I have been using the Amp Dynamics Automated test to help measure an amp/receiver/intg amo’s Dynamic Headroom per CEA-490-A par. 5.2. I was testing a Sansui receiver circa 1982 yesterday, and ran into a problem where I could not generate an input signal level greater than 6dBV- screenshot attached:
I was able to work around this in this case, since I was able to adjust the volume control for 27dB of gain instead of my normal 25dB of gain, but have run into this problem testing an amp with a fixed gain of 25dB, I am not sure if the 6dBV limit was intentionally put there. It would be nice- my Christmas wish list for QA40x software- to have the settings I showed in the example for the dwells and transition times as defaults, and you provide the signal for Level 2 in dBV and it calculates Level 1 and 3 to be 20dB less than level 2. The graph plot would not be needed, but if there as a display of the TIME plot of the Level 2 portion of the waveform to where you can see if clipping is occurring and measure the P-P waveform using markers manually at that point- if that makes sense. Maybe it would be a stand alone Automated Plugin ? Maybe there is not a lot of interest in being able to measure dynamic headroom these days….
In the 1970s and 1980s integrated amplifiers and receivers had 100-200mV for full rated power line sensitivities. Most were 150mV. -13dBV is 224mV. (some Marantz’s were 200mV IIRC) When doing a dynamic headroom test, it was typical to have the amplifier driven to rated power and that was usually (like many other tests) run the volume pot at maximum and adjusting the input level up until the peaks of the 20dB overload clipped or just started to clip.
I haven’t had much luck with the dynamic power plugin due to the same bug you have found. The maximum should be the maximum of the gen (18dBV). None of the fields will take it.
Sadly, it’s way easier to do it with a CD player and an EIA/CEA track (or the JIS headroom track) and a ‘scope. It’s proved to be much more accurate for my testing.
I do a lot of transient/dynamic testing of my vintage amps too and having this fixed would be helpful. Also, for power amps with much lower sensitivity, (1-2V or more) the plugin really can’t be used as 20dB above even 1V exceeds the capability of the generator. If however we could parallel the output of gen2 (option checkbox maybe) we could mostly get there.
@restorer-john I have only been doing the headroom test for maybe 3 months using just the plug in and have had pretty good luck except when the 6dBV input is reached and I need more. Looking back at some of the data on the amps that I have measured, most hit their rated power limits at 6dBV in when their gains are 28-29dB, so testing for DH with the plugin as it stands can’t be done- I am guessing you would need at least 3-4dBV more- the most I have seen is 2.5dB of DH. I am glad I am not the only one doing this
