Preamplifiers

Parasound 2100 Stereo Preamplifier and 2250 Stereo Power Amplifier

ARTICLE INDEX

 

On the Bench

Measurements were made with PHS SpectraPlus FFT analysis software and a Roland Edirol UA-101 24 bit 196 kHz USB sound card. 8 ohm 300W power resistors were used as the load for the amplifier, with a divide by 100 voltage divider to reduce the amplitude of the measured signal at the input of the sound card.

2100 Preamplifier

Here we see the output of the preamp with a 1 kHz sine wave at the input. Harmonics are at least 90 dB down from the signal, with the second harmonic the highest in amplitude. The more objectionable third harmonic is more than 10 dB lower in amplitude.

The intermodulation spectrum shows the output of the preamp with 2 and 3 kHz sine waves at the input. The 1 kHz intermodulation product is also about 90 dB down from the signal tones.

Frequency response is flat as a pancake from 20 Hz to 50 kHz, and rolls off by less than a dB to the Nyquist frequency of the sound card ADC at 96 kHz. These data have been normalized to the frequency response of the sound card.

Crosstalk is below the noise floor of the sound card at -85 dB below 1 kHz, and rises to around -60 dB at 20 kHz. The crosstalk from the left input to the right output (solid line) is a bit higher than the crosstalk from the right input to the left output (dashed line). These data have been corrected for the frequency response of both the preamp and the sound card.

The THD+N vs. Frequency is 0.002% at 20 Hz and rises to 0.02% at 20 kHz. These are vanishingly small. In my opinion, the first plot showing the harmonic spectrum is a more important measurement, but the THD+N results shown here are still very good.

2250 Power Amplifier

The output of the model 2250 with a 1 kHz sine wave at the input into a 8 ohm power resistor is shown here. Harmonics are at least 60 dB down, with odd harmonics at higher amplitude than the even harmonics. Harmonics are clearly visible to relatively high order (10th harmonic).

The intermodulation spectrum resulting from 2 kHz and 3 kHz sine waves at the input shows a 1 kHz intermodulation product 60 dB down.

The frequency response of the amp is also flat to about 50 kHz and then very gently rolls off. The rolloff is very small (less than 1 dB) and may be a measurement artifact, as with the preamp measurement. Amplifier crosstalk was not measurable with my measurement setup. The dynamic range of the setup with the voltage divider was insufficient to measure the crosstalk above the noise floor of the measurement setup.

The THD+N vs. Frequency of the 2250 is a low 0.2% from 20 Hz to 20 kHz, and is essentially flat. I also measured THD+N into 4 ohms and 2 ohms and got essentially identical results.

For both the model 2100 and model 2250, the measured results show solid engineering that is fully consistent with the high quality performance I experienced with my ears.

Conclusions

As I said at the beginning of this article, now is a good time to be an audiophile. The Parasound 2100 and 2250 offer sound quality across the board so good I would have thought you'd have to pay at least $3,000 to get it. At a mere $1,800, the Parasounds are a steal. The $600 Model 2100 preamp offers a killer phono stage in addition to its already great performance. When combined with the big 250WPC Model 2250, the combo can drive almost any speaker and deliver first class performance. And unlike my reference Emotiva RSP-1 and RPA-1, it can be found in many brick and mortar audio retailers, so you can listen before you buy. If you have $2K to spend on a preamp and amp, you can't go wrong with the Model 2100 and 2250, and you'll have to spend quite a lot more to do significantly better.