F2 amp - What difference to the original Zen amp?

AD · 4th July 2005, 09:59 AM

Mr. Pass, looking at the description and the basic schematic of your F2 First Watt amp, it looks to me exactly the same as your original Zen amp design, published in TAA February 1994 issue (which I have been using for a number of years).
Please excuse my ignorance, but why is the F2 amplifier a transconductance amplifier, and the original Zen isn't (original Zen had no NFB either)?
Or put it the other way around, what is different about the F2 compared to the original Zen design?

Andrej

lumanauw · 4th July 2005, 10:54 AM

You can never guess

Nelson Pass + Resistor + Transistor is better than David Copperfield

jh6you · 4th July 2005, 11:59 AM

Regards
jH

apassgear · 4th July 2005, 03:59 PM

We will wait for the answer from the Master

In the mean while, as far as Nelson has described the F2 circuit is the same topology of the original Zen but with almost no feed back and a 25V single rail, good for 5W class A intended to be used with a high efficiency Full range drivers.

You may have a look to the thread “ Zen w/o FB some place in the second page of the forum.

zen without feedback

Let me add that the original Zen does have feedback through the biasing resistor. In the F2 this resistor seems to have a high value.

I will post a revised schematic of my interpretation.

AD · 4th July 2005, 05:11 PM

Tony, thank you for your comments and pointing out the already ongoing thread about F2/Original Zen - I have completely overlooked it!
Had I seen it before I would not have asked my question. In the thread you pointed out to me Mr. Pass suffiecently comments on the similarity of the two amp designs and I understand through the thread what would make the original Zen a transconductance amp in the fashion of the Pass F2.
It was not my intention to try to squeeze out of Mr. Pass more information about his F2 amp than he wishes to divulge at the time being. I have sufficient information now to try making a transconductance amp out of the original Zen design.

Regards everyone, Andrej

Nelson Pass · 4th July 2005, 09:06 PM

The biggest difference is that the feedback is for the DC
operating point only, making it a current source. This is
accomplished by using very high values for the bias network
resistors. The gain is set by Source resistance in the
single gain transistor. And the bias is higher.

AD · 5th July 2005, 06:36 AM

Thank you for your reply, Mr. Pass!
I shall be looking forward to your next article on the Trasconductance Zen amps, when it appears.
Andrej

4th July 2005, 09:59 AM	#1
AD diyAudio Member Join Date: Jan 2003 Location: Slovenia	F2 amp - What difference to the original Zen amp? Mr. Pass, looking at the description and the basic schematic of your F2 First Watt amp, it looks to me exactly the same as your original Zen amp design, published in TAA February 1994 issue (which I have been using for a number of years). Please excuse my ignorance, but why is the F2 amplifier a transconductance amplifier, and the original Zen isn't (original Zen had no NFB either)? Or put it the other way around, what is different about the F2 compared to the original Zen design? Andrej

4th July 2005, 05:11 PM	#5
AD diyAudio Member Join Date: Jan 2003 Location: Slovenia	Re F2 comp to original Zen Tony, thank you for your comments and pointing out the already ongoing thread about F2/Original Zen - I have completely overlooked it! Had I seen it before I would not have asked my question. In the thread you pointed out to me Mr. Pass suffiecently comments on the similarity of the two amp designs and I understand through the thread what would make the original Zen a transconductance amp in the fashion of the Pass F2. It was not my intention to try to squeeze out of Mr. Pass more information about his F2 amp than he wishes to divulge at the time being. I have sufficient information now to try making a transconductance amp out of the original Zen design. Regards everyone, Andrej

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4th July 2005, 10:54 AM	#2
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	You can never guess Nelson Pass + Resistor + Transistor is better than David Copperfield

4th July 2005, 11:59 AM	#3
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	Regards jH

4th July 2005, 03:59 PM	#4
apassgear diyAudio Member Join Date: Nov 2002 Location: Viña del Mar, Torreon	We will wait for the answer from the Master In the mean while, as far as Nelson has described the F2 circuit is the same topology of the original Zen but with almost no feed back and a 25V single rail, good for 5W class A intended to be used with a high efficiency Full range drivers. You may have a look to the thread “ Zen w/o FB some place in the second page of the forum. zen without feedback Let me add that the original Zen does have feedback through the biasing resistor. In the F2 this resistor seems to have a high value. I will post a revised schematic of my interpretation.

4th July 2005, 09:06 PM	#6
Nelson Pass The one and only Join Date: Mar 2001	The biggest difference is that the feedback is for the DC operating point only, making it a current source. This is accomplished by using very high values for the bias network resistors. The gain is set by Source resistance in the single gain transistor. And the bias is higher.

5th July 2005, 06:36 AM	#7
AD diyAudio Member Join Date: Jan 2003 Location: Slovenia	Thank you for your reply, Mr. Pass! I shall be looking forward to your next article on the Trasconductance Zen amps, when it appears. Andrej

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