Crazy little miniDSP keeps giving me white noise!!! - AVS Forum
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post #1 of 20 Old 10-07-2013, 03:38 PM - Thread Starter
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I have posted in the miniDSP forum...and some of the fellas there have made some good suggestions...mostly focused on gain staging. However, I have continued to get an audible white noise-like sound from the passive subwoofers I built in my thread. I have 4 identical, passive sealed 18" DA subwoofers being driven by two Behringer EP4000 amplifiers which are receiving a balanced signal from each of the four miniDSP 2x4 Balanced outputs. I am using a 2-Way Advanced Plug-In if it matters in this case.

The two gain knobs on each amplifier are at maximum. The amplifiers are looking for input of 1.23Vrms @ 8ohms to achieve max. The amplifiers have a voltage gain of 50x (34dB). They are rated at -100dB from 20 to 20.

The sound is present even when I disconnect all input wires feeding the DSP. Sound is also present and unchanged if I hook everything up to DSP inputs.
Here are some things I have tried with no input wires feeding the DSP. (keep in mind I have tried all of the below with the DSP using three different, and new, power supplies from different manufacturers on same and separate circuits, both through an isolator and without. The power supply changes did not seem to affect the white noise in any way.)

If I disconnect the DSP from the amplifiers, the subs go perfectly quiet.

If I reduce the amplifier front panel gain knobs by half, the volume of the white noise gets reduced by half.

Why is this sound present when I hook up the miniDSP? Is this a DSP board grounding issue? Any ideas for a solution or steps I could follow to isolate the issue?

I tried many different hook-ups with combinations of a Matchbox HD , miniDSP and some without one or the other as well as none and both.
Messed around with DSP jumpers in all combinations as well as trim levels, and gain levels in the plug-in. There were times when I experienced the same white noise as originally and times when I did not and there was hum introduced instead...which might have been masking the white noise?

All in all, the only definitive times the white noise was completely gone was when the DSP was out of the signal path.
The only assured way I could reduce the white noise with the DSP in the chain was by lowering gain knobs on the amps.

Behringer confirmed that the EP4000 amps look for a 1.23Vrms signal to function at max.
I had a Denon rep call me back Friday and he said the the sub pre-out voltage on the 2810 was not 2.1V as originally thought, but 1.75Vrms.
I can't imagine this makes a difference seeing that I get the same white noise even when there is no signal at the DSP inputs.
Of course, it made me question where the DSP jumper SHOULD be with that input level...I am assuming .9V position???

Something interesting I did note through all of this...
I had no hum to speak of when the receiver was hooked up to DSP, just white noise.
When I connected PC to DSP via USB cable, a low-volume electronic-like hum was introduced and audible through the subwoofers.
Gone as soon as USB was disconnected at either side of connection.

I am not sure what to do next....????????

I've had enough beers trying to work this out the last several days, so I have that part covered for sure.


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post #2 of 20 Old 10-08-2013, 02:30 AM - Thread Starter
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I will reserve this area for any solution that is later arrived at:D


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post #3 of 20 Old 10-08-2013, 08:21 PM
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Quote:
Originally Posted by blah450 View Post

I will reserve this area for any solution that is later arrived at:D

I certainly hope you get something to post here.......I don't own a mini, but:

Questions:
  1. Are you using the mini strictly for subwoofer filters?
  2. How do you have the amplifiers physically connected, and what is the dip switch configuration? A sketch or image would be helpful.
  3. Have you tested all of your audio cables with a VOM to make sure they are OK (no crossed or shorted pins, etc.)? Are you using all XLR? There is little front page information on the mini site showing factory or required custom cabling, some details are needed.
  4. Do you get noise from both amps/subs individually when either one is completely removed from the audio chain?
  5. Do you have the means to power the mini with a battery for testing?
  6. As a last resort is warranty service an option?

Good luck.
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post #4 of 20 Old 10-09-2013, 02:44 AM - Thread Starter
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Quote:
Originally Posted by zhillsguy View Post

I certainly hope you get something to post here.......I don't own a mini, but:

Questions:
  1. Are you using the mini strictly for subwoofer filters?
  2. How do you have the amplifiers physically connected, and what is the dip switch configuration? A sketch or image would be helpful.
  3. Have you tested all of your audio cables with a VOM to make sure they are OK (no crossed or shorted pins, etc.)? Are you using all XLR? There is little front page information on the mini site showing factory or required custom cabling, some details are needed.
  4. Do you get noise from both amps/subs individually when either one is completely removed from the audio chain?
  5. Do you have the means to power the mini with a battery for testing?
  6. As a last resort is warranty service an option?

Good luck.

Thanks, zhillsguy. Great questions. I was thinking there were no answers to my dilemma despite the amazing mind meld we have here on the forum.

