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miniDSP 2x4 HD Sweetspot-audio Mod Review

Rate this DSP Mod:

  • 1. Poor (headless panther)

    Votes: 193 87.7%
  • 2. Not terrible (postman panther)

    Votes: 17 7.7%
  • 3. Fine (happy panther)

    Votes: 2 0.9%
  • 4. Great (golfing panther)

    Votes: 8 3.6%

  • Total voters
    220

Flexecutioner

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As a practical matter in your situation, unless you have the world’s least sensitive speakers or are powering a concert venue, you should be able to get loud enough (which is what matters). I usually have 25-40 dB of excess gain available on my 2x4 HD when using an amp with similar gain (Fosi V3) and 88 dB efficient speakers (Revel F206). Even a speakers in the low 80s sensitivity with an amp gain in the high teens will get quite loud.
Still not ideal to be using a preamp that can't use all the power someone paid extra for. I'd add that this can be an issue for those who upgrade their 2x4HD to a DDRC-24. The Dirac calibration typically lowers levels a bit and minidsp recommend keeping 10dB of headroom in the preamp for Dirac. I had a very similar setup and ran into a few instances where a source volume was unusually low and I was pushing the limits of that unit. I eventually caved and bought a used SHD.
 

peng

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You are not getting it quite. The internal brain of this device is digital. All signals pass through the digital. That is how it can do the DSP. 0dBFS gives 2V.

As a practical matter in your situation, unless you have the world’s least sensitive speakers or are powering a concert venue, you should be able to get loud enough (which is what matters). I usually have 25-40 dB of excess gain available on my 2x4 HD when using an amp with similar gain (Fosi V3) and 88 dB efficient speakers (Revel F206). Even a speakers in the low 80s sensitivity with an amp gain in the high teens will get quite loud.

How do you know I am not getting "it"? May be you are the one not getting it?

Seriously, I just want all my preamps and power amps to operate in well below their rated output level, say at least 10 dB below at all times including during the highest peak of any contents I listen to. If you only need yours to play loud enough and 2 V maximim is all you need then that's good for you, but don't assume others have the same requirements. May be an example can help you understand. Lots of ASR members want their gear's measured SINAD bettet than 100 dB from very low to maximum output, when for practical use they probably would not know the difference if their gear only clear 90 dB? Get it?

By the way, even some AVRs can output 4 V maximum at well below clipping point, so I don't know what the fuss is about. At the moment I am only using the minidsp as a crossover for a sub so I am not really worry, just don't feel like it.
 

YSC

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Woo this is a huge surprise!

I was expecting no improvement whatsoever, but turns out it is worse...
 

Herbert

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miniDSP was optimized to work on 12V DC. The adapter accepts input of 100-240V, 50-60Hz. So continents won't make a difference.
Don't know what they meant by "improved 12V input voltage" though.

View attachment 339384

View attachment 339386
Maybe they added bypass capacitors for reducing noise at the inputs. Or the highest internal voltage is 9v, so a Low drop voltage regulator is insude, besides the possible need to produce negative voltages for the opamps. Also the DSP needs voltages around 3.3 and 5V so one could tweak there. Matter of fact, those tweaks won’t do much.
 

Koeitje

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Let me present you 2.500 USD Apple TV …..



BTW - i loved my 2x4HD as 4 subs controller, my first experiments with DRC, filters, MSO.
People on a Dutch home theater forum (htforum.nl) also love these kind of mods. They really believe that physically modding a digital output video playback device will create a better image.
 

Holy Spirit

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"Replacement of all operational amplifiers". What operational amplifiers? I do not see any. Apparently 2x4HD uses very poor codec AK4626. Outputs of AK4626 are connected to RCA through these ridiculous red caps.
 

voodooless

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"Replacement of all operational amplifiers". What operational amplifiers? I do not see any. Apparently 2x4HD uses very poor codec AK4626. Outputs of AK4626 are connected to RCA through these ridiculous red caps.
You may be confused by the non-HD version? As can be seen here, it has a BB DAC (PCM3168A), and on the backside of the PCB, there are clearly opamps (JRC2068).

