This morning we’re glad to resume production of C5D! UPS delivered parts at 10am and I’ve been listening to C5D for more than two hours with a smile on my face.

In case you missed the drama, we caught a tiny error in the first batch of C5D and temporarily halted production. Our terrific engineers, George Boudreau and Ken Mathews, collaboratively resolved the mistake in less than 48 hours. We owe them many thanks.

Customers

A few C5D’s shipped on Monday and Tuesday without the correction. We’re emailing affected customers today and will offer an easy exchange.

Distributors

C5D shipments to distributors resume next week:

• Headphone Bar / Canada
• Munkong Gadget / Thailand
• Headsound Audio / Germany
• Kingsound Audio / Hong Kong
• Noisy Motel / Australia

C5D samples also ship to reviewers by Monday.

Technical Explanation

If you’re curious, C5D is a complex device that makes use of 12 highly regulated, onboard power supplies.

Prior to the production fix, the first batch of C5D exhibited an extremely low level hum under USB data transfer. Hum vanished while music was not playing over USB, so it was easy to miss while listening. And by nature of its presence, it could never appear in Noise measurements, and was simply a tiny component of THD measurements (all excellent). This type of problem could only be found by an engineer actively looking for it. Conclusion: Subjective results matter as much as Objective measurements!

Working backwards, we disabled individual power supplies in C5D to isolate the issue. We found that when the USB controller placed its heavy load during data transfer (0.5W), it brought the primary +7V rail to 60% capacity. The +7V rail has been stable in C5, and the amplifier and DAC measure well independently. While powering both amp and DAC, the higher power draw pushed the rail slightly out of regulation. Line ripple increased by a factor of 10.

The solution was shockingly simple–we added a larger capacitor to the +7V rail (this capacitor will be hand soldered on the first batch of C5Ds). Ripple decreased more than 10x, to levels better than ever. Performance is restored. Low level hum is gone.