1. miniDSP is being used strictly for subwoofers.
2. The amps are connected to miniDSP via four separate, balanced XLR cables. Two outputs from DSP to two inputs of each amp. Dip switches for both amps are identical and are:
clip limit off (left), 30Hz (right), LC off (right), stereo (left and left), bridge off (left and left), LC off (right), 30Hz (right), clip limit off (left).
3. Did not test audio cables with a VOM (???). All XLR feeding DSP and as I stated, exiting DSP.
4. I can remove each amp (or or sub pairs) from chain and still get noise from what remains.
5. I will try powering mini with battery and report back.
6. Will try to test wires and use battery...and pursue warranty if needed.


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post #5 of 20 Old 10-09-2013, 03:59 AM
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My MiniDSP started acting up lately...
IT was fine for a while and now am getting a pretty good hum along with a thumping sound noise (Like someone walking upstairs)
It would come and go...it was really weird!

I tried everything...it came down to my power supply feeding the MiniDSP.

Out of despair I hook it up to my car battery and it completely removed the hum and thumping noise!
I then tried and connected the MiniDSP to a 12 volt PC line (black and yellow wires) and again no hum or thumping!
That's the way mine has been connected since and have no problems at all.

Try changing your MiniDSP's DC input supply.

Good luck
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post #6 of 20 Old 10-09-2013, 02:12 PM - Thread Starter
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Quote:
Originally Posted by Freniata View Post

My MiniDSP started acting up lately...
IT was fine for a while and now am getting a pretty good hum along with a thumping sound noise (Like someone walking upstairs)
It would come and go...it was really weird!

I tried everything...it came down to my power supply feeding the MiniDSP.

Out of despair I hook it up to my car battery and it completely removed the hum and thumping noise!
I then tried and connected the MiniDSP to a 12 volt PC line (black and yellow wires) and again no hum or thumping!
That's the way mine has been connected since and have no problems at all.

Try changing your MiniDSP's DC input supply.

Good luck

What is a PC line?


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post #7 of 20 Old 10-09-2013, 03:10 PM
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Quote:
Originally Posted by blah450 View Post

What is a PC line?

I think he's referring to the 12 volt line of a computer's power supply.

That being said, I don't own a miniDSP but I plan on buying one, so I'm not sure what people use to power them, but this seems to be the best PSU you can get for the money.

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?search_type=jamecoall&catalogId=10001&freeText=220898&langId=-1&productId=220898&storeId=10001&ddkey=http:StoreCatalogDrillDownView

Close enough to the amperage rating, and it's regulated.
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post #8 of 20 Old 10-10-2013, 07:19 AM
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Quote:
Originally Posted by blah450 View Post

Quote:
Originally Posted by Freniata View Post


Try changing your MiniDSP's DC input supply.

Good luck

What is a PC line?

what thatsnasty said.

Well did you try a different power supply for the MiniDSP?
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post #9 of 20 Old 10-10-2013, 08:59 AM
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A bit of a hassle but a 12V battery would supply noise free juice. Pull the the battery out of your car and try it with the minidsp.smile.gif If the noise disappears than you'll know that the stock PS is the culprit.
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post #10 of 20 Old 10-10-2013, 01:34 PM - Thread Starter
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Quote:
Originally Posted by blah450 View Post

(keep in mind I have tried all of the below with the DSP using three different, and new, power supplies from different manufacturers on same and separate circuits, both through an isolator and without. The power supply changes did not seem to affect the white noise in any way.)

Quote:
Originally Posted by Freniata View Post

what thatsnasty said.

Well did you try a different power supply for the MiniDSP?

Quote:
Originally Posted by rajacat View Post

A bit of a hassle but a 12V battery would supply noise free juice. Pull the the battery out of your car and try it with the minidsp.smile.gif If the noise disappears than you'll know that the stock PS is the culprit.


Well....I tried 3 different supplies already with no changes...but, I did notice upon looking at the three that each one of them was a regulated supply. Try an unregulated??? That will be next.
Car battery??? Yeow....will try that second. Hope an unregulated supply works...car battery test seems a little unorthodox and unwieldy.

Thanks for the leads.
Will keep posted with results.


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post #11 of 20 Old 10-10-2013, 06:01 PM - Thread Starter
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Well....I tried 3 different supplies already with no changes...but, I did notice upon looking at the three that each one of them was a regulated supply. Try an unregulated??? That will be next.

Just tried an unregulated 12V supply...blue light blinking...looks good....no dice mad.gif
Same sound again from each of the 4 subs.

Car battery?...I still need to think about this one.

Anyone else ideas?


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post #12 of 20 Old 10-10-2013, 08:03 PM
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Originally Posted by blah450 View Post

Just tried an unregulated 12V supply...blue light blinking...looks good....no dice mad.gif
Same sound again from each of the 4 subs.

Car battery?...I still need to think about this one.

