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Old 14th September 2012, 10:09 AM   #1141
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Esperado View Post
...But the power supply.
Eww, that is one of the most important part of an amplifier, especially this topology
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Old 14th September 2012, 10:20 AM   #1142
Jay is offline Jay  Indonesia
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Originally Posted by mikelm View Post
. . . and I think my new supply will be a mix of chokes & cap multiplier
Can you teach me how to design a proper choke supply? I had a feeling that it should be done through measurement, no?

My experience is that we cannot just throw any values and hope nothing to loose. Actually wrong values will degrade the sound (because we increased the impedance already). Trial and error is very tedious.

Say I have some coils that I can use for this purpose. I have the tool to measure the inductance. Then I need the correct capacitance, right? If I do it simply using LTSpice, what parameters that I need to watch out in order to know that the filter will work? Same as general solid state power supply design?
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Old 14th September 2012, 11:08 AM   #1143
AndrewT is offline AndrewT  Scotland
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choke value and current draw are the inter-related factors. Not choke & capacitance.
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Old 14th September 2012, 11:22 AM   #1144
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Originally Posted by AndrewT View Post
choke value and current draw are the inter-related factors. Not choke & capacitance.
Then I cannot just pick any off-the-shelf choke?
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Old 14th September 2012, 12:06 PM   #1145
mikelm is offline mikelm  England
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Hi Jay,

I began my experiment with choke regulation by going for simple full choke regulation ( Luddite tendencies ) but now I am thinking of letting the chokes deal with only VHF and letting more conventional regulation deal with the audio frequencies. I think this will give best overall AC & DC regulation but having said that I am very satisfied with the subjective performance of full choke regulation. I recommend chokes in all power lines from the transformers.

I always design my supplies in spice but didn't have much success with transformers & inductors in LT spice.

Two things have to be considered - how the supply behaves in use & how it behaves during turn on. These two factors can pull in opposite directions and so we have to balance between them.

If the overall DC resistance of transformer & choke is too low the supply can ring & go over voltage during turn on. If there is too much DC resistance the voltage will drop too much during loud passages. The tendency for ringing can be reduced by having the cap after the choke larger than cap before the choke.

This is a reasonable starting point for Full choke regulation:

http://www.diyaudio.com/forums/attac...r-p1020970.jpg

each coil perhaps 0.1R

I use the secondaries of regular EI transformers as chokes and they work just fine.
The DC polarization will mean the effective inductance is less than measured inductance - but you can make allowances for that.

But if you would like to PM me your detailed criteria I will check out something in spice and optimize it for you.

Last edited by mikelm; 14th September 2012 at 12:11 PM.
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Old 14th September 2012, 01:33 PM   #1146
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by mikelm View Post
I always design my supplies in spice but didn't have much success with transformers & inductors in LT spice..
That's in line with my intuition.

Quote:
Originally Posted by mikelm View Post
If the overall DC resistance of transformer & choke is too low the supply can ring & go over voltage during turn on. If there is too much DC resistance the voltage will drop too much during loud passages. The tendency for ringing can be reduced by having the cap after the choke larger than cap before the choke.
Okay, noted. I'm not sure tho that for practical reason the DCR can be too low. Aren't low DCR choke expensive. I have seen and used low DCR air-core but that is I think overkill (if proven very effective, no problem tho).


Quote:
Originally Posted by mikelm View Post
This is a reasonable starting point for Full choke regulation:

http://www.diyaudio.com/forums/attac...r-p1020970.jpg.
Thanks, I will read that later. I have tried many references in the past, but couldn't learn anything and just took the shortcut: trial and error by ears

Quote:
Originally Posted by mikelm View Post
I use the secondaries of regular EI transformers as chokes and they work just fine.
I have many big choke transformers that I want to use. If necessary I can use audio output transformers (very big tho).

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Originally Posted by mikelm View Post
But if you would like to PM me your detailed criteria I will check out something in spice and optimize it for you.
Thank you very much but I don't know yet where to start (and may still be a long way to go). I have noted your approach to separate system ground from transformer secondary with chokes. I have done the same thing but there is one other approach that I like to do. It is more like EMI filter. I install the CLC directly after the secondary, so before the rectifiers.

The other CLC (with big caps) I used to do is after the rectifier, usually before a cap multiplier. Class-A amps of course, like my TSSA.
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Old 14th September 2012, 01:44 PM   #1147
mikelm is offline mikelm  England
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If you put the chokes before the diodes the resultant PSU internal impedance is very high so this kind of regulation is only suitable full class A which needs constant current.

Chokes after the diodes is much lower internal impedance so is suitable for Class AB & Class A.
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Old 14th September 2012, 02:40 PM   #1148
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Quote:
Originally Posted by mikelm View Post
Two things have to be considered - how the supply behaves in use & how it behaves during turn on. .
... That you can reduce to one, adding a soft start circuit.
One of the rare things i agree with audiophiles blind beliefs is the benefit to overkill the PSU current.
My 1100VA transformer +big caps are affraying, if directly plugged in sector: The Lights flicker in my home, and the noise in the transformer terrorize my dog
With soft start, everything runs smoothly, and i can hear my caps's thanks and look at their smiles during much more years.
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Old 14th September 2012, 02:59 PM   #1149
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Christophe, your bias spreader in your CFB Crescendo is 220 Ohm and when you bias the output correctly it will be even less. Your cascode VAS has a current output and the bias spreader will convert that into a voltage. In that sense you have a voltage drive due to Ohms law U = I x R so you could say you make an I/U conversion and current and voltage is interchangeable due to that formula as long as the VAS does not go out of steam current wise. The bias spreader resistor then forms a low pass with the input capaciatnce of the output stage. The lower the driving resistance the better you control the input capacitance of you MosFet output stage. On the other hand you have to roll off the open loop gain somewhere. In my preamp that is also a small lateral mosfet current feedback power amp with 2W class A i simply use the gate stoppers for that to form a low pass. The gate stoppers are arranged in such a way that the gate stopper to the P-Channel is somewhat smaller in value. I have not tried a miller cap or other options but it works just fine.
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Old 14th September 2012, 03:09 PM   #1150
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To L. C., (Please comment ?) I'd like to see an improved SSA BIGBT HP's PSU for the following reasons:
I prefer a single power supply (when it is possible) for the both (or more) channels (as opposite to audiophiles) for the stereo localization (i explained it earlier).
If it is impossible, by example in my muti-ways active speakers, i prefer to use the same supply for all the channels (coherency of bass and treeble during big transients, same player shoot again).
For all those reason, i will prefer a PSU separated from the amp board.

Unless the rails are so perfectly regulated or stabilized, that you can forget about that, and enjoy the short wires low self.

Even here, i would prefer a single transformer, preferably a C core one with shield between the primaries and secondaries coils, to get no capacitive coupling between them , in order to minimize hf leakages between them.

I always use a ferrite on the power cord, (in fact on all the cords, including signal) and a HF rejection filter in the AC plug too.
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