Yay my Step Dance arrived! I've had it since yesterday evening and I've been putting it through it's paces with my iphone 4 as the source and pairing it with my UM3X.
I'm very pleased with the resulting sound. Based on my initial exposure, if I were to use one word to describe its performance, it would be 'refined'. The amp has a very neutral sound and provides a noticeable improvement in clarity, detail, instrument separation and space. It's a very clean and well controlled sound.
The UM3X are also new to me and initially I was disappointed by how warm they sound when compared to my HD 25-1, I felt they sounded overly warm. As such I'm glad the STEPDANCE is neutral as I certainly don't feel the UM3X need any extra warmth. After using the UM3X exclusively over the last day I've gotten used to their sound signature and I'm now very happy with them. When working with the STEPDANCE they provide all the great aforementioned technical improvements, such as increased detail, but with a great smoothness. They're very relaxing to listen to, with very solid bass and a precise treble which isn't harsh at all.
The STEPDANCE certainly has a quality feel to it. Almost all components, such as the battery door latch and volume knob, are made from aluminium. It has a feeling to it, perhaps imparted by it's design, which make it seem different to other - mass produced - electronics. I want to say "home made" but this isn't correct; there's a quality about it which confirms that it's the product of one man. It's quite a chunk when paired with the iphone and is barely pocket-able. It still seems like a great portable solution though, especially when you consider the quality of sound. I was expecting the volume control to be notched, given that it's described as 'stepped', but it's totally smooth. This goes for the way the volume increases when turning the volume up too, there's no hint the volume is increasing in set increments.
The only niggles I have with the STEPDANCE, and I would be grateful for other owners input here, is that even on low gain - with the STEPDANCE hooked up to the iphone line out - the lowest volume setting is surprisingly loud. When listening late at night I suspect I may want the volume a little lower than it's possible go with the STEPDANCE and the UM3X. I was expecting the lowest volume setting to be silent. It also eats through batteries. I was expecting this, based comments in this thread and Jan's stated design objectives, but still I was surprised to get less than approx. 6 hours out of it on low gain (but with the current switch set to high) with a Duracell Plus 9V Alkaline battery. I'll be investing in some rechargeables and a regulated DC power adapter for sure. With no music playing the amp is silent all the way up to about 2 o'clock, after which I can detect hiss which gets quite loud at full volume (again on low gain setting). Noise or interference, like a clicking, can also be heard while turning the volume control up past 2 o'clock. The amp is very sensitive to mobile phone interference, which is a problem when your DAP is also a phone!
I had a brief listen to my HD 25-1 with the STEPDANCE, and while it wasn't long enough to form any solid impressions, I was very impressed, and the lowest volume setting was more acceptable (but still not silent). The biggest proof of how good the STEPDANCE sounds was when I plugged the UM3X back into the headphone out of the iphone 4 - when the battery died on the STEPDANCE. It sounded a touch warmer, but also almost fuzzy by comparison, such was the loss in definition and control that I had become used to in my short listening time with the STEPDANCE.
A few photos of the STEPDANCE in situ. I hope you can forgive the impromptu and make-shift use of cable ties and Velcro to construct a portable rig!