- Written by Chris Heinonen
- Published on 11 November 2013
The Pioneer SC-79 Receiver On The Bench
The Pioneer SC-79 is one of the first products to be tested using an Audio Precision APx585 analyzer. With the ability to fully test HDMI, Coaxial, Optical, RCA, XLR and power amplifier sections, the APx585 allows completely reliable, accurate measurements to be made on components. After all, it's what most of the companies use to design them. We'd like to thank Audio Precision for their time and for providing access to their test equipment and knowledge.
First, the analog input signal test results.
Running two channels at 1 kHz to 1% THD+N the Pioneer SC-79 managed to put out 129 watts into 8 ohms. With 0.1% THD+N power output drops to 125 watts into 8 ohms. Future tests will utilize 20 Hz – 20 kHz testing as well as 1 kHz tests as I'm still refining the APx585 tests.
The curve below shows output power at 1 kHz into 8 ohms vs. output level. Note that the distortion starts to increase at only 10 watts. The steep knee on the power output vs. THD-N chart is at 127.4 watts.
For the SC-79 first we will look at performance using the analog inputs with the volume set for unity gain (2V input, 2V output). Looking at THD vs. frequency with a 2V RMS signal, we see that THD remains constant from 200 Hz – 20 kHz. Many preamps show a rise in THD beyond 5 kHz but the SC-79 does not. The absolute value of 0.01% is higher than expected and the lower distortion below 200 Hz is uncommon to see.
With a 1 kHz sine wave at 2 volts input as the test signal, THD+N was 019%. The harmonics are higher than expected, and the odd harmonics are larger than the even. The harmonics also do not reduce significantly with increasing harmonic order that you would normally expect.
IMD was -76.2 dBV, or 0.01542%, using the standard SMPTE 60 Hz, 7 kHz combination of test tones.
With 19 khz – 20 kHz test tones, IMD dropped to -89.00 dBV, or 0.00355%. What you can also see is that the noise floor rose with increasing frequency.
Frequency response was flat out to 50 kHz, with a maximum deviation of 0.012 dB from 20 Hz – 20 kHz.
Crosstalk was low, with a minimum at 100 Hz of -120dB and a maximum at 20 kHz around -76dB.
Signal to Noise ratio came in at 109.3 dB unfiltered and 116.1 dB with filters at 20 Hz and 20 kHz. Adding A-Weighing to that increases it to 118.6 dB.
And, now the digital test signal input test results.
The results were identical for HDMI, Optical, or Coaxial inputs, as all use the ESS SABRE chipset.
THD+N vs. Frequency from the digital inputs was similar to the analog input test results. Distortion was flat from 200 Hz to almost 20 kHz, and drops down below 200 Hz. The biggest change here is that THD+N increased when using the digital inputs instead of the analog inputs by a factor of 3. Given the quality of the ESS DAC, this appears to be an analog implementation issue.
THD+N using a 1 kHz sine wave resulted again in higher odd-ordered harmonics, but they began to fall off, unlike the analog test. However the harmonics are higher to begin with than with the analog tests.
With the SPMTE IMD test, the 60 Hz tone had larger odd-order than even-order harmonics. IMD was only -64.35 dBV or 0.06800%. Once again, this is a level that is higher than with analog inputs.
The low level linearity of the ESS DAC was excellent. We can see this in a plot of a sign wave at -90 dB down with a 24 bit word. The amplitude is almost at the theoretical 90 mV peak, and the shape of the waveform is well preserved. This time domain result combined with the 116 dB SNR (Signal-to-Noise Ratio) shows the SC-79 can resolve 19 bits. The number of bits in the 24 bit word that can be resolved is derived by the following formula: (SNR - 1.76)/6.02. See David Rich's article for a complete explanation of bit resolution.
The performance of the Pioneer is a bit surprising. The high odd-ordered harmonics over RCA inputs indicate that it may run into some issues when used as a preamp. For full-scale digital signals, the distortion is even higher, which is unexpected; however, for low-level signals, the performance is close to the best achieved in an AVR at about 19 bits. It is not likely the distortion of the SC-79 will be audible, but the extraordinary (for an AVR) low level linearity and noise makes this an excellent candidate to reproduce high-resolution music.