The idle noise of PA5 from Topping's spec is 16 μV (A-weighted).
The idle noise from the Hypex NC252MP is 30 μV (unweighted, which will give a worse number than A-weighted). Its noise is therefore about 6 dB (worst case) higher than the PA5. The 6 dB number also corresponds to the double distance sound attenuation. Therefore, for example, if you can't hear noise from the PA5 at 4 inches, you shouldn't hear noise from the NC252MP at 8 inches.
Hi again!
Yes, this was my understanding. The final noise output should be approx 6db worse. Well, I got that number from looking at the gain. 25.5-19.1 = 6.4db. And if what Mdsimon said last time still holds true here (I think it does), the M4's noise after being mangified by 25.5db gain dominates the amp's own noise. And so increase in noise should in theory be approx 6.4db.
My best friend has a new pa5 w/ Kef R3 and says they can hear noise few inches away w/ Motu UL5! Not entirely sure if he's hearing ghosts or if his hearing is really that acute.
I would not service the unit for Topping either. Topping should service them and do it properly and no mickey mouse club stuff!
You are a wealth of info on most all days so don't go hard on yourself.
I told my mom what happened and she tells me never to buy Topping ever again and sprint for another brand lol. To me there is some difference between LA90 and PA7 though. LA90 has been out for over a year now with no angry thread of people. It's the LA90 Discrete now though and there isn't good visibility on what happens after the first year or two. But yes, the idea of getting another Topping amp in particular is not that appealing. To me, the horrendous customer support ended up being worse than the defect itself. If I got a partial refund (which I might've if I harrassed Hifigo when warranty claim was still on them TBF) I might feel differently but I didn't.
OK, but how does a 2 channel preamp fix that problem?
The OP suggested the LA90 as a solution, but it doesn't have any line level output.
So regarding the preamp, you have the same question I do. Unsure what that's supposed to do when there is more than enough gain in the system already.
My comment about the LA90 was with respect to interfacing with a sub and providing a single volume control, which as you noted, the M4 can't do. The description of the signal chain by the OP doesn't address how that is accomplished.
My experience has been that power amps have always been the source of more speaker hiss than any of the upstream components, at least for the past 20 years or so. Haven't found a noise-only spec for the M4, only that Motu specs THD+N on the balanced outputs at -111 dB which matches Amir's measured SINAD. I've run 3 different power amps between a Topping E30 with a similar SINAD and my speakers, and the tweeter hiss was minimal and no different than when I put shorting plugs on the input of the power amps.
Thanks to Mdsimon for explaining everything while I was away better than I can. My understanding is based on
this post:
The rule of thumb is to put a much of the gain as possible to the front of the chain, and therefore as little gain as possible in the speaker amp (just enough to reach your desired listening level).
You can solve the problem by placing an analog volume control (can be a passive "pre-amp" or one of the headphone/pre amps) between the speaker amp and source. The combination effectively gives you adjustable gain for the speaker amp, so you don't have to run it at full gain all the time.
I thought that I could just use a 2 channel preamp that reduces the level going from M4 -> Amp and fix the noise that could only be heard from mains rather than the sub. So I turn the preamp knob down some and would have to turn the volume on back of my sub some as well to compensate. Am I totally wrong here? Preamps weren't discussed in depth last time so I don't know as much. If my power amp only operates at high gain, then I get around this with an amp with adjustable gain or get a preamp. And an amp with adjustable gain is hard to find especially ignoring Topping.
I think it is highly unlikely that you have audible hiss with a NC252MP. I'd get a Buckeye or Audiophonics NC252MP and see how it goes. If it is too noisy get a 10 dB XLR attenuator. That will give noise performance slightly better than the PA5 and you will still be able to drive the NC252MP to full power.
Michael
Never heard of XLR attenuators.
Do I just look em' up on Amazon? They say stuff like "-20dB at 300ohm" and I dunno how to relate that to a speaker which aren't 300ohm.
Sounds like you have a preferred budget of < 500$ USD? Any other preference, like small form?
How does something like the Sabaj A20a fit?
Newer designs like these don't have much track record yet (doesn't mean there will be problems) so your 10yr trouble-free wish is tricky to fulfill.
Plenty of 'traditional' integrated amps but they are less likely to offer balanced inputs.
Do you need the Motu ... the AUDIOPHONICS DA-S125NC measures pretty well (also new though)
https://audiosciencereview.com/foru...phonics-da-s250nc-dac-power-amp-review.44379/
Recently tested, cheap, with an excellent hypex amplifier module, unfortunately it has no analog inputs but only digital inputs
Thanks for the suggestions. TBH, I'm not sure what digital input means. There's just some cables that go out of the M4 dac and goes into the amp. I assume that's analog as most as in this case?
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The reason why I didn't list the new Ncx Buckeyes was because the Purifi stuff have been out for far longer and measurements don't show some big lead the Ncx has above the Purifi. Pricing are identical. Features look the same.