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Old 3rd July 2014, 03:07 PM   #1
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Default how to avoid bus pumping

I had bus pumping problem with my classdaudio sds-254, when playing some deep and punch bass, what would be a good way to avoid it, except turn volume down? right now I power it with connex SMPS300R, +/-45V, undersized I know, thinking to get a big one, like SMPS800RE, or go old way with 600VA transformer and some big caps, will it help? Thanks
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Old 3rd July 2014, 03:39 PM   #2
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big caps - the more the better
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Old 3rd July 2014, 05:34 PM   #3
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An expensive option, but get another SDS-254 and run them BTL.
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Old 3rd July 2014, 05:56 PM   #4
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Running 2 in BTL would effectively half the impedance. this may or may not be good.
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Old 3rd July 2014, 06:06 PM   #5
jcx is offline jcx  United States
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I've seen that suggestion but don't understand it - "bus pumping" is the consequence of bidirectional power flow in switching output stages - energy stored in the speaker's mass/spring reactive components being returned to the PS during part of the output waveform

I don't see how bridging makes any difference in the basic power flow issue

if X Joules is stored in the moving cone mass then that X Joules gets returned to the PS Caps by the switching stages while decelerating the cone mass (with some reduction from <100% efficiency in switches and speaker)

I have definitely seen bus pumping in DC motor full bridge drives - had to explain to the Mech E why he blew up his drive electronics

https://www.google.com/#q=motor+brak...+dump+resistor

Last edited by jcx; 3rd July 2014 at 06:22 PM.
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Old 3rd July 2014, 06:39 PM   #6
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Quote:
Originally Posted by ViennaTom View Post
Running 2 in BTL would effectively half the impedance. this may or may not be good.
exactly, I have 4R speaker and sds-254 BTL is only good for 8R

Now another question, the 254 support both balanced and SE input, i'm using SE now, would balanced input make any difference?
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Old 3rd July 2014, 06:44 PM   #7
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Originally Posted by jcx View Post
I've seen that suggestion but don't understand it..
Here's a good explanation of bus pumping and why it doesn't exist for full-bridge (page 12)...

http://www.irf.com/technical-info/appnotes/an-1071.pdf
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Old 3rd July 2014, 07:14 PM   #8
jcx is offline jcx  United States
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and that doesn't address the load energy storage at all - the example only talks about the switching inductor energy storage

my analysis is for load energy storage
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Old 4th July 2014, 12:32 PM   #9
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Check Tripath's application notes as well.
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Old 4th July 2014, 02:48 PM   #10
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Quote:
Originally Posted by Albrerta View Post
I had bus pumping problem with my classdaudio sds-254, when playing some deep and punch bass, what would be a good way to avoid it, except turn volume down? right now I power it with connex SMPS300R, +/-45V, undersized I know, thinking to get a big one, like SMPS800RE, or go old way with 600VA transformer and some big caps, will it help? Thanks
Do you use it in bridge mode or in stereo mode ? ( should be no bus pumping in bridge mode) If in stereo mode reverse the input polarity of one channel ( with the jumper , one channel inverted and one channel non inverted ) and reverse the polarity of one of your speaker outputs ( put the - wire in the + output and vice versa ) and you should be fine .

Cheers ,

Rens
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Last edited by doctordata; 4th July 2014 at 03:11 PM.
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