Hi!
Please bear with me, I have been inactive on diyaudio for over ten years...
I have read everything I could find on "bus pumping" with more than one class D (in my case preferrably a IRS2092S design) amplifier supllied by a single supply. I know that for example on a stereo amp the second channel should be inverted by an input buffer, with the inversion being undone at the speaker output.
The supply (supplies...) will be a switching power supply (haven't decided yet).
But what about three or more channels? Since all channels are connected in parallel, would bus pumping not also occur with every channel which has the same phase?
In other words: In order to avaoid bus pumping alltogether, would it be better to never use more than two channels on a single supply?
Although leaning towards a 4 channel LJM L25D, 2 channels LJM L30D setup, with all the hassle I am also thinking about building a class A/B amplifier, which will of course has higher requirements (=cost) for heat sinking...
I am aiming for a minimum of 4 * 150 W into 8 ohms, 2 * 300 W into 8 ohms.
Kind regards,
Arndt
Please bear with me, I have been inactive on diyaudio for over ten years...
I have read everything I could find on "bus pumping" with more than one class D (in my case preferrably a IRS2092S design) amplifier supllied by a single supply. I know that for example on a stereo amp the second channel should be inverted by an input buffer, with the inversion being undone at the speaker output.
The supply (supplies...) will be a switching power supply (haven't decided yet).
But what about three or more channels? Since all channels are connected in parallel, would bus pumping not also occur with every channel which has the same phase?
In other words: In order to avaoid bus pumping alltogether, would it be better to never use more than two channels on a single supply?
Although leaning towards a 4 channel LJM L25D, 2 channels LJM L30D setup, with all the hassle I am also thinking about building a class A/B amplifier, which will of course has higher requirements (=cost) for heat sinking...
I am aiming for a minimum of 4 * 150 W into 8 ohms, 2 * 300 W into 8 ohms.
Kind regards,
Arndt
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I had to consult the Internet to know about this problem. The specialists state it to be worst for bass frequencies. And, their first recommendation is to use generously large supply line decoupling capacitors to cope with the energy being returned by the chokes (and reduce supply voltage ripple in general).
Compensating currents in one filter with currents in another filter is a possibility if the signals are clearly correlated. If not, this approach is less succesful.
Another possibility is what is known as an active noise filter. It is in short a power amplifier that injects or absorbs the excessive or missing current on a noisy line through a storage capacitor, controlled by a feedback loop. The last solution increases circuit complexity somewhat.
Compensating currents in one filter with currents in another filter is a possibility if the signals are clearly correlated. If not, this approach is less succesful.
Another possibility is what is known as an active noise filter. It is in short a power amplifier that injects or absorbs the excessive or missing current on a noisy line through a storage capacitor, controlled by a feedback loop. The last solution increases circuit complexity somewhat.
As a general rule, bus pumping is an issue specially with half-bridge topology.
In that case the recommandation is driving both channels of a stereo setup antiphase.
Which is, when you look at it, just the same as a full bridge.
Or in other words: There is no bus pumping with full-bridge topology.
You may add as much full-bridge channels to your common supply without bus pumping.
In that case the recommandation is driving both channels of a stereo setup antiphase.
Which is, when you look at it, just the same as a full bridge.
Or in other words: There is no bus pumping with full-bridge topology.
You may add as much full-bridge channels to your common supply without bus pumping.
So if for example I decide to go for an IRS2092 setup, I could simply choose 5 stereo modules with lesser power rating (2 * 125 Watt for example), giving me 10 channels, and bridge them (if they have the means to do that on board) to five channels and this problem would be gone?
OK. And what about the switching frequency, is matching the frequency closely on all channels - or using at least an offset of 25 Khz between each channel - really that important?
And given the price increase of the whole design maybe the option of simply using a supply for each two channels (thre supplies) would be easier to implement...?
Sadly the only affordable TPA3055 design I can find omits all onboard means to switch the amp to BTL mode, ohterwise the 3055 would be the perfect fit...
OK. And what about the switching frequency, is matching the frequency closely on all channels - or using at least an offset of 25 Khz between each channel - really that important?
And given the price increase of the whole design maybe the option of simply using a supply for each two channels (thre supplies) would be easier to implement...?
Sadly the only affordable TPA3055 design I can find omits all onboard means to switch the amp to BTL mode, ohterwise the 3055 would be the perfect fit...
