Thoughts and issues: Audioholics Marantz SR8015 Measurement Video
There are a number of issues with the Audioholics video on the SR8015. Here are some of them:
1) Based on the audio and labeling of the graphs, it appears that Gene is often only measuring THD, not THD+Noise. THD-only will give lower (better) numbers and can't be compared with the THD+N that Amir measures.
2) The bandwidth used for the THD measurements is not clear. A lower bandwidth means that less of the harmonics are included in the results and the numbers look better.
3) The square wave response is representative of the use of a non-standard reconstruction filter in the DAC process. Gene repeats Marantz's frankly nonsensical reply concerning their filter selection. It sounds like a marketing reply.
Gene should know, and point out that the DAC IC would allow a selection of filters with a little effort on Marantz's part. This would allow Marantz to include the unacceptable filter and allow others to use a standard filter. Perhaps he just doesn't understand the concepts and technology involved here, which really isn't good for a site that claims technical knowledge.
The square wave also has a slightly sloped top. This typically means that there is low frequency roll-off. The Frequency Response graph shows a low frequency roll-off, after a slight amount of peaking, which really shouldn't be there. Minus is OK if undesirable, plus should be zero. One thought on this: consumer AVR's have numerous electrolytic capacitors in the signal chain to block DC. This isn't a problem if the resultant high-pass filter cutoff frequency is at say 1Hz or less, this is, if the capacitor has a high enough value. There will be no lost bass and phase issues, and essentially no significant voltage drop across the capacitor. Voltage drop across an electrolytic capacitor in the signal chain causes distortion. This isn't to claim that this problem exists, it is just something to keep in mind.
4) Note at the top of the Power Measurements section that, "We tested power using three methods all of which were taken at <.1% THD+N." In the actual measurement the Continuous Full Power Bandwidth measurements are only given at <1%. This lack of attention to detail brings much of what is presented into question. Lab work requires knowledge and attention to detail. The tester has to get it correct or there is a loss of credibility, as in, if this is simple item to get correct is wrong, what else that can't be checked is wrong?
Gene also says that the SR8015 is rated at 140W per channel and he got 159W per channel. Per Marantz, the140W rating is at .05%. Gene measured at 1% according to the text. The difference in distortion is 26dB. These two levels of distortion aren't even close. Does anyone review any of these written results? Again, credibility takes a hit here. It is easy to note the .05% and 1% are very far from equal.
5) 1kHz Power Test. The Marantz 5-channel power guarantee can be found on this webpage:
https://www.us.marantz.com/en-US/support/glossary
To quote from the page above, "A standard THD value is 0.08%"
Gene tested at 1% and .1% and tested 7-channels. 7-channels may be interesting, but why not test the actual 70% guarantee for 5-channels at .08%. Again, what gives here? Does anyone check any of this? How is the equipment configured for the actual test? These errors in simple to understand numbers raise serious questions.
6) Use of ECO auto adds another variable to the tests above and is really bad experimental practice. A test is run with odd results Instead of redoing the test with ECO off to determine in the really odd results are due to the ECO mode, Gene just guesses at the issue. Didn't Gene immediately look at the results? Why not rerun the measurements? The Audioholics review has few measurements compared to an ASR review. Is Gene so busy that he can't rerun a simple measurement?
7) Frequency Response: If the preamp frequency response graph was developed using a broadband analog signal input then a -3dB point at 63KHz is too low. The comment about excessive noise ingress is odd. Lots of equipment has preamps with wider bandwidths without excess noise. The comment sounds more like a marketing comment (excuse).
8) Power Test ECO On vs ECO Auto: Are these power sweeps?
If the ECO mode actually goes on and off with signal level and not the setting of the volume control then that is a poor design. ECO mode at least in past D/M units was implemented with a mechanical relay and was dependent on the setting of the volume control. If the volume control was set at a high enough level higher rail voltages were used. Changing to a low enough volume control setting and lower rail voltages were used. At a constant volume control setting there were was no switching between higher and lower voltage rails.
An amplifier that uses let's call it Class G mode, switches, using high speed silicon switches, between two DC power rail voltage levels after the rectifier and filter (storage) capacitors. ECO mode is implemented with a relay that switches AC voltages between two different transformer windings, before the rectifier and filter capacitors, very slowly in electronic terms, and won't handle the duty cycle. Even with fast electronic switches Class G puts glitches in the output.
It really isn't clear what Gene is testing here. Perhaps the ECO mode has changed.
9) Comparisons with ASR measurements:
The Preamp Out THD vs Frequency chart gives a
very rough indication of performance since the chart is hard to read. The THD for the worst channel is about .0014% which is -97dB. ASR measures THD plus noise so the equivalent measurement would likely be worse. The bandwidth for the measurement is also not given so this is another variable. All of the issues with the quality of the measurements based on the issues noted above add to the mix.
Ignoring all that, which may be ill-advised, -97dB is inline with the worst measured Denon AVR's, but is still very good. For >$3k perhaps not so much.
What's next?
If and when measured in the future, the ASR measurements will more detailed and conducted in line with past measurements. These measurements will give higher quality view of the actual performance of the SR8015.
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