chipamp resistor feedback

fellic · 16th July 2008, 05:21 PM

Hi everyone, I am tube diy but I want to try building a LM3886 amp. I ordered the stereo pcb set from Brian at chipamp.com. My question is regarding the feedback resistor, in tube design I usually like the non feedback designs but can anyone tell me if you have been listening to the LM3886 with and without the feedback. I am not interested in distortion, I read about National data and measurements made by several guys, I want listening opinions.
Thanks.

leadbelly · 16th July 2008, 05:24 PM

You need feedback for it to work and not go poof, there is nothing optional about it.

fellic · 16th July 2008, 07:06 PM

Sorry, rereading the manual, I realise he is talking about a feedback capacitor, not a resistor.
The assembly manual gives 2 options, I quote:

- for using the standard configuration, R3 is installed as shown on the right.
-for using the feedback capacitor, R3 is installed as shown on the left.
As for the preferred configuration, the standard configuration has been said to sound better, but lower dc offset can be obtained through using the feedback capacitor.

R3 is the 680 ohm setting the gain with 22K feedback resistor.
So has anyone been listening to the different configurations?

lineup · 16th July 2008, 09:36 PM

hi.

http://chipamp.com/docs/lm3886-manual.pdf

If you use the optional 47uF Capacitor, which is standard for LM3886 typical circuit,
you may have less problems with DC-offset at the output.
You can read about and see this in the LM3886 datasheet:
http://www.national.com/ds.cgi/LM/LM3886.pdf

My opinion: You will not be able to hear any diffrence in sound.
Cap or no cap.

So my advice would be to try without, if you wish.
But then measure the DC-offset at output, with different volume potentiometer settings.

You will then see if you need to use this CAP 47uF.

fellic · 17th July 2008, 04:04 PM

Thanks,
That is exactly what I will do, I wont use the cap and measure the DC offset.

Dxvideo · 22nd July 2008, 06:49 AM

Quote:

Originally posted by lineup

My opinion: You will not be able to hear any diffrence in sound.
Cap or no cap.

I think you WILL HEAR a lot of difference! Go and see..

Ted205 · 22nd July 2008, 02:19 PM

Quote:

Originally posted by Dxvideo

I think you WILL HEAR a lot of difference! Go and see..

the difference being ?

Dxvideo · 22nd July 2008, 03:15 PM

????
Sorry, I dont understand what you mean...

Ted205 · 22nd July 2008, 04:21 PM

In your opinion what did you think.
Which is better? etc

fellic · 22nd July 2008, 04:34 PM

hi Ozgur,
it is difficult to compare (to my ears) when you have to make a long pause between one way and the other, having to desolder and solder again. But I think I liked more without the cap, I usually like it more with less components.

16th July 2008, 05:21 PM	#1
fellic diyAudio Member Join Date: Oct 2004	chipamp resistor feedback Hi everyone, I am tube diy but I want to try building a LM3886 amp. I ordered the stereo pcb set from Brian at chipamp.com. My question is regarding the feedback resistor, in tube design I usually like the non feedback designs but can anyone tell me if you have been listening to the LM3886 with and without the feedback. I am not interested in distortion, I read about National data and measurements made by several guys, I want listening opinions. Thanks.

16th July 2008, 05:24 PM	#2
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	You need feedback for it to work and not go poof, there is nothing optional about it. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

16th July 2008, 09:36 PM	#4
lineup diyAudio Member Join Date: Dec 2005 Location: the north	hi. http://chipamp.com/docs/lm3886-manual.pdf If you use the optional 47uF Capacitor, which is standard for LM3886 typical circuit, you may have less problems with DC-offset at the output. You can read about and see this in the LM3886 datasheet: http://www.national.com/ds.cgi/LM/LM3886.pdf My opinion: You will not be able to hear any diffrence in sound. Cap or no cap. So my advice would be to try without, if you wish. But then measure the DC-offset at output, with different volume potentiometer settings. You will then see if you need to use this CAP 47uF. __________________ lineup

22nd July 2008, 03:15 PM	#8
Dxvideo diyAudio Member Join Date: Nov 2003 Location: Turkey	???? Sorry, I dont understand what you mean... __________________ Best regards, Ozgur

22nd July 2008, 04:34 PM	#10
fellic diyAudio Member Join Date: Oct 2004	cap or no cap... hi Ozgur, it is difficult to compare (to my ears) when you have to make a long pause between one way and the other, having to desolder and solder again. But I think I liked more without the cap, I usually like it more with less components.


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16th July 2008, 07:06 PM	#3
fellic diyAudio Member Join Date: Oct 2004	Sorry, rereading the manual, I realise he is talking about a feedback capacitor, not a resistor. The assembly manual gives 2 options, I quote: - for using the standard configuration, R3 is installed as shown on the right. -for using the feedback capacitor, R3 is installed as shown on the left. As for the preferred configuration, the standard configuration has been said to sound better, but lower dc offset can be obtained through using the feedback capacitor. R3 is the 680 ohm setting the gain with 22K feedback resistor. So has anyone been listening to the different configurations?

17th July 2008, 04:04 PM	#5
fellic diyAudio Member Join Date: Oct 2004	Thanks, That is exactly what I will do, I wont use the cap and measure the DC offset.

22nd July 2008, 04:21 PM	#9
Ted205 diyAudio Member Join Date: Jun 2008	In your opinion what did you think. Which is better? etc

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