Preproman,
I know diddly about HP amps, but I think people are excited because of Lukasz's FBook post:
OMG it feels good! The concept I had actually works like a dream. We use balanced DAC output into the push-pull transformer but in this scenario it is not the "bad" push pull because we dont split phase. We keep intact the whole signal in each phase and the transformer is working like two opposite SE amps. The secondary winding sums up the signal into the headphone SE output and while doing it - it cancels out the digital errors from conversion process. We have 30 x iron core headroom which sounds very open and pure, because we used small speaker cores, only primary winding is customized for the DAC. We can drive any headphones even 4 ohm ones. We used 6N6P - the super powerful and clean miniature triode, biased at 25 mA at 200V supply. PSU is also tube so we have a pure tube, zero capacitor, zero resistor headphone DAC. Even my cheapest 10 dollar headphones sound spectacular, and the Beyerdynamics are just a bliss.
and the preamble:
I miss the times when we actually invented and prototyped things EVERY DAY. And never went to bed before hearing them in the main system. Nowdays it is work work work.
All work and no play makes Jack a dull boy.
So it is time to CREATE something. I have the DACs, I have the amps, I have the preamp too. I failed on the phono stage front. Total GRENADA. So my decision is to build a HEADPHONE DAC. No, not the headphone amp. but the DAC. There are great synergies and gains to be had if we blend the DAC and head amp into one. Pure tube of course.
My first choice would be the OTL - a tube amp stage without output transformers. We only need low power and the impedance is high. It seems easy, and I know how to make speaker driving OTL. So what's the problem ?
First problem is that the OTL sounded weird, and very very much "inside the brain". I just did not like the character of this sound.
Another problem is that to get satisfying volume, I needed so much power that the DAC started to look like a monoblock amp. it is definitely not a small task for small tubes.
Long story short - a good headphone OTL is a) a can of worms , and b) too expensive project to be done properly and stay in budget.
Now I am prototyping various types of transformer-coupled DACs. Single ended triode, push pull balanced triodes, capacitor couples transformer, airgap, gapless, choke loaded anode follower with transformer, etc. Early tests are very encouraging.
We want to be able to use DAC chip directly coupled to the good triode with just an inch of silver wire, no caps, no resistors - nothing in between. We want to combine DAC output I/V vonversion, analog filtering, balanced to SE conversion, signal amplification and impedance matching - all these features in one tube genius circuit. There will be just three parts in total: Chip - triodes and transformer.
This week we will finalize the choice of tubes, next week - the choice of transformer.
. Can't wait to get infos (to décide if I cancel my EC4-45 pre-order )
