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Old 30th June 2012, 08:14 PM   #2651
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Originally Posted by Lazy Cat View Post
New PCB will make things much easier now ...
Hi, LC, beautiful, wonderful realization, as habit.
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Originally Posted by Jay View Post
How about capacitor quality issue? I don't know why, I don't like the sound of a big cap in the feedback loop. If it is high ESR problem, I think theoretically it doesn't matter? 1000uF is not enough for 1K/35R but 2200uF. And once I forgot to replace back the cap with voltage source and I saw horrible simulation result?
I have tried to use opamp to eliminate the cap but it seems that opamps do not work in this circuit?
I was talking about parasitic caps to ground.
Well, If you are talking about high pass filter in the feedback loop to reduce DC shift, there is no reason why op amps did not work, as long you can find one with enough current capability (not so easy with low FB impedance) and, of course; low DC error. You can use too discrete transistors, or add a low impedance current amplification stage after the CI ?

I do not use active DC regulation, here, because i'm lazy, and never found any audible problem with good electrolytics, (not talking about their life duration), and because simple is beautiful. Why don't you try to parallel lighter ones (equal values) ?

If any issue with electrolytic caps, it will occur at high frequencies, and, as you said it is not so critical, here ? Proof ? The serial self of the electrolitic caps is acting like a cap in parallel with the FB resistance. Right ? And, on my amp, even with such a chemical cap i was obliged to add a little parallel cap with the FB resistance to smooth a little peak near the high extremity of the bandwidth.

I'm not sure if, for that kind of question, we can rely on simulations. too much parasitics elements, due to cabling, differences between components etc.. I had used stock electrolytic caps in real life. When i short circuit them, i don't hear such a difference in the sound on my system.

Last, if your amp is DC stable enough for DC shift don't reach a dangerous level: you can afford it without DC regulation, as L.C. did ?
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Old 1st July 2012, 01:49 AM   #2652
Jay is offline Jay  Indonesia
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Originally Posted by wahab View Post
Literaly translated , it s "counter reaction" , that is , not FB but NFB..
Oh, so that makes sense now
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Old 1st July 2012, 02:07 AM   #2653
Jay is offline Jay  Indonesia
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Originally Posted by Esperado View Post
never found any audible problem with good electrolytics, (not talking about their life duration), and because simple is beautiful. Why don't you try to parallel lighter ones (equal values) ?
Actually I'm not sure if I have a big problem with the cap in the FB loop (even tho they are audible). It is just too big that I cannot use high quality cap and short path as I usually do. I use that axial ERO cap. Slightly to big for 2x1000uF and 1XMKP on top of each other.

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Originally Posted by Esperado View Post
Last, if your amp is DC stable enough for DC shift don't reach a dangerous level: you can afford it without DC regulation, as L.C. did ?
Ah, yes. I prefer this option than using opamp. Thanks to remind me, I will try this approach tho I have still to prepare the space for the cap on the PCB. I just wasn't sure if it was save due to possible issues external to the amp itself, like RCA cable plugged out while music is on, and the like.
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Old 1st July 2012, 10:11 AM   #2654
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Originally Posted by Jay View Post
Actually I'm not sure if I have a big problem with the cap in the FB loop (even tho they are audible). It is just too big that I cannot use high quality cap and short path as I usually do. I use that axial ERO cap. Slightly to big for 2x1000uF and 1XMKP on top of each other.
New CSA PCB has 28 transistors (bipolar, fet, mosfet), 7 TL zeners, separate power supplies for input and output, elcos in feedback GND connection, which can be disabled if prefered. All functional parts of each stage were tested separately and will be tested together at the first channel assembly in seeking to find optimum current-components values for complete front end. I will start with CCS-s, input stage, VAS and finally all together as voltage amplifier. Front end itself counts 22 transistors and 7 TL zeners which clearly indicates complexity but also opportunity to squeeze out maximum performance from all the stages. I am quite sure to know what am I looking for so the goal is well defined, the path to get there will be something like action road movie.
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Old 1st July 2012, 11:14 AM   #2655
Jay is offline Jay  Indonesia
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I am quite sure to know what am I looking for so the goal is well defined, the path to get there will be something like action road movie.
Is very good bass included in the goal definition? I hope so
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Old 1st July 2012, 11:34 AM   #2656
wahab is offline wahab  Algeria
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Originally Posted by Esperado View Post


In a so called "curent feed back", the CR is mixed with the original strait at the output of the input stage. Without any additional pole*. That makes all the difference.
The only difference wich yield an advantage is speed , for all the rest ,
particularly linearity , a VFB do better....


