Willow Revisited

UPDATE September 2015: The Willow revision is slated for December 2015 AudioXpress.

*Boards and programmed chips will be available for this design.*

Willow Revisited (W2) is a complete update of Willow's power supply and amp board. I took special care to make W2 especially quiet from a very low noise power supply to biasing the new LM49600 buffers.

The case is lucite with brass and copper. (It got a little banged up as it started out as a tube project. I'll have to redo it.)

Below is the 250 Khz square wave of W2, the lower trace is at the input, the upper one is at the output:
(More technical data to follow)

The bias for the buffers is through the negative 15V regulator. Because all the resistors in the signal line are Panasonic low noise 0.1% SMD's I was able to keep the bias very tight and even on both the output buffers so very little bias adjustment is required. Biasing through the 15V supply also keeps carbon pots out of the input line. Using ultra low noise regulators also means that noise on the buffer inputs is kept to a minimum. (RV1 changed to 20k on latest revision)

The trimpot on the negative supply side:

The bias circuit is comprised of the 470k and 20k resistors on the +15V side and the 470k on the -15V side going to the input (pin 2) of the LM49600 buffer

Because some CD inputs run relatively high voltages I put a divider on one input. You do not have to use this arrangement, simply leave out R44 and R45 and place jumpers across R42 and R43:

I experimented with different case designs. This slim case works well in my office with my other components. I'm also using stainless steel knobs now. I like the color tone and weighty feel, also SS will look the same in fifteen years from now.