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Old 17th June 2012, 09:01 PM   #21
sjalloq is offline sjalloq  United Kingdom
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Not balanced no.
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Old 17th June 2012, 09:13 PM   #22
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As far As I know only the balanced version suffers from noise. The unbalanced version does not. That is to say, I never noticed it.
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Old 18th June 2012, 02:28 AM   #23
minidsp is offline minidsp  Hong Kong
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Hello,

Hard to say remotely what could be the reason and how we can help here but we're always happy to help.

- First off, for those of you who would indeed hear some noise floor, we'd need to understand your gain staging. Now telling us you have an amplifier, a source and some speakers model isn't going to help.. :-) Gain staging is how your 3 elements (the Source, the miniDSP gain settings (digital + analog) and Amplifier volume) are set. You have some digital gain in this DSP and a lot of you may not realize that running the board with a very low signal (or digital gain turned down say for the tweets) and amps without a volume control at max may not be the best way to run your system. That's the key element in this story and something that Curryman also mentioned in his post. Once we know that, we can help. Otherwise, I hope that you realize that you have 4 potential locations (Source + Digital gain input + digital gain output + Master Digital gain (via pot) + Amp volume) where this can be tweaked. With each configuration being a DIY setup (i.e. I'm pretty sure that none of you have the same setup), We'd recommend that you investigate with these gain staging as a test. A google search for "Gain structure" (please take the time to actually do that google search.. ;-) is really worth it... Finally, taking some measurements with a PC can be a way to help too.. (not acoustic) .

- Now down to the online forum in Dutch. There are few translation words that seems not really clear what's meant but we're getting the gist. e.g. Did I misread that this person testing the board doesn't have the software? We don't have a neutrik tester over here, but do have some Audio Precision units (APx515 used for this test). We grabbed 2 units out of the stock for a test back then with a similar post (most likely from the gent testing) and here is the spectrum we're seeing (overlaid graphs for outputs). See below.
I'm maybe guessing that this is an analog to analog configuration in his test?

So obviously, we don't see readings of such high noise floor which is quite odd and making use wonder which version of the board is used(There are now 3 rev online by the way). Central part seems to be hacked off/soldered.. With an analog analyzer (hard to see out of band noise) and not knowing the setup, it's hard to know why such readings are here though. Maybe this gent could send us his board?

We're doing a new batch of Balanced boards so before doing so, we could investigate once again a full array of test to track down a potential noise issue. Adding some better line drivers on the outputs (e.g. That corp) for better CMRR could be a way.. It won't solve (and wouldn't on any Digital DSP system for that matter) incorrect gain structure though. That's a key design element which we don't have control over and end users would need to take care off.

Hoping this info helps.

DevTeam
Attached Files
File Type: pdf miniDSP Balanced FFT spectrum.pdf (137.0 KB, 135 views)
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Old 18th June 2012, 10:22 AM   #24
sannax is offline sannax  Norway
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Thanks minidsp! This is very helpful. I will certainly read up on gain structure.
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Old 18th June 2012, 10:41 AM   #25
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@DevTeam

As you might have guessed I'm no electronics expert. So here's another question.

If I restore my balanced MiniDSP to default and then connect it to my balanced power-amp should this situation be totally silent? So only MiniDSP and power-amp.

Jan
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Old 20th June 2012, 09:25 AM   #26
superR is offline superR  Netherlands
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I can understand the tip of using a volume control after the dsp. That would damp the niose. However, for a 2.1 setup that is just not practical. I replaced the psu in hopes of improvement, but the results were identical. The dsp is a great little tool for testing, but I am thinking of changing the filter I have implemented to an analog alternative.
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Old 20th June 2012, 09:05 PM   #27
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Quote:
Originally Posted by Leeuwarden View Post
@DevTeam

As you might have guessed I'm no electronics expert. So here's another question.

