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| OK audio gurus: What are the highly regarded FET-input op amps these days? |
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| CodyDowling:
I just designed in the OPAx140 from Texas Instruments. (I'm using the OPA2140, for dual op-amps, but they also have a single and a quad version, IIRC). The specs that I cared about looked good, but without knowing what you're using for it's a little hard to say if it's a good fit. I was worried about relatively low noise, relatively good accuracy, and ridiculously high input impedance with a reasonably low input capacitance. It fits nicely for that application (monitoring audio signal to feed into a DC servo), but it will depend on your application specifics. |
| cvanc:
Thanks for all the comments. A couple of you asked what the specific repair was. It was an old piece of stereo equipment, a "Quad 34" preamplifier. I'm guessing here, but it's maybe early 80's vintage? The preamp is op-amp based and is populated with TLE2071 and TLE2072 chips (http://www.ti.com/lit/ds/symlink/tle2071a.pdf). This is a part I had not encountered before, and as I said at the beginning you can still get them but they're kind of expensive. The board has many high impedance nodes and a fairly spread out layout - not something to blindly drop a super fast modern chip into. It would probably oscillate. It wasn't really about improving the performance after repair. It was about finding a replacement part that was more common and hopefully less costly. Again, thanks for the advice and opinions. |
| RandallMcRee:
Just for grins, here is the bible on opamps for low distortion applications. The 4562 *is* very good. http://www.nanovolt.ch/resources/ic_opamps/pdf/opamp_distortion.pdf There are some applications where these specs do matter. Samuel Groