Different GC - Page 2

GregGC · 20th July 2004, 02:23 PM

To get a better DC output offset you need to have R19=R4||(R10+R7) and R20=R5||(R11+R8).

Why didn't you use Non iverting topologie? It'll solve the low impedance voltage much easier.

/Greg

gengcard · 22nd July 2004, 02:56 AM

Thanks for the suggestion. I think that inverting type challenge me to design balanced GC more than non inverting type. But I think that my new design might be better. neither non inverting and inverting type.

djk · 22nd July 2004, 06:00 AM

It helps to have input bias.

If using an FET opamp like an OPA604 use 470K from pin 3 to ground on both U2 and U3.

gengcard · 22nd July 2004, 07:55 AM

Is it not too high input impedance? What's your idea if R100k is connected pin 3?

djk · 22nd July 2004, 08:07 AM

Do you know how to read a spec sheet?

The input impedance of an OPA604 is 10^12 ohms

(1,000,000,000,000)

Virtually anything will work, your design had nothing.

Nothing doesn't work.

gengcard · 23rd July 2004, 03:03 AM

Yes, I know how to read spec. sheet but at that time I had no spec sheet on my hand, I just downloaded it to read the spec. Anyway, I have simulated with both input impedance 470k and 47k by PSpice. The output waveform results indicated me that 47k better than 470k. Eventhough the simulation results indicated 47k better but I will try the both because in actually maybe R470k will be better. By another thing, R470k is matched with C 0.1uF that is cheaper than C 1uF.

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20th July 2004, 02:23 PM	#11
GregGC diyAudio Member Join Date: Oct 2003 Location: Toronto	To get a better DC output offset you need to have R19=R4\|\|(R10+R7) and R20=R5\|\|(R11+R8). Why didn't you use Non iverting topologie? It'll solve the low impedance voltage much easier. /Greg

22nd July 2004, 06:00 AM	#13
djk diyAudio Member Join Date: Feb 2001 Location: USA	It helps to have input bias. If using an FET opamp like an OPA604 use 470K from pin 3 to ground on both U2 and U3.

22nd July 2004, 07:55 AM	#14
gengcard diyAudio Member Join Date: Jun 2004 Location: Bangkok	Is it not too high input impedance? What's your idea if R100k is connected pin 3?

22nd July 2004, 08:07 AM	#15
djk diyAudio Member Join Date: Feb 2001 Location: USA	Do you know how to read a spec sheet? The input impedance of an OPA604 is 10^12 ohms (1,000,000,000,000) Virtually anything will work, your design had nothing. Nothing doesn't work.

23rd July 2004, 03:03 AM	#16
gengcard diyAudio Member Join Date: Jun 2004 Location: Bangkok	Yes, I know how to read spec. sheet but at that time I had no spec sheet on my hand, I just downloaded it to read the spec. Anyway, I have simulated with both input impedance 470k and 47k by PSpice. The output waveform results indicated me that 47k better than 470k. Eventhough the simulation results indicated 47k better but I will try the both because in actually maybe R470k will be better. By another thing, R470k is matched with C 0.1uF that is cheaper than C 1uF.

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