My experience with the Valhalla 2 is it is good, I prefer most headphones with the tube magic now. Some issues to consider when moving into an OTL such as the Valhalla.
- Tubes can be weird sometimes, just turn the amp off and switch the left and right, and listen again.
- Power tubes can get freaking hot,
- nearly all tubes I have tried are not micro-phonic so don’t put a tube dampener on the back tubes they will just stink up your room
- Nearly all tubes sound different, when you power off/on the amp you will notice the sound of the tubes sound like creaking/ breaking glass. Just have your headphones unplugged before each power cycle to prevent any nasties into your headphone
- try both “gain modes” find the right sound for you.
- A DC offset power strip might be a good investment for your future.
Now for sound, I will describe it based on some of the tubes I tried, but some generalities first that I believe are true regardless of drivers. This amp can be a bit bright on other headphones. I didn’t have much luck on something like the DT880 600 ohm, I believe it needed a higher output impedance. On the PortaPros this amp made them quite bright, not the pairing I would recommended with them. 6xx though it is nearly a perfect match.
This amp really rocks on the 6xx.
The front tubes can be a pain to roll, I had some cheap socket saves, but I would recommended the tube monger ones. They fit much nicer, and aren’t atrocious on the inside. To me to roll on an amp like the Valhalla 2 it has to be easy. They didn’t degrade the sound at least not on my 6xx. The OTL aspect feels that it just grabs the driver and takes it for a ride. Effortless interaction between the 6xx and the Valhalla 2.
It extends the bass to go a little past what people claim is impossible through eq on the driver and does it (might be some IMD aspects of an OTL) The slight glare on the Valhalla 2 is a good thing for the 6xx as it can miss a little on some regions.
Tubes:
stock tubes; I thought the stock tubes did the job, but felt like you can miss some details.
Raytheon 5670WA; These gave me a sparkly top end and nice tight bass.
Apmerex A frame(Bugle Boys); These are just an upgraded stock tube, good midrange, way better bass(yes more is better here) and the top end is sweet. No complaints.
6CG7 Halo getter; These I feel are a sweet compromise and the biggest deal for this amp. If you want to roll off the stock tubes, and don’t want to pick up socket savers. These are longer than the stock tubes so you can roll them out, on the stock tubes it felt nearly impossible to remove them. Their sound is hard for me to describe other than good and it would be pleasing for most people. These are a good upgrade if you don’t want to get a bugle boy or another tube pair that is half the cost of the amp. Though their imaging is very good, highly recommended tube, I can see why so many people also love this tube on the lyr3. A true gem in my eyes.
Overall I would recommend this to anyone tube curious with a 6xx. Other pairing that might be worth considering are some Grado headphones, and maybe even some Focal headphones(I have not tested the focal clears with the V2 yet and may not be a good pairing but they do deserve some investigation due to both their low OI)