Question about my first GC

amisdad · 21st September 2004, 11:15 PM

I'm trying to finish my first GC. I have a few questions. Can I use a 20k Caddock for my NFB? If so, what kind of effect will it have as opposed to the 22k? My second question is: Can I use my 100k Noble pot without a shunt resistor? It is the same pot available at partsconexion.com. Sorry about the dumb questions. I searched the forums and could not find my answer.

thomas997 · 22nd September 2004, 02:07 AM

You can use 20k, and I think your supposed to pair it with a 620 ohm (instead of 680).

Is the noble a log pot or linear?

Depending on your speakers efficiency you might need to modify it or get a 50k/10k pot.

amisdad · 22nd September 2004, 02:33 AM

Quote:

Originally posted by thomas997
You can use 20k, and I think your supposed to pair it with a 620 ohm (instead of 680).

Is the noble a log pot or linear?

Depending on your speakers efficiency you might need to modify it or get a 50k/10k pot.

Here is my dilema. I lost my job and my wife would kill me if I spent another penny on anything other than bills. I do have a few 20k caddock resistors as well as a few 680 ohms. As far as the pot goes, it's logarithmic and my speakers are 91db.

amisdad · 22nd September 2004, 09:33 PM

My main question is do I solder the 20k NFB resistor in place or wait until I can get a 22.1K?

thomas997 · 23rd September 2004, 01:24 AM

National uses 1k in their design, so I dont think the value is too critical.

Its used to set the gain so it might affect that slightly. (Rfeedback/R1).

The datasheet is your friend: http://www.national.com/ds/LM/LM3875.pdf

You should be fine with that pot.

21st September 2004, 11:15 PM	#1
amisdad diyAudio Member Join Date: Mar 2004 Location: Chicago	Question about my first GC I'm trying to finish my first GC. I have a few questions. Can I use a 20k Caddock for my NFB? If so, what kind of effect will it have as opposed to the 22k? My second question is: Can I use my 100k Noble pot without a shunt resistor? It is the same pot available at partsconexion.com. Sorry about the dumb questions. I searched the forums and could not find my answer.

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22nd September 2004, 02:07 AM	#2
thomas997 diyAudio Member Join Date: Feb 2004 Location: Vancouver	You can use 20k, and I think your supposed to pair it with a 620 ohm (instead of 680). Is the noble a log pot or linear? Depending on your speakers efficiency you might need to modify it or get a 50k/10k pot.

22nd September 2004, 09:33 PM	#4
amisdad diyAudio Member Join Date: Mar 2004 Location: Chicago	My main question is do I solder the 20k NFB resistor in place or wait until I can get a 22.1K?

23rd September 2004, 01:24 AM	#5
thomas997 diyAudio Member Join Date: Feb 2004 Location: Vancouver	National uses 1k in their design, so I dont think the value is too critical. Its used to set the gain so it might affect that slightly. (Rfeedback/R1). The datasheet is your friend: http://www.national.com/ds/LM/LM3875.pdf You should be fine with that pot.

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