NAD C420 audioXpress 6/02, Measurements- Parasound Fm Section, $129, Design speaker boxes with

mance was 54dB at 1kHz.

THD+N at 1kHz was 0.087% mono, and 0.29% stereo. During distortion testing, I engaged the test set 80kHz low-pass filter to limit the out-of-band noise. THD from 100–10kHz, mono, did not exceed 0.22%.

The mono audio distortion residual waveform shows mainly the second harmonic, overlaid with noise.

The C 420 tuner quieting charac-

teristics are shown in Fig. 2. I had to switch to FM/Mute mode to measure mono sensitivity. The sta- tion auto search threshold, where it would stop at the signal genera- tor’s frequency during a station scan, was 27dBf. There was no overload at the maximum RF input of 100dBf. The audio output disap- peared when I moved the FM test signal ±50kHz to either side of the tuned center frequency. Stereo audio output was −0.9dB below

the mono audio at 65dBf signal strength.

The seven bars of the display’s tuning strength meter change at the RF signal levels are:

Bar 1 (always on)

Bar 2 at 25dBf

Bar 3 at 30dBf

Bar 4 at 33dBf

Bar 5 at 36dBf

Bar 6 at 39dBf

Bar 7 at 41dBf

MEASUREMENTS— PARASOUND FM SECTION

Again, I did not run any tests on the AM section, except to verify its operation. The TDQ-150 inverted polarity; the tuner’s audio output being out of phase with the com- posite audio signal fed to the FM signal generator’s varactor modu- lator. The output impedance at 1kHz was 600Ω, delivering 580mV into a load of 100k.

The TDQ-150 tuner frequency response (Fig. 1) was within +0,

−0.5dB from 20Hz to 15kHz.

Crosstalk performance at 1kHz

THD+N at 1kHz was 0.09% mono, and 0.15% stereo. THD from 100–10kHz, mono, did not exceed 0.28%.

The mono audio distortion residual waveform again showed mainly the second harmonic, over- laid with noise.

The TDQ-150 quieting character- istics are shown in Fig. 3. The sta- tion auto search threshold was 20dBf. There is no method for manually switching the FM/Mute mode, and the tuner switches back to mono at a high 40dBf, right where the −50dB stereo quieting occurs.

The audio output didn’t disap- pear until I moved the FM test sig- nal ±150kHz to either side of the tuned center frequency, probably reflecting the reduced sensitivity of the two-stage IF design. This is not an issue with the U.S. 200kHz FM radio station spacings. There was no overload at the maximum RF input of 100dBf. Stereo audio output was only −0.3dB below the mono audio at 65dBf signal

strength.❖

PHOTO 4: Interior view of Parasound TDQ-150.

measured 58dB.

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64 audioXpress 6/02 www.audioXpress.com