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Old 5th August 2013, 08:15 AM   #1241
Bonsai is offline Bonsai  Taiwan
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I thought I gave technical reasons why your assumptions were not correct.

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Old 5th August 2013, 08:36 AM   #1242
mcd99uk is offline mcd99uk  United Kingdom
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I'm sticking my neck out here as a beginner in these things.

If slew rate is related to the speed of the amplifier. The faster an amp the higher the ULGF. The higher the ULGF the more available feedback at high frequencies. Therefore there is more THD reduction due to feedback. This leaves the amps original linearity as a factor. This assumes the compensation schemes in each amp is of the same order.

As CFB amps and VFB amps can share the same VAS / Output topologies other than the front end. Can we not boil this down to CFB front ends vs LTP front ends?

Please forgive me if I am completely wrong.
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Old 5th August 2013, 08:43 AM   #1243
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Originally Posted by Bonsai View Post
I thought I gave technical reasons why your assumptions were not correct.

I didn't quote you? You weren't the one in a sudden mentioning listening tests?
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Old 5th August 2013, 08:55 AM   #1244
banat is offline banat  Serbia
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Originally Posted by dvv View Post
And rightly so.

By now, you should have realized that the forum you are talking about has a couple of people who:

1. Have learnt how to connectect two semiconductors without explosions, which makes then instant geniuses,

2. The name of the game is FET - if it ain't a FET, no way it can ever work properly,

3. Nelson Pass is God and nobody else matters, or even exists,

4, The owner and head honcho is a serviceman, who believes that a voltage regulator built around a MOSFET really can't "sound" good unless it is preceeded by a Darlington BD TO-220 device, etc.

Therefore, the initial mistake is yours, you assumed people would even bother to listen.

I understand that one of the few people who really knew their stuff there, Sipi, has also left the forum for more or less the same reasons you encountered. I was never really there, just dropped in a few times, but made sure I discussed nothing seriously, being a BJT guy I knew I'd end up being burned at the stake for blaspheming.
DVV

As member of local DIY Audio RS site must say that all of your claims against DIY people from DIY Audio RS site is baseless , very malicious and wrong !!!
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Old 5th August 2013, 09:58 AM   #1245
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by mcd99uk View Post
I'm sticking my neck out here as a beginner in these things.

If slew rate is related to the speed of the amplifier. The faster an amp the higher the ULGF. The higher the ULGF the more available feedback at high frequencies. Therefore there is more THD reduction due to feedback. This leaves the amps original linearity as a factor. This assumes the compensation schemes in each amp is of the same order.

As CFB amps and VFB amps can share the same VAS / Output topologies other than the front end. Can we not boil this down to CFB front ends vs LTP front ends?

Please forgive me if I am completely wrong.
Slew rate and ULGF can be varied independently in VFA - you can have very high SR's and still have a ULGF of 1 MHz for example. Typically, you would set ULGF to between 1 and about 1.5 MHz in a VAF. Much higher than this and phase shifts in the output stage make it difficult to make the amp stable. Similarly, the -3dB open loop corner frequency in a VAF can be set to a very low frequncy (few Hz) and still produce a very fast, high SR amplifier. In power amplifiers, the slew rate can be independently set by adjusting the LTP tail current in MC designs; MIC alows even more freedom because the feedback capacitor (which sets the front end ULGF) is driven from the TIS, so the tail current does not set the slew rate.

You can experiment with LTspice to see these relationships and how they work.
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Old 5th August 2013, 10:10 AM   #1246
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Originally Posted by nigel pearson View Post
Did anyone try the FET/Bipolar CfbP where FET comes first ? Easy bias and good linearity I suspect ? Exicon + Motorola ?
Did-you mean this Simple Symetrical Amplifier ?

About distortion of LTP in VFB, let see what happens in a simple way.
Let say the amp is open loop gain of 100, a closed loop gain of 1, and the LTP with a gain of 1.
Signal = 'S' and distortion of each side of the LTP= 'd'.

After amplification by the positive input of the LTP, the signal will be S+d.
After the 100X amplification of the following stages (considered as perfect) and feedback bridge attenuation, the feedback signal applied to the - input will be:
0.99 (S+d).

Once subtracted: S+d -0.99(S-d)= 0.01S+0.01d witch is the final signal. Amplified by the gain of the amp. result at the output in closed loop will be: S+d.

This is for the positive input and a perfect feedback path.

Now, let see what happens with the distortion added by the inverting input.
With a signal 'T'. similar to S.
The inverting input invert the previous numbers:
-(d- 0.99d)= -0.01d added at the collector.

So the final result is: S+d-(0.99(S+d))=0.01S+0.01d-0.01d = S

DS was right on this point, and i was wrong. i have to apologize. Shame on me.
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Old 5th August 2013, 10:12 AM   #1247
mcd99uk is offline mcd99uk  United Kingdom
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I recall a short discussion in one of my threads where much higher ULGFs were discussed. 40Mhz was seen as a reasonable upper limit. Self's book was used as a reference. Is this only true for CFAs? I'm thinking 1Mhz ULGF is a little low.

I understand the idea of "excess phase" from the output stage. But would this not be consistent for both VFA and CFA amps?

My understanding is that CFB front ends can drive much higher currents than LTPs and this would account for the higher slew rates for a given miller compensation scheme.

I will experiment in spice as you suggest to see the relationships you mention above. They challenge my belief system so need to be investigated.
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Old 5th August 2013, 10:14 AM   #1248
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Originally Posted by banat View Post
DVV

As member of local DIY Audio RS site must say that all of your claims against DIY people from DIY Audio RS site is baseless , very malicious and wrong !!!
Please excuse my comment for being incomplete. I was ridiculed at diyaudioproject.eu, not on diyaudio.rs.
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Old 5th August 2013, 10:30 AM   #1249
dvv is offline dvv  Serbia
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Originally Posted by banat View Post
DVV

As member of local DIY Audio RS site must say that all of your claims against DIY people from DIY Audio RS site is baseless , very malicious and wrong !!!
You have the same right to your opinion as I have to mine.

I wonder then why some of the very old members, such as Sipi, have left the forum, not to even mention several very good people who know of it, but are not interested in joining it.

Why the management allows some people to behave in a most uncivilized way is a mystery to me.

Ultimately, this is to the detrement of quite a few members of the silent majority, who are probably quite nice people, but it's the bad boys who are always the loudest. And the best organized.

And this is all I have to say about it, I won't post anything else on this subject.
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Old 5th August 2013, 10:31 AM   #1250
dvv is offline dvv  Serbia
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Originally Posted by ivanlukic View Post
Please excuse my comment for being incomplete. I was ridiculed at diyaudioproject.eu, not on diyaudio.rs.
Quite a difference, isn't it?

Not that it changes much ...
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