Got only plots on those? Given that these things just have a regular dome tweeter, they should not have a falling impedance with frequency unless they did something stupid with the crossovers.
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Roland68
Master Contributor
There are no differences between the devices—at least not regarding the components.
I have attached the official measurement data for both units.
The issue regarding the analog input measurements stemmed from a misconception. The analog input utilizes the PCM1804 ADC; however, in this specific implementation, the analog input's performance falls short compared to other designs featuring the PCM1804.
First off: there has always been only one version of the A30a.
I also do not believe that a genuine "V1.2" version of the VMV A2 ever actually existed; had it done so, SMSL surely would have advertised it as such.
Instead, I suspect that a critical connection was inadvertently omitted during the PCB's design or manufacturing phase, and was subsequently added—either during the next production batch or via a retroactive modification.
Presumably, the A30a benefited from its later release date, ensuring that this particular error was not repeated.
All the menus for sound customization and subwoofer control are powered by the STA309A DSP chip.
Furthermore, regarding the various speculations about differing measurement results—specifically in relation to the design and component changes—you are all falling victim to the same logical fallacy.
This amplifier operates entirely in the digital domain from input to output (with the sole exception of the dedicated analog input). There are no op-amps, no potentiometers, and no analog signal path. How, then, could the measurement results vary so drastically?
It is only at the output stage that the digital signals are converted into analog PWM by the Axign chip.
Incidentally, the VMV A2 has also been discontinued and removed from the website.
Hi @Roland68, if 80K–100kHz is the issue, with the A30a to Dunlavys Mid/High +ve connection, would it be ok/acceptable to add an inductor in-line, set for say 50K-60KHz or even 40K-50KHz, at the Dunlavys Mid/High +ve connection?
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Roland68
Master Contributor
We’ve already covered this topic a few times in this thread—most recently just a few pages back.
A resistor and/or an inductor proved to be the effective solution in those instances as well.
It would be even better if someone were to simulate the crossover network.
As far as I recall, all similar issues in the past have consistently pointed to extremely low impedance in the crossover within this high-frequency range.
Thank you, @Roland68, Yes, but note that this is not for me, it is for @Vlasis....
- Apologys, No, last time it was for a pair of Magnepan speakers (inductor in series from about 12-15kHz)....
@Vlasis, if you can find an Impedance Graph for your Dunlavy speakers, that will be helpful :=)
- You have mentioned fairly benign but conciseness will be helpful....
Roland68
Master Contributor
Exactly—and if you look at the thread history, everything suggests that the low impedance in the high-frequency range dropped all the way down to zero at the higher, inaudible frequencies.
The point here is not that there is any signal present in this range, but rather that the amplifier is subjected to a short circuit within this frequency spectrum. That is a major and fundamental distinction.
For the Dunlavy 3a
- Nominal: 4 ohms
- Typical range: ~3 ohms (low‑frequency minimum) to ~6.5 ohms (high‑frequency maximum) US Audio Mart+1
- Low‑frequency minimum: ~2.9 ohms at ~63 Hz Stereophile
- High‑frequency maximum: ~6.5 ohms US Audio Mart
This is from the IV, not III. But if similar, it will not have a short-circuit at high frequencies.
Apologys, @Vlasis, best left to @Roland68 and @voodooless to assist you with this. Note that, as the Sabaj A30a is working, it could (simplely) be Thermal Shutdown, why?.... the enclosure is not Ventilated, is it? High Volume and Enclosure Temperature would be an indicator. The minimum Impedances, mentioned, indicate no issue/s, there, don't they/reasonable?
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