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Old 8th August 2012, 09:25 PM   #411
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Nice. Lets see for the other caps.
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Old 8th August 2012, 09:27 PM   #412
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Quote:
Originally Posted by Nico Ras View Post
You may just have a good opportunity here Harrison.
Give each of these gentlemen one completed amplifier with exact same components then allow each of these gurus to paste on his KICK-*** power supply.

Now rotate to the left and each person gets his colleagues amp to listen and measure, then one final rotation - thereafter let them report their findings both objective and subjective..

The resultant is the best of the best rules of thumb compared objectively and will conclude this thread
With more funding , this is possible. as is since the BOM is up and standardized, they may be able to assemble accurately.
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Old 8th August 2012, 09:56 PM   #413
gootee is offline gootee  United States
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Quote:
Originally Posted by dry joint View Post
Rather than buying a lot of pricey caps to a formula, try seperate PSUs with transformers for each channel and even seperate PSUs for the output stage and input+VAS stage of a given channel. I'd say dimishing returns kicks in more quickly for more caps than it does seperating the PSUs. A secondly, cheap amp boards with highly expensive caps just seems dumb.
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Its proportionally cheaper to up the transformer VA than capacitance. Online you'll find people doing classic class A amps with capacitance in the 100,000s UF with a single transformer. If mono blocks are better due to the seperation of PSU and signals, then to me thats the direction to go in, to which rules of thumb and technical analysis can then be applied.
Maybe the formula will end up telling us it's better to buy just a few cheap caps. ;-)

Your opinions may be correct. We can't say, yet. But here in Nico's thread we are trying to actually determine what tends to be better and what does not, and possibly even uncover a "formula" or two for later, so we don't have to do all of this work again every time, or just rely on opinions and hearsay. But suggestions for what to try could be useful. Anyway, it's been a slow process so please be patient.

Cheers,

Tom

Last edited by gootee; 8th August 2012 at 10:20 PM.
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Old 8th August 2012, 10:34 PM   #414
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Originally Posted by gootee View Post

But one key to "keeping it up" might be the proper use of "decoupling capacitance"

The main criterion, still, for me at least, is "accuracy of reproduction".
If you mean "decoupling capacitance" to mean additional reservoir capacitance placed local to the output transistors, it will help with accuracy of reproduction due to minimizing the effects of reservoir ESR and the inductance of the supply leads. But the rails will still sag, a little slower due to the added capacitance, but to the same level as without for the same output power.
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Old 8th August 2012, 10:37 PM   #415
AndrewT is offline AndrewT  Scotland
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I am still not understanding what is happening inside that transformer model.
How can a 25Vac transformer give 73Vdc, inless the regulation is enormous? We know that transformers used for power amplifier PSUs have a regulation between 3% and 10%, that limits the off load voltage.
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Old 8th August 2012, 11:03 PM   #416
fas42 is offline fas42  Australia
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Quote:
Originally Posted by AndrewT View Post
I am still not understanding what is happening inside that transformer model.
How can a 25Vac transformer give 73Vdc, inless the regulation is enormous? We know that transformers used for power amplifier PSUs have a regulation between 3% and 10%, that limits the off load voltage.
Because, as Tom stated, the sim has been fudged, the transformer is actually working at well above its design parameters, eg, the primary voltage. This has only a marginal effect on getting reasonable results in the sim, but if you want to play completely fair simply add another, same spec'd, transformer in each leg and wire the secondaries in series. Then it's all ridgey didge, and doesn't cost any moolah, either ...

Frank
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Old 8th August 2012, 11:19 PM   #417
gootee is offline gootee  United States
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Welcome back, Andrew! We really missed you!

I don't know what makes transformers have regulation. But the model is probably way too simple to account for that.

But the way a 25-volt-output transformer gives 71 Volts out is for it to get about 342 Volts p-p as input. It's just a simple matter of turns ratio. Yes, it was not meant for this job. Yes, I used it only because it was convenient and I thought it would be better than an ideal voltage source and an ideal transformer model.

Or are you wondering how I am getting 71 Volts when I only put in 321 Volts (instead of 342)?

If someone looks at the transformer model schematic (in post 400 of this thread, which is at http://www.diyaudio.com/forums/solid...ml#post3119281 ) and tells me what component values to change to make it more suitable for higher current and voltage than the one the measurements came from, I can change it with just a few mouse and keyboard clicks.

Better yet, if anyone has a variac and a suitable transformer to measure, it only takes a few minutes.

Cheers,

Tom

Last edited by gootee; 8th August 2012 at 11:35 PM.
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Old 8th August 2012, 11:46 PM   #418
fas42 is offline fas42  Australia
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Like this:

AltTrans.gif

Trouble is, now have double the resistance in the secondary windings feeding the rectifier, so the sag is even worse at full load, down to around 53V. Which is why you need a transformer with sufficient VA rating, giving better regulation, more cost! Or, use switching mode supplies, etc.

Frank

Last edited by fas42; 8th August 2012 at 11:48 PM.
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Old 9th August 2012, 12:18 AM   #419
fas42 is offline fas42  Australia
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Quote:
Originally Posted by gootee View Post
To properly-implement the error plotting, I had to try to remove the other sources of error, i.e. those that were always present due to the amplifier itself. So I replaced the amplifier output stage with an idealized amplifier made from spice Behavioral Current Sources (B-sources). I was able to use the u() "unit step" function to provide a "polarity" factor that is 1 when the input voltage is on one side of zero, and is zero otherwise. That way, I could make perfect push-pull current sources, driven by equations.
Just a cautionary thought, Tom ... my belief is that real circuitry should be used to load the PS, otherwise one's thinking can possibly be led down an unnecessarily torturous detour. Ultimately, what one comes up with in terms of results has to relate to real, on the bench, bits of circuitry, because that's what the whole exercise is about ...

Cheers,
Frank
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Old 9th August 2012, 12:40 AM   #420
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Frank & Tom:

If you remove the entire amplifier & modulated load from the sim, and replace with a resistor, you will see the droop caused by the transformer "regulation" - which will be mostly due to the leakage inductance and the narrow conduction angle. I'd also look carefully at the rectifier model as well - its probably fine, but there are, for example, 10BQ100 spice models with 100R slope resistance (I found them the hard way)
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