Yes, all hand soldered. It is a two sided board and the bottom side has almost as many components as the top layer :D. And yes it has an integrated DAC, based on the PCM5102A.

Hi all! I'd like to share my creation with you guys.   A 4th order Linkwitz-Riley active 3-way crossover for IEMs. Now that’s a mouthful :)   It uses a fully analog active crossover, giving a much improved performance over passive “crossovers” normally found in IEMs, including steeper roll...

Actually you can use just a capacitor without the resistor for a mild lowpass effect. Here I have a 47uF capacitor parallel with a ED-23147 driver (red=with cap, blue=without):  

I think the low end roll off is mostly due the measurement setup. I tend to see that kind of roll off often when I measure. Still, when I listen to these, the bass is quite powerful and deep, without being bloaty in the mid bass region. I can't say that there isn't any roll off for sure, but...

    Here's a frequency response graph I measured from the finished IEMs. I'm not sure if says too much, everyone has a different test setup that affects the curve. I couple the IEM to a WM-61a mic with a 6x20mm(DiameterxLength) silicone tube.   I only use these measurements as a reference...

  Right now I only have some measurements from the unfinished stages when the drivers were still out of their shells. I'll try to get some done of the final product as well.

  The crossover is my own design. Based on the Linkwitz-Riley crossover, with input and output buffers at unity gain. All-in-all that's 25 opamps :)    Powered from a 3.7V cellphone battery, the power supply is split with a virtual ground to ±1.85V and also includes battery charging...

  After a long time in development, my latest IEMs are done.   5 drivers per ear (CI,DTEC and TWFK), with an external battery powered, 3-way, 4th order active crossover system feeding them. Simply amazing sound, easily rivals some of my high quality full sized cans.

I've used this to make custom earplugs:   http://www.amazon.co.uk/Hiflex-Silicone-Putty-Rubber-Moulding/dp/B007DKSH9Q   Works well enough and you can make about a hundred pairs from the kit, so the price for one pair will be quite low.  

Anyone know how to safely remove the pads on these? On of the pads on mine is slightly misaligned, and I'd like to adjust it without breaking anything.   Thanks.

Sounds like the amp isn't supplying enough current. This could be caused by the power supply or the design of the amp itself. What headphones are you using? I once built a somewhat similar amp and it could only drive some more efficient headphones, while more power hungry phones would distort...

Quote:   I'm using the sensorcom tubing. Seems to work well enough.

True, but smd film caps are rare, expensive and aren't available in very high capacitances. Hence, ceramics are used, which I believe are better than tantalums at least. There's really not much room for better caps in iems.

Maybe if you'll send me one driver (or ten), I'll plot the impedance for you     I was under the impression that tantalums are worst kind of cap for audio. Why not use ceramics instead? They'll also have lower ESR for sure. I have no idea about the quality of niobium caps.

Well, the TWFK seems to have to most pronounced highs of the knowles drivers. Whether thats a good thing is a matter of taste. My suggestion: experiment with the rear port on the TWFK. It has to be completely isolated from your ear canal, otherwise you'll get a very harsh sound in my experience...