[sdiy] The TL072

[Ingo Debus]

Am 20.02.2009 um 19:59 schrieb Antti Huovilainen:

> On Fri, 20 Feb 2009, Ingo Debus wrote:
>
>> I once replaced the opamp in the summing amp in my DIY 12 input  
>> mixer (5534 vs TL072) and got noticably less noise. The summing  
>> amp has a gain of only 1 for each input, but with 12 inputs the  
>> noise gain is 13.
>
> Do you mean sqrt(13)? (the noise inputs are not correlated and  
> hence you need to add the power, not voltage)

No, I meant the noise gain, not the noise itself.

AFAIK noise gain is defined as
G_n = 1 + R_fb/R_in
with R_fb = feedback resisitor and R_in = all input resistors in  
parallel for an inverting summing amplifier. For a single-input  
noninverting amp, noise gain and gain are equal.
Hope this definition is correct, I can't find a reference right now.

Ingo