Hybrid amps with a tube output?

I am wondering if there is a hybrid headphone(or speaker) amp that uses an SS driver but a tube power output?

Now you might be wondering why such an arrangement would make sense? Well from more then a few articles I have read, tubes have the biggest effect at the electromechanical interface; which means with speakers, microphones, guitars and phono cartridges. The biggest contributor is the output transformer and then the power tube.

So is one available or would I have to build one?

 

Tubes are stunningly bad at current output, if you're talking OTL, so they're not a good choice for low-impedance loads. Not that it can't be made to work, but...heroics. That's why you don't see a lot of tube-out hybrids.

If you're talking transformer-coupled, that's a whole 'nother thing entirely, because you are really dealing with the transformer interaction with the load, more than the tube (not that the tube has nothing to do with the sound, it's just the transformer magnetics dominate.)

In short, it's not something I'd take on as an experiment, but that doesn't mean that it shouldn't be explored. Just that there are a lot of challenges.

 

I wasn't expecting to see any OTL amps like this but I don't see how it wouldn't work since OTL amps do exist. While reading the description of the Project Horizon by garage1217 I actually thought it was a tube output hybrid since its for high impedance headphones and describes the output as "single ended OTL class A output stage".

My curiosity was peeked when I was reading an article by Leonard Audio.

http://education.lenardaudio.com/en/14_valve_amps_3.html

Afterwards it shows an amp using opamps as a driver for a KT88 amp. Here is another quote from an AES article that discusses transistors vs tubes.

http://www.dwfearn.com/tubes_vs_transistors.html

So it seems like if I really want to experience 'tube' sound I need to do it with an amp with a tube output. So far the only way for me to do this is with an all tube amp. However it seems like if you are going to be tube rolling, a power tube has a much bigger effect then a preamp tube and so if I were to get a hybrid I would like to see a hybrid using a 6080 rather then a 6sn7. Just trying to gauge if someone was crazy enough to commercialize such an amp.

 

Musical Fidelity X-can v1 has an OTL tube output stage and opamp input stage.

 

If you'd like to see a whole lot of tube hybrid topologies, many incorporating solid-state at least as an intermediate stage but with tube/transformer out, take a look at www.tubecad.com. John Broskie has had more original ideas than, well, pretty much all of the other audio designers put together.

Fair warning: many of these topologies are not fully worked out—they're not easy DIY projects with a nice parts list. But they are a starting point.

 

Wouldn't using LISST in place of the input tubes on the Valhalla 2 essentially do this?

 

That is true ... but as Schiit themselves say in the FAQ, why would you use LISST in an OTL amp, where its entire raison d'etre is to sound like an OTL amp and drive like an OTL amp.

Then again, I might just try this in my Val2...

Jason! Can you please ship more Schiit stuff to Headphone Bar?

 

LOL, yep, I am an idiot. I've never tried that, though...hmmmmmm.

 

Please try and report back

 

http://diy.ecpaudio.com/2014/06/apsara-amplifier.html

 

Thanks! I already have a lot of DIY on my plate but it seems like this is rare enough that this will be something I need to just build myself also. I used tubecad as a great educational resource but I didn't know he worked on hybrids like this. I'll have to look through his archives.

Seems like an interesting experiment. Clean gain stage through LISST with a vacuum tube output.