Hello
@shadyJ , I just noticed you mentioned the SR8015's measurements and that was measured by the AP so am wondering why for the HTTP-1 you didn't use the AP. Is the QA401's accuracy comparable to Gene's AP?
Also, you mentioned measurement the 7706, is the results going to be published? Since AH has measured 3 recent Marantz models albeit all AVPs, it would be nice to measure a Denon AVR in preamp mode too, any plan for that? I would love to see AH do a little more bench tests of the popular AVR/AVPs, so we don't have to rely on ASR all the time.
I know its a lot of work but I have to ask.
Almost forgot, do you know if Monolith has recently put a limit (via FW update) on the maximum output to 4 V XLR? I got that from someone on ASR, hope that is not true.
Thank you
Hi Peng,
I am actually the better person to answer this as I was the one who measured the Monolith.
First let me say the simple answer to your question is that we don’t all work in an office together. At the time of this review I was in Chicago area. As is James. I was in the process of moving. I have the Quantum Asylum and Gene has the AP. He was in Florida. As such, it wasn’t possible for us to measure the Monolith on the AP without delaying the review. Gene had packed his AP as he was getting ready to move into his new house.
now in terms of accuracy. The answer is yes the QA is as accurate as the AP as long as the user doesn’t do something ham fisted. It’s a factory calibrated device with very good native specs. However, like all devices, it has a limit. It can only measure distortion (THD+N) down to around .0015% or so. That is the limit of the AD converter in its best mode and using an external pure source.
The AP would also have a similar limit if not for some tricks. AP has a notch filter. This notch filter is extremely precise and adjustable to any frequency. The addition of the notch filter allows you to dewarp the incoming signal and leave only the distortion of the DUT, canceling all distortion of the testing device hardware. I have that ability too. I also have a notch filter. But I have a problem. Fully adjustable notch filters are very expensive to make. Instead, mine is limited to just 1khz. I also have a 1khz pure sine wave oscillator. That means I too can measure extremely low levels of distortion.
this is where the ham fisted issue comes in. When I measured this device I accidentally forgot to account for the gain adjustment of the oscillator and notch filter. Further, I had been trying to ensure it was calibrated right because I was getting odd results and once I found the problem, forgot to undo the calibration value. None of this has any impact on distortion or noise measurements. It only threw off the voltage measurement at the output. We corrected it (or at least I submitted a correction once I found the problem).
so to answer your question. It is absolutely accurate. It’s capable of measuring noise and distortion down to -120dB and with software updates and new hardware boxes, it’s getting better. It is simply limited to 1khz for such measurements. All other measurements would be limited to more like -98dB or so. However I need to make a checklist for myself when I do this to be sure I don’t do something goofy. There are so many sources of error with modern processors and measurement gear that if you aren’t careful you can produce totally erroneous results.
as a case in point, it’s been noted that you can be too fancy for your own good. The same tech that allows you to measure these crazy low numbers can also cancel a portion of the DUT noise and cause an artificially low number. This often happens when the FFT is very high and a very long accumulation period is used. As such, a reviewer for a trade oriented publication measured a Purifi module and came up with results that are in fact lower than factory spec. I had asked Bruno if this implied the amp bring lower noise than the AP he uses. He said no, then sent me a graph that showed a good 20dB of additional margin. He told me that in reviewing the other measurements in question he found the results unlikely. How they were obtained? Who knows, but Bruno was confident they weren’t right. One guess was that the use of the oscillator, notch filter, and a large accumulation period might have combined with improper signal processing to lead to a bogus result.
as for the Marantz. My fault. I have it sitting here in a box. I was supposed to move into my new place 2 months ago. But long construction delays put us at October. I had assumed I could setup a good measurement space here, but it turns out that 1000 sq ft is not enough for two young kids, a dog, cat, wife, two crabs, and lots of life crap. Gene is 90+ minutes from me and it’s been hard to find a good time for both of us to focus just in measuring the preamp at his house.
if all you want is a THD+N spec and voltage max, it should be close or the same as the 7705. That didn’t change the audio hardware. We will get to this eventually. I should reach out to Gene again to get that going.
