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Old 7th November 2011, 03:02 PM   #3071
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I told you that the transimpedance line stage can be arranged to include global feedback. So here it is : the full monty Transimpedance Line Stage Buffer. Actually it includes transimpedance and conventional feedback in one circuit.
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File Type: pdf Transimpedance Linestage Buffer FB.TSC - TINA.pdf (14.0 KB, 106 views)
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Old 7th November 2011, 03:21 PM   #3072
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Unhappy Feedback

Hi Joachim,

It looks OK but for whatever reason, I think the feedback, I prefer the other.
I will (perhaps) try this one also but still I prefer the one without feedback.

Just a personal thing not based on measurements or technical specs.

I hope you don't hold it against me again it's nothing personal

atb,

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Old 7th November 2011, 04:07 PM   #3073
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No, i like the non feedback version too. It is more simple and different and has low enough distortion and output impedance to not introduce audible problems . The feedback version will just measure better in terms of distortion and speed but that does not imply that it sounds better. Charles Hanson of Air may like the simple version better too. He thinks that negative overall feedback always sound worse. It is just hard to explain in conventional measurements. Maybe it is the time domain behavior. A transimpedance circuit rolls of with 6dB octave in the treble and a feedback amp with 12dB octave and the transimpedance circuit is unconditionally stable. Add more capacitance at the output and it will get even more stable because the treble will be rolled of and the distortion in the treble goes down because of local current feedback.
Call it degeneration if you will. At first glance that is hard to understand but the output of a transimpedance amp is a current source and the output of a global feedback amp with emitter follower is a voltage source. Put a cap behind a high feedback amp and it sure will oszillate.
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Old 7th November 2011, 04:43 PM   #3074
MiiB is online now MiiB  Denmark
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Funky brainset on that man..
Why not build it like your pure JFet transimpedance riaa, just with oppesite current lowering of the mirrors and a resitor to gnd. With the jfet buffer and funky servo....I'll run a simulation....

Last edited by MiiB; 7th November 2011 at 04:53 PM.
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Old 7th November 2011, 05:53 PM   #3075
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Yes, i thought about that too. Would be more then happy to see a simulation. This transimpedance thing brings us into the uncharted territories. I hope Scorpius and the Peacekeepers do not catch us ! We can always Starburst to the rescue though.
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Old 7th November 2011, 06:33 PM   #3076
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Could you please draw the schematic too ? i am simply too busy at the moment.
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Old 7th November 2011, 06:39 PM   #3077
MiiB is online now MiiB  Denmark
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I'll do tomorrow, I think we can use some lower gain fets so the initial gain will be lower..an then just shunt to gnd with a resistor to get app 6 dB gain.
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Old 7th November 2011, 06:54 PM   #3078
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Thanks. Maybe you should simulate 9dB and 12dB too. Sometimes people need more gain.
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Old 8th November 2011, 06:38 PM   #3079
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Have a hard time with the needed input-sving, must work some more with the concept...
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Old 8th November 2011, 06:52 PM   #3080
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Sure, this is something else then a low level phono. Anyway, thanks for the effort.
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