Chokes on psu lines

Pierre · 9th March 2006, 03:05 PM

Hello all.

I recall that my latest class-D half-bridge designs sometimes shown a little bit of whistle when two boards were connected to the same (linear) PSU.

I guess that it is due to some switching noise going back from each module to the PSU and back to the other module, interfering between them and generating audible beat tones.

I was thinking on adding chokes in series with + and - inputs of each module so hf noise doesn't leave the amplifier boards theoretically.

I have selected a choke from Digikey, part number is 240-2170-ND and you can find it at:

http://dkc3.digikey.com/PDF/EU051/0679.pdf

They are specified at 7A max. current. I don't know if it is RMS or peak current, but anyway, the thing is that my amp should be able to operate at +/-60V or so on 4 ohm loads, so peak current is more than 15A. I was wondering what would happen: will the chokes saturate during the high current peaks and simply behave like a shortcircuit so they don't affect the circuit? In that case, it's ok, because the HF noise is only annoying with very low volume or no signal. (I can't imagine what other effects can appear, as the wire is not going to fuse, that's for sure).

Is then a good idea to add one of these chokes in series with the positive rail (before a 100uF/100V capacitor) and another in series with the negative rail (also before the cap)?

I think that LC audio and Hypex also use similar ones, am I right?

Thanks!

fredos · 10th March 2006, 07:59 PM

Your noise is probably comming from ground, not PSU HV. It was a free running amplifier? Try to sync them with crystal...

Free running amplfier have never work very well for me...

Fredos

www.d-amp.com

Pierre · 11th March 2006, 09:06 AM

Thanks, Fredos.
They are both clocked (triangle driven) modules. I know I could get rid of the noise probably by synchronising them, but I anyway would like to clean up things a little bit.
What you say makes sense, because I recall having got rid of most of the noise by simply tying the GNDs at both INPUTS together...

The amps share a PSU. The speaker returns go to the PSU also. Perhaps wiring it to the amplifiers GNDs directly could improve things?

fredos · 11th March 2006, 01:02 PM

Good grounding solution for me is that the ground of output fiter is isolated from audio section and all ground go to a single point on the case. What I mean is the ground for each output filter, each power supply (Lo voltage and hight voltage), audio ground of power amp, speaker ground and input ground. And dont forget AC ground for EMI!

bye

Fredos

www.d-amp.com

Pierre · 11th March 2006, 07:04 PM

I assume you are talking about half-bridge output (grounded speaker). Then your boards don't have the modulator / audio section and power section GNDs connected together and you make it externally, at one point (the PSU GND or the audio input connectors?) What about earth, do you connect that common point GND to earth in the case?

Thanks!

fredos · 12th March 2006, 02:28 PM

That's right!

fredos

Pierre · 12th March 2006, 08:54 PM

Thanks for your help, Fredos.

9th March 2006, 03:05 PM	#1
Pierre Banned Join Date: Nov 2004 Location: Paris	Chokes on psu lines Hello all. I recall that my latest class-D half-bridge designs sometimes shown a little bit of whistle when two boards were connected to the same (linear) PSU. I guess that it is due to some switching noise going back from each module to the PSU and back to the other module, interfering between them and generating audible beat tones. I was thinking on adding chokes in series with + and - inputs of each module so hf noise doesn't leave the amplifier boards theoretically. I have selected a choke from Digikey, part number is 240-2170-ND and you can find it at: http://dkc3.digikey.com/PDF/EU051/0679.pdf They are specified at 7A max. current. I don't know if it is RMS or peak current, but anyway, the thing is that my amp should be able to operate at +/-60V or so on 4 ohm loads, so peak current is more than 15A. I was wondering what would happen: will the chokes saturate during the high current peaks and simply behave like a shortcircuit so they don't affect the circuit? In that case, it's ok, because the HF noise is only annoying with very low volume or no signal. (I can't imagine what other effects can appear, as the wire is not going to fuse, that's for sure). Is then a good idea to add one of these chokes in series with the positive rail (before a 100uF/100V capacitor) and another in series with the negative rail (also before the cap)? I think that LC audio and Hypex also use similar ones, am I right? Thanks!

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10th March 2006, 07:59 PM	#2
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Your noise is probably comming from ground, not PSU HV. It was a free running amplifier? Try to sync them with crystal... Free running amplfier have never work very well for me... Fredos www.d-amp.com

11th March 2006, 09:06 AM	#3
Pierre Banned Join Date: Nov 2004 Location: Paris	Thanks, Fredos. They are both clocked (triangle driven) modules. I know I could get rid of the noise probably by synchronising them, but I anyway would like to clean up things a little bit. What you say makes sense, because I recall having got rid of most of the noise by simply tying the GNDs at both INPUTS together... The amps share a PSU. The speaker returns go to the PSU also. Perhaps wiring it to the amplifiers GNDs directly could improve things?

11th March 2006, 01:02 PM	#4
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Good grounding solution for me is that the ground of output fiter is isolated from audio section and all ground go to a single point on the case. What I mean is the ground for each output filter, each power supply (Lo voltage and hight voltage), audio ground of power amp, speaker ground and input ground. And dont forget AC ground for EMI! bye Fredos www.d-amp.com

11th March 2006, 07:04 PM	#5
Pierre Banned Join Date: Nov 2004 Location: Paris	I assume you are talking about half-bridge output (grounded speaker). Then your boards don't have the modulator / audio section and power section GNDs connected together and you make it externally, at one point (the PSU GND or the audio input connectors?) What about earth, do you connect that common point GND to earth in the case? Thanks!

12th March 2006, 02:28 PM	#6
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	That's right! fredos

12th March 2006, 08:54 PM	#7
Pierre Banned Join Date: Nov 2004 Location: Paris	Thanks for your help, Fredos.

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