Lme49830 - Page 8

AndrewT · 20th February 2009, 10:46 AM

I think it was MJL or KP that showed inverse parallel diodes across that ground linking 10r resistor.
After thinking about it, I came to realise that adding the diodes offers a safer solution and that the resistor can probably be omitted leaving just the diodes to isolate the two grounds.

nickarsow · 20th February 2009, 10:51 AM

You are right.
What about the OpAmp - nothing but price and small Cin.

nickarsow · 20th February 2009, 10:53 AM

I mean that the price of LM833 ( could be used instead LME49720 ) is about USD0.3 , and the small Cin=1uF( 25V ) are cheaper than one BIG cap of 10uF/100V

AndrewT · 20th February 2009, 11:05 AM

but you can omit the opamp and eight other components, to feed the 49830 with the same input filters that you show feeding the opamp.

nickarsow · 20th February 2009, 11:13 AM

Then explain the original usage of MKP 10uF/100V which is huge and too expensive?

nickarsow · 20th February 2009, 11:38 AM

Just for fun - see the 3D bottom view

AndrewT · 20th February 2009, 11:38 AM

Hi,
set Zin of the 49830 to 91K and use 1uF as the DC blocking capacitor.
F-1dB ~3 to 4Hz. Add on an appropriate series resistor and grounding pF cap and you have both your input filters. Add another pF cap across the input RCA.
Just make sure that the amplifier has a bandwidth wider than that set by the input filters.

You can now use a small 47uF as the DC blocking cap in the NFB loop for a gain of ~26 to 30 times.

nickarsow · 20th February 2009, 11:40 AM

Thanks AndrewT,
This is very usefull proposal!
When I have a little time I'll modify the PCB - that should be version V2.0.
Thanks again
Nick

jackinnj · 20th February 2009, 12:26 PM

Since you have a buffer, why not try inverted? You won't have to worry about the impedance and it WILL sound better.

nickarsow · 20th February 2009, 12:29 PM

Dear Jackinnj,
Could you draw your idea?

20th February 2009, 10:46 AM	#71
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I think it was MJL or KP that showed inverse parallel diodes across that ground linking 10r resistor. After thinking about it, I came to realise that adding the diodes offers a safer solution and that the resistor can probably be omitted leaving just the diodes to isolate the two grounds. __________________ regards Andrew T.

20th February 2009, 11:05 AM	#74
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	but you can omit the opamp and eight other components, to feed the 49830 with the same input filters that you show feeding the opamp. __________________ regards Andrew T.

20th February 2009, 11:38 AM	#77
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, set Zin of the 49830 to 91K and use 1uF as the DC blocking capacitor. F-1dB ~3 to 4Hz. Add on an appropriate series resistor and grounding pF cap and you have both your input filters. Add another pF cap across the input RCA. Just make sure that the amplifier has a bandwidth wider than that set by the input filters. You can now use a small 47uF as the DC blocking cap in the NFB loop for a gain of ~26 to 30 times. __________________ regards Andrew T.

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20th February 2009, 10:51 AM	#72
nickarsow diyAudio Member Join Date: Feb 2009	You are right. What about the OpAmp - nothing but price and small Cin.

20th February 2009, 10:53 AM	#73
nickarsow diyAudio Member Join Date: Feb 2009	I mean that the price of LM833 ( could be used instead LME49720 ) is about USD0.3 , and the small Cin=1uF( 25V ) are cheaper than one BIG cap of 10uF/100V

20th February 2009, 11:13 AM	#75
nickarsow diyAudio Member Join Date: Feb 2009	Then explain the original usage of MKP 10uF/100V which is huge and too expensive?

20th February 2009, 11:40 AM	#78
nickarsow diyAudio Member Join Date: Feb 2009	Thanks AndrewT, This is very usefull proposal! When I have a little time I'll modify the PCB - that should be version V2.0. Thanks again Nick

20th February 2009, 12:26 PM	#79
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Since you have a buffer, why not try inverted? You won't have to worry about the impedance and it WILL sound better.

20th February 2009, 12:29 PM	#80
nickarsow diyAudio Member Join Date: Feb 2009	Dear Jackinnj, Could you draw your idea?

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