Classé CAM 350 monoblock power amplifier Measurements

Sidebar 2: Measurements

As is usual with Stereophile's tests of amplifiers, I soak-tested the Classé CAM 350 by running it for an hour at one-third power before performing any further tests. At the end of this period, its heatsinks were way too hot to touch, as was the rear of the chassis, which suggests that the amplifier's thermal capacity is optimistically specified. This probably won't be a problem unless you use the CAM 350 for sustained high-power use with notoriously low-impedance speakers like the Thiel CS5.

When I tested the unbalanced input, I used a shorting strap to tie pins 1 and 3 of the XLR input together. The unbalanced input impedance was a high 100k ohms, the balanced 200k ohms. The voltage gain into 8 ohms was the same with both inputs: a high 30dB. The amplifier didn't invert signal polarity from either input, suggesting that the XLR jack is wired with pin 2 positive, the modern convention.

The output impedance from the reassuringly industrial binding posts was a low 0.08 ohm across most of the audioband, rising to a still-low 0.1 ohm at 20kHz. As a result, any response interaction between the CAM 350 and the loudspeakers with which it will be used will be minimal. This can be seen in fig.1, which shows the balanced frequency response into our simulated loudspeaker load as well as into various resistive loads. (The set of unbalanced responses was identical.) The CAM 350's ultrasonic response is sensibly rolled-off, reaching -3dB at 120kHz, which gently slows the rise of a 10kHz squarewave (fig.2). The amplifier's reproduction of a 1kHz squarewave (fig.3) was essentially perfect.

Fig.1 Classé CAM 350 (balanced input), frequency response at (from top to bottom at 2kHz): 2.83V into dummy loudspeaker load, 1W into 8 ohms, 2W into 4 ohms, and 4W into 2 ohms (0.5dB/vertical div.).

Fig.2 Classé CAM 350, small-signal 1kHz squarewave into 8 ohms.

Fig.3 Classé CAM 350, small-signal 10kHz squarewave into 8 ohms.

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