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Old 7th October 2005, 05:22 PM   #1
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Default Is it wise?

For home theater amp, usually it is needed 5 or 6 amplifier module in 1 casing, with common power supply for all of the amps.

Is it wise to :

1. make 5 or 6 (2 is bridged for subwoofer) self-oscilating amp for this purpose? With 6 selfoscilating modules, there will be 6 working frequencies, while all is connected to common rail supply.
Will they all work properly (especially the sub woofer amp, 2 in bridged)? Or is it better to make triangle forced type, so all 6 modules is operating at the same clock? I noticed classD switching artifacts also injects to supply, making them has "crosstalk". Plus the problem of "rail pumping" for half bridge type?

2. Using selfoscilating classD for small loads in bridge mode, when the subwoofer load is 2 or 1 ohm, in bridge mode, each amp will experience 1 or 0.5ohm load. Is it wise to use selfoscilating type, or is it better to use triangle forced clock for this bridged+low impedance load?
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Old 7th October 2005, 11:42 PM   #2
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I know people on here think that triangle/ carrier type amps are somewhat inferior but in your case i would reccomend that if you intend to use a high number of amps in one case then they are a good choice as you can use the same triangle or clock to synchronise them so you won't get clashing frequencys. I won't say any more on this subject because i stand alone in thinking that carrier type amps are good regardless of the application. People on here will prob read this and shoot me down but hey, it's a question of subjective taste!

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Mad.P
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Old 9th October 2005, 04:26 AM   #3
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Well, I'm seduced by the good quality of selfoscilating classD.
Is there a way to use 4 or 5 modules using the same 1 common power supply without any problem/crosstalk between each other?
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Old 9th October 2005, 06:51 AM   #4
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Quote:
Originally posted by lumanauw
Well, I'm seduced by the good quality of selfoscilating classD.
Is there a way to use 4 or 5 modules using the same 1 common power supply without any problem/crosstalk between each other?
It is impossible to do multichannel with a single supply with out multiple ground loops unless all inputs are fed separate balanced signals. I donít personally know of a source for these signals unless you get into astronomically expensive units. One more practical solution would be an input transformer for each channel. This also would be expensive, about the same cost as the amp modules for reasonably high quality transformers. The less elegant solution would be a power supply for each module and all grounds floating. It would be a gamble to do it any other way and take a chance on the grounds. There have been others that have done multi channel in a single box but I donít recall any reports on them.
The nicest solution would be a mono amp per channel. This would be the most complex in sheer number of parts.
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Old 9th October 2005, 07:58 AM   #5
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Quote:
It is impossible to do multichannel with a single supply with out multiple ground loops unless all inputs are fed separate balanced signals. I donít personally know of a source for these signals unless you get into astronomically expensive units. One more practical solution would be an input transformer for each channel. This also would be expensive, about the same cost as the amp modules for reasonably high quality transformers. The less elegant solution would be a power supply for each module and all grounds floating. It would be a gamble to do it any other way and take a chance on the grounds. There have been others that have done multi channel in a single box but I donít recall any reports on them.
The nicest solution would be a mono amp per channel. This would be the most complex in sheer number of parts.
Roger
Could you write down the specification for how much crosstalks are allowed? I have made a 5-channel UcD amplifier and could not heard any idle tones in the loudspeakers.

Jan-Peter
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Old 9th October 2005, 01:23 PM   #6
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Hi, Jan Peter,

Quote:
I have made a 5-channel UcD amplifier and could not heard any idle tones in the loudspeakers.
Once I made 1 power supply for feeding 2ch of classAB + 1ch of selfoscilating classD.

The artifacts of classD switching can be seen in the classAB output via scope. When I turned off the classD, those artifacts disappear.

I also read in IRFaudamp paper, that half bridge topology can do "bus pumping".

But if your experience that putting 5 modules with common supply (1 transformer, 1 set bridge diode, 1 set cap bank) is OK, I will try it

Oh, another thing, Jan Peter. Is selfoscilating classD suitable for driving low impedances load (like 2 or 1 or less ohm)? They won't change operating point (like oscilating frequency) when headed to low loads or bridge mode?
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Old 9th October 2005, 05:54 PM   #7
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Default Crosstalk?

Quote:
Originally posted by Jan-Peter


Could you write down the specification for how much crosstalks are allowed? I have made a 5-channel UcD amplifier and could not heard any idle tones in the loudspeakers.

Jan-Peter

Jan-Peter,
I wasnít even thinking of crosstalk as the ground impedance is far lower than the input impedance so shared signal currents shouldnít generate any significant crosstalk signal. Depending on the inductance of the cables used this could be a problem with higher frequencies and longer cables would be far more of a problem all around. The problem is that with all the grounds connected together at the source and amp, line frequency magnetically induced noise due to transformers, power cords or the refrigerator motor, can induce significant currents into the ground causing noise and hum. If the amps power supply is done with 2 bridge rectifiers to keep ripple current out of the grounds this end of the ground connections should not be that much of a problem. If the interconnects are all twisted together a couple of turns every foot or so the noise pickup can be minimized. In any audio system line noise is one degrading factor that we usually can do something about as DIYíers. The closer we can keep grounds to being references only with no currents circulating the lower the noise floor will be and the better the sound staging will be too.
Reducing a line hum or buzz from something you can only hear when you are right at the speakers to something that can only be heard if you put your ear within an inch of the speaker is the difference between hearing the back wall of the sound stage or not! I have found every reduction of noise has a significant effect on sound quality and is worth pursuing even to extremes, like my beating on people to twist their wire pairs. Human hearing has an amazing ability to pick out coherent signals from the noise and this low level information retrieval is a significant clue to us to be able to put it all back together in our heads as real music. Any line related noise will distract from this ability.
Roger
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Old 9th October 2005, 09:39 PM   #8
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Quote:
Originally posted by Jan-Peter
I have made a 5-channel UcD amplifier and could not hear any idle tones in the loudspeakers.Jan-Peter
Its not about hearing the crosstalk, its the interference it will induce in the whole soundstage at even the smallest crosstalk. The human ear is a very, very discriminating device.
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Old 9th October 2005, 09:56 PM   #9
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Default Re: Is it wise?

Quote:
Originally posted by lumanauw
For home theater amp, usually it is needed 5 or 6 amplifier module in 1 casing, with common power supply for all of the amps.

Is it wise to :

1. make 5 or 6 (2 is bridged for subwoofer) self-oscilating amp for this purpose? With 6 selfoscilating modules, there will be 6 working frequencies, while all is connected to common rail supply.
Will they all work properly (especially the sub woofer amp, 2 in bridged)? Or is it better to make triangle forced type, so all 6 modules is operating at the same clock? I noticed classD switching artifacts also injects to supply, making them has "crosstalk". Plus the problem of "rail pumping" for half bridge type?

2. Using selfoscilating classD for small loads in bridge mode, when the subwoofer load is 2 or 1 ohm, in bridge mode, each amp will experience 1 or 0.5ohm load. Is it wise to use selfoscilating type, or is it better to use triangle forced clock for this bridged+low impedance load?
For an unbalanced system: take 1 big transformer, give every module its own supply, bridge+2caps+fuses, ground at transformer/cap.bank 0V, take enough space between modules and twist all the wires!!!!!. Than take my modified input cable and feed them to the unbalanced inputs, ground free. These recommendations apply to the UCD's. This will have the best crosstalk possible hence Dolby/Cinema experience. But only if you use good caps(lowest ESR).
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Old 10th October 2005, 12:32 AM   #10
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Quote:
Than take my modified input cable
What is that?
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