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Old 25th January 2012, 06:24 AM   #1
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Default Hiss in Hypex PSC2.400

Hello, guys.

Recently bought three PSC2.400 plateamps for my LCR speakers. One of them is a 400d, but that is not important here.
I have pretty sensitive DIY speakers (102-103dB/2.83V) and I have severe hiss and noise in all three speakers. The noise is easily audible in my listening position. The noise is there even with nothing connected at the input, and even with the input shorted, so I'm assuming this is coming from the amp itself somewhere. Turning the amp volume down helps slightly, but even muting the amps don't remove the hiss, only reduce it. Even muted the noise is audible in the MLP.

The amps are mounted outside the speakers. 1,5m powercord, and less than a meter speakerwire. I run XLR interconnects from my pre, but that is irrelevant as the noise is there even without the source connected.

Any tips?

Hypex customer support told me to sod off, the noise is normal. I beg to differ. The amps all sound great apart from this. I suspect the DSP board is just very noisy, but I can't confirm it as the UcD400 modules are all mounted to the DSP and the 36-pin arrangement makes disassembly and testing difficult.
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Old 25th January 2012, 07:18 AM   #2
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Quote:
Originally Posted by atledreier View Post
Hello, guys.

Recently bought three PSC2.400 plateamps for my LCR speakers. One of them is a 400d, but that is not important here.
I have pretty sensitive DIY speakers (102-103dB/2.83V) and I have severe hiss and noise in all three speakers. The noise is easily audible in my listening position. The noise is there even with nothing connected at the input, and even with the input shorted, so I'm assuming this is coming from the amp itself somewhere. Turning the amp volume down helps slightly, but even muting the amps don't remove the hiss, only reduce it. Even muted the noise is audible in the MLP.

The amps are mounted outside the speakers. 1,5m powercord, and less than a meter speakerwire. I run XLR interconnects from my pre, but that is irrelevant as the noise is there even without the source connected.

Any tips?

Hypex customer support told me to sod off, the noise is normal. I beg to differ. The amps all sound great apart from this. I suspect the DSP board is just very noisy, but I can't confirm it as the UcD400 modules are all mounted to the DSP and the 36-pin arrangement makes disassembly and testing difficult.
This is the limitation of the used DSP with build in A/D and D/A converters. If you use the PSC2.400D version with the digital input AND drive them with a digital signal the noise will be lower. You are having a pretty high efficiency loudspeaker.....
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Old 25th January 2012, 08:03 AM   #3
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I am aware that my speakers are very efficient, and I am prepared to accept a little hiss in them of course. Digital is not an option, as there are no processor on the market that has digital pre-outs that I am aware of. I have tried the AES inputs on my single 'D' amp, and the noise is very slightly less, but still very audible in my listening position.

The S/N numbers and Dynamic range figures of your DSP board is noteably worse than those of other cheap DSP boards like MiniDSP. Now, that could be more honest specs from your part and I will not hold it against you at all until I have tested the MiniDSP in my setup.
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Old 25th January 2012, 08:23 AM   #4
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Quote:
Originally Posted by atledreier View Post
I am aware that my speakers are very efficient, and I am prepared to accept a little hiss in them of course. Digital is not an option, as there are no processor on the market that has digital pre-outs that I am aware of. I have tried the AES inputs on my single 'D' amp, and the noise is very slightly less, but still very audible in my listening position.

The S/N numbers and Dynamic range figures of your DSP board is noteably worse than those of other cheap DSP boards like MiniDSP. Now, that could be more honest specs from your part and I will not hold it against you at all until I have tested the MiniDSP in my setup.
I doub't the MiniDSP will have a lower noise level, as far as I know they use the same DSP with build in A/D and D/A converter.... We have paralelled some inputs and outputs to reduce the noise. There is a trick possible to reduce the gain of the HF section and to reduce the noise. Advisable to have experience in SMD....please contact support at hypex dot nl.
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Old 25th January 2012, 08:25 AM   #5
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I have, and I'm not comfortable with SMD soldering, so I won't do that mod. I might see if I can get someone more comfortable doing that mod. Besides, the non "D" amps are Rev2 boards and don't have the HW gain mod available.

I might try to sell the amps and get some UcD and SMPS modules and try with some other DSP or even passive crossovers. Normal speakers don't have this issue. I have a pair of Klipsch RF-82 for rears, and even though they are not much lower in stated sensitivity the noise is barely audible at 1m from the horn in those.

Thank you for the help, Jan-Peter. It's pretty much a carbon copy of the advice I got from Matthijs over at CS. :-)

Last edited by atledreier; 25th January 2012 at 08:30 AM.
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Old 25th January 2012, 10:39 AM   #6
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Quote:
Originally Posted by atledreier View Post
Digital is not an option, as there are no processor on the market that has digital pre-outs that I am aware of.
Maybe I don't understand, but what kind of digital signal do you need?
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Old 25th January 2012, 10:41 AM   #7
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This is for the front three speakers in a home theater setup, so I would need a digital equivalent of the analog pre-outs. As far as I know there are none or very few processors that have this, strangely enough.
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Old 25th January 2012, 10:44 AM   #8
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still, what kinda of digital signal, s/pdif, i2s or some other maybe?
So it the processor is the problem (you do hae one right?), can't you bypass it with analog signal?

are you running stereo or 2.1 or like that
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Old 25th January 2012, 10:51 AM   #9
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My processor is an Onkyo PR-SC5508. It has analog preouts for all channels it can process, but only a 2-channel SP/Dif output. And as stated in a previous post, I have tried with that stereo digital signal to the amps and it didn't do much to the actual problem anyway.
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Old 25th January 2012, 10:54 AM   #10
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well I guess if this is all in one board, I would disconnect the dsp to see wha ONLY amp does... I hope power supply is not adding noise to the amp...again I don't what PSC2.400 has on board
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