The modded version also had some of those red caps on the backside. They probably replaced all the small ceramic decoupling caps. This may be the main cause of the added noise: the caps should be as close to the chips as possible. The longer leads just make it easier to pick up noise and add inductance.

Edit: nope, it's not decoupling caps:
image.png

it's (some of) the filter caps.
 
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RandomEar

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Random noise increase when we talk -125dB is maybe... well. Maybe you can hear it. My point is that IF you would hear any difference at all it would be for the better.
The opposite is true. The noise floor is about 6 dB higher with the mod (it ends up around -91 dB, not -125; google "FFT gain"). It's extremely unlikely that anybody will be able to hear the difference between a distortion of -103 dB (before mod) and -110 dB (after). Try it yourself. In any case, the difference in distortion is actually irrelevant here because it's literally below the noise floor of the device. That may change if we're not only playing pure test tones, but as tested, the statement is true.

The higher noise floor, however, will result in more tweeter hiss and will be audible on some setups, especially with sensitive speakers and higher gain amps. That is an actual audible difference and - in contrast to some inaudible change in distortion - it will result in a lower dynamic range of the system due to the increased noise floor.

If you knew that your own ear is producing up to 10% 2nd harmonic, and that stated 0.001% of 2nd harmonic is not recognizable, and those amps with adjustable 2nd harmonic generation (yes there is such devices) can mask away odd harmonics and make the music experience more life like. and thats why we should not bother so much about the audibility of it compared to higher order and odd harmonics which is generated when amplifiers is clipping. Not hat pleasant if you are not into Heavy Metal where this effect is used not only on instruments but even on voice. One have to learn the audibility of odd and even harmonics and low order and higher order and the difference in how it is percieved by the brain. It is simply not science in an audio perception context to just sum the harmonic components in to one figure.
[Source?]
 

mdsimon2

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Still not ideal to be using a preamp that can't use all the power someone paid extra for. I'd add that this can be an issue for those who upgrade their 2x4HD to a DDRC-24. The Dirac calibration typically lowers levels a bit and minidsp recommend keeping 10dB of headroom in the preamp for Dirac. I had a very similar setup and ran into a few instances where a source volume was unusually low and I was pushing the limits of that unit. I eventually caved and bought a used SHD.

Are you using the volume control on the DDRC-24? If so, there is no reason to worry about leaving 10 dB of headroom. If you need to turn up the volume past -10 dB, it is very likely the source level is so low that you won't be clipping.

Also, in my experience Dirac will not add a full 10 dB of boost, you can measure the actual boost by using the bi-directional USB audio of the DDRC and REW.

I wish the miniDSP software had a clipped sample counter to indicate if you were actually experiencing clipping, but without this you can still look at the output level meters to get a feel for how close you are to clipping.

Michael
 

Calleberg

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If a guy were tempted to get a miniDSP 2X4 HD just to do simple HP/LP filter duty only... that wide band THD+noise @90kHz BW mesurement, (Thanks again Amir for going the extra mile ☺) should be enough for said guy to reconsider maybe using an analog active filter instead. I'm sure there are loads of pro audio filter gear out there that could beat that 73dB sinad, (and as a bonus, also beeing able to output way more than 2V)

Here's one:
 
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D

Deleted member 48726

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but its called the DDRC-24
And it's the same hardware as the 2x4 HD so same noise THD.
Are you using the volume control on the DDRC-24? If so, there is no reason to worry about leaving 10 dB of headroom. If you need to turn up the volume past -10 dB, it is very likely the source level is so low that you won't be clipping.

Also, in my experience Dirac will not add a full 10 dB of boost, you can measure the actual boost by using the bi-directional USB audio of the DDRC and REW.

I wish the miniDSP software had a clipped sample counter to indicate if you were actually experiencing clipping, but without this you can still look at the output level meters to get a feel for how close you are to clipping.

Michael
You could also make sure when forming your house curve in Dirac, that it doesn't boost.
 

