Mpp - Page 308

Joachim Gerhard · 7th November 2011, 02:02 PM

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.

Audiofanatic · 7th November 2011, 02:21 PM

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,

Audiofanatic

Joachim Gerhard · 7th November 2011, 03:07 PM

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.

MiiB · 03:53 PM

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....

Joachim Gerhard · 7th November 2011, 04:53 PM

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.

Joachim Gerhard · 7th November 2011, 05:33 PM

Could you please draw the schematic too ? i am simply too busy at the moment.

MiiB · 7th November 2011, 05:39 PM

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.

Joachim Gerhard · 7th November 2011, 05:54 PM

Thanks. Maybe you should simulate 9dB and 12dB too. Sometimes people need more gain.

MiiB · 8th November 2011, 05:38 PM

Have a hard time with the needed input-sving, must work some more with the concept...

Joachim Gerhard · 8th November 2011, 05:52 PM

Sure, this is something else then a low level phono. Anyway, thanks for the effort.

7th November 2011, 02:21 PM	#3072
Audiofanatic diyAudio Member Join Date: Oct 2002 Location: The Netherlands, Utrecht	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, Audiofanatic __________________ Be nice to animals.

7th November 2011, 03:43 PM	#3074
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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 03:53 PM.

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7th November 2011, 03:07 PM	#3073
Joachim Gerhard diyAudio Member Join Date: Mar 2009	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.

7th November 2011, 04:53 PM	#3075
Joachim Gerhard diyAudio Member Join Date: Mar 2009	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.

7th November 2011, 05:33 PM	#3076
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Could you please draw the schematic too ? i am simply too busy at the moment.

7th November 2011, 05:39 PM	#3077
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	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.

7th November 2011, 05:54 PM	#3078
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Thanks. Maybe you should simulate 9dB and 12dB too. Sometimes people need more gain.

8th November 2011, 05:38 PM	#3079
MiiB diyAudio Member Join Date: May 2005 Location: Denmark	Have a hard time with the needed input-sving, must work some more with the concept...

8th November 2011, 05:52 PM	#3080
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Sure, this is something else then a low level phono. Anyway, thanks for the effort.