QSC audio - floating supply amplifiers

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#42
wg_ski said:
In the Crown grounded bridge the whole power supply floats. One big cap (per channel). Any node can therefore be tied to "ground". I that case, it's one side of the bridge (and the reference for the balanced inputs).
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Yes I saw that in the Crown paper. But I was wondering what is the benefit of make the PSY floating with one cap, but not tie any side of the bridge to ground.

With kind regards,
Bas
 
#44
Sebastiaan said:
Yes I saw that in the Crown paper. But I was wondering what is the benefit of make the PSY floating with one cap, but not tie any side of the bridge to ground.

With kind regards,
Bas
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There is always two transistors in series in the Crown which means in operation there is half the power supply voltage across the transistors. 100 volt transistors can provide +/-100 volts of swing with a single 100 volt supply. All this, of course, is slightly less because of drops and losses but the idea result reduces voltage required on the transistor by half.
 
#48
sumaudioguy said:
Bad grounding even in a bridge amplifier can cause ground current error on the input. Bad grounding is bad grounding and load ground current error are two different problems but can be "tied together" through poor design.
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thanks for your insight. Seems interesting to keep everything floating in that aspect. I might try it out one day with a bridged chip amp for experiment sake.

With kind regards,
Bas
 
#49
a separate supply for each channel does make it easier to get system gnding right

gnded bridge floating supply does sound attractive for doubling op amp V output with high Z headphones - 3-wire TRS jack plug requires common R/L driver gnd
 
#54
If I remember correctly from my repair days and doing warranty repairs for QSC, I believe the Powerlight series is a switch mode power supply, (SMP). A ballast lamp won't work very well on a SMP. The problem is not because of a floating supply but simply the nature of SMP. The SMP will draw whatever current is required to maintain a constant output voltage. The ballast is limiting that current causing the SMP to shutdown. On shutdown the load is removed, the SMP starts up again and the cycle repeats.
 
#55
Yes, the Powerlight series use a switching power supply or SMPS. They do not like bulb limiters. What happens is the power supply tries to fire up but finds it cannot do the job and so shuts itself down, at which time it powers up but finds it cannot do the job and shuts down, at which time it... and so on. Which is what davada said.

The only real difference between the "conventional " power amp circuit, and your floating supply type (Also known as grounded emitter or flying rail) is which end of the load we call ground.
 
#56
QSC PL has under-voltage lockout, so once mains voltage drop to a certain point SMPS shuts down. There is also overcurrent protection that could trigger if there is a short. And there is DC offset protection for both channel which turns off the SMPS as well.
 

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