[sdiy] Happenin' new opamp

[Tim Ressel]

I've gotten an education on op amps after looking at all the noise 
specs. There are some real surprises, both good and bad. Look up a TL062 
sometime. Also how close they can get to the rail has been an issue. I 
do Eurorack and with 12 volt rails, and it becomes tough to get to 10 
volts with older amps. The 1678 can fly within 0.8V of the sun, er, 
rails. Sometimes that extra volt makes a difference.

--tim


On 5/23/2017 6:59 PM, Michael E Caloroso wrote:
> A few months ago I lowered the noise floor in the notoriously noisy
> ARP 16 voice piano by replacing all the 4558s in the audio path with
> OPA2134s (amongst other circuit corrections).  The original opamps
> were RCA and the circuits were single rail designs - wouldn't had been
> hard to improve the noise.  OPA134 is about on par with the OPA1678,
> give or take some pros and cons.  The OPA2134s were almost $4 apiece
> from Mouser.
>
> MC
>
> On 5/23/17, rsdio at audiobanshee.com <rsdio at audiobanshee.com> wrote:
>> Thanks for the link, Tim. I am a fan of Texas Instruments' op-amps,
>> especially the Burr Brown family (isn't that where OPA comes from?). I've
>> investigated the OPA1662 / OPA1664 as well as the OPA1641 / OPA1642 /
>> OPA1644, but had not seen the OPA167x before.
>>
>> I don't know whether I can find the citation now, but I remember reading
>> that through-hole chips actually have more problems than SMT. The reason
>> given is that the through-holes themselves introduce inductance that affects
>> the performance of the circuit. SMT chips suffer from stray capacitance, but
>> only if there is a power plane directly under the SMT pads. You can avoid
>> the unintended capacitance in SMT designs by voiding the power plane under
>> the pads; in contrast, there is no way to avoid the unintended inductance of
>> through-hole designs because those pins have to go through the PCB.
>>
>> I seem to recall someone mentioning non-plated holes and soldering both
>> sides of through-hole parts - component side and solder side - in order to
>> avoid the inductance, but that is not a design-for-manufacturing technique
>> that average folks can afford (it effectively requires manual soldering).
>>
>> Anyway, I have no qualms about SMT designs. I have my doubts that I'll ever
>> run into circuit that literally sounds "bad" because there aren't pins going
>> through the PCB. I mean, the working parts of the chip - the die - are
>> exactly the same for both packages.
>>
>> Brian
>>
>>
>> On May 23, 2017, at 2:14 PM, "Jarno Verhoeven at ziggo.nl"
>> <jarno.verhoeven at ziggo.nl> wrote:
>>> I don't think I'll ever finish that stick of DIP TL074's I bought a while
>>> back, do love quad SMT opamps, nice n compact :-)
>>>
>>>> Op 23 mei 2017 om 21:30 schreef Tim Ressel <timr at circuitabbey.com>:
>>>> Writing to say the OPA1678 from TI is a pretty nice little amp. Low
>>>> noise, low distortion, low bias current, low cost. Is a dual; OPA1679 is
>>>>
>>>> a quad. SMT only, sad to say, but that be the times we live in.
>>>>
>>>> http://www.ti.com/lit/ds/symlink/opa1678.pdf
>>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com