[rusitnpiece]

Im quite impressed with the sound of the MB Quart QP 805 HS for the £20 that i paid for them. What a bargain. 
 
Does anyone know of any Mods to improve the bass? It just doesn't go quite low enough for my liking.

 

[shnitz]

They're 300 Ohm headphones, you aren't driving them well enough.  I've found that through various sources that aren't headphone amps, even with my AKG K518 the bass improves with volume.  At low listening levels, the bass sounds all pokey and weak, even though the mids and treble sound all right.  When turned up to "partying" listening levels, everything sounds good.  So, you need to get a headphone amp that can:
-Properly drive your headphones
-Provide solid bass, even at low listening levels
 
The "mod" is to properly match your equipment.  Don't bother with portable amps, for the most part they don't sound all that amazing, especially for the ridiculous prices that they go for.  Get yourself a solid desktop amp.

 

[rusitnpiece]

Mine are the 100 Ohm version and i have several solid state amps that can drive them but they are always a bit bass shy for my liking.

 

[Acix]

Try to add some felt on the drivers, and of course at 300 ohm you'll need some hp amp.