Low Noise opamps for 2014?

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#121
> Euvl, there are no more leftover boards but you can get the gerbers.
> I will do a rededign to get rid of the 1 dB droop at 1 MHz, with 2 channels for cross correlation and RS-170 relays to automate the setup somewhat.

Many thanks. Just send me a email when you are ready.
If you so wish, we'll get the PCB done and make them available to those interested.
Any positive (financial) balance will be donated to the forum.


> But that may take some time.

No rush. Ready when you are.


> Proposals for the coupling C are most welcome. Must be easily available, no snake oil please.

My vote is for WIMA MKS2 6.8µ. Much easier to get than the same for 10µ.
(e.g. from Reichelt)
Else Panasonic has a SMD polyester 1µ, and Rubycon even a SMD 10µ.
But they are rather expensive, compared to the WIMA.

http://www.digikey.de/product-detail/de/ECP-U1C105MA5/PCF1132CT-ND/285459
http://www.digikey.de/product-detail/de/16ST106MC44532/1189-1792-1-ND/3719908


Patrick
 
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#122
gerhard said:
KGRLEE, I have never used that for audio. A 5 Ohm MC probably would have more thermal noise, so there is no point to do it
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A 5R MC has 0.28nV/rtHz. My headamp raises the noise by (slightly more than) 3dB ie a Noise Factor of (slightly more than) 3dB (This is in fact one of my test cases)

Your amp with 0.22nV/rtHz will raise the noise by 2.1dB so (slightly more than) 0.9dB better than mine 🙂

The 'nearly 3dB' difference I mentioned in my previous post is of course short circuit Env.
 
#125
jcx said:
a question is, is it "bad" compared to any other low noise fet op amp solution - the AD743/745 has large input C, a few other fet input op amp datasheets warn of the input fet C Vcm modulation too - OPA134 has a paragraph but no plot

since no one else plots it the same we really don't know - many low distortion audio op amp datasheet plots are done with the super low Z "distortion magnifier" noise gain circuit that hides the effect

the "Difet" OPA627/637 is unusually good in this regard - Groner includes a test of this input impedance nonlinearity in his work SG-Acoustics · Samuel Groner · IC OpAmps

Walt had an article showing how composite amps can largely overcome the effect http://www.analog.com/static/imported-files/application_notes/742022599AN232.pdf

while Dimitri went even further: http://www.epanorama.net/sff/Misc/O...g to reduce distortion in op-amp circuits.pdf


depending on the bootstrap technique - you can get negative input Z over a frequency range if the bootstrapping has to be rolled off for to stability (if bootstrappinng both rails or the one with the Ccomp you can bootstrap away its effect too at unity gain)
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Just curious, if you wanted to bootstrap two followers from the same supply, there would have to be some kind of isolation?
 
#126
 
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#129
Lol, the words "so called Hi End Amps" sums it up nicely.

The 2068 isn't a bad device at all, far from it, but its just been totally outclassed by devices such as the LM4562.

Its all relative though... even a 741 heard in isolation can sound pretty good.

Try these and see which you prefer.
File A

File X
 
#135
Mooly said:
🙂 Its one guys take on it in a specific very low impedance application circuit. The designer of any circuit has to make the choices he/she feels are correct for the application.
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Exactly. My take is that with MOST applications, NJM2068 will equal or better LM4562 for noise.

Of course it doesn't have the street cred so get your Marketing to prepare some "hand build by virgins" labels to stick on.

2068 also doesn't have the evil latching behaviour that LM4562 is prone to on single supply stuff.

As always, horses for courses.
 
#137
From my investigations so far, the lowest noise opamp below 700 ohms is the AD4948, 700 ohms to 2.5 k is the AD4948, AD797 and LME49990. 2.5 k to 15 k is the NE5534 (amazing) and above 15 k the OP627.

The LM4562 and LME49710 are 'quite' noisey compared to the above - still very good of course.
 
#138
Yes, my lowest noise phono amp uses an input transformer withing a differential, shunt, feedback loop. That amp is so low noise that the cartridge is the limiting factor.
I use a Lyra Atlas that has around 4.4 Ohm DC impedance and puts out 1mV ( DIN ) with 5cm/sec.
After 30years of seach i also found very low voltage noise BJT´s made today.
i will not spoonfeed you here. Read the MPP thread, they are there somewhere.
When you do a parallel symmetric MC input with parallel devices you have to match for Hfe and Ube but also for early voltage. Usually the PNP goes astray. I also found very symmetric pairs, made today.
In my more affordable phonos i use paralleled Opamps. That works very well too so guys make your homework and everything is fine.
 
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