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Status: PCBs now released and available at AMB audio shop. Official website is now up.
Background
As outlined in the Other DCX2496 mods thread, I was looking to develop a simple but effective master clock upgrade for the Behringer DCX2496, DCX2496LE and DEQ2496. That effort resulted in a circuit described in that thread using an Analog Devices ADM7150ARDZ-3.3 ultra low noise and high PSRR local voltage regulator, powering a low jitter and phase noise Crystek CCHD-957-25-24.576 oscillator. It's basically the same thing taken from the γ3 DAC (actually, the γ24 DAC core), except there is no clock buffer, because the oscillator(s) will drive only one load.
I then realized that the circuit could be generalized to make it useful as an upgrade for many other digital audio devices, such as CD players, digital streamers, DACs and ADCs. Some of these need only a single master clock frequency whereas others need two, to support multiples of 44.1KHz and 48KHz sample rates.
I am calling this new circuit ο1 ("omicron 1").
Circuit details
See the schematic diagram below. There is a 3P Molex header providing connections to a DC power source and ground.
Starting with the ADM7150 + CCHD-957 circuit, I added the option of a second oscillator and the ability to select between the two. This is accomplished with the SEL pin on the 3P header. A logic "high" enables oscillator X1 and disables X2. A logic "low" does the opposite. For this control signal, resistors R3 and R4 perform logic level attenuation from 5V to 3.3V if needed. Otherwise, R3 can be shorted and R4 omitted.
If only one master clock frequency is needed (as in the case of the Behringer DCX2496, DCX2496LE and DEQ2496), then everything enclosed by the dashed line box should be omitted. The SEL pin will have no function and X1 will be enabled by default.
The CCHD-957 has a form factor of 14x9mm. Since it's only available in a few frequencies, 7x5mm pads are also included to broaden the usable oscillator types in order to make the circuit usable in more devices. The Fox Xpresso FXO-HC736R series 7x5mm oscillators as used in the γ1.5 are good alternatives.
Some devices need 3.3V logic level clocks whereas others need 5V. The CCHD-957 and FXO-HC736R series are 3.3V-only, but there are other 5V oscillators that fit the 14x9mm or 7x5mm form factors. This highlights the need to make the circuit support a variety of oscillators.
For 3.3V master clock, the VCC input should be 5V-15V, U1 should be ADM7150ARDZ-3.3, and the oscillators should be 3.3V types.
For 5V master clock, VCC should be 6-15V, U1 should be ADM7150ARDZ-5.0, and 5V oscillators should be used.
The master clock output is via a Hirose U.FL coaxial connector and shielded cable, excellent for high frequency transmissions (rated to 6GB).
The PCB is small at 1.5" x 1.0", with one single a mounting hole. There is soldermask and silkscreen on both sides. It should be easy to fit the ο1 into equipment with some interior space. The board is all-SMD except the 3P header. Nothing should be too small to hand-solder. The smallest passive parts are 0805, others are between 1206 oand 1210. U1 is SOIC-8, U2 is SOT-23, and the oscillators should all be relatively easy to solder.
PCB top view:
PCB bottom view:
Schematic diagram:
Parts list
Please refer to the official ο1 website for the most up to date information, including the parts list and instructions.
