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| OK audio gurus: What are the highly regarded FET-input op amps these days? |
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| Zero999:
--- Quote from: spec on December 07, 2018, 10:19:59 am --- --- Quote from: Mechatrommer on December 06, 2018, 06:22:02 pm ---1) you may not like the answer (since you provided open question) 2) i'm not audio guru, just a repair stuffs, like you mentioned... but... TL072 (from AQ-2000R 2KW Class-D amp) (picture 1) 4558D (from PA37-M350 2.5KW monoblock) (picture 2) 4558D (from AQ-854 1.5KW Class-AB amp) (picture 3) another i checked 4558D from AQ-2580R 350 x 4W ab-amp (no picture) its looks like 4558D wins but it aint fet opamp, if you want fet, then we have TL072 there appearing once in my statistics. they are not new chip, but they are far from obsolete, even in hung low grey beard market, and they cost like dirt... ymmv. --- End quote --- Apart from not being MOS input, the 4558 is two 741s, which are not good for audio work... sorry :) --- End quote --- The RC4558 is a bit better than the uA741. It's faster and lower noise. http://www.ti.com/lit/ds/symlink/rc4558.pdf https://www.st.com/resource/en/datasheet/cd00001252.pdf And why are those op-amps no good for audio? --- Quote from: Marco on December 07, 2018, 10:34:07 am --- --- Quote from: floobydust on December 06, 2018, 06:00:58 pm ---OPA627 or OPA637. But $40-57 each :o --- End quote --- OPA637 might make some sense if it just fits your application perfectly and component cost is largely irrelevant. Getting an OPA627 instead of an OPA140 is just throwing money away though. OPA627 is a joke at HiFi nutter's expense. --- End quote --- --- Quote from: spec on December 07, 2018, 10:28:11 am --- --- Quote from: floobydust on December 06, 2018, 06:00:58 pm ---It's not that simple, you have to consider what the op-amp is seeing and doing. Line driver? Tone controls? DAC reconstruction filter? The better FET-input op-amps are expensive because they are laser-trimmed and prices can be crazy. I would recommend OPA2134 or OPA134 and if you have money the OPA627 or OPA637. But $40-57 each :o Careful swapping in a higher bandwidth part, they can oscillate in "old" circuit designs and not all parts are unity-gain stable. --- End quote --- Second the OPA2134 and OPA134. Nicely behaved, nice price, and sound nice too. :-+ --- End quote --- If this were a new design then I'd agree use the OPA2134, OPA627 etc. but blindly replacing an older LF412 in an existing piece of equipment with them is a very bad idea and the OPA637 isn't even unity gain stable, just no! If you have the schematic for the existing piece of equipment or it can be easily reverse engineered and the layout appears to be suitable for these faster op-amps, then you stand a good chance of being able to do it, without any ill effects, but additional supply decoupling and compensation capacitors may be necessary. |
| Kleinstein:
The OPA627 is mainly good for very low input bias - usually no need for this with audio. Noise and distortion wise OPA1641 or OPA827 perform better. It depends very much on the circuit if a faster OP can be used. If there are more complicated parts (especially active parts) in the FB path, a faster OP can be a problem. However typical preamplifier circuits with just some gain or filtering may very well work with an faste OP too. For a better (lower noise) replacement with not much higher GBW, the OPA145 could be an option - though no THT. The OPA134 is not the highest performance, but still available in DIP and not that much faster. |
| cvanc:
Thanks everyone for your input and suggestions, they are always appreciated. I'm going to sidetrack my own thread and ask a question now about the various versions of OPA2134. They look nice to me, but Digi-Key stocks 2 slightly different part numbers. Here's the kicker: As far as I can see even the T.I. datasheet (link below) doesn't explain what the difference is. The 2 part numbers read identically in all specifications. They are OPA2134PA and OPA2134PAG4. The 'G4' is never explained in the datasheet. Any idea what it all means? And thanks again. http://www.ti.com/lit/ds/symlink/opa134.pdf |
| SiliconWizard:
--- Quote from: HB9EVI on December 06, 2018, 06:54:29 pm ---If need super low noise, I use an OPA2134, but as far as I remember this a BJT input opamp. --- End quote --- No it's actually not. "A true FET input stage is incorporated" as stated in its datasheet. |
| Bassman59:
--- Quote from: SiliconWizard on December 06, 2018, 06:04:46 pm ---Some references come to mind: OPA2134 OPA2604 OPA1652 --- End quote --- Thumbs up to all three. |
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