Xilica XM-2040 output hiss

[mica]

Hello everyone and compliments to LH forum.

I am using two Xilica XM-2040 DSP cards to drive a pair of 4-way loudspeakers with JBL components.
The problem is that these cards have a hiss tone at the outputs that is much above -115dB S/N declared by the manufacturer. First I tried Cosel LDC30F-1 switch mode power supplies that were supplied with cards but the problem was emphasized and even worse when one PS was used for two cards. Then I used Traco Power TML20212 20w switch mode PS, the result was slightly better but the problem persists. Finally, I used two 12V batteries connected in series in order to get +/-12V. The result was better but this hiss tone (between 3-4KHz) was still present, at lower and acceptable level although audible in close vicinity of JBL 2450SL-8 with PT-H95HF waveguide.

Otherwise, those little cards are doing the job quite well.
Does anyone know how to suppress this annoying hiss tone?
Grateful for your help.

[Ed Zeppeli]

Maybe you need to turn down the cards' outputs and turn up the amp output.

Try searching about gain-staging and see if that helps. Those compression drivers are very sensitive and will sound hissy.

[mica]

Maybe you need to turn down the cards' outputs and turn up the amp output.

Try searching about gain-staging and see if that helps. Those compression drivers are very sensitive and will sound hissy.

Thank you Ed.
The cards inputs are at -10dB. Amps inputs are at maximum. I have to check cards outputs, not sure about that.
By the way, I used Xilica XD-4080 in the same setup before and it was very, very silent.

[allen mueller]

Thank you Ed.
The cards inputs are at -10dB. Amps inputs are at maximum. I have to check cards outputs, not sure about that.
By the way, I used Xilica XD-4080 in the same setup before and it was very, very silent.

You are looking to improve your signal to noise ratio so you need have to have a hotter signal coming into the amp to make it better, so you need to do the opposite. The hiss is your noise floor so you need to get your signal above it as much as you can and the way to do that is not run the input trim on your amp at the max.

AL

[mica]

You are looking to improve your signal to noise ratio so you need have to have a hotter signal coming into the amp to make it better, so you need to do the opposite. The hiss is your noise floor so you need to get your signal above it as much as you can and the way to do that is not run the input trim on your amp at the max.

AL

AL-I agree with your statement in general but the problem here is of different nature.
When the crossover is disconnected from the amps, there is no audible noise at all. It seems that this hiss tone generates in some of XM-2040 circuits, besides expectable white noise. Possibly as an intermodulation product of Traco Power SMPS frequency (100KHz) and sampling frequency (96KHz). Even there is a miniature SMPS on digital board of XM-2040 that could be responsible for the hiss. I suppose this mini SMPS generates voltage for CPU.
Xilica customer support staff stated that XM-2040 is not supported any more in spite of the fact that this DSP card is in actual price list of European distributor Interstate from Nederlands. Regular firmware updates are available, too.

[mica]

Solved.
Switch mode power supply issue.

[1audiohack]

:applaud:Good work!

Barry.

[ivica]

AL-I agree with your statement in general but the problem here is of different nature.
When the crossover is disconnected from the amps, there is no audible noise at all. It seems that this hiss tone generates in some of XM-2040 circuits, besides expectable white noise. Possibly as an intermodulation product of Traco Power SMPS frequency (100KHz) and sampling frequency (96KHz). Even there is a miniature SMPS on digital board of XM-2040 that could be responsible for the hiss. I suppose this mini SMPS generates voltage for CPU.
Xilica customer support staff stated that XM-2040 is not supported any more in spite of the fact that this DSP card is in actual price list of European distributor Interstate from Nederlands. Regular firmware updates are available, too.

Hi mica,

As You have stated a kind of power supply switching frequency interacts with the XM sampling frequency making about 4kHz hissing sound (100kHz-96kHz), possibly can be measured with high quality spectrum analyzer, at the XM output, or power amp output.
So it can be suggested to apply a kind of high frequency filtering at the power supply outputs.
Analog filters using high quality parts can help (capacitors and even coils), So start with ceramic caps and tantalum caps.
I have some good experience introducing a diodes in such filers (behaves as non linear resistor) too.

Generally speaking, dealing with any kind of 'regular noises' ( broom, hiss ) while using very sensitive speakers is tedious work and would need a lot of cut-and-try experiments.

regards
ivica