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Help a newbie understand gain structure: Minidsp Flex to Power amp

RosalieTheDog

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Dear all

I recently swapped a Topping D70s for a Minidsp Flex as source for my 2.1 hifi system. The benefits of the Dirac room correction are definitely there. However, I'd like to understand better why the SPL seems lower at the listening position with similar attenuation at the volume control. There are of course many new variables, and I'm not even sure which ones matter. I've tried listing the variables of the system here:

Source : Wiim mini through optical or a TV through optical
  • Wiim mini volume controle disabled
  • The TV through optical requires much less attenuation to reach the same output level as the Wiim, but that is a whole other issue!
Volume control / input selection / DAC : Minidsp Flex balanced
  • DIRAC enabled. There is debate on how DIRAC in minidsp deals with headroom, some suggesting it applies -10 db attenuation. (See here and here on the Minidsp forums and here on audiosciencereview.) The Minidsp Device Console and DIRAC itself are very mysterious, and at any case don't show or communicate this.
  • The 'max output level' on the balanced output (4Vrms) is different from the Topping D70s (5Vrms @ 0dBFS through XLR). Is this the main reason for the perceived difference?
Amplifier : Audiophonics MPA-S125NC XLR with NCore NC122MP with 25.5dB gain and "Max power at 1.17V RMS (2x0.59V RMS)"

Speakers : Buchardt S400 mkii (87 dB sensitivity)

Would anyone care to walk this neophyte through the gain structure? Which variables in this gear determine the output volume? Is the amp sufficiently powerful, or is it related to gain? I'm not looking for new gear, at least not in the near future, but just understanding a bit better what's going on.

Thanks in advance!
 

staticV3

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A simple $10-15 multimeter is enough to diagnose all thses issues yourself, which is infinitely better than us theorizing about what might or might not influence the volume.

Just plug the XLR cables out of the Amp, play a 60Hz 0dBFS test tone via the Flex, your TV, the D70s, or via the WiiM, and see what kind of output voltage you get at the XLR cable end (Pin2&3).
 
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RosalieTheDog

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A simple $10-15 multimeter is enough to diagnose all thses issues yourself, which is infinitely better than us theorizing about what might or might not influence the volume.

Just plug the XLR cables out of the Amp, play a 60Hz 0dBFS test tone via the Flex, your TV, the D70s, or via the WiiM, and see what kind of output voltage you get at the XLR cable end (Pin2&3).
Thank you for this advice!

And the idea is to test this with the same attenuation (or 0) on the Flex' volume control?

I'm having some trouble finding cheap multimeters capable of measuring low AC voltage, as I understand is necessary from this thread. (https://www.audiosciencereview.com/...ds/how-do-i-measure-dac-output-voltage.14446/) I'll report back!
 
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RosalieTheDog

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A simple $10-15 multimeter is enough to diagnose all thses issues yourself, which is infinitely better than us theorizing about what might or might not influence the volume.

Just plug the XLR cables out of the Amp, play a 60Hz 0dBFS test tone via the Flex, your TV, the D70s, or via the WiiM, and see what kind of output voltage you get at the XLR cable end (Pin2&3).
Hi staticV3. Thank you for your advice.

The Topping D70s measures 5 Vrms @0dBFs as advertised.
The Minidsp Flex measures 4.11 Vrms @0dBFs both for USB input and for Optical input via Wiim.

I have a couple of follow up questions to help me interpret and go on, but don't feel obliged to answer them.

1) How do these figures relate to the specs of the NCore NC122MP with 25.5dB gain and "Max power at 1.17V RMS (2x0.59V RMS)"? Should I make additional measurements at the attenuation I usually listen at (up to -20dB for music through the Wiim, up to -15 for classical music through the Wiim and TV)?
2) I wanted to test if the Nvidia Switch > TV > Minidsp Flex results in the same Vrms output, but I am still working on finding a way to play the REW 60Hz 0dBFS tone here. I'll find it.
3) I only measured one output profile of the Minidsp Flex: 2.0 without DIRAC. Three of the presets I use are 2.1, with the bookshelves crossed over with a subwoofer, and various DIRAC curves. There is a lot going on at 60hz (crossover slopes, DIRAC boosts or dips, DIRAC headroom?). Would there even be a point in making comparisons here? Should I choose a different test tone?
 

Keith_W

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If you are using your MiniDSP for room correction, then you need to understand that ALL DSP DRC products sacrifice volume for linearity. This may be a contributing factor as to why you have lower volume at the listening position with the same volume setting.

The other major reason is different output voltage from your Topping vs. your MiniDSP.
 
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Hi staticV3. Thank you for your advice.

The Topping D70s measures 5 Vrms @0dBFs as advertised.
The Minidsp Flex measures 4.11 Vrms @0dBFs both for USB input and for Optical input via Wiim.

I have a couple of follow up questions to help me interpret and go on, but don't feel obliged to answer them.

1) How do these figures relate to the specs of the NCore NC122MP with 25.5dB gain and "Max power at 1.17V RMS (2x0.59V RMS)"? Should I make additional measurements at the attenuation I usually listen at (up to -20dB for music through the Wiim, up to -15 for classical music through the Wiim and TV)?
2) I wanted to test if the Nvidia Switch > TV > Minidsp Flex results in the same Vrms output, but I am still working on finding a way to play the REW 60Hz 0dBFS tone here. I'll find it.
3) I only measured one output profile of the Minidsp Flex: 2.0 without DIRAC. Three of the presets I use are 2.1, with the bookshelves crossed over with a subwoofer, and various DIRAC curves. There is a lot going on at 60hz (crossover slopes, DIRAC boosts or dips, DIRAC headroom?). Would there even be a point in making comparisons here? Should I choose a different test tone?
You are right. When you have applied EQ you can't just choose a test tone and measure output voltage. For all we know the output at 60 Hz could be cut 10 dB by the room correction (not unrealistic to have a room mode around this area). Then your measurement would mean absolutely nothing.
If anything you should find out where on the spectrum the signal is the highest on the EQ curve and measure output voltage with the corresponding test frequency tone.

Or you should do a frequency sweep with the DMM on max. hold function.
 
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