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Old 15th January 2013, 08:08 PM   #8101
a.wayne is offline a.wayne  United States
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DVV, I was talking about your ears .....
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Old 15th January 2013, 08:10 PM   #8102
dvv is online now dvv  Serbia
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Originally Posted by a.wayne View Post
OK , change of pace .....

What determines the output impedance of an amplifier, the amt of outputs, source resistors? what's necessary to lower the output impedance as much as possible..

I'm thinking current drive like this ....

http://apogee-acoustics.de/download/..._Apogee_EN.pdf
The way I see it, to lower an amp's output impedance you need:

Multiple pairs at the output, as they are in a series/parallel connection;

Low value emitter resistors (implying larger bias currents, and given the low impedance of your speakers, you're likely to have that anyway);

As wide as you can manage open loop babndwidth, to keep it as even as you can across the audio band without too much global NFB (whatever that means);

Global NFB, paradoxically as much as possible, in clear contradiction with the above;

A low, low, low impedance power supply, which again, given the low impedance of your peakers, you're likely to need anyway if you're to get the prodigious amperes of current which you need, and

Obviously, a high quality, whopping big power transformer(s).

No big deal.

Might I suggest a direct link to the Hoover dam?
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Last edited by dvv; 15th January 2013 at 08:14 PM.
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Old 15th January 2013, 08:11 PM   #8103
dvv is online now dvv  Serbia
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DVV, I was talking about your ears .....
The hell you were, Wayne old buddy.
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Old 15th January 2013, 08:14 PM   #8104
a.wayne is offline a.wayne  United States
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Multiple caps or Just large values to lower PSU impedance ....

My goal ..

http://apogee-acoustics.de/en/Amplifier.html
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Old 15th January 2013, 08:38 PM   #8105
dvv is online now dvv  Serbia
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Originally Posted by a.wayne View Post
Multiple caps or Just large values to lower PSU impedance ....
Well, I think it depends on the capacitors. Sometimes, a say 22,000 uF cap has a lower output impedance of two of the 10,000 uF caps in parallel.

In principle, I like a "capacitor cascade", meaning a say 22,000 uF cap in parallel with 10,000 uF in parallel with 4,700 uF. Theoretically, assuming they are of the same make and model, larger caps filter better but are slower to charge up, smaller ones don't filter as well, but are naturally faster. When you add it all up, you have 36,700 uF per supply line, or 73,400 uF per channel.

What comes after that cascade you know from the most worthwhile work of our German colleague right here, just look back (100uF // 3.3 uF foil // 100 nF foil).
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Old 15th January 2013, 08:42 PM   #8106
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You know, many, many years ago I read a text in an audio magazine (no Internet way back then), about a US company which built its power supplies with numerous 680 uF caps.

I remember it only because the text author asked the engineers why 680 uF and why so many?

They said they had no idea of how and why, but found by trial and error that this particular cap was the best compromise between size and sound quality.

They used, approximately from a photo, around 24 or so of these caps in parallel per supply line.

Not having tried it myself, I cannot comment.
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Old 15th January 2013, 09:33 PM   #8107
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Originally Posted by DF96 View Post
Bass equalisation and loudness controls may do roughly the same thing (or not - 12dB/octave vs 6dB/octave?) but they do it for completely different reasons. One compensates for speaker response; the other compensates for ear response.
First loudness control was found in German radio receivers, to EQ speaker response. Then Americans second-guessed it and decided that it was based on F-M curves for EQ of ear - response, as the result the public now needs an EQ of brain-response, even on this forum.
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Old 15th January 2013, 10:34 PM   #8108
a.wayne is offline a.wayne  United States
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lend me yours ....
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Old 16th January 2013, 02:04 AM   #8109
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Originally Posted by a.wayne View Post
lend me yours ....
It needs to be fine-tuned, I am working on my own curve adjustment. So far so good, but still could be better.
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Old 16th January 2013, 06:41 AM   #8110
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Originally Posted by a.wayne View Post
Multiple caps or Just large values to lower PSU impedance ....

My goal ..

Audiophile Manufaktur | Amplifier
You need to have an array of many caps, on a two-sided PCB with unbroken planes of copper on both sides (drill holes only, with denuded hole edges on one side of pcb, for cap leads). You'll have one of those as each power rail.

With a 10x10 array of 1000 uF electrolytics, and a 1mm thick FR4 board, you should be able to get the total inductance seen at the load down to less than 1 nH; possibly 0.5 nH.

The illustrious Terry Given, electromagneticist extraordinaire, presented a prototype, with actual network analyzer measurements, and design guidelines, right here on diyaudio.

I created a set of links directly to his posts about it, so people wouldn't have to search for them individually, and wouldn't miss any, which I put at the bottom of the post at:

LM3886 component selection

NOTE that in the first link, Terry meant to say RADIAL instead of AXIAL.

Enjoy,

Tom
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