A 50-100 volt drop for regulation? That's a bit untidy. Most regulators only need a few volts drop across them to regulate.The way I always saw it: to get a regulated 250V I would have to start with 300V-350V before the regulator. OTOH if I built the stage with good PSRR I could feed it all 350V.
Where does this "extra headroom" come from? Does a signal peak somehow conjure up a rise in the line voltage? Can you only listen to "loud peak" music when the line voltage in your neighborhood is higher?
No that's not it. The idea is that without a regulated supply and an average music load, the power supply is higher than under heavy constant max power output. So if a high level burst in a regular program comes along it can benefit from the max supply voltage. Of course, if the burst is long, the supply eventually sags and the advantage is lost.
There exists also a measurement protocol to measure this headroom and express it in dB; numbers you see are generally in the 0.5dB to 1.5dB range.
Jan
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I think you should also consider how sensitive the amp is for hum and noise on the supply. A non-regulated supply not only has mains ripple but also all kinds of noise and junk coming in through the mains and the mains transformer.
A good regulator makes short shrift of all that junk, which can significantly improved the sound. Some amps benefit more than others but it always helps.
Jan
I agree. Every amplifiers have different PSRR.
But I prefer capacitance multiplier.
Cap multipliers are good. They are halfway, performance-wise, between unregulated and fully regulated. They are simple, uncomplicated and hard to do wrong.
Jan
Jan
Is this one of those how long is a wet piece of string and what sort of tea bags should I use with my KTxeexees questions?
Added cost.
Added power loss.
Added complexity.
Technical Ecstasy.
What disadvantages can you suggest?
In DIY, there are no disadvantages as long we can afford it. Small improvement is matter.
Except you design for mass production, you should consider price per performance and target market.
But some religion said, all amplifier sound same. Then you should make as cheap as possible.
Cap multipliers are good. They are halfway, performance-wise, between unregulated and fully regulated. They are simple, uncomplicated and hard to do wrong.
Jan
I agree again 🙂 It is simple than design good voltage regulator.
If I can make good voltage regulator, maybe I will try it. But my current CM is better than DX regulator in listening test.
Best of both worlds?
How about a regulator followed by a cap multiplier as JC Morrison has done?
t
How about a regulator followed by a cap multiplier as JC Morrison has done?
t
How about batteries?
As long you can afford it, you can try it.
How about nuclear power plant?
How about a regulator followed by a cap multiplier as JC Morrison has done?
t
That for me is backwards. If you have a good reg, why spoil it with a cap multiplier? If you want the characteristics of a cap multiplier, why prefix it with a regulator?
Jan
From the PSU, which does not have time to droop.dotneck335 said:Where does this "extra headroom" come from?
There is another problem with regulators: their feedback loops may need to be designed as carefully as the main amp, and they may provide a supply rail with a complex impedance (typically, somewhat inductive - which may interect with decoupling capacitors).
If you only needed a few volts of regulation then you don't need a regulator. I don't think you have thought this through.A 50-100 volt drop for regulation? That's a bit untidy. Most regulators only need a few volts drop across them to regulate.
Yes, OK, I see your point. In my case, that would be about 1 db headroom difference. So, like all things electronic, it's a tradeoff. Additional costs of two regulators, four pass transistors, and some diodes and resistors---maybe $25. Certainly too much for a commercial design, but for a one-off DIY design power amp, it's doable without too much pain. Loss of 1 db of headroom. Maybe 80 db less ripple and noise. Which is more audible? I don't know for sure, but it seems to me that the quietness would be preferable to the headroom. YMMV.The idea is that without a regulated supply and an average music load, the power supply is higher than under heavy constant max power output........... numbers you see are generally in the 0.5dB to 1.5dB range. Jan
Yes, a lot is just personal preference.
I just put some numbers in the calculator, just for kicks. +1dB is about 12% in extra voltage, and about 25% in extra power. More than I expected, but probably not enough to make the difference between clipping and not clipping..
Jan
I just put some numbers in the calculator, just for kicks. +1dB is about 12% in extra voltage, and about 25% in extra power. More than I expected, but probably not enough to make the difference between clipping and not clipping..
Jan
If you have a good reg, why spoil it with a cap multiplier? If you want the characteristics of a cap multiplier, why prefix it with a regulator?
A (high NFB) voltage regulator has excellent performance at low frequency. Very low Zout, very good ripple rejection / PSRR.
