F5 power amplifier - Page 667

EUVL · 16th January 2010, 08:48 PM

> That's one. I can think of a couple others...

Let me make a fool of myself :

Connect the source of Q1 & Q2 on each (left or right) half together, then connect these two junctions across the two halves with a 10R resistor. The feedback resistors are then 25R and goes from output to the source junction. Non-inverting then.

According to John Curl, this "H" diff pair has very good distortion cancellation.

Patrick

gaborbela · 16th January 2010, 09:58 PM

Hello
Please try to use GR type .
Greets.

Zen Mod · 16th January 2010, 10:23 PM

Quote:

Originally Posted by EUVL

> ......
Let me make a fool of myself :

.......

No , Patrick - that's my job usually ......

Blues · 16th January 2010, 11:22 PM

Quote:

Originally Posted by umut1001

I do not have low idss jfet.All of them are above 8ma.Does not them work well ?

They will work very well, but are "over qualified". Keep in mind 2SJ074s are very hard to find nowadays. The F5 has P & N ch jfets at the input so high Idss jfets are not necessary.

GR and lowish BL jfets will work very well too.

I am matching BL jfets and will soon make some available to diyers. Some appear to be in the 6 to 7mA range.

bobodioulasso · 17th January 2010, 09:31 AM

Quote:

Originally Posted by wensan

Oh! I am wrong.
Most of signal will be amplified without feedback control.

Thx Wen-san, i understand my mistake now.
It seems there is no way to keep the 2 ways NFB with a symetrical input.
It has to be as follows. But nothing new then.

generg · 17th January 2010, 09:32 AM

Would be great to have a solution!
I dont´t want to double all components only to test balanced driving.
I was also looking about an hour over the different possibilities, but I am not experienced enough. No clear result.
Thank you bobodioulasso for trying to get the answer!

bobodioulasso · 17th January 2010, 09:42 AM

Quote:

I dont´t want to double all components only to test balanced driving

Neither to have a lot more dissipation.

generg · 17th January 2010, 09:48 AM

Exactly!

rikkert1978 · 17th January 2010, 04:04 PM

So its Showtime for my F5!

I got it hooked up via a 100watt lamp and all seems fine. All the voltages are present, and everything is stable.
I do however measure like 8mV on r12 and r 11 for the bias.
After turning the potmeters for quite some time I suspect something is wrong.

I meseured r3 and r4 and they give about 8 ohms.

Is it possible that I have to turn quite some more (slow pots?)

tinitus · 17th January 2010, 04:18 PM

Rikkert, be certain that you measure correctly
Does amp get hot or not ?

17th January 2010, 09:32 AM	#6666
generg diyAudio Member Join Date: Jul 2009 Location: Near Frankfurt	Would be great to have a solution! I dont´t want to double all components only to test balanced driving. I was also looking about an hour over the different possibilities, but I am not experienced enough. No clear result. Thank you bobodioulasso for trying to get the answer! __________________ and the First Wtt is......a really First Class PSS Idea !

17th January 2010, 09:48 AM	#6668
generg diyAudio Member Join Date: Jul 2009 Location: Near Frankfurt	Exactly! __________________ and the First Wtt is......a really First Class PSS Idea !

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16th January 2010, 08:48 PM	#6661
EUVL diyAudio Member Join Date: Oct 2003	> That's one. I can think of a couple others... Let me make a fool of myself : Connect the source of Q1 & Q2 on each (left or right) half together, then connect these two junctions across the two halves with a 10R resistor. The feedback resistors are then 25R and goes from output to the source junction. Non-inverting then. According to John Curl, this "H" diff pair has very good distortion cancellation. Patrick

16th January 2010, 09:58 PM	#6662
gaborbela diyAudio Member Join Date: Sep 2005	Hello Please try to use GR type . Greets.

17th January 2010, 04:04 PM	#6669
rikkert1978 diyAudio Member Join Date: Aug 2005	So its Showtime for my F5! I got it hooked up via a 100watt lamp and all seems fine. All the voltages are present, and everything is stable. I do however measure like 8mV on r12 and r 11 for the bias. After turning the potmeters for quite some time I suspect something is wrong. I meseured r3 and r4 and they give about 8 ohms. Is it possible that I have to turn quite some more (slow pots?)

17th January 2010, 04:18 PM	#6670
tinitus diyAudio Moderator Join Date: Nov 2005	Rikkert, be certain that you measure correctly Does amp get hot or not ?