[rEEcEj]

My Sennheiser HD650's have always felt like they need serious tweaking everywhere except for the low end, are there any amps with built in equalizers?

 

[SDBiotek]

What kind of source and amplification are you currently using with your HD650s? What are you trying to change about the sound signature through EQ?
 
Instead of extensive use of EQ, perhaps whatever amp you are using now isn't driving the HD650s very well, and maybe after changing amps you won't feel the need for EQ. Or, if you really want the headphones to sound different, it may make more sense to get a different set of headphones.
 
Not sure if you're looking for a desktop solution or something portable. Usually you EQ on your digital music source (phone, iPod, DAP, computer, etc.). Some portable headphone amps have some basic tone controls, but not anything closer to a parametric equalizer. There may be some stereo preamps or receivers that have EQ built in, but I'm not aware of dedicated headphone amps that have it. With all of the options commercially available, though, I am sure someone else will chime in with something specific that fits your needs.

 

[zapcovirtuoso]

I went with my Zapco SP7-SL powered with a Meanwell power supply and Iota DLS-45 power supply for the Meanwell. It's a lot of gear just for an EQ but it allows for a nice desktop 7 band analog EQ for the Grado325is. In my opinion an EQ for these cans is mandatory. Especially around the 2kH and up range.
 
You may want to check out MiniDSP. They have some good options for EQing.