JLM DiNGO Questions

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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JR.
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Re: JLM DiNGO Questions

Post by JR. »

I used to have the equations memorized... you need to factor for bandwidth (I typically used 20kHz bandwidth to keep everything apples to apples) but you just need to compare same to same (hint more bandwidth means more noise so not normalizing the bandwidth can make better circuits measure worse on paper).

5k is not low or high impedance.

I can dig the equations up if you want, you need to factor the op amp ein...equivalent input noise voltage, and input noise current times the source impedance and times the feedback network impedance, added to the johnson (thermal) noise of the 5k resistance. So multiple terms, the reisistor's noise, the op amps noise, and the opamp noise current times the resistors around it.

For 5k with a decent op amp it may not tell you much...

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Gold
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Re: JLM DiNGO Questions

Post by Gold »

Since my math skills are atrocious that’s a better answer than the equations. The reason I chose 5K attenuators was that it seemed like the best value to work as both a source and load impedance.
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JR.
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Re: JLM DiNGO Questions

Post by JR. »

If you are dealing with line level signals they should be adequately quiet.

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Gold
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Re: JLM DiNGO Questions

Post by Gold »

I think I got this now. I hand selected LME29720's with less than a mV of DC offset for each half. I then removed C5, C7, C12 and C13. I checked the headroom and it clips at the same point as it did before removing the caps. Double confirmation there isn't any significant DC offset. The trimmer doesn't make any scratchy noises when I turn it so I think that's okay too.
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