[sdiy] Cheap low input current opamps?

rsdio at sounds.wa.com rsdio at sounds.wa.com
Thu Sep 12 10:14:43 CEST 2013


Since I have the numbers in my notes, I'll put them in your format.  
The list starts with the cheapest and goes up to the more expensive  
parts. Where documented, I'm also adding the input impedance after  
the typical currents.

$0.39 LM224D {2000/20000}
$0.52 TL084 {5/30}
$0.54 TL074 {5/30}
$0.62 LF353MX {25/50} 1.0 T½
$0.63 LMV324I {11000/11000}
$0.68 LF347D {25/50}
$1.05 OPA4348 {0.5/0.5} 10.0 T½
$1.65 LF444 {5/10} 1.0 T½

Prices are obviously less in quantity.


On Sep 11, 2013, at 17:11, David G Dixon wrote:
> Thanks for your reply.  Here's my assessment:
>
> Opamp {Typical input offset current/input bias current in pA}:
>
> TL06X {5/30}
> TL07X {5/65}
> TL08X {5/30}
>
> Hence, it would appear as if either the 06 or the 08 beats the 07.   
> Here's
> LF444:
>
> LF444 {5/10}
>
> I have used these in my updated CGS ASR design, and no one has  
> complained
> about droop.  I think I'll be happy with 06 or 08, but I'd prefer  
> something
> a little better.
>
> I'll definitely have a look at the others you mentioned.
>
>
>
>> I have shipped commercial products with S&H based on the OPA4374 (0.5
>> pA) and TLV2374 (1 pA), but those are more expensive than the LF444.
>>
>> Looking back at my selection notes, I considered the LM224D,
>> TL084CD, TL074CD, LF353MX, LMV324I, LF347D, OPA4348, and
>> compared them all to the venerable S&H LF398. Of those, the
>> TL084 might meet your specifications, and it's been used in
>> classics like the Prophet 5 (IIRC).
>>
>> Your best choice might be the OPA4348. It's cheaper than the
>> LF444 and has typical offset and bias currents of only 0.5 pA.
>>
>> Brian Willoughby
>> Sound Consulting
>>
>>
>> On Sep 11, 2013, at 11:19, David G Dixon wrote:
>>> I'm looking for a cheap alternative to the LF442/LF444 opamps, which
>>> have very decent input current specs and therefore recommend
>>> themselves for use as S&H buffers (typical offset current 5 pA,
>>> typical bias current 10 pA).
>>> I'm coming up short with Google searches.  Does anyone here have any
>>> suggestions?  The TL06X series is pretty good with typical bias
>>> current of 30 pA, but I'm not finding anything else that isn't much
>>> more expensive.
>




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