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Chip Amps Amplifiers based on integrated circuits

My_Ref Fremen Edition - Build thread and tutorial
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Old 18th September 2017, 07:27 AM   #3481
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Joseph K View Post
I mean: raising the value of R3 lowers the gm, the conversion factor of the current pump. So it brings more stabilty ( less loop gain)
So it is a change which brings .more stability, at the price of less performance and more circuit losses. If Mauro had decided to use less of it, he considered worthwile - why should we explore backwards..
The current pump relies on accurate matching of the ratios R8:R9 to R5:R6
R3 is the change made for the improved current pump. This now requires R9:{R3+R8} to be ratio matched.
R3's precise value is not critical to the proper operation of the current pump.

http://www.ti.com/lit/an/snoa474a/snoa474a.pdf
Note the 1% tolerance for R13 in figure 6.

I wonder if the slight change in R3 resulted in a more accurate ratio match?
Could that have given rise to the apparent improvement?
Quote:
Originally Posted by Joseph K View Post
I have shown recently, the evolution of the distortion performance at different stages of the design.
The clear visible step between classic and rev-A compensation is in a nice part due to the R3 changed.

For stabilty it is probably less critical. Did not do a deep investigation. Don't see a reason for it..

Ciao, George
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Last edited by AndrewT; 18th September 2017 at 07:37 AM.
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Old 18th September 2017, 07:35 AM   #3482
Joseph K is online now Joseph K  Hungary
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Andrew,

I have been explaining in the wider context, with the current pump and it's amplification factor as part of the composite amplifier. R3 is the single most important part in defining the current pump's transconductance.
Then this transconductance is working on the actual load impedance.
By changing R3 one changes the open loop gain.

Ciao, George
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Old 18th September 2017, 09:16 PM   #3483
atupi is offline atupi  Romania
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Thanks for all replies, very useful! I was trying to understand if I really need to order 0.33ohm resistors or is ok to keep old 0.47ohm ones in order to have Rev A Evo mods
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Old 18th September 2017, 11:24 PM   #3484
soongsc is offline soongsc  Taiwan
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In my experience increasing current gain did provide a more clean uncolored sound. I think i also posted some damping measurements in the original Myref thread.
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Old Yesterday, 12:30 AM   #3485
Joseph K is online now Joseph K  Hungary
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In fact, Mauro's revA mod and these recent successive modifications/ versions are all raising the current gain in the pump - with respect to the original, or standard configuration.
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