Measurements and Analysis

The red trace shows the frequency response via the analog inputs after they go through ADC and DAC conversion stages.  As you can see, there is about 0.5dB roll off at 20KHz followed by a sharp brickwall filter response rolloff at ½ nyquist frequency of 22kHz (44kHz sampling rate).  The green trace represents  "Pure Direct" mode, where the 3dB point was well above 100kHz.

When the analog preamp was driven at 1Vrms (typically ½ signal strength to achieve ½ of max power of most power amps with voltage gain of 29dB) distortion levels were (+.0446 + 100.511)dBv = 100.957dBv or 100*alog(-100.957/20) = .000896%!  The yellow trace represents "Pure Direct" mode, while the red trace represents DSP analog input.  As you can see it is only slightly higher in distortion, certainly not dramatic enough to be audible.  This is good testament to the ADC design and implementation in this product!

Integra Research distortion spec at 1Vrms was .05%, about 5 times higher than I measured, or 35dB worse.  Talk about conservative!

When I drove the analog preamp to its limits it was able to output 7Vrms unbalanced and 15Vrms balanced (about 10dB more gain than you should ever need) and distortion levels were (+18.298 + 68.449)dBv = 86.747dBv or 100*alog(-86.747/20) = .00459%!

Note:  In "Pure Direct" mode the analog inputs were able to handle about 7Vrms before clipping input circuits and 2Vrms when engaged in analog DSP.  Most consumer equipment (ie. CD players, VCR, etc) drive 1-2Vrms max via their analog outputs so there shouldn't be any compatibility problems here.  If for some reason you find the input levels too high, causing clipping, the RDC-7.1 provisioning for independent level trims for each input will come in quite handy here.  This is great foresight on their part!

Editorial Note on Balanced vs Unbalanced

I measured the voltage gain of the RDC-7.1 via balanced and unbalanced inputs and found the following:

Unbalanced:  Av = 17dB

Balanced:  AV = 23dB (6 dB higher than unbalanced)

This is a standard practice in most consumer and pro audio.  The power amp therefore usually has 6dB less gain via the balanced outputs to compensate.  I verified the RDA-7. achieved full rated power with less than 1.3Vrms driving it unbalanced, and about 2.5Vrms via balanced.

Check out our Balanced vs. Unbalanced Connections Article for more information.