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Old 19th August 2012, 05:28 PM   #711
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Tom, you're not wrong, it is surprisingly complex. Barton has a detailed analysis in his book on rectifiers (IIRC), but ISTR he assumed a stiff supply, which is far from the case here.

theres nothing wrong with some sort of nonlinear curve-fit of the sim results

I think you'll find the transformer stuff is actually pretty easy, if you normalise the various transformer parameters to its nameplate ratings (Volts & VA).

all we really care about is:
- magnetising inductance (this is much more useful than mag current)
- primary & secondary Resistances
- primary & secondary Leakage Inductances

we could probably reflect the leakage inductance & winding resistance over to the secondary, and ignore the magnetising inductance entirely (as long as the transformer isnt driven too far into saturation - which gives very "peaky" magnetising current (which is just the unloaded primary current)

choose P_base = xfmr VA rating, V_base = secondary voltage rating, w_base = 2pi*Fac

you can then define Z_base = V_base^2/P_base, L_base = Z_base/w_base.

then normalise the xfmr parameters to these base values (aka Per-Unitising):

VA_pu = VA/P_base = 1 (by definition)
Vsec_pu = Vsec/V_base = 1 (by definition)
w_pu = 2*pi*Fac/w_base = 1 (by definition)

Ls_leak_pu = (effective) secondary leakage inductance/L_base < 1 (typ < 10%)

Rs_pu = (effective) secondary resistance/Z_base << 1 (typ < 5%)

[assuming you reflect leakage & resistance to the secondary. If not you need to normalise a few more parameters]

then you can "create" any arbitrary transformer by de-normalising with the desired VA & Voltage ratings.

Voila, any transformer you like, having the same design characteristics of the original.

likewise you can fiddle with the PU resistance & leakage parameters and create new transformers

Audio mains transformers might be a bit different, but the PU leakage and resistance ought to have similar ranges (a bunch of different xfmr measurements would certainly help though).

Last edited by Terry Given; 19th August 2012 at 05:30 PM.
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Old 19th August 2012, 06:02 PM   #712
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Quote:
Originally Posted by magnoman View Post
Already done that as posted earlier, it appears not "low" enough for all.

Hope this helps
-Antonio
Can you give a copy of that posting?
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Old 19th August 2012, 06:12 PM   #713
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Terry Given,

we could probably reflect the leakage inductance & winding resistance over to the secondary, and ignore the magnetising inductance entirely (as long as the transformer isnt driven too far into saturation - which gives very "peaky" magnetising current (which is just the unloaded primary current)

Does this hold true for both standard transformers wound on a steel core and for toroidal wound transformers. Is there a difference in the saturation of the two that change any of this information you presented or are they similar enough to leave that out of the saturation statement you have made?

Steven
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Old 19th August 2012, 06:36 PM   #714
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Quote:
Originally Posted by liching1952 View Post
For a 2x 100Watt amp you need at least a 600Watt transformer.
So for a 2 x 225W amp, as your Nak Stasis, you'd need a 1350VA transformer.

Truth is that the nominal power figure of the Nakamichi PA-7 is much higher, more like 300W in 8 ohm (the 225W number is for 0.05% THD)
2 times 300W would translate to a 1800VA transformer.
Reality is that the PA-7 runs on a single 700VA for two channels, totally inadequate by your own rule of dumb.

(Papa mentioned years ago that he merely got paid for the Stasis concept by Nakamichi, actual design of the power amps is by Nak. You could ask him yourself how high he ranks the PA-5 and PA-7 designs)
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Old 19th August 2012, 06:56 PM   #715
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Originally Posted by jacco vermeulen View Post
So for a 2 x 225W amp, as your Nak Stasis, you'd need a 1350VA transformer.

Truth is that the nominal power figure of the Nakamichi PA-7 is much higher, more like 300W in 8 ohm (the 225W number is for 0.05% THD)
2 times 300W would translate to a 1800VA transformer.
Reality is that the PA-7 runs on a single 700VA for two channels, totally inadequate by your own rule of dumb.

(Papa mentioned years ago that he merely got paid for the Stasis concept by Nakamichi, actual design of the power amps is by Nak. You could ask him yourself how high he ranks the PA-5 and PA-7 designs)
I know that the transformer of the Nak is inadequad for continous full power use. Thats ok for me. However a toroidal can easily deliver much more power then rated for some time.
Last time you show me a picture of a Swiss build amp which costs 50k with a 1kva transformer. In the picture however is only seen a small transformer not more then 200va or so.

Last edited by liching1952; 19th August 2012 at 07:00 PM.
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Old 19th August 2012, 07:03 PM   #716
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The Orpheus lines read : 1050VA total power supply transformers.

The 1050VA total includes the little toroidal you saw on the pics, plus two 500VA toroidals under the black steel box in the middle of the amp.

For a monaural power amp : 1050VA divided by 350W (1% THD, 8 ohm) is 3 times the nominal power rating.
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Old 19th August 2012, 07:11 PM   #717
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Quote:
Originally Posted by jacco vermeulen View Post
The Orpheus lines read : 1050VA total power supply transformers.

The 1050VA total includes the little toroidal you saw on the pics, plus two 500VA toroidals under the black steel box in the middle of the amp.

For a monaural power amp : 1050VA divided by 350W (1% THD, 8 ohm) is 3 times the nominal power rating.
Are you sure? That there are 2 transformers under the black metal? There was at least 1 brand that put sand in it to make it heavy. How much capacity does they use? I only see 8 small capacitors. Its clever, very clever to let people pay 50k. Piega is also very clever to sell cheap boxes for big money.
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Old 19th August 2012, 07:25 PM   #718
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Quote:
Originally Posted by jacco vermeulen View Post
The Orpheus lines read : 1050VA total power supply transformers.

The 1050VA total includes the little toroidal you saw on the pics, plus two 500VA toroidals under the black steel box in the middle of the amp.

For a monaural power amp : 1050VA divided by 350W (1% THD, 8 ohm) is 3 times the nominal power rating.
350W at 8ohms needs about plus and minus 80 volt supply voltage. A 100 volt elco with the size as in the picture are approx. 1000uF. There are 8 so it means that there are only 4000uF Cap for each PSU. Not much for a 50k amp.
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Old 19th August 2012, 07:33 PM   #719
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Yeah, I'm sure, they even like low profile custom jobs.

Orpheus started as a sideshow by Anagram technologies in Geneva.
Those guys develop digital solutions they license to others, e.g audio stuff to Cambridge for CDP's, but also for computers, cell phones.
No need for them to screw customers.
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Old 19th August 2012, 07:39 PM   #720
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Quote:
Originally Posted by jacco vermeulen View Post
Yeah, I'm sure, they even like low profile custom jobs.

Orpheus started as a sideshow by Anagram technologies in Geneva.
Those guys develop digital solutions they license to others, e.g audio stuff to Cambridge for CDP's, but also for computers, cell phones.
No need for them to screw customers.
What is their claim for the high price? 5k is already too much for what I see.
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