how to avoid bus pumping

[Albrerta]

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

 

[Viennatom_new]

big caps - the more the better

 

[theAnonymous1]

An expensive option, but get another SDS-254 and run them BTL.

 

[Viennatom_new]

Running 2 in BTL would effectively half the impedance. this may or may not be good.

 

[jcx]

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+braking+load+dump+resistor

 

[Albrerta]

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?

 

[theAnonymous1]

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

 

[jcx]

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

 

[TheShaman]

Check Tripath's application notes as well.

 

[doctordata]

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

 

[theAnonymous1]

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 .

The board has the option to invert the signal while keeping each channel independent?

That's the way to go then. Same effect as running BTL.

 

[Albrerta]

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

thanks for the tip, exactly what I should do? see the pic below, so just jump another side (in yellow) for one channel, then switch +/- on speaker of this channel? any change on input? (reverse the polarity of input of this channel?)

 

[Viennatom_new]

Reversing one polarity in case of 2 channels should ALWAYS be done by default. The benefit is a more equal utilization of the supply rails - double frequency through interleaving plus it helps against pumping. Powersoft calls this "balanced supply operation mode"..
Still there is no guarantee that low frequency is always mono - I know of some songs that use left right effects also in the bass range. In this case, bass should be converted to mono - convert L and R to stereo sum (L+R) and stereo difference (L-R), highpass the difference signal, then combine again.

 

[doctordata]

thanks for the tip, exactly what I should do? see the pic below, so just jump another side (in yellow) for one channel, then switch +/- on speaker of this channel? any change on input? (reverse the polarity of input of this channel?)

Yes correct , Jumper in yellow , speaker reversed on that channel . that's it .

Cheers ,

Rens

 

[Albrerta]

tried but didn't work, jumper in yellow made no sound, and reversed input caused a big hum noise

 

[doctordata]

tried but didn't work, jumper in yellow made no sound, and reversed input caused a big hum noise

Don't you have a manual ? The website states that you can reverse the input polarity by changing jumpers : "The balanced input stage is one of the finest available and normally only found on very expensive high-end equipment. When using single ended inputs, you can change a jumper to select inverted or non-inverted input as well... useful in some instances"
Looked for a download for the manual , but couldn't find it .
If you figure this out , the buspumping will be gone or at least much less.

Cheers ,

Rens

 

[basreflex]

another option is a charge balancer between the supply rails. you need 2 isolated bridge drivers 4 nfets and a good pump cap capacitor. you could run it at 30khz, above the audio .
not very heavy fets needed. an fdd1600 (only80-100V needed) could do the job, plus 2 SI8234's and some clock signal. 47u 100V electrolytic lowZ.