F5 power amplifier - Page 16

TimS · 17th April 2008, 09:32 PM

Let me the first to X the F5.

(Is it X or Super symmetry, I am not sure which is which)

Cheers

Tim

TimS · 17th April 2008, 09:39 PM

Quote:

Originally posted by TimS
I have simulated my previous balanced F5 and i got it to work after tweaking a few resistor values and reorienting some output devices (after my stupid mistake in the previous version of this schematic).

Ignore this schematic I resent the previous schematic by mistake.
I have attached the correct one.

Cheers

Tim

Nelson Pass · 17th April 2008, 11:35 PM

A concept error

that happened to the bias

Who will first spot it?

KSTR · 18th April 2008, 12:02 AM

Papa was quicker, doh.

It won't work like this, biasing is via the 100R's, not the 10R's.

And to get the same voltage swing accross the load as with the straight and simple bridge, R4/R5 would be like 4 Ohms or so (and the other 4 all 10 Ohms). According to my quick sim, it gives x10 the distortion...

- Klaus

spencer · 18th April 2008, 12:10 AM

The dc bias on J1 will be very small current <1ma due to high source resistor R1. Thus voltage drop across R5 will be too low to turn on M2.

Zen Mod · 18th April 2008, 12:16 AM

hehe

typical reactions of us , greedy boyz ;

Papa gave us new toy , now we want twice ......... or " double naked " , literally translated proverb from my native .......

anyway - I can't see easy X-ing that circuit , without resorting to good ole "out to gate " feedback scheme , and that way we are loosing virtues of low impedance feedback path .........

Papa certainly tried that iteration , so he can say is it worthwhile to x-it , or just plain bridging is best in this case ......

interesting dilemma .............

X , or low impedance feedback?

or - is it best to grab this bull between the horns ?

TimS · 18th April 2008, 01:15 AM

In reply How it currently works:

J1 is biased through R1. The offset that would be caused at Vout+ is cancelled by the equal current drawn by J2 and R2.

According to the simulation at 0V in J1 and J2 both draw about 3mA, this would in turn generate a 3V drop across R5, which in my simulation is enough to bias M2 to about 1A.

I think I see the Biasing error that Nelson is referring too, I should have source resistors on my mosfets to help stabilise the bias currents.

One of the nice advantages to this approach is that it has a common mode gain of 1 but a differential mode gain of (R1+R7)/R3

spencer · 18th April 2008, 01:46 AM

Assume supply is +/- 24v, current through R5, R1, R2, R6 will be :

48v / 2.2k = 2.2 mA max, assume J1 and J2 is not there.

GRollins · 18th April 2008, 01:49 AM

Quote:

Originally posted by Nelson Pass
A concept error

that happened to the bias

Who will first spot it?

Nelson has written
In traditional haiku
Five, seven, and five

Grey

hayenc · 18th April 2008, 02:07 AM

May AudioXpress arrived today. Nice article. But no caps. Whatever will we argue about now?

18th April 2008, 12:16 AM	#156
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	hehe typical reactions of us , greedy boyz ; Papa gave us new toy , now we want twice ......... or " double naked " , literally translated proverb from my native ....... anyway - I can't see easy X-ing that circuit , without resorting to good ole "out to gate " feedback scheme , and that way we are loosing virtues of low impedance feedback path ......... Papa certainly tried that iteration , so he can say is it worthwhile to x-it , or just plain bridging is best in this case ...... interesting dilemma ............. X , or low impedance feedback? or - is it best to grab this bull between the horns ? __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery

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17th April 2008, 11:35 PM	#153
Nelson Pass The one and only Join Date: Mar 2001	A concept error that happened to the bias Who will first spot it?

18th April 2008, 12:02 AM	#154
KSTR diyAudio Member Join Date: Jul 2007 Location: Central Berlin, Germany	Papa was quicker, doh. It won't work like this, biasing is via the 100R's, not the 10R's. And to get the same voltage swing accross the load as with the straight and simple bridge, R4/R5 would be like 4 Ohms or so (and the other 4 all 10 Ohms). According to my quick sim, it gives x10 the distortion... - Klaus

18th April 2008, 12:10 AM	#155
spencer diyAudio Member Join Date: Jun 2004 Location: Hong Kong	The dc bias on J1 will be very small current <1ma due to high source resistor R1. Thus voltage drop across R5 will be too low to turn on M2.

18th April 2008, 01:15 AM	#157
TimS diyAudio Member Join Date: Feb 2004 Location: Auckland	In reply How it currently works: J1 is biased through R1. The offset that would be caused at Vout+ is cancelled by the equal current drawn by J2 and R2. According to the simulation at 0V in J1 and J2 both draw about 3mA, this would in turn generate a 3V drop across R5, which in my simulation is enough to bias M2 to about 1A. I think I see the Biasing error that Nelson is referring too, I should have source resistors on my mosfets to help stabilise the bias currents. One of the nice advantages to this approach is that it has a common mode gain of 1 but a differential mode gain of (R1+R7)/R3

18th April 2008, 01:46 AM	#158
spencer diyAudio Member Join Date: Jun 2004 Location: Hong Kong	Assume supply is +/- 24v, current through R5, R1, R2, R6 will be : 48v / 2.2k = 2.2 mA max, assume J1 and J2 is not there.

18th April 2008, 02:07 AM	#160
hayenc diyAudio Member Join Date: Apr 2005 Location: Glendale, AZ	May AudioXpress arrived today. Nice article. But no caps. Whatever will we argue about now?

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