miniDSP users read this.

[johnk...]

Re: miniDSP users read this.

I use a Meanwell GS18A12-P1J with my 2x8.

Order it from PowerGate, http://www.powergatellc.com/mean-wel...er-supply.html

$15.

[Deward Hastings]

Re: miniDSP users read this.

Bob measured an issue that hadn't previously come up.

That's because it's Bob's problem, not a common-to-them-all problem. He may have a defective sample, or more likely he's got either dirty power or is overdriving it (improper gain staging being by far the most common cause of "digital" distortion and/or noise). But that is not the implication of the original post, which suggests instead (and incorrectly) some previously undiscovered fundamental flaw in the miniDSP.

[GranteedEV]

Re: miniDSP users read this.

I agree that gain staging is a possible culprit here.

[natehansen66]

Re: miniDSP users read this.

+1 on gain staging......what are you driving it with Bob? You might try changing the sensitivity jumpers. I have a cheap dac that would easily overdrive the minidsp on the .9v input sensitivity setting, resulting in a lot of quite audible distortion. Changing to the 2v setting or lowering the input volume solved this.

[Bob Brines]

Re: miniDSP users read this.

+1 on gain staging......what are you driving it with Bob? You might try changing the sensitivity jumpers. I have a cheap dac that would easily overdrive the minidsp on the .9v input sensitivity setting, resulting in a lot of quite audible distortion. Changing to the 2v setting or lowering the input volume solved this.

OK, that makes sense. I have the version A. I'll open it up and change it to version B.

I know a lot of you want this to be a power supply problem, but it isn't. I got a decent 1A wall-wart with a ferrite slug on the output. No change. \

I've made a post on the miniDSP forum. Let's see what comes from that.

Bob

[HokieAudio]

Re: miniDSP users read this.

This reminds me of something I see at my job pretty often.

High odd-order harmonic distortion can be caused by the use of high-k ceramic capacitors in the output filters of a D-to-A converter (any dielectric other than C0G). The voltage coefficient of these capacitors is significant and so their actual value is changing quite a bit depending on the waveform being produced. Likewise, there may be significant variation in the severity of this distortion between caps of the same value and dielectric.

I work as an applications engineer for a semiconductor company and have seen this type of behavior quite a few times with our audio customers who buy a great DAC and then cut cost on the passive components.

Just a thought...

[gregbegland]

Re: miniDSP users read this.

Speaking of which, I'm going to pick up an 8x8-in-a-box when they start shipping (few weeks, they've said). Any rec's for a good (not audiophool stupid expensive, just solid) 12V PS for an 8-channel miniDSP.



I think it's a fair title and post. Bob measured an issue that hadn't previously come up. Worth every miniDSP owner reading, and figuring out how to measure their own.

It is NOT an inherent miniDPS problem, it is a defective unit or a user implementation issue such as over-driving the inputs. Bob's original post makes it sound as if the miniDSP itself is poorly designed. Not fair and rather hasty judgement in a very public forum.

Greg

[Bob Brines]

Re: miniDSP users read this.

OK, that makes sense. I have the version A. I'll open it up and change it to version B.

Not going to happen. The gorilla that put the thing together set the screws so hard that I stripped the heads trying to remove remove them.

Bob

[Wushuliu]

Re: miniDSP users read this.

Not going to happen. The gorilla that put the thing together set the screws so hard that I stripped the heads trying to remove remove them.

Bob

That is a problem I have found with a lot of straight out of HK/China electronics. The enclosure is a cheap afterthought. Mine didn't even have correct input/output labeling.

[Pallas]

Re: miniDSP users read this.

It is NOT an inherent miniDPS problem, it is a defective unit or a user implementation issue such as over-driving the inputs. Bob's original post makes it sound as if the miniDSP itself is poorly designed. Not fair and rather hasty judgement in a very public forum.

Agree to disagree.

From his perspective, given what Bob measured, that's not necessarily an unreasonable first assessment. (Keep in mind I'm a big fan of the miniDSP.) Most of us (myself included) probably haven't done distortion measurements of our own miniDSP's.

But the bottom line is either that
(a) we all discover a potential build defect to look out for in our current and future miniDSP's;
(b) Bob's process of troubleshooting teaches many of us something about how to optimally use the miniDSP, and some of the audible pratfalls of suboptimal setup.

PS: Thanks John K for the PS recommendation.

[weinstro]

Re: miniDSP users read this.

Something to think about:

Noise is noise, and as long as it is below the noise level of the listening room, who cares?

The problem I am addressing is THD, which is totally different from noise. Even it the computer power to the miniDSP is dirty, the result should be to push the THD curves up the scale. It is extremely rare to see the 3rd harmonic higher, even an order of magnitude higher than the 2dh.

Bob

If you've convinced yourself that this isn't a power supply problem, then it is probably a defect on the board, e.g., dead/damaged op amp, incorrect parts, etc. just return it for a replacement.

Regards,

Rob

[minidsp]

Re: miniDSP users read this.

For information sake, note that Bob was indeed able to toggle the jumpers to a RevB version (i..e lower input sensitivity) and the problem of raised THD was solved (i.e. normal specs). Here is some info.

When over-driving an ADC, one of the symptoms is the raised THD displayed in the chart so that can be useful information for those of you seeing similar symptoms (may it be a miniDSP or any piece of A/D to D/A gear actually.

Hoping this info helps and feel free to post your questions on our forum if you ever have some concerns. We're always happy to answer ...

miniDSP DevTeam

[MSaturn]

Re: miniDSP users read this.

minidsp dudes:

don't worry, one thing like this isn't going to scare everyone off from your product. plenty of us use and like it.

[gregbegland]

Re: miniDSP users read this.

Pallas, are you out there? ;)

[jonpike]

Re: miniDSP users read this.

I got to this party late... but good to see the suggestions of investigating overdrive got things to a solution.

Unless there's some reason I can't think of now that would stop you (haven't got a MiniDSP, yet) you should easily be able to measure noise and distortion by setting up for a loopback test (input cabled to output) with your sound card, then just put the MiniDSP in series with the loop, measure with software. There's a few free options out there like RMAA, or better, REW. RMAA will do several "other" tests like crosstalk and so forth with some distortion, REW is more detailed for FR measurements but won't do distortion. (I think? John's adding features to REW at a rather serious clip) You do have a real time Spectrum Analyzer graph.

Since I'm forgetting that HD measurements are the topic I should include ARTA or HOLM as free(ish) programs to get you to full on distortion measurement. These programs go up in learning curve though.

Bascially, something easy like REW or RMAA will allow you to see the effect when you overload an input or an output, and let you see where and at what level you do in your setup. It's good to know, so you can get close and use most of those bits, but never clip digital OR analog, along the way...