I purchased two of these units, one as a present and have used the unit with the Real Voice Spider ear buds. I made sure to follow the instructions regarding first time charging and had no problems from the first connection on. I first connect the Real Voice Spiders directly to the output of my iphone 4S and listened to several selections, primarily Jazz, classic rock and blues. All recordings were at least 256 bit and i set the all parametric values to flat. The sound from the iphone 4s output jack was average at best (apple should really be ashamed) even with the Real Voice Spiders which are a substantial (understatement) improvement from the earbuds supplied by apple. I then plugged in the iFuzen (no break in) and connected the Spiders to the Low output side (there is also a hi for difficult to drive headphones such as my HD800s). The sound improvement with the iFuzen/Spiders was DRAMATICALLY better in every way. I then connected my HD 800s to the hi side of the iFuzen and again listened to the same selections, incredible. The iFuzen/HD800 combination (on these 256bit songs) was so close to my dedicated head phone amp (Audio GD NFB 10WM) it was almost impossible to tell the difference. The iFuzen had a little more bloom (tube warmth if you will) and a slight emphasis in the mid to low bass register (quite pleasant and relaxing actually) and the Audio Gd had a higher level of resolution but these are all insignificant and quite frankly, the iFuzen is easier to listen to with lower resolution media. The iFuzen has a sound shaping feature witch allows the user to select between 4 different effects. They did have an effect on the sound but i prefer my music as recorded so i have not explored it other than to run through all the selections once or twice per song to test it. I have read some complaints about the volume control on the iFuzen but at least i have not had any problems with it (it appears as though some had not read the manual). Things to watch for: 1 when you plug the iFuzen into your mac (or whatever) with the supplied cable it turns the unit on. Once charged or synced and the cable removed, the unit must be turned off manually or it will drain to the iphone until empty. I have never had any problems syncing with my mac once iTunes is started. 2 when plugged in to the mac, it doesn't always fire iTunes off (if you have iTunes set that way) but it does always start charging.
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