[sdiy] Spare op-amp useful in gain stage?

[Quincas Moreira]

I would expect signal to noise ratio to be worse, but distortion to be
less using Roman's two opamp idea.  Probably not by much, but each
opamp stage would add a tiny bit of noise...  Am I wrong?  I usually
go this route when I need high gain, two stages....



On Thu, Jan 28, 2016 at 7:43 AM, Michael Zacherl
<sdiy-mz01 at blauwurf.info> wrote:
>
> On 28.Jan 2016, at 13:36 , Roman Sowa <modular at go2.pl> wrote:
>
>> In high gain application it's better to split to 2 opamps, this way you get much higher bandwidth than when done on single opamp.
>> For example if 60dB gain on one opamp would have 3dB bandwidth ending at about 10kHz, while 30+30dB on 2 opamps of the same kind it jumps over 300kHz.
>
> hm .. so what’s the impact on the SNR?
>
>> W dniu 2016-01-28 o 13:03, Mattias Rickardsson pisze:
>>> Hi!
>>>
>>> I was in a discussion about what to do with a spare OP-amp. These
>>> fellows come in duals and quads, and sometimes the quantities don't
>>> end up perfectly and you stand there with an extra unused op-amp.
>>>
>>> Is there any clever way of using two op-amps instead of one in, say, a
>>> noisy high-gain stage in order to reach lower noise or something like
>>> that?
>>>
>>> Douglas Self's small signal book suggests paralleling two gain stages
>>> ("multipath amplifiers"), having their outputs tied together with 10
>>> ohms to the destination, winning 3 dB SNR. Are there other clever ways
>>> of using a spare op-amp, particularly in a stage with high gain?
>
>
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-- 
Quincas Moreira
Test Pilot at VBrazil Modular