Portable Headphone Amp with Wall Charger

You should check out the Fiio E12, a true giant-killer!

Jl35, try to google "Oppo HA-2" and "HD700" or "HD-700".  You might find additional info on the use with Senheissers.

thanks much

It comes with a wall charger (micro USB type).  You can charge it with any phone (micro USB) wall charger, but one provided is recognized by the unit as rapid charger and charges much faster (if it makes any difference).

the Oppo looks very interesting.  How do I charge it if I do not have a computer? Thanks 

I bought Oppo HA-2 headphone amp recently and it sounds amazing. It has async USB, SPIDIF, DSD an analog in/out. I use USB. Sounds better than my Benchmark DAC1. D/A converter IC is SABRE 32-bit. It has lithium battery (7-8 hours) and can be used with a phone, but I’m using it as stationary unit only (next to my computer).

https://www.oppodigital.com/headphone-amplifier-ha-2/

You can charge it with any micro USB charger and connect to iPod touch with provided short cable. It comes with rapid wall USB charger. I used it with my Samsung phone and it played beautifully. It should be able to drive your HD700 - compare power ratings at 300 ohm.

Ray Samuels products come to mind.