After I was done with my listening, I brought the amp into the electronics lab and removed the bottom cover. Inside I found a fairly basic layout using a single sided PCB and thru-hole parts. The build quality was good, especially for an amp of this price range.
For those of you that keep score, the power supply uses three high temp 2200µF 25V caps, and the audio section has a total of 13,200µF of capacitance. The power supply switching is handled by six 50N06 MOSFETS, and each channel is driven by a dedicated pair of complimentary bipolar transistors.
On The Bench:
Okay, time then to get the performance numbers out of the ZRS C9, and see how she performed on the unerring Cogent test bench. As I suspected from my listening session, the amp is a very good performer for the dollars invested. Power figures were just a hair shy of the published numbers, but in fairness the difference would be completely inaudible to even the most skilled listeners. The ZRS C9 excelled in the signal to noise department, measuring a seldom reached -94dBA at 1 watt. Stereo separation was also very good at better than-65dB.
Other high points included measurements showing the C9 has very low output impedance, and the frequency response extended well past human audibility, way out to 80kHz in fact! The overall frequency response was extremely flat, with less than 0.3dB of difference from below 10Hz to 20kHz. This kind of performance is seldom found in a 300 dollar amplifier!
It wasn’t all roses and sunshine, however. I found that at certain points in the rotation of the gain controls there was about 1.5dB of difference between left and right channels, which could easily explain the lack of focus I’d previously noted in the stereo image. Yes, it was possible to get them to track almost identically, but that only happened at either end of the pots rotation, places where the gains are not likely to be optimized for most systems. One other niggle, the “Clone Function” seemed to be more of a “distant cousin” function, as it did not achieve the perfect matching of the gain settings I expected. This problem could be related to the tracking problems of the gain pot, and I could get better results matching the gains individually with my multi-metre. Still, the crossovers were very accurately duplicated, which I suppose is what most people will be more worried about. And to be fair, I have to admit I still prefer amps with individual gain pots for each channel because I’m one of the very few people who uses a meter to adjust gains to within 0.1dB. Keep in mind the differences I measured in the ZRS C9 would be only barely audible, but they were there so I had to mention it.
After all my usual tests were performed I tested the protection functions by dead shorting the outputs during operation. The circuits worked as intended, I removed the short, cycled the power and all was well again. While I was at it, I also checked for any audible turn-on or off noise, but the ZRS C9 was dead quiet in that regard.
The Cadence ZRS C9 is a very good amplifier for the money. In many respects it has better performance and more useful features than many of its competitors. I especially liked the Bass Focus feature- a useful control in almost any system. The build quality is good, and my abusive tests seem to indicate that the amp should be very reliable. The flexibility of the crossovers and the inclusion of bandpass capability make this amplifier a joy to do system tuning with. If you’re a fussy listener on a tight budget, you’d do well to check out a ZRS C9 at your local Cadence dealer. It’s a lot of amp for the money.