If I restore my balanced MiniDSP to default and then connect it to my balanced power-amp should this situation be totally silent? So only MiniDSP and power-amp.

Jan
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Old 22nd June 2012, 02:01 AM   #28
minidsp is offline minidsp  Hong Kong
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@ Leeuwarden,

The fact that you restore your miniDSP back to default won't solve the concept of gain structure. Did u get a chance to do a bit of reading on the topic by any chance? That's really valuable information when doing any audio chain. It's all about impedance, gain staging of the various elements of your system. All to the way to ProAudio and inside an full product (e.g. AVR with source + DSP + DAC + AMP in one box), you need to take care of the gain structure to optimize your SNR.

One thing to remember is that the balanced board outputs 4Vrms while the unbalanced board outputs 0.9Vrms at its max. So expecting that the 2 boards would behave the same on the same amp with the same gain setting would not be right. You'd obviously have to perform some gain control somewhere (in digital/analog)

Do u see what I mean?

Hoping this info helps

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Old 22nd June 2012, 06:44 PM   #29
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I see what you mean. But.... As also mentioned by SuperR my set-up does not provide the means to do a set up as you say. I have an expensive pre-amp, al lot of power amps and two nice speakers. There is no way I could implement a volume control after the MiniDSP as you say. It would mean I could just throw away my expensive pre amp.

I look at it this way. There is an balanced in and balanced out on your product. In my very simple mind that means I can make an active audio system by putting a MiniDSP between my pre-amp and power amps. I would expect this to work without uninvited noises as it happens now. On your website you mention the MiniDSP works wit line level input. In my opinion I'm feeding line level input from my pre amp so I did not expect noise coming from my set-up. I guess your website is not clear about the use of a volume regulator after the MiniDSP.

Solving the, also not mentioned on your website, turn on/off thump cost a lot of effort but I solved it. This noisething is coming from the balanced MiniDSP board. And obviously I'm not the only one being a bit dissapointed. After all, I bought 2 Balanced MiniDSP boards and the situation as it is now I might as well throw them in the trashcan. If it was mentioned on your website I had to solve a (very loud, very dangerous for at least tweeters) turn on/off thumb and it was mentioned I have to use the onboard volume option, I would probably not have bought it. Really funny thing is I bought 2 unbalanced versions at first and being satisfied (except for the turn on/off thumb) I decided to go balanced all the way and bought two balanced versions. Maybe MiniDSP offers a cheap solution but if its not working as an audio device should, it is still very expensive... Not to mention the import tax I had to pay...

Last thing about the turn on/off thump. I was given the advise to last turn on the power amps and turn them off before the rest. I guess my daughter and son (12-14 years) would forget this sequence sooner or later... not to mention my wife. A safety relay is unavoidable if you want to keep your speakers in one piece...

Having said all of this it would be nice if MinI DSP offers a solution.

Regards,

Jan
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Old 22nd June 2012, 07:18 PM   #30
superR is offline superR  Netherlands
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Quote:
Originally Posted by Leeuwarden View Post
In my very simple mind that means I can make an active audio system by putting a MiniDSP between my pre-amp and power amps. I would expect this to work without uninvited noises as it happens now.
I know it's bit tricky. The succes of the minidsp is in it's price, period. Like the movie said, "something's gotta give". No expensive ADC's, no expensive DAC's and no circuitry for an output shutdown/delayed-on. That leads to noise and plops.
Thanks to the fact I use my power amplifier as a master in a master-slave powersocket, the minidsp/pre/cd shutdown "instantly" as soon as I shutdown the power amp. Therefore I have no thumps/plops.
Indeed if I had know my minidsp would be noisy, I would not have bought it. I would have made an analog x-over which suits my wishes.
But rather than complaining, I would rather have a solution to the issue. I assume I cannot replace the ADC or DAC. The psu is a very nice piece so I am out of idea's. Although my preamp is not as expensive as Leeuwarden's, I still want to use it as my volume control and source selection.
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