Anyone else ideas?
is the minidsp sitting inside a case?
the pcb board ground is earthed. if it's sitting inside a case try and take it out.

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post #13 of 20 Old 10-10-2013, 09:08 PM
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Somehow I didn't find this clear. Do you have a full-range white noise problem, or a hum problem? Because my guesses...if white noise, gain staging. If hum, then ground loop or pin1 problem. You may want to open that amplifier and verify ground connections and XLR hookups inside. Same with the miniDSP... double check it. Use diode continuity check while tapping on things to detect intermittents or physically poor connections.

There should be no need for a 9V battery, the miniDSP should run fine from a 9V battery even if you want to test a battery supply. Or a lantern battery. Or four AAs. Whatever you have around and have a holder for that is 5+ Volts, use it.

If it's happening equally on all four subs, then simplify your life and take three out of service for the time being and disconnect all signal lines. Troubleshoot one signal chain, and when you have a fix then apply it to the others.

For the USB cable are you using the one that came with the miniDSP that has a ferrite on it?

Do you have an REW/Holm/ARTA/whatever rig or something else with which to RTA the noise?

Do you have any known-clean signal chains in another system or at a buddy's place you could put the mini into?
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post #14 of 20 Old 10-15-2013, 03:12 AM - Thread Starter
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Originally Posted by paskal9 View Post

is the minidsp sitting inside a case?
the pcb board ground is earthed. if it's sitting inside a case try and take it out.

The miniDSP I have is a kit. No case. I have tried it sitting on different things, including mounted at 4 corners on a piece of cardboard and then metal.
Made sure the DSP is also away from other fields such as those that might be near amps.


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post #15 of 20 Old 10-15-2013, 03:15 AM - Thread Starter
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Originally Posted by aackthpt View Post

Somehow I didn't find this clear. Do you have a full-range white noise problem, or a hum problem? Because my guesses...if white noise, gain staging. If hum, then ground loop or pin1 problem. You may want to open that amplifier and verify ground connections and XLR hookups inside. Same with the miniDSP... double check it. Use diode continuity check while tapping on things to detect intermittents or physically poor connections.

There should be no need for a 9V battery, the miniDSP should run fine from a 9V battery even if you want to test a battery supply. Or a lantern battery. Or four AAs. Whatever you have around and have a holder for that is 5+ Volts, use it.

If it's happening equally on all four subs, then simplify your life and take three out of service for the time being and disconnect all signal lines. Troubleshoot one signal chain, and when you have a fix then apply it to the others.

For the USB cable are you using the one that came with the miniDSP that has a ferrite on it?

Do you have an REW/Holm/ARTA/whatever rig or something else with which to RTA the noise?

Do you have any known-clean signal chains in another system or at a buddy's place you could put the mini into?

Following up on some of these suggestions this week.

Thanks!


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post #16 of 20 Old 10-20-2013, 06:44 AM - Thread Starter
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Okay.
In possession of a passive Jensen Transformer for low-frequency use.
Will be trying to insert Jensen after DSP.


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post #17 of 20 Old 10-21-2013, 07:25 AM
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Just had a thought...
On your "low pass filter settings" if your cutoff is high you'll get noise.
Make sure it's not bypassed

Just a thought and just trying to help
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post #18 of 20 Old 10-24-2013, 05:43 AM
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Quote:
Originally Posted by blah450 View Post

If I disconnect the DSP from the amplifiers, the subs go perfectly quiet.
If the problem goes away with the miniDSP out of the signal chain, then it’s obviously the problem, either the unit itself or (as others have mentioned) the power supply. The AVR should be a reliable noise-free signal source, so I’d suggest running your sub output to max. That would allow you to use lower gain settings on the mini, which may cut down on the noise.

Quote:
Originally Posted by blah450 View Post

2. The amps are connected to miniDSP via four separate, balanced XLR cables. Two outputs from DSP to two inputs of each amp.
Not that it will do anything for the noise problem, but that’s a lot of unnecessary cabling and connections. Why not just run the amps in parallel mode and use a single output to each from the miniDSP?

Regards,
Wayne A. Pflughaupt





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post #19 of 20 Old 10-24-2013, 05:54 AM
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Quote:
Originally Posted by blah450 View Post

I have posted in the miniDSP forum...and some of the fellas there have made some good suggestions...mostly focused on gain staging. However, I have continued to get an audible white noise-like sound from the passive subwoofers I built in my thread.

How loud is this white noise?

If you have to put your head up to the subwoofer drivers to hear it then this is normal.

If you can hear it across the room, then not so much.

General rule of thumb is run the power amp level controls as low as possible consistent with obtaining adequate bass.

Hum being added by a USB connection to a PC can be normal. Let's get the hiss under control before we chase that.
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post #20 of 20 Old 10-24-2013, 01:25 PM
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What does the input side look like going from your receiver/pre-pro to the mini? Can you shoot us a picture?


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