the most portable of the kind I saw in the market. If this I can plug to a 12V dc energy supplier, others were 12V ac or 15 or 24 Vdc which limited my options.
after comparing technical specs of various equipments that would satisfy my requisite of a portable device, and concluding this model would be one of the most powerfull (higher amplification gain values), but still, with 32 ohm headphones I would be expecting at maximum gain I would get a louder sound level, anyway, they provide a good level ( for my purposes I would want more but they give satisfactory results)
yet, at higher values of amplification, my perception is that you start to listen to noise... but in the end this aren´t yet an expensive option and at mid levels of gain you will not feel it.
I tested if I would listen to any noises while rotating the gain knobs.... zero!!!! excelent results!!!!
the product seems to be very good... I feel satisfied although for the environments I will be using (noisier) I would wish higher levels of amp
downside for this product is that ART (manufacturer) has not showned to me, a good client support ( I e-mail them and sent messgaes on facebook more than twice... got no answers until from them... only from the mother company that holds ART when later on I got to know about it