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Old 24th June 2012, 07:09 PM   #6381
1audio is offline 1audio  United States
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Quote:
Originally Posted by Pano View Post
Many amps have either an L or an R element in series after the rectifier and 1st cap. That's gotta make a difference.
Less than you would hope for. If the load is fairly static, like a preamp, those tricks can work pretty well. But a load with huge dynamics like an Class AB, B G or D amp they mostly just add heat and loss to the supply.

Carver took a different approach with a very high voltage raw supply that was allowed to sag a lot under load. However that brings the question of modulation of the audio signal as the supply rails change. I don't see a lot of diy efforts toward duplicating a Phase Linear amp so maybe its not the way to go.

At the other extreme is the large cap bank. Biggest challenge is charging it on turn on without blowing breakers. But with 5 and 10 degree conduction angle the 1A RMS from the wall can become 10-20A peaks. The AC power source has a finite impedance, say .5 Ohm (500' loop of 10 AWG to the pole and assuming a "perfect" transformer to make things easier) that is a 5V drop during the charge period. This explains the 3% THD on the power line (flattened peaks). And the peak current will really stress the power connections way beyond what seems reasonable. I have seen 15A power inlet modules melt under these conditions.

I would focus on a balance based on the amps sensitivity to supply changes and ripple, regulate the parts that can be without a huge power premium (figure a linear supply will probably be less than 50% efficient) and then struggle with the radiated fields, the line noise coupling through the transformer and supply circuits etc. which are much knottier problems to solve.

An array of small caps can have a much lower esr than a single large cap of the same value, but it can all be blown if not implemented well. Start by following the current paths. If any end up in series with a voltage or feedback reference you have a problem. Its easy to overlook a hidden negative or positive feedback node from the currents. They don't show on schematics.
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Old 24th June 2012, 07:19 PM   #6382
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Originally Posted by simon7000 View Post

Now for a thorough answer... well I am doing an article on power supplies, it is well past novella length, no matter how I try to edit it. That is for what is supposed to be a short tutorial!
Well, then, we're agreeing. There is no "rule," you have to actually engineer competently to get a desired performance.
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Old 24th June 2012, 07:22 PM   #6383
popilin is offline popilin  Argentina
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If in the 30's/40's the Internet had existed, in this discussion, the values of C would be several orders of magnitude lower.IMHO

Some mJ more, some less mJ due to chokes, E = (1/2) L i^2

Ofcourse, just at that time were designed valves that we use today, and the people who did was stupid enough to suggest, at least, a rule of Dumb.

BTW, hi-end audio was not a major issue in those days.
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Old 24th June 2012, 09:18 PM   #6384
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Quote:
Originally Posted by Pano View Post
trends
Like anything else over the last decade and a half, bigger and bigger in the top end.
Most of which is marketing, where there's bundles of free cash, there's demand, supply will follow.
Not necessarily proves any technical arguement, as little as me telling you that it sounds better.

Either larger size transformers, increased capacitance, or both, has been a trend for decades.
Capacitance multipliers for SS output stages have gained popularity since the Metaxas Soliloquy of the mid '80s, there's the sporadic 3-phase powersupply, triple "boost" powersupplies of an MBL, and for a number of years SMPS's, as e.g. Levinson.

Another cap multiplier example, Orpheus monaural : http://2.bp.blogspot.com/_FbSDy9bT53...e_Mono_PCB.jpg

> 3J/10W (4Ohm)
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Old 24th June 2012, 10:43 PM   #6385
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Thanks Jacco. I know a lot of it is driven by fashion or customer demand, thanks for tracking the trend.

I still wonder if there is a flat part of the "energy stored" vs subjective cajones.
Of course SY will tell me I'm looking for a rule - when I think I'm just looking for a curve.
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Old 24th June 2012, 10:51 PM   #6386
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Perhaps someone can help me out here.

Capacitance multipliers are good at reducing ripple, but what you want in a power amp is not just low ripple, but also a supply that can deliver large currents at short notice. To that end, you need to store energy that can't be instanteneously delivered by the transformer. A capacitance multiplier does not store much energy.

From the perhaps misguided idea that a power supply for an end stage needs to store an immediately available amount of energy. Isn't it so that a capacitance multiplier would loose steam as soon as the stage that feeds the capacitance multiplier can no longer keep up with the instantaneous current demand? If so, you would need to store the required joules of energy in the stage preceeding the capacitance multiplier, requiring pretty much the same capacitance as you might without a capacitance multiplier in the loop.

This would change if that preceeding capacitance were run at a higher voltage than the rails, with the capacitor multiplier dissipating the delta. But that, in effect, would be pretty much the same as a regulator.

Just some free thinking on the late Sunday night, questioning what the role of a capacitance multiplier in an end stage PS might possibly be.

vac

Last edited by vacuphile; 24th June 2012 at 10:56 PM.
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Old 24th June 2012, 11:02 PM   #6387
wahab is offline wahab  Algeria
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Quote:
Originally Posted by vacuphile View Post
Just some free thinking on the late Sunday night, questioning what the role of a capacitance multiplier in an end stage PS might possibly be.

vac
Its role is to eat the ripple , in some way.

Of course a big cap is also needed at its output ,
let say 20000uF before and 10000uF after...
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Old 25th June 2012, 03:32 AM   #6388
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Originally Posted by DF96 View Post
Not necessarily. Motorola were mainly hard-headed engineers, so it is very likely that their rule of thumb was derived in the way I explained i.e. the criterion was not 'sound quality' but x% droop in 10 ms (or 8.33 ms in US). This could be regarded as a ripple calculation, but ripple calcs usually assume full power sine-wave; I assumed full power square wave.

If your amp has good PSRR (including low power supply IM) then it may be the case that there is nothing more to be said: low enough ripple guarantees good enough sound. When people try to explain anything further they usually quickly fall back on myths and legends rather than genuine explanations. Now it may be that we don't know how much hum is low enough, or how much ripple IM is low enough, given that we can't have zero of either unless we use battery power. 'Too low to measure' is meaningless, as you can always measure lower if you try a bit harder.
Exactly.

My rule of dumbs is to design power supply according to sag and ripples that I can tolerate on max RMS power infinitely long. The same rule applies to power dissipation, both in power supply and output components, passive and active. Hi-fi designers usually assume short period of time for peak power levels, so they downsize power supplies, heatsinks, output components, also they assume that all channels can't work at once on full power. However, it is wrong, that's why amps with bigger power supplies tend to sound better. But let me repeat, it is not because bigger is better. It is because not enough is worse than enough.
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Old 25th June 2012, 03:42 AM   #6389
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Sure, but here's a question for you:
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My rule of dumbs is to design power supply according to sag and ripples that I can tolerate on max RMS power infinitely long.
How do you determine what you can tolerate?
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Old 25th June 2012, 03:46 AM   #6390
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Originally Posted by Pano View Post
Sure, but here's a question for you:

How do you determine what you can tolerate?
It is design criterion. One of many other criteria. No rules of dumbs here. Well, almost no. You know that we deal with art translated to design by science.
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Last edited by Wavebourn; 25th June 2012 at 03:49 AM.
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