A lot of folks have asked me about this. Can I use a HAGCLOCK at 12MHz to drive a HAGUSB? And is it better? My answer is usually yes and no. Yes, but you have to add a +/-12V or so power supply to drive the clock board. No because it may not really help, as the word clock is dependent on the USB data packets from PC. You spend a lot of money for possibly very little gain.
So I came up with another way. Use just the 5V oscillator section on the clock board and power it via the USB. This keeps the audio grounds clean and separate, isolated via the S/PDIF tranny. The problem is that now the clock has no regulated supply and is dependent on the cleanliness of the 5V supplied by USB. I do have low pass filtering, but there is nothing to clean up any low frequency grunge.
My one and only listening A/B test with a stock HAGUSB gave me nothing. I was listening through a CHIME (my only DAC), which erased any possible benefits via it's own reclocking. That's not to say there isn't an improvement to be had with other DACs. Anyway, here's how I did it:
First, I cut the HAGCLOCK board into a small piece (see pic). Lined up the "+" pin on D1 with R13. Then drilled two holes in the clock board to line up with the mounting holes on usb board. Partially stuffed both boards, left three component leads long. Added standoffs and mounted the clock board on top routing the long leads into appropriate holes.
On usb board, Change R12 to a ferrite bead. Move R7 to the output side of T1, make it 130 ohms (this is a separate improvement in transmission line matching). Leave off D1, C8, Y1, R6, C9, C11, C12, C13, C14, R8, R9, R10, R11, and J3.
On clock board, leave ground lead of C12 long. Tie one lead of R15 to it (ground), leave other side of R15 long. Leave +5V side of R13 long. Put LED into C13 spot. Change L1 to a 330 ohm, tie one lead to anode of LED. Only stuff parts as shown. Xtal is 12.000MHz.
When mounting, bend the clock output and ground leads so that the ground falls into the C8 ground hole and the output lead falls into the R8 hole that is XTI on the usb chip. By having such short output wires, the comparator normally used as output buffer is not needed.
jh
