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Old 13th July 2012, 12:33 PM   #41
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Quote:
Originally Posted by coit View Post
I have 2x8 and when used with unbalanced outputs and 3xSure amps had noise.
Changed to balanced outputs and 6 channel amp-dead silent.
Both with 100 to 109dB drivers.
I had noise problems with the Sure 6-channel amps by themselves...
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Old 14th July 2012, 08:58 AM   #42
coit is offline coit  Australia
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I have not tried the newer Sure amps like the 6x100,as I am wary of their fears about overheating.
I have used heaps of the 2050 2x100 amps with no problems till connecting them to the MiniDSP.
The 2024 amps are bulletproof.
This is not hum from bad earths.The board is making the noise.
Using a Pro amp with balanced inputs made it disappear.
It's up to a cleverer person than me to explain why.
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Old 14th July 2012, 04:51 PM   #43
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Quote:
Originally Posted by coit View Post
...
It's up to a cleverer person than me to explain why.
My one (and only) neuron tells me that answer has to come from somebody else...

To be fair, I still need to eliminate the possibility of the faint noise be associated with the power supply and cabling arrangement I am currently using. Other than that, the board sounds better than I expected.

Once I get my miniDSP I will experiment and report back.

Cheers!
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Old 14th July 2012, 07:17 PM   #44
Pallas is offline Pallas  Pakistan
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Quote:
Originally Posted by coit View Post
This is not hum from bad earths.The board is making the noise.
Using a Pro amp with balanced inputs made it disappear.
It's up to a cleverer person than me to explain why.
Maybe the new amp is just a better design than the boards.

FWIW, I don't get noise running my miniDSP's to a well-designed amp with unbalanced inputs, on speakers with mid-90's 2.83V/1m sensitivity. However, I'm always interested in reducing the footprint of my audio system, and increasing its energy efficiency. So if there was an inexpensive 6-channel class D board could provide adequate power and equally low noise...I'd be all over that.
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Old 26th August 2012, 03:36 AM   #45
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I've had hiss with both the unbalanced and balanced versions of the minidsp..

After reading more about gain structure I finally got around to fixing my issue ...

I had my high end attenuated digitally ( -3db ) in the minidsp plugin...

So.. I made a t-pad for about 6db (closer to 6.3db with the resistors I had on hand) to go between the minidsp and upper end amplifier... I did attenuate the sub portion to account for the additional 3ish db on the upper end, but I'm having to boost everything on the low end by at least 3db so there should be little loss...

IT'S SILENT!

I removed the digital attenuation, so I'm also back to my original volume on the high side speakers.... it's wonderful... I should've done this a long time ago....

in case anyone is wondering, I'm using tang band w1808's and dayton reference HF 15" subs in an open baffle... (I know, I didn't think the dayton's would work in OB - but talked to a PE tech and he thought it should be fine).. they sound awesome .. just have always had this annoying "feature"

Last edited by OracleGuy; 26th August 2012 at 03:48 AM.
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Old 26th August 2012, 04:28 AM   #46
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Ok, after more tweaking I've removed the digital attenuation and modified the levels for the low side...

Another note... as far as balanced vs unbalanced, the balanced version is far easier to tweak since you have to power it externally anyway, you don't have to shut it down to connect it to a pc...
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Old 28th August 2013, 03:08 PM   #47
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Hi,
I agree with MiniDSP that this is a gain structure problem.
In my opinion digital filtering and DAC volume control has a limit, when you get too closer to the noise floor.

I am using 118db BMS drivers with a 71A (0,5 Watt) tube amplifier.

I just bought a pair of xlr balanced -20db attenuators.
I expect to solve the issue with this.

Best,
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Old 8th February 2014, 09:10 AM   #48
Rewind is offline Rewind  Sweden
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I bought a 5$ 1:1 isolation transformer with rca-connectors. Fixed my random static noise that I had with the minidsp and my tube amps.

It is made for subs and is making the highs sound slightly dull. Next step would be a Lundahl 1:1 trafo but they only come in XLR versions.
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Old 23rd March 2014, 11:25 AM   #49
zog666 is offline zog666  Australia
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Just thought I'd mention my setup here, which is adequate but not perfect with my older miniDSP 2X4 and high sensitivity speakers:

I'm using a FaitalPro HF144 (110dB) for HF and a Lorantz 15" woofer (98dB) for LF.
I've tried a rotating fleet of amps before settling on a small group that are adequately quiet (a collection of some of the "usual suspects" from DIYaudio, but right now its a JLH1969 class A on HF and a Tripath TA3020 module from ConnexElectronics on LF).

Input is entirely via optical SPDIF (minidigi) - to keep the PC side isolated from the audio side as much as possible.

I had to LPAD my compression driver 7dB down to 103dB to get any amp handy not to have audible hiss at the listening position, connected to the miniDSP or not.

Even even with the 7dB attenuation even lower power amps (5W-15W) seem fine for driving the HF portion crossing over at 600hz or above.

I have found the MiniDSP 2x4 doesnt have enough output to drive a lot of my amps at anywhere near full power at their default gain, I've made some very simple opamp buffers with stepped attenuators I use to control the levels coming out of the miniDSP so I get a broad "enough" range of volume for the amplifier fleet using the software volume control. At highest gain these increase the noise levels, but for most sensible settings it is quiet.

With this and "OK" amps I can keep the noise level down audible hiss with ear close to the drivers, but quiet at the listening position.

I'm using a 12VDC linear power supply to power the miniDSP (and the opamp buffers) - when I plug in the laptop via USB to reconfigure the system the noise level increases a lot, but I dont leave the laptop connected when not making changes so thats OK.

One smallish gripe with the software volume control is it doesnt go to 0 when at minimum? why make a volume control that when you turn all the way down... goes almost all the way down, but not silent?
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