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Old 8th February 2012, 01:00 PM   #2021
dvv is offline dvv  Serbia
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I would really love to know how you folks determine how much filter capacitance/energy storage you need in your projects.

As an example, take a preamplifier and a power amplifier rated at say 100W/8 Ohms nominally, but also to be very load tolerant.

And a special question for JC, since I know him to be involved in the indutry on the manfuacturing side (but also to anyone else who is in the same position) - how much of a factor in determining above is the price, if any?

Last edited by dvv; 8th February 2012 at 01:04 PM.
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Old 8th February 2012, 02:16 PM   #2022
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Quote:
Originally Posted by godfrey View Post
Getting back to SY's idea of using multiple Vrefs to get lower noise, it seems to me there's another way to do this. If the references are connected in parallel, instead of in series, then you get the desired noise reduction even in a voltage regulator with Thorsten's "magic cap" reducing the AC gain to unity.

E.g. The circuit below should be 6dB quieter than if a single reference were used, assuming the opamp and averaging resistors don't add too much noise themselves.
I affraid this setup would lead to more noise (6dB), since the 'signal', to speak in SY's words, does not increase, but you will have two times 3dB noise addition.

vac
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Old 8th February 2012, 03:29 PM   #2023
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Quote:
Originally Posted by dvv View Post
I would really love to know how you folks determine how much filter capacitance/energy storage you need in your projects.

As an example, take a preamplifier and a power amplifier rated at say 100W/8 Ohms nominally, but also to be very load tolerant.
I calculate by amplitude of ripples on max current on lower frequency.
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The Devil is not so terrible as his math model is!
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Old 8th February 2012, 03:38 PM   #2024
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I tend to use as much capacitance as we can afford in a specific design. I have found that even smaller amps (100W/ch or so) should have at least 20,000 uF/ch, to get the bass right. It is not so much ripple, but return impedance. For my larger amps, maybe 100,000 uF/ch, like the JC-1.
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Old 8th February 2012, 03:42 PM   #2025
dvv is offline dvv  Serbia
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Quote:
Originally Posted by Wavebourn View Post
I calculate by amplitude of ripples on max current on lower frequency.
Correct me if I'm wrong, but you are a total tube guy. I do believe that a power supply for an extremely load tolerant transistor amp will be rather different, wouldn't it?

I mean, using say two tubes capable of 5A each and three pairs of transistors each of which is capable of say 15A per channel is not quite the same thing. Or am I wrong?
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Old 8th February 2012, 04:01 PM   #2026
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Hi,

Quote:
Originally Posted by wahab View Post
My degree is in economical sciences
Really?

Well, mine are in Electronics and Business Information Systems and I'm a part qualified accountant...

Math matters heavily in all three.

Quote:
Originally Posted by wahab View Post
i can tell you that mathematical theories are quite relevant but the fact is that everything that doesnt support the cuurent system of wealth transfer by predation is systematically diabolized and downplayed.
Now that sounds just like what is happening in a "discussion forum" I am familiar with, where "everything that doesnt support the current ideas held by some influential people as to how things ought to work is systematically diabolised and downplayed.".

Nothing new under the sun.

Ciao T
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Old 8th February 2012, 04:30 PM   #2027
bcarso is offline bcarso  United States
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Quote:
Originally Posted by vacuphile View Post
I affraid this setup would lead to more noise (6dB), since the 'signal', to speak in SY's words, does not increase, but you will have two times 3dB noise addition.

vac
Godfrey is correct.

The resistors are effecting an average of the four uncorrelated noise sources. If you think of any one of them having an effect on the average at the n.i. input of the opamp, its noise voltage is attenuated by a factor of 4 by the other three resistors. So the net noise at the opamp is the root-sum-of-squares of each contribution; if each noise source has the same rms noise voltage, but of course uncorrelated, the net noise assuming some noise bandwidth is ({[En/4]^2}*4)^0.5 (the r.m.s. sum of four sources each attenuated by 4). So each term is (En^2)/16, four of them are (En^2)/4, and thus the total is the square root of (En^2)/4, or En/2.

Signal averaging has helped, as we would hope.

Brad
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Old 8th February 2012, 04:38 PM   #2028
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThorstenL View Post
Hi,

Really?

Well, mine are in Electronics and Business Information Systems and I'm a part qualified accountant...

Math matters heavily in all three.
Indeed.
My favourite math fast compilation was and still is the ingeenering
orientated memo by Bronstein and Semendiaev , wich you surely know
since you were in east Germany...

Quote:
Originally Posted by ThorstenL View Post
Now that sounds just like what is happening in a "discussion forum" I am familiar with, where "everything that doesnt support the current ideas held by some influential people as to how things ought to work is systematically diabolised and downplayed.".

Nothing new under the sun.

Ciao T
Obviously , economical theories cant be checked with experimentations
contrary to electromagnetical theories.

As such , it will be intenable to support a claim in electromagnetism
related matters without substanciating with measured effects in an
experience wich itself must be reproducible , that s why basically
the subjectivist position is branded more than doubtfull , as no valid
explanations are brought to explain effects that for the time seems
to be more the fruit of imagination than actual phenomenons.
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Old 8th February 2012, 04:44 PM   #2029
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I learned how to count on my toes. Gives me a great understanding of digital.
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Old 8th February 2012, 04:48 PM   #2030
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by dvv View Post
I would really love to know how you folks determine how much filter capacitance/energy storage you need in your projects.
Usually I look at the space available, subtract that needed for the signal circuits (usually not a lot), for way, way oversized mains transformers (e.g. 1,200VA wound on a 1,500VA C-Core for a 180WPC stereo amp) and fill the rest with cap's, usually set up as CRLC filter chain, with R & L designed into the PCB.

Quote:
Originally Posted by dvv View Post
As an example, take a preamplifier and a power amplifier rated at say 100W/8 Ohms nominally, but also to be very load tolerant.
My preamp's are generally passive, so a big fat nada for that.

But my old Arthur Loesch derived design had 6,800uF per channel AFTER the regulator, but that was for the Phono Stage, the line section was passive...

For the power amp in solid state, based on my current experiences, around 100,000uF, but I think more may still be better better. I would also still regulate the rails (yes, the output stage ones).

In my current "modify an Amp" project I'm quite limited by space, my demands on cap quality and all, this one will be around 150WPC/8R and each channel will get 4pcs 18,000uF Elna For Audio Cap's (they have measurable lower distortion than generic caps, lower microphonics too, incidentally) with 4pcs 1mH/10A Magnan/Iron core chokes plus two separate bridges (Hexfred Bridge Schottky enhanced), so 144,000uF in total...

I'd probably like more, but the transformer and heatsinks take a lot of space...

In Tube Amp's with around 430V rails and extrapolating from my 35 Watt'er I might put at least 2 * 2,200uF per channel and a massive 3H/0.4A Choke between the two.

In tube amp's I do however often use film cap's only and "finesse" circuitry instead.

Ciao T
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