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This is very interesting as I had the exact same question a while back and did not receive an answer.
So basically 2 channels max if you want to keep it in half bridge and invert the signal to assist with bus pumping.
It sounds as if the best option might be to add capacitors to the PSU supply. Can anyone provide a bit of info as to what size caps to use and how many, how to connect them etc? Sorry for the thread hi-jack.
So basically 2 channels max if you want to keep it in half bridge and invert the signal to assist with bus pumping.
It sounds as if the best option might be to add capacitors to the PSU supply. Can anyone provide a bit of info as to what size caps to use and how many, how to connect them etc? Sorry for the thread hi-jack.
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I also plan on using SMPS. I am in the same boat as you, I'd like to use 4 to 6 L15D amp boards with a single PSU and am also looking for ways to combat the bus pumping.
Conter productive in what sense? Even if it were a regulated SMPS?
Sorry, I am still very new and still lots to learn for me.
Conter productive in what sense? Even if it were a regulated SMPS?
Sorry, I am still very new and still lots to learn for me.
In this issue, use 3 power sources
2 channels in each phase.
Sorry for my bad english
I use a similar setup with 5 L15D's on one 1000W SMPS for years now.
phase shifter on the left Front and one on left Rear , other 3 channels original .
extra 10.000 uF per rail . No problems with pumping even at extreme volume .
You can build the phase shifter yourself ( see : My design L20D IRS2092+IRFI4020H 200W8R ) or buy them online , for instance this one : Balanced Input Phase Shifter | Connex Electronic
Cheers,
Rens
Why a phase inverter only on 2 of the channels and why those 2 specific channels?
Also why a phase inverter and extra caps per rail? I am trying to understand if there is something I am missing.
I plan on using my amps for an active setup, so 2 channels for tweeters, 2 channels for mids and 2 channels for subs (therefore 6 channels in total, off a single PSU).
I am wondering whether the phase inverters are still required with the 10000uf caps per rail, or whether it is just extra precaution.
Perhaps it would assist if I were to invert the one sub channel, or not really?
Or a separate PSU for the 2 sub amp channels?
Also why a phase inverter and extra caps per rail? I am trying to understand if there is something I am missing.
I plan on using my amps for an active setup, so 2 channels for tweeters, 2 channels for mids and 2 channels for subs (therefore 6 channels in total, off a single PSU).
I am wondering whether the phase inverters are still required with the 10000uf caps per rail, or whether it is just extra precaution.
Perhaps it would assist if I were to invert the one sub channel, or not really?
Or a separate PSU for the 2 sub amp channels?
But you still have three channels on one supply, with two of those channels not running BTL and sharing one phase...
I am leaning towards using a DRV124 balancer, if I decide to only use SRS2092 modules.
Like this Module Kit unbalanced to balanced symetrizer DRV134 stereo - Audiophonics
or with everything on board (like connex): Symmetric to Asymetric Buffer RCA TO XLR /XLR TO RCA - Audiophonics
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Bus pumping mainly occurs on low frequencies and can be reduced by driving 2 channels out of phase, because the low frequencies are mostly present in mono in both channels and so singled out .
Most important Left Front and Right Front , they have the strongest low frequency content !
So one inverter on the front channels.
Centre channel , there’s nothing to single out , there’s no second channel ( and not much bass anyway), so no inverter needed .
Surround channels , 1 inverter but not really needed ( not much bass )
Surround back channels , 1 inverter but same as above .
To be sure I added the extra capacitors to eliminate the residual pumping in case the low frequencies are not equal on L and R channel and in case the C channel causes bus pumping .
In case the surround and center speakers are set to "small" or "medium" in the surround processor , most of the low frequencies are directed to the LFE channel anyway ,so not much to pump here !
Hope this helps.
Cheers,
Rens
Most important Left Front and Right Front , they have the strongest low frequency content !
So one inverter on the front channels.
Centre channel , there’s nothing to single out , there’s no second channel ( and not much bass anyway), so no inverter needed .
Surround channels , 1 inverter but not really needed ( not much bass )
Surround back channels , 1 inverter but same as above .
To be sure I added the extra capacitors to eliminate the residual pumping in case the low frequencies are not equal on L and R channel and in case the C channel causes bus pumping .
In case the surround and center speakers are set to "small" or "medium" in the surround processor , most of the low frequencies are directed to the LFE channel anyway ,so not much to pump here !
Hope this helps.
Cheers,
Rens
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