A (zero NFB) capacitance multiplier has excellent performance at high frequencies. Low and FLAT Zout, good PSRR.
Cascading the two might be viewed as an attempt to get the best of both worlds. Eliminate crud from one end of the frequency axis, then eliminate crud from the other.
I don't think that's the case Mark. The same mechanism causes increase in Zout with frequency in both cases. I have yet to see a cap multiplier that has lower Zout than a good regulator anywhere in the frequency range, all other things being equal.
Jan
Jan
A (high NFB) voltage regulator has excellent performance at low frequency. Very low Zout, very good ripple rejection / PSRR. A (zero NFB) capacitance multiplier has excellent performance at high frequencies. Low and FLAT Zout, good PSRR......
I missed where OP stated actual Design Goals:
... bipolar supply (+/- 40 volts) for ... bridge mode at 200 watts into 8Ω. ... lower ripple and noise, avoidance of exceeding the SOA of output devices, and elimination of power supply modulation on the output signal.
*For these goals*, super-low rail impedance is not needed. I remember when SOA really limited our designs (I thot those days were gone?). Recent decades and >999 products show that good honest PSRR makes PS ripple a non-issue for low-level work.
Leaving us at ripple modulation in *clipping*. Well, you shouldn't be clipping a High Fidelity amplifier. (It is a major flavor in guitar amplifiers.) But also: what have you gained? Say a choice between a raw supply rippling 44V-41V, or a smooth supply at 40V. Up to 39V of signal, there's really no difference. At "42V" output, the smooth supply is clipping flat and the raw supply is throwing 120Hz trash on 1% of signal peaks. Well, turn-down from "42V" to 39V peaks. The 0.6dB drop is really unimportant. And when you are stoned out of your mind and "enjoy intermodulation", the raw supply gives you a dB more plus "flavor".
This all assumes that, like most modern transistor amps, the output stage (with overall NFB) has lots of PSRR. It is typically the same sort of emitter follower you would use for a regulator, only with signal in it.
To reduce ripple one can also use a three phase mains supply. Without a smoothing capacitor, the output never goes below 86% of peak voltage, irrespective of load current.
Yet another way, is to use a mains supply that is not a single sine wave, but square wave with the first 10 harmonics present, and the rest removed. Iron cored transformers don't like the presence of high power high freqency harmonics.
Last but not least, use a DC mains power supply. This can be achieved mechanically using a motor and dynamo mounted on the same armature. I have seen this arrangement to provide a 3 phase mains supply from single phase. The owner operatures a milling machine and a lathe using this kind of power conversion.
These are all theoretical possibilities, albeit based in Physics and technology, but for mundane situations, costs play a very limiting role. Costs are often the first thing to consider in anything.
Yet another way, is to use a mains supply that is not a single sine wave, but square wave with the first 10 harmonics present, and the rest removed. Iron cored transformers don't like the presence of high power high freqency harmonics.
Last but not least, use a DC mains power supply. This can be achieved mechanically using a motor and dynamo mounted on the same armature. I have seen this arrangement to provide a 3 phase mains supply from single phase. The owner operatures a milling machine and a lathe using this kind of power conversion.
These are all theoretical possibilities, albeit based in Physics and technology, but for mundane situations, costs play a very limiting role. Costs are often the first thing to consider in anything.
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How does one determine a power amplifier's PSRR? Although I do see this specification quoted on opamps and chip power amps, I don't see it on commercial amps. Can it be determined by a calculation from the schematic? I have seen it graphed for an LM3886 power amp chip as ~ -95db @120Hz from the -V supply. How does one design a power amp for excellent PSRR? I suppose that this is perhaps a separate discussion for a new thread............like most modern transistor amps, the output stage (with overall NFB) has lots of PSRR. It is typically the same sort of emitter follower you would use for a regulator, only with signal in it.
A properly designed amplifier and suitable unregulated rectifier-bulk capacitance power supply would not need a regulator.
You would be chasing diminishing returns for higher cost...
The widespread use of current mirrors and constant current sources means noise on supplies is either cancelled or not passed on.
You would be chasing diminishing returns for higher cost...
The widespread use of current mirrors and constant current sources means noise on supplies is either cancelled or not passed on.
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I would like to understand this further. How exactly do current mirrors and constant current sources avoid power supply noise and ripple from getting on the signal?The widespread use of current mirrors and constant current sources means noise on supplies is either cancelled or not passed on.
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