Quote:
Originally Posted by Lazy Cat View Post
Front end itself counts 22 transistors and 7 TL zeners which clearly indicates complexity but also opportunity to squeeze out maximum performance from all the stages.
A chain resistance is the one of its weakest element , as such ,
it is useless to improve intermediary stages since the input stage
will inherently be the one that decide for the perfs , at least in
this kind of amp.

Remember that NFB provided by a following stage cant cancel
non linearity of a preceding stage...

Said shortly , the available gain of a VAS used for NFB
cant correct preceding stages in the global loop.
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Old 1st July 2012, 11:47 AM   #2657
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The only difference wich yield an advantage is speed , for all the rest ,
particularly linearity , a VFB do better....
Could not dissagree more. I really don't have time to explain the things that were already said in this thread before. The only thing VFB is better are DC conditions, but that we do not hear through our speakers. You should make one medium complex SSA and you'll get an impression of what we talk about here. LTP's are sounding dull compared to CFB.


Quote:
Originally Posted by wahab View Post
A chain resistance is the one of its weakest element , as such , it is useless to improve intermediary stages since the input stage
will inherently be the one that decide for the perfs , at least in
this kind of amp.
Less talk more try. Besides at CSA's new input stage +20 dB gain is linear (-0,5 dB measured) to 3 MHz.

Last edited by Lazy Cat; 1st July 2012 at 11:53 AM.
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Old 1st July 2012, 11:52 AM   #2658
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Originally Posted by Jay View Post
Is very good bass included in the goal definition? I hope so
When listened SSA with Ktema speakers, bass was for the first time integrated with the rest of the spectrum, superbly controlled. Other amps make this speakers looks like they have separate subwoofers with a little delay on lower notes.

Also at Piegas bass was perfect, as confirmed by very experienced recording-mastering engineer using the system for audiophile HR/CD production.

Last edited by Lazy Cat; 1st July 2012 at 11:54 AM.
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Old 1st July 2012, 12:02 PM   #2659
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Originally Posted by wahab View Post
[snip]Remember that NFB provided by a following stage cant cancel
non linearity of a preceding stage...

Said shortly , the available gain of a VAS used for NFB
cant correct preceding stages in the global loop.
Apart from the fact that a stage doesn't 'provide NFB' this is incorrect.

If at any place within an nfb loop you increase gain you get a larger difference between open loop gain and closed loop gain.
And it is the difference between these two that determines how well the nfb improves the performance of the whole amp.
So in a power amp, with nfb from output to input, you increase the Vas gain, that definitely is of benefit to the amp performance.

jan didden
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Old 1st July 2012, 12:13 PM   #2660
wahab is offline wahab  Algeria
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Originally Posted by janneman View Post
Apart from the fact that a stage doesn't 'provide NFB' this is incorrect.

If at any place within an nfb loop you increase gain you get a larger difference between open loop gain and closed loop gain.
And it is the difference between these two that determines how well the nfb improves the performance of the whole amp.
So in a power amp, with nfb from output to input, you increase the Vas gain, that definitely is of benefit to the amp performance.

jan didden

Jan , that s not correct , mind you...

When you increase the gain of the VAS , the added NFB can
reduce distorsion of the VAS as well as the one of the following stages ,
but it wont reduce distorsion from the preceding stage , let say the IPS ,
other than due to byproducts of this higher VAS gain , i.e , the IPS
will be less loaded since it will provide less output voltage to drive the VAS.

Edit : The IPS is not enclosed in the gain loop of the VAS ,
while the latter is enclosed in the IPS gain loop , all this
seen from a GNFB point of view.

Last edited by wahab; 1st July 2012 at 12:23 PM.
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