[SpecChum]

Xpost from here: http://www.head-fi.org/t/794419/low-impedance-headphones-on-otl-amp-little-dot-mkii (sorry, completely missed the MASSIVE red text saying questions like this go here, cos I'm an idiot)
 
I've been given a Little Dot mkII to lend with a view to buying it for a decent price but the bass seems a bit loose.
 
Some google-fu has shown me that it's possibly not best suited for my SoundMAGIC HP200 headphones as they're quite low impedance at 20ohm (DC, innerfidelity shows it as 35ohm at 1Khz) and this won't work particularity well with an OTL amp?  Would a LD I+ be better?  Or even a Vali2?  I'd have to buy those new though.
 
I'm very new to all this, so getting a it bogged down in details, can anyone ELI5?
 
I don't *have* to have a tube amp but I so if anyone has any other (SS?) amp ideas for around £150 that'd be much appreciated also.  I'm currently using a Fiio E11k which I find a bit bright on the mids (I don't mind a bright treble, I seem more sensitive to mids - my other headphones are the DT990 pro's) so thought tubes might tame the mids down a bit...

 

[LBailey33]

I'm no expert and I am far from understanding the science behind it but OTL headphone amps use tubes as the output stage instead of transformers and as a result have higher output impedance. Low impedance headphones when used with high output impedance amps tend to become loose in the bass as far as I am aware. The general consensus is that when using an OTL tube amp, you want headphones with high impedances. Hybrid tube amps (such as the little dot 1+) and solid state amps work better with low impedance headphones.

 

[LBailey33]

And to expand on the point, the OTL tube amp should work perfectly with your DT990s as they are 250 ohm. The tubes should somewhat tame the treble of the 990s (I had a pair bit the treble was always too much for me). However, this is the problem to having headphones with varying impedances, a single amp may not be able to do everything you need it to do. But I would probably suggest the Schiit Asgard 2 as it is fairly warm sounding in my opinion and can handle both low and high impedance headphones.

 

[SpecChum]

Thanks for that, seems to mirror what I read so I suspect you're spot on.
 
Asgard 2 is above budget, however.  Vali 2 looks favourite so far as that's got a gain switch.
 
But dayum, asgard 2 looks nice...

 

[LBailey33]

Yeah the vali 2 would probably work nicely for you. You could maybe find a used Asgard 2 on the for sale forums here, that is where I bought mine.