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Old 28th March 2012, 12:28 AM   #2221
brianco is offline brianco  Ireland
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Hi LC,

I have read (much was simply scanned) this thread from the beginning and all of the early comment I found indicates that this amp is for me....but in its simplest form. I want to build it, but, with over 2,200 posts, I cannot find the "Official, approved by You" schematic for the amp and PS. IF you know where to find them will you please give the post numbers or repost the .pdfs/drawings.

Very many thanks.
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Old 28th March 2012, 01:20 AM   #2222
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Quote:
Originally Posted by Jay View Post
So it is more about one's priority and preference over music.
Yes. As a sound engineer, i ask, for my reproduction system to be as transparent and analytic as possible. Reason why i do not look for that kind of "tube sound" able to make agreeable even a disagreeable recording.
I don't believe a low distortion/fast amp produce more agressive treeble. On the contrary, the two things i can notice with my SSA mod is more detailled basses and more natural (smoother) trebles (specially cymbals). Probably due to less TIM. More space too between instruments, they are easier to separate and follow, with less listening fatigue.
As it is the same amp, same VAS, same drivers and same power stage, i credit this change to the slew-rate and distortion improvement.

My high efficiency and very analytic 2 ways satellites are equipped with JBL drivers (and kind similar wooden circular horns as LeCleac''s ones) for the top range, from 1Khz. They do not go high in treble, and my amp was quite fast before. So, it is definitely a question of TIM, not bandwidth.
(For the basses, i run a 48cm JBL in a 500L BR sub, down to 30hz).

About impedance curves of the speakers, they are totally compensated, and the total curve is very linear at 6 Ohms.(less than -+1 Ohm around)

About switching amps, i agree that, if the quiescent current is enough to make them running in class A at normal (medium) listening levels , there is no real improvement to produce more heat in tuning them up to full class A.

About tube amps, one of the reason they sound agreeable is, i believe, because tubes are very fast and have a large linear slope. But, because the output transformer, no one i know is able to reach the definition and dynamic of my actual (SSA like) 135W amp. And my friends said that he has kind of a "tube's" transparency, ease and smoothness.
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Old 28th March 2012, 06:02 AM   #2223
mikelm is offline mikelm  England
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Quote:
Originally Posted by hahfran View Post
Back to the roots
provided the model provided by Bob Cordell is correct and the schematic is correct
I get an op of 1.8 amps drain current .
Is that correct?
Try adjusting R11, R12 or R3, R4 to set bias drain current to whatever you prefer.

p.s. preference for this varies. I would suggest 200mA - 500mA

Last edited by mikelm; 28th March 2012 at 06:31 AM.
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Old 28th March 2012, 07:15 AM   #2224
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Quote:
Originally Posted by hahfran View Post
No it is the correct approach because B*l*I= d2/dt2+ d/dt+....
that is the mechanical motion equation.
All one has to do is to feed a current amp with the output of an "analog computer" ( 3 integrators and one adder ) to cancel out all of the mechanical
constants such as mass compliance...and electrical constants such as resistance and inductivity of the voice coil. So far only swedish co ACE employs this approach. It gets a bit simpler with positive feedback from a resistors in series with the speaker.
of course the real speaker does not follow a simple second order de but it is a simple and easy to implement approach.
I guess that you are thinking some kind of this way: Current-Drive - The Natural Way of Loudspeaker Operation
and JBroskie too: PS-12 & Trim-1
I am going to check if TDA2040 will beat my Yamaha A1: Transconductance amplifier project - Current-Drive - The Natural Way of Loudspeaker Operation
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Old 28th March 2012, 07:50 AM   #2225
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by mikelm View Post
Try adjusting R11, R12 or R3, R4 to set bias drain current to whatever you prefer.

p.s. preference for this varies. I would suggest 200mA - 500mA
If you adjust R11 R12 ( R3 R4 has of course no effect) you reduce the cascode current AND the feedback factor. When the thermally stable op of 100 mA is set, you'll find the cascode also adjusted in class AB .
In the original schematic it is a class A with about 130 Watts power dissipation.

It is possible to adjust the op of the cascodes to zero thus that the switching is
in the cascode. That can drive a BJT class B current amp and in simulation it can be done, but possibly not in practice. because of exponential depednecy
of Vbe.
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Old 28th March 2012, 07:55 AM   #2226
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by padamiecki View Post
I guess that you are thinking some kind of this way: Current-Drive - The Natural Way of Loudspeaker Operation
and JBroskie too: PS-12 & Trim-1
I am going to check if TDA2040 will beat my Yamaha A1: Transconductance amplifier project - Current-Drive - The Natural Way of Loudspeaker Operation
Current drive is the natural way because of the motion equation. If the electrical equivalents of the mechanical factors are cancelled out electrically
there is no more resonant frequency no more phase shift no more timing error
of multi way speakers. You don't even need to know the speaker's data.
All you need is a precise microphone and a scope and then adjust every speaker to max rectangle reproduction.
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Old 28th March 2012, 08:22 AM   #2227
mikelm is offline mikelm  England
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Quote:
Originally Posted by hahfran View Post
( R3 R4 has of course no effect)
my mistake, I should have said R1, R2
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Old 28th March 2012, 08:22 AM   #2228
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Quote:
Originally Posted by hahfran View Post
Current drive is the natural way because of the motion equation. If the electrical equivalents of the mechanical factors are cancelled out electrically
there is no more resonant frequency no more phase shift no more timing error
of multi way speakers. ...
but the current makes no sence without the voltage
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Old 28th March 2012, 08:23 AM   #2229
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If the bias trimmer disconnects, or the cap across it shorts (not likely?), the outputs will turn on full-blast.

EDIT: nevermind, I got here 45 pages too late.

Last edited by keantoken; 28th March 2012 at 08:26 AM.
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Old 28th March 2012, 09:44 AM   #2230
hahfran is offline hahfran  Germany
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The elegance of the SSA topology is certainly not that it is just another CF class A, but that it elegantly avoids the need for a second set of power supplies which CF always requires due to poor CMRR.
Replacing the zeners with CS being biased by thermal trak diodes is apparently nice.
No Vbe is required just a resistor or trimmer in Vas. And the diodes are out of the signal path.
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