Aaronb1138

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Mine is 3 to 4 years old.
That would put it as likely having the AKM ADC (& DAC?) which has been replaced in post 2020 models with a TI / BB one that is *supposed* to improve SINAD around 3db.

BTW @amirm, could you also test analog input on both (or even better all 3 - AKM vs TI vs Sweetspot)? I recall the 2x4 HD and C-DSP models seem to have somewhat poor analog input stage and ADC performance.
 
D

Deleted member 48726

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That would put it as likely having the AKM ADC (& DAC?) which has been replaced in post 2020 models with a TI / BB one that is *supposed* to improve SINAD around 3db.

BTW @amirm, could you also test analog input on both (or even better all 3 - AKM vs TI vs Sweetspot)? I recall the 2x4 HD and C-DSP models seem to have somewhat poor analog input stage and ADC performance.
 

voodooless

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that wide band THD+noise @90kHz BW mesurement, (Thanks again Amir for going the extra mile ☺) should be enough for said guy to reconsider maybe using an analog active filter instead. I'm sure there are loads of pro audio filter gear out there that could beat that 73dB sinad, (and as a bonus, also beeing able to output way more than
Or just add a line level low pass. The wide band stuff is probably mostly noise. The stop and attenuation of the chip is fairly poor with only 75dB. A bit more filtering may elevate this. Running the DAC at a higher rate as well, but I think the plugin only runs at 48 kHz?

Would be interesting to actually see the noise spectrum above 20 kHz, as well as the usual multitone plot. If the latter is clean enough, there sound be no audible issues.
 
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olieb

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As you see, the main indication that the 2x4HD has been modified is their sticker.
They would have done a better job if they had left it at that. Would have been an expensive sticker though.
Now it's even worse.
 

ah-ra

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Interesting results and quite disappointing.... Would be interesting to hear what Sweetspot Audio says to this results...
 

Mnyb

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Its rarely worth the effort to send stuff to modders , there’s usually something wrong with the whole mindset behind the “engineering” :/

There could be exceptions ofcourse
 
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The modded version also had some of those red caps on the backside. They probably replaced all the small ceramic decoupling caps. This may be the main cause of the added noise: the caps should be as close to the chips as possible. The longer leads just make it easier to pick up noise and add inductance.

A good observation, it was one of about half a dozen things I was hypothesizing might have lead to the increased noise, including the possibility of instability. This board wasn’t laid out with these unnecessary parts in mind. With digital hardware traces in proximity to the analog section, it may very well be pickup. In all-analog designs, stacked metalled film types are fine for both signal coupling and rail decoupling, though other precautions, such as additional series resistance for damping, may need inclusion.

That means measuring, which is something these modders didn’t do. Modders are obsessed with capacitors.

In higher impedance circuits, these can be susceptible to EMI pickup. They’re not as bad as wound films, but care has to be taken. Electrolytics for coupling and SMD ceramics for decoupling would have been appropriate. They overlooked this.
 
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Paweł L

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Clowns over on the WiiM forums are claiming "improved sound" after replacing op amps on their WiiM Pro+ streamer. Laughable.

It might change something, yeah, it can sound different as I noticed similar thing with my old CD player from '90s - very slight change BTW and nothing to scream about. If it really improved something I would like to see the measurements and what are the areas the improvement can be 'seen'.
 

TheBatsEar

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@amirm can you tell if the stock unit you measured was the older or newer version?
@amirm said his unit was 3 to 4 years old. I sold my MiniDSP to the guy that then had it sent to and tuned by Sweetspot-audio, the base unit was 2 and a half years old. So they are likely the same PCB revision. As for the power supply, these cheap things are glued together. There isn't much to mod, and if Sweetspot-Audio did, they would have to recertify VDE, CE, EMI and likely other standards.

Hopefully someone gets a regular V2 and sends it in to @amirm eventually.

BTW, thanks to @baron-bob for taking a chance with Sweetspot-Audio and then sending the modded device to @amirm!


Last thing: who voted for great? Explain yourselves!:D;)
 
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