I see no pots for manual adjustment).
No manual adjustment, all auto. Has to be like that, as toroidal output transformers are very easy to saturate with bias unsymmetry. The transformers are designed by Menno van der Veen and we have strictly followed the recommendation about autobias.
I can say about Vandeveen transformers is that they have the least sound of "iron" I've ever experienced! Also, the response at the end of the bandwidth (~32kHz) is a very nice and wide low-Q knee, without any traces of ringing. A very remarkable achievement for a 100 :1 transformer (10000x impedance conversion) for both bandwidth and lack of parasitic reactive components. It's bonkers and it sounds like an OTL with ba..s!
As the loading of the transformers is basically the cable resistance of 0.4 Ohms, we've made sure that cable parasitic Inductance is kept to a minimum, the same requirement as for the JotR. Not recommended to use with any other cables, as the cable is the actual load (ribbon is only 0.018 ohms) and you don't want unknown inductance to be multiplied 10000x and load the anodes as voltage-spiking reactance.
The amp is Class AB (70% of possible swing is class A) Push-Pull with a pair of EL34's, driven with high current/voltage swing capability of another EL34 that doubles as a phase splitter.
The input tube is 6SL7 triode, loaded with a CCS.
No overall feedback.
Output power at 0.4 Ohms is 21 Watts, about 3dB higher than what SR1a and SR2a can use cleanly, so basically, it all works in Class A, until you overload the headphones.
Input is only XLR with awesome Cinemag transformers, for audio ground isolation from source gnd and best possible CMRR.
Initially, we've had the speaker output, BUT...the sound of the feedbackless amp was so enchanting on SR1a that we ditched the speaker output as that can't work without feedback.
So, audio purity at it's finest all the way!
The one that got broken in shipping to the show was my piece and I'm still weeping over it's sudden death! However, it's martyrdom made me redesign the transformers mounting and it will be rock solid, worthy of MIL-spec hardware. Also, packaging is getting redesigned so it will arrive safely to any point on the planet, with all modes of transport.
We're really rushing to get the VM-1a into sales, and we'll do everything humanly possible to shorten that amount of time!
Again, circuitry is designed by Solaja Audio, with parts choice input by Danny and me and the sound is brought to the very summit through several iterations. And I'm so glad we all did it!