TOPIC:

So about a year ago I purchased 2 PWR-ICE 250 plate amps and built myself some 3 way towers. tweet&mid on 1 channel and sub on second channel. I noticed right away that using rca cables there was a lot of noise coming through the highs, first thought was maybe it is just that channel so I swapped it. This did not correct my problem, i changed cables bought really expensive ones even went as far as to remove amp completely and power up with nothing connected and logged into unit to find even on the graph for input there was a sign of noise on the line -90 to -95 jumping around. I then tried different circuits in my house made sure my receptacles were grounded took amp to work and tested it there with the same issues.

After much deliberation I decided to go XLR so my source is laptop or Bluetooth receiver to rca in cleanbox pro XLR out to Pwr-ICE 250 and now my noise floor is -100 to -105 but still I see it jumping around and i hear a hiss from my tweeter which is much lower now but bugs me.

So I have a few questions
#1 is this normal behavior of these style of amps?
#2 Which input would be best analog rca / analog XLR Balanced / AES/EBU for the lowest noise floor im looking for -115+ to remove hiss
#3 Cables matter so what OHM cable should I be looking for I have seen little info on the recommended cable resistance which i think plays a huge role in THD 110 OHM XLR 75 OHM RCA ???
#4 Last I read www.minidsp.com/forum/pwr-ice-support/13...-white-noise-hissing
that using emi/rfi blocking material cleans up sound as well as adding a resistor 100-200 OHM in the input stage will clean up this noise as well but lower overall performance, is this true and should I do this???

I spent almost a grand on these 2 amps from Parts Express and I just love them to death but when no music is playing the hiss is driving me nuts and I am willing to do whatever it takes to fix it even if I have to modify this to get what i want.

Thank you to all in advance for your reply's and help in this matter, I greatly appreciate your time.

Might be interresting to qualify this noise in term of frenquency.
I can see two solutions for you :
First and easier one : decrease overall volume so that when no music is playing, the noise should be reduced.
Second one : switch to AES/EBU inputs. You'll need a digital source (SPDIF ou AES/EBU) or an external A/D converter, but using digital input completly remove any noise.
You can even test without any source just to make sure, just switch inpt settings of the PWR-ICE to AES and listen to noise wether it is still here or not.

Thank you very much for your responses on both threads, Tonight I will go in and change the input to aes/digital and see if this resolves my issue. I also ordered a Hosa ODL-312 Optical SPDIF and AESEBU Digital Format Converter yesterday so i can test out an all digital path, should be here by weeks end. I do agree I have the volume up loud, just not used to hearing noise from my gear at high volume levels when nothing is playing. The tweeter is a Morel ET 338 1-1/8" with 92.5 dB 1W/1m and I am running the amp right up to the limit. I would just like to bring the noise floor down a little more. In my home theater I run way more power through my front mains and I hear no noise what so ever.

I will update tonight my findings and if anyone else has an opinion please let me know.

P.S. How would i qualify the noise?? Possibly with rew and my umk 1 mic?? any thoughts

Hello,
Yes REW using the spectral analyser to see which frequencies are favoured in this noise. Mic close to the speaker.
Considering volume, I guess you are not using the PWR-ICE volume as main volume control for your system. So might be good to lower down PWR-ICE general volume even if you have to increase you main volume at the source. Amplifiers are prone to generate noise when their volume is set at te maximum. So it is always preferable to increase input signal level rather than amp output level.
Very good tweeter this Morel

time to sleep now for me in my area so I will see your findings tomorrow.

So i went ahead and changed input from analog to digital and have nothing plugged into amp except power no network no input. I have found the noise has dropped quite a bit but is still there oh and the input volume is set at -2 as well. I used my umik 1 mic and rew and attached you can see the static in the graph I am hearing. Please let me know your thoughts, I greatly appreciate your input and anyone else who would like to jump in.

Respectfully

Hello,
OK, thanks for the measurement. This noise is full bandwidth. and has nothing we can cope with. It is more or less standard.
So I gyess the only thing you have to do is to decrease PWR-ICE overall volume and try to increase your input signal level.

Hi,
I've just finished my project of active monitors using one PWR-ICE125 and one PWR-ICE 250 per box.
I experienced the same noise as you through the mids and highs. I just have to decrease the general input volume of each PWR-ICE by 6 dB so that this noise becomes unhearable and that's all.

Hi,
I figured out where the noise was comming from., both on my PWR-ICE 125 and my PWR-ICE 250.
Input signal routing from the miniDSP I/O board to the ICEPower amplifier in the main contributor. The wiring from DSP board to P102 connector on the amplifier board, despit using shielded wires for input signal, is tighten together with AUX supply wiring. I then first release the clips between input signal and AUX supply wires and I can hear that moving the signal wires closer or farther from the amplifier board increase or decrease output noise.
I had two kind of noise : 50 Hz and its harmonics, and a sweep sine. Sweep sine must be some kind of hooking whereas 50 Hz and its harmonics result from power supply. I ended up by enclosing the signals wires using a self-adhesive copper tape connected to GND, each L and R individually and I positionned carefully the wires to the a position where noise were at their minimum (away from the amplifier).
Sweep sine has been reduced drastically and power supply noise has been reduced by 20 dB which is a lot. At the listening position I now can't hear anything even when pushing the gain at its maximum which was not the case before modification.

Can you attach some photos so I may see what you did exactly, I would greatly appreciate it. I am using the aes ebu connection which has helped but I still have noise as well and would love some pictures to be able to try your resolution.

Thanks a million

Hi,
I'm sorry but the amplifiers are back into the loudspeakers and I did not take time for picture !
Modification is very simple, you take wiring from P102 connector of the ICEPWR amplifier board, you should see two shielded wires which correspond to the low level L & R input signal routed to the amplifier board from the DSP board. These are the two wires which require carefull shielding and routing.
Even doing nothing, to them, you should notice that moving them away from the amplifier electronics modify noise density and level.

Here is a picture taken from mini-DSP with explainations :

Thanks for trying and explaining. This seems like a pretty sloppy designed by miniDSP in the first place, switching power supplies and class D without care taken in cable management in a system cramped into one unit..

Yes. the Power-ICE really exhibit poor built quality while they are the most versatile plate amplifiers on the planet,
The two main features being the capability to chain modules (when using digital inputs) and FIR filtring. I'm not aware onf any other plate amplifier providing these capabilities despit they are essential.
Hopefully, MiniDSP will extend plate amplifiers product line with high end products, keeping these two major capabilities and correcting early defaults like using enhanced amplifier modules, a proper metalic plate (essential), a better schielding between digital and Class-D/Analog modules and first class built quality.

mh... i did that but still get an acoustic noise... not loud but i can hear it from my couch...

The two audio cables now isolated so the power-cable from the dsp has no effect anymore if it comes near the audio cable.

Any other ideas? I bought two 250 and one 125 amps... a lot of money for that much noise...^^

I parallely created a support ticket.. lets see what minidsp tells me...

Hey thanks for posting these. I have just ordered a pair of active monitors from Danley and they are using the 250 in them. I will have a look at the amp when they get delivered