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Old 7th April 2012, 07:48 PM   #22111
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi Brad,

Quote:
Originally Posted by bcarso View Post
Well I got self-snookered into looking at this, my own damn fault.
Sure, it will work. But do we really need the CM?

If we must have high impedance loads (which I'd question), there are ways that do not carry DC stability penalties (bootstrap instead of CM).

Ciao T
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Old 7th April 2012, 07:51 PM   #22112
bcarso is offline bcarso  United States
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Quote:
Originally Posted by ThorstenL View Post
Hi Brad,



Sure, it will work. But do we really need the CM?

If we must have high impedance loads (which I'd question), there are ways that do not carry DC stability penalties (bootstrap instead of CM).

Ciao T
No, we don't. That's why I say I was snookered. The mountain I didn't see the point to climbing kept leering at me in my troubled sleep.
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Old 7th April 2012, 08:35 PM   #22113
KBK is offline KBK  Canada
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Quote:
Originally Posted by VladimirK View Post
Here is the relative variation of the impedance modulus of various resistors with frequency. The vertical axis is |Z(f)| / |Z(200Hz)|, total span of the axis is +-2%.
Even at medium frequencies there are some ripples of impedance (possibly some electrostrictive deformation).
These results are taken at the same 1V RMS test sine signal. Impedance will also vary by the test signal amplitude variation. I am afraid to imagine what goes on with a given resistor when unstable schematics usually oscillate (10...100MHz).

Constructional aspects into higher impedances (resistor value) at higher frequencies creating capacitive flashover. ie the complex LCR of the materials comes notably into play at the higher 'resistor value impedances'.

IMO, high delta or high V/s will also achieve the same effect. (hopefully that's a 'duh!' statement)(high V differential across the given resistor will also encourage the condition - more 'duh!')

There are ways to deal with this.

Last edited by KBK; 7th April 2012 at 08:39 PM.
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Old 7th April 2012, 08:46 PM   #22114
KBK is offline KBK  Canada
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Quote:
Originally Posted by scott wurcer View Post
Still would benefit from cascode in output. These circuits get so linear that the Vas non-linear Ccb can add even up to 20dB to the thirds at 10kHz

BTW the avatar is "woman ball player", the Mayan version of "ball" had unfortunate consequences for the loser.

Serious game. decaptiation and...thus.... 'new ball' (IIRC). Until the summer heat sets in, that is.

Like backwoods teenagers with their partridge feet they take to school to scare the girls (by pulling on the tendons and making the toes move). But at a slightly different level.

Last edited by KBK; 7th April 2012 at 08:50 PM.
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Old 7th April 2012, 08:49 PM   #22115
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Brad,

Quote:
Originally Posted by bcarso View Post
No, we don't. That's why I say I was snookered. The mountain I didn't see the point to climbing kept leering at me in my troubled sleep.
As there is only one good reason to climb a mountain ("It was there") you are totally excused. Carry on Soldier.

Ciao T
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Old 7th April 2012, 09:26 PM   #22116
gerhard is offline gerhard  Germany
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Quote:
Originally Posted by elektroj View Post
Oh yes, there is something about the beauty of circuit drawn and imagined in engineers head and final sonic result. I've always believed in that.
Some airplane designer once said : "Only beautiful aircraft can fly".
The picture looks most like this p-diff & n-diff input combination that seemingly only
survives in self-acclaimed hi end audio.

Well, with regard to the airplanes, they said the Ka-8 glider airplane really doesn't fly,
but is repelled by the earth for being ugly. Nevertheless, it's very forgiving and a real
fun for beginners.

Gerhard
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Last edited by gerhard; 7th April 2012 at 09:31 PM.
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Old 7th April 2012, 10:05 PM   #22117
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Quote:
Originally Posted by ThorstenL View Post
Brad,



As there is only one good reason to climb a mountain ("It was there") you are totally excused. Carry on Soldier.

Ciao T
Mount analogue Mount Analogue - Wikipedia, the free encyclopedia
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Old 7th April 2012, 11:02 PM   #22118
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Quote:
Originally Posted by gerhard View Post
The picture looks most like this p-diff & n-diff input combination that seemingly only
survives in self-acclaimed hi end audio.

Well, with regard to the airplanes, they said the Ka-8 glider airplane really doesn't fly,
but is repelled by the earth for being ugly. Nevertheless, it's very forgiving and a real
fun for beginners.

Gerhard
Hello Gerhard,

As they say, beauty is in the eye of the beholder. I see nothing wrong with KA-8. It flies by the forces of nature and one can not fool these with some marketing tricks... Have you tried it?

Here are some ugly ducklings:
20 World's most Ugliest Aircraft Designs Ever | Techxilla

Best,

Last edited by elektroj; 7th April 2012 at 11:14 PM.
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Old 7th April 2012, 11:16 PM   #22119
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Waly View Post
I am again really surprised on how much confusion this topology is creating. No, I don't your topology would work outside the simulator, other than by accident, and with the known thermal issues.

Can you tell, by inspecting the schematic, how much is the voltage in the Q9 base? Hint: no, it is ill defined.

At least, Godfrey schematic tries to define the VAS bias by using the input stage differential bias voltage (about 2Vp) divided by the VAS collector resistor. This one is, bias wise, practically identical to the Slone's fig 11.4 famous blunder.
The confusion is in your brain , firstly...

Any moderatly trained eye will tell you that Q9 base voltage
is the sum of the diodes losses + Vce SAT Q9 + 1/2 tail current x R1.

Since the higher base voltage allow energic degeneration at the VAS
emitter , any CM unbalance is easily corrected by the global NFB
without unbalancing the VAS differential current.

Without this heavy degeneration the VAS current will be unbalanced
as a side will enter full conduction while the other one will be almost switched off.

Anyway , i built such an amp , although with a simple BJT VAS ,
not a darlington one as in the schematic above , and providing
minimal but not excessive components matching ;, it can be made
to work quite well.
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Old 7th April 2012, 11:28 PM   #22120
wahab is offline wahab  Algeria
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Quote:
Originally Posted by ThorstenL View Post

You are putting the diodes into the wrong line.

Let the CM Transistor carry the voltage, it needs it for high impedance (I'd say give it at least 3V), put extra diodes in line with your VAS to up voltages if needed...
There s some advantage in implementing them this way...


Quote:
Originally Posted by ThorstenL View Post
Now past that, the only reason to use CM on the IPS is to maximise looped negative feedback and to maximise the impact of the non-ideal behaviours of the next stage on the systems linearity.

Someone please remind why exactly would I want to do something so monumentally devoid of intelligence, apart from DS's say so?

CM load has it's uses and places, but maybe not there...
The IPS has way better linearity with a CM , that s not only
a matter of NFB maximization.

The reduction in IMD that it allow is simply stunning.
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