2.3 x 1.6 x 0.75-inches (5.7 x 4.1 x 1.9 cm)
1.5 ounces (ca. 43 g)
AD8620 op-amp chip
Cascode current source class-A biasing
Separate output buffers for optimal channel separation and imaging
3.5mm input and 3.5mm output jacks
Digital volume control (64 steps)
Runs on one 9-volt NiMH battery
15+ hours playback per charge
Ouptut up to 110mA per channel!
XinFeed (crossfeed) with bypass switch
Bass-Boost with bypass switch
Output impedance switch (0-75 ohm, can be used to make Etymotic ER4P equal to the ER4S model)
This SD has the sound quality upgrade done by Xin, and during the upgrade process Xin also modified the crossfeed for me for a wider imaging. Crossfeed is now very much like on the Porta Corda II, and doesn't sound like a mono switch any more.
I used it only for bed listening, very rarely used, perfect condition. I did a 100 hours break-in. An DC Adapter with central-european plug type is included.
Price is EUR 100,- in Europe plus shipping costs. Will ship to the US too. PayPal possible.