My New CFB Frontend with balanced input biasing current requirements

Workhorse · 02:29 PM

Hi,

Most of the time CFB[current feedback] frontend has huge difference in input biasing current requirements. I came up with this new approach in order to balance the input current demand from both inverting and non-inverting nodes, so that it could be used like normal voltage feedback amplifiers. Bandwidth is spectacular and use of complementary rush cascodes at inverting side makes it very fast. Compensation networks are not used for simplicity, as its only a simulation yet. I don't know if similar topology exists or not, but its just i came up with...........

Waiting for comments.

Kanwar

Bigun · 5th February 2011, 02:24 PM

Wow ! looks very interesting indeed.

You will find a partner-in-crime with Keantoken:

http://www.diyaudio.com/forums/headp...put-stage.html

Workhorse · 5th February 2011, 02:34 PM

Thanks Bigun,

Keantoken is using single ended rush cascode only, whereas mine is fully symmetric design from input to output, an improvement in regular CFB frontend. I am thinking of making a mic preamp with this topology, because it permits the balanced input configuration with quite an ease like a normal opamp but with very high speed. There is still room for plenty of improvement like CCS in front EFs loading and so on.

Cheers
Kanwar

Workhorse · 5th February 2011, 02:40 PM

Both CC EF input nodes are biased at Ic=1mA thereby permitting equal input drive current demands for operating point and AC signal swing is in pure Class-A

Telstar · 5th February 2011, 02:53 PM

Very nice

If you need balanced input of course.

ontoaba · 5th February 2011, 09:33 PM

You add small hum supply on your signal path through 22K, using zener regulated will fine

.

Workhorse · 6th February 2011, 04:48 AM

Quote:

Originally Posted by ontoaba

You add small hum supply on your signal path through 22K, using zener regulated will fine

.

I already stated that CCS are needed in frontend EF,s in my previous post. 22k is just for simplicity to check the operation of whole circuit.

AndrewT · 6th February 2011, 09:23 AM

Hi,
it looks like an LTP, but each half is a diamond arranged buffer.

Are the pairs of Qs attached to the 330e, the Rush Cascode?

Are the BAS21 diodes anti-saturation? or soft clipping?

Workhorse · 6th February 2011, 10:40 AM

Quote:

Originally Posted by AndrewT

Hi,
it looks like an LTP, but each half is a diamond arranged buffer.

Are the pairs of Qs attached to the 330e, the Rush Cascode?

Are the BAS21 diodes anti-saturation? or soft clipping?

Yeah both input nodes are diamond buffer arrangements.

Yeah the pair at inverting node followed by 330e are forming complementary Rush cascodes.

BAS21 diodes are for anti-saturation + non-sticky clipping.

Samuel Groner · 6th February 2011, 02:38 PM

It doesn't seem to be a CF amp; inverting input is high impedance. It looks like a revival of the 741 frontend...

Samuel

5th February 2011, 02:24 PM	#2
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	Wow ! looks very interesting indeed. You will find a partner-in-crime with Keantoken: http://www.diyaudio.com/forums/headp...put-stage.html __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

5th February 2011, 02:34 PM	#3
Workhorse diyAudio Member Join Date: Dec 2004	Thanks Bigun, Keantoken is using single ended rush cascode only, whereas mine is fully symmetric design from input to output, an improvement in regular CFB frontend. I am thinking of making a mic preamp with this topology, because it permits the balanced input configuration with quite an ease like a normal opamp but with very high speed. There is still room for plenty of improvement like CCS in front EFs loading and so on. Cheers Kanwar __________________ It's a fruitless endeavor to try and educate a fool that rejoices in ignorance

5th February 2011, 02:40 PM	#4
Workhorse diyAudio Member Join Date: Dec 2004	Both CC EF input nodes are biased at Ic=1mA thereby permitting equal input drive current demands for operating point and AC signal swing is in pure Class-A __________________ It's a fruitless endeavor to try and educate a fool that rejoices in ignorance

5th February 2011, 02:53 PM	#5
Telstar diyAudio Member Join Date: Dec 2007	Very nice If you need balanced input of course. __________________ The response of the inner ear extends to at least 200khz - Dr W. Tempest

5th February 2011, 09:33 PM	#6
ontoaba diyAudio Member Join Date: Nov 2009 Location: Kudus, & Malang	You add small hum supply on your signal path through 22K, using zener regulated will fine.


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6th February 2011, 09:23 AM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, it looks like an LTP, but each half is a diamond arranged buffer. Are the pairs of Qs attached to the 330e, the Rush Cascode? Are the BAS21 diodes anti-saturation? or soft clipping? __________________ regards Andrew T.

6th February 2011, 02:38 PM	#10
Samuel Groner diyAudio Member Join Date: Jun 2005 Location: Zürich	It doesn't seem to be a CF amp; inverting input is high impedance. It looks like a revival of the 741 frontend... Samuel

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