A few chipamp configuration questions

GregH2 · 11th February 2010, 11:48 PM

Hi all,

I've been looking at some of the commercial kits available to try and get a handle on typical resistor values for gainclones. The one that seems to vary the most is the input resistor which varies from 220R to 1k, while the feedback resistors are universally 22k and 680R.

I am interested to know the relative merits (if any) of these different values for the input resistor.

Additionally, some place the 22k resistor from the input to ground before the input resistor and some place it after the input resistor. Is there any advantage to either method?

Your advice is appreciated.

Greg.

pacificblue · 12th February 2010, 11:09 AM

Quote:

Originally Posted by swordfishy

I am interested to know the relative merits (if any) of these different values for the input resistor.

Judging from the values you are refering to the blocking resistor. The datasheet describes its function like this.

Quote:

Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load upon power-down of the system due to the low input impedance of the circuitry when the under-voltage circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.

The bigger the resistor, the better the protection and the bigger its potential bad influence on the sound.

Quote:

Originally Posted by swordfishy

Additionally, some place the 22k resistor from the input to ground before the input resistor and some place it after the input resistor. Is there any advantage to either method?

If the blocking resistor (1k) is placed before the input resistor (22k to ground) they form an attenuator. That reduces the input voltage by 1/23. If the blocking resistor's value was higher, you could use that as a limiter with powerful sources. With the blocking resistor after the input resistor you don't loose any input voltage, which may be an advantage with weak sources. No big difference either way.

GregH2 · 13th February 2010, 11:24 AM

Great thanks. Just what I needed to know.

AndrewT · 15th February 2010, 01:56 PM

and you can combine that input protection resistor/blocking resistor with a small capacitor to create an RF filter to help the chipamp perform as intended.
I've seen 100r to 2k2 for that resistor.

11th February 2010, 11:48 PM	#1
GregH2 diyAudio Member Join Date: Oct 2009	A few chipamp configuration questions Hi all, I've been looking at some of the commercial kits available to try and get a handle on typical resistor values for gainclones. The one that seems to vary the most is the input resistor which varies from 220R to 1k, while the feedback resistors are universally 22k and 680R. I am interested to know the relative merits (if any) of these different values for the input resistor. Additionally, some place the 22k resistor from the input to ground before the input resistor and some place it after the input resistor. Is there any advantage to either method? Your advice is appreciated. Greg.

15th February 2010, 01:56 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	and you can combine that input protection resistor/blocking resistor with a small capacitor to create an RF filter to help the chipamp perform as intended. I've seen 100r to 2k2 for that resistor. __________________ regards Andrew T.

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13th February 2010, 11:24 AM	#3
GregH2 diyAudio Member Join Date: Oct 2009	Great thanks. Just what I needed to know.

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