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MiniDSP 4x10 HD Measurements
MiniDSP 4x10 HD Measurements
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Old 15th May 2016, 03:35 AM   #11
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Salas View Post
Since shapes like hiss that is why I thought it may contribute something like extra bit of brightness in busy tracks.
"Shapes like that"... It all depends on what you're measuring. In case of the multi-tone IMD, the input signal is 32 tones distributed logarithmically from 16 Hz to 20 kHz. The resulting IMD is the grass you see in the plot between the tones. The reason the IMD rises at higher frequency is that the various opamps and circuits have lower loop gain at those frequencies. It has nothing to do with noise (hiss). For that, see the noise spectra and integrated measurements I posted.

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Originally Posted by Salas View Post
BTW did you ever measure the 2X4 model? I got one and it does not sound that great to me when in the chain. Although nice to trace paths for a crossover design etc.
I do have those measurements. I didn't do as thorough a job when measuring the 2x4, though. I'll see if I can dig those plots out for you.

Tom
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Old 15th May 2016, 04:14 AM   #12
Jim the Oldbie is offline Jim the Oldbie  United States
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MiniDSP 4x10 HD Measurements
Tom, as a 4x10HD owner I really appreciate your taking the time to do this.

This too-much-gain thing seems to be a common problem. Is there some reason why non-commercial power amps rarely have input level controls? Seems they would help with a lot of this. Is it the effect they have on input impedance, or something else?

-- Jim
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Old 15th May 2016, 04:42 AM   #13
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Jim the Oldbie View Post
Tom, as a 4x10HD owner I really appreciate your taking the time to do this.
You're welcome.

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Originally Posted by Jim the Oldbie View Post
This too-much-gain thing seems to be a common problem. Is there some reason why non-commercial power amps rarely have input level controls? Seems they would help with a lot of this. Is it the effect they have on input impedance, or something else?
I've seen one commercially available amp with an input attenuator - the Parasound A23. Unfortunately, the input attenuators/level controls are really just another volume pot, so they don't help much with the gain structure. They do allow you to run higher signal levels to the amp, so you'll get a little EMIR benefit there.

If you wanted to optimize the gain structure, you'd need to change the gain of the amp by changing the feedback factor in the amp. Changing the feedback factor will require a re-tweak of the compensation networks so it's not that easy to do well. That's probably why manufacturers don't implement those controls. In reality the customer would probably leave them cranked to max gain anyway.

Tom
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Old 15th May 2016, 05:40 AM   #14
Jim the Oldbie is offline Jim the Oldbie  United States
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Quote:
Originally Posted by tomchr View Post
...Unfortunately, the input attenuators/level controls are really just another volume pot, so they don't help much with the gain structure. They do allow you to run higher signal levels to the amp, so you'll get a little EMIR benefit there.
But isn't that level mismatch sometimes part of the problem? For example:

At home I'm using a different miniDSP product, the nanoAVR-HDA. This unit has RCA outputs producing the usual 2V RMS at 0 dBFS. My power amps on the other hand have 1V input sensitivity for full output of 75 watts or so. (Gain is rated at 28 dB.)

I can hear a noticeable increase in noise from my tweeters with the nanoAVR connected as opposed to amp inputs shorted (and since I'm using the nano's digital volume feature, its output noise is constant for all volume settings).

This isn't a problem for me using cones & domes, as the higher noise is just barely audible from about 18-24 inches but not at the listening position. But I see how it's an issue with the big horn setups. If it were needed, it looks to me like I could add 6 dB of passive attenuation between the nano and the power amp right off the bat because of the unused extra output level; and since I live in an apartment, I could realistically get away with at least another 6 dB or so with more efficient speakers without "running out of volume." Any attenuation at this point would reduce the miniDSP output noise accordingly, correct? Or am I missing something here as usual?

-- Jim
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Old 15th May 2016, 08:11 AM   #15
5th element is offline 5th element  United Kingdom
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The natty little benchmark amp has variable gain.
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Old 15th May 2016, 09:26 AM   #16
billshurv is online now billshurv  United Kingdom
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Quote:
Originally Posted by tomchr View Post
Without better data, my opinion is that the folks who are concerned with the noise of the MiniDSP are running their DSP into a high-gain power amp. 25 V into a power amp with 32 dB gain (40x) is 1 mV RMS of noise. Into a 95 dB efficient full-ranger or tweeter that's certainly audible. That's my current, skeptical, guess of why some report noise issues.

Tom
Until a couple of days ago I agreed with that, and I accept that there are better solutions where you are using the DSP as the volume control into horn speakers, but as we have someone we are trying to help with a Pass amp with only 14dB of gain its not that. I fear though he's pumping analog in and using the pre-amp as a volume control before the DSP.

Not a problem for my ribbons of extreme inefficiency of course. And you could always put a different DAC on if you whipped the lid off.
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Old 15th May 2016, 03:42 PM   #17
Omholt is offline Omholt  Norway
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Nice test.
Is it possible that how the cables are connected to the phoenix connectors can have an effect on the noise? I personally really detest phoenix connectors and think it's unfortunate miniDSP couldn't use XLRs instead.

miniDSP seems to basically offer mediocre products and I'm not sure they will change that. Good value for the money but not great quality.

Last edited by Omholt; 15th May 2016 at 03:59 PM.
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Old 15th May 2016, 03:52 PM   #18
Davey is offline Davey  United States
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If you are attaching speaker cables to the Phoenix connectors, then I think we've identified at least one problem with your setup.

Dave.
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Old 15th May 2016, 04:00 PM   #19
Omholt is offline Omholt  Norway
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Quote:
Originally Posted by Davey View Post
If you are attaching speaker cables to the Phoenix connectors, then I think we've identified at least one problem with your setup.

Dave.
Oops. Edited.
Yeah, that would be a problem.
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Old 15th May 2016, 06:20 PM   #20
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Jim the Oldbie View Post
At home I'm using a different miniDSP product, the nanoAVR-HDA. This unit has RCA outputs producing the usual 2V RMS at 0 dBFS. My power amps on the other hand have 1V input sensitivity for full output of 75 watts or so. (Gain is rated at 28 dB.)
The mismatch between the DAC output voltage and the amp input sensitivity is not really a problem per se but it is a sub-optimal (ok, fine! "crappy" ) gain structure.

The best way to address this would be to increase the amp sensitivity to 2 V, but with a commercial product that's not really an option. The second best would be to use the 0.9 V gain setting on your DAC if it has one. If you were using the MiniDSP 4x10 HD, you'd get slightly lower noise that way.

Quote:
Originally Posted by Omholt View Post
Is it possible that how the cables are connected to the phoenix connectors can have an effect on the noise?
No. The termination of the cables to the Phoenix blocks has no impact on audio band noise, assuming that you keep the wire lengths reasonable (<20 mm, say). My connections are about 10-12 mm long.

Quote:
Originally Posted by Omholt View Post
I personally really detest phoenix connectors and think it's unfortunate miniDSP couldn't use XLRs instead.
The Phoenix connectors are annoying. I do agree with that. They're not annoying enough to deter me from using the MiniDSP but annoying nonetheless. I do understand why MiniDSP chose the Phoenix connectors over XLR connectors, however. First off, cost. Secondly, eight XLR connectors take up 200 mm of board length. A stack of Phoenix connectors, maybe, 50 mm? So there are *huge* savings to be had both in board area and chassis size by using the Phoenix connectors.

What I would rather have seen is the use of stacked TRS connectors. Like the NSJ12HF from Neutrik.

Click the image to open in full size.

The stacking jacks still fit in a 1U chassis and hardly take up more room than the Phoenix plugs. Then you get to use standard cables (yay!). Focusrite use stacking jacks like that on their external sound cards. Works great.

Tom
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