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Old 4th February 2004, 12:02 AM   #1
DC Dave is offline DC Dave  United States
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Default First GC design. Any thoughts?

Here is my first attempt at a NIGC. Before I order the parts I wanted to know if anyone had any thoughts on the design.

I am alittle worried on my choice of a 10K attenuator and the 22.1k input resistor. I don't know the output impedance of my CD player (only source) which is an older mid-fi Denon.

Would it be a good idea to put in a 4.7uFd input cap or atleast order one and then see?

I want to keep the design down to as few components as possible and then listen and tweak. Thanks

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Old 4th February 2004, 09:35 AM   #2
Nuuk is offline Nuuk  United Kingdom
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The 10K pot may work but I would prefer a higher value.

Not sure about DC on the input? Then use a 4.7uF cap. better safe than sorry1

Not sure about component values, then use a tried and tested design. Choose one from HERE
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Old 4th February 2004, 01:05 PM   #3
loong is offline loong  United Kingdom
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I experienced with a NIGC: 22K + 680, with 20K pot (a cheap one)and C 2.2UF (SCR), 35+35V, with (1000+1000+10) UF per rail. All register are normal metal oxide film. It's really good!
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Old 4th February 2004, 02:49 PM   #4
GregGC is offline GregGC  Canada
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Default Re: First GC design. Any thoughts?

Quote:
Originally posted by DC Dave
Here is my first attempt at a NIGC. Before I order the parts I wanted to know if anyone had any thoughts on the design.

I am alittle worried on my choice of a 10K attenuator and the 22.1k input resistor. I don't know the output impedance of my CD player (only source) which is an older mid-fi Denon.

Would it be a good idea to put in a 4.7uFd input cap or atleast order one and then see?

I want to keep the design down to as few components as possible and then listen and tweak. Thanks

Click the image to open in full size.
First get a larger value pot. 47-100K. If no Input cap configuration you'll need a resistor (220-500) in ser to +in of the amp. I'd also try configuration without feedback cap. and if you want try it with an input cap also (if you don't have DC on the source output).

http://www.diyaudio.com/forums/showt...471#post309471

http://www.diyaudio.com/forums/showt...794#post298794
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Old 4th February 2004, 07:24 PM   #5
DC Dave is offline DC Dave  United States
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Thanks for all your input. I modified the design a bit, and I am going with a 20k pot and a 244ohm resistor in series with the input. I am also going to try with and without the feedback cap and also check for DC on input to see if I need the input cap
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Old 5th February 2004, 03:03 AM   #6
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polarized cap in the feedback? i didn't think that worked.
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Old 5th February 2004, 03:12 AM   #7
HDTVman is offline HDTVman  United States
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You can just remove C1. You don't need it.

Later BZ
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Old 5th February 2004, 05:26 AM   #8
GregGC is offline GregGC  Canada
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Quote:
Originally posted by DC Dave
Thanks for all your input. I modified the design a bit, and I am going with a 20k pot and a 244ohm resistor in series with the input. I am also going to try with and without the feedback cap and also check for DC on input to see if I need the input cap

I would connect a res. to gnd from the slider of the pot in case the pot is not extremely good quality. If the slider of the pot doesn't make a very good connection all the time you may see a lot of spikes on the output especially if you don't use the feedback cap (the DC gain will be more than 20). God forbid the pot at one point decides not to conduct to gnd. You'll see a lot of DC on the output and the speakers wont like it at all.
Do it like this (and keep the feedback cap if you want):
http://www.diyaudio.com/forums/showt...473#post309473
The res (R3 in the sch in the link) can be anywhere from 22k to 47k, but keep in mind that the amp input impedance at max volume will be around 10k-15k depending on the value of R3(the sch in the link).

C1 in your sch will make the output DC ouffset les dependant on the position of the pot. but it might deteriorate the sound quality. You decide on C1. By the way if you decide to leave it in use atleast 100uF and higher. I'd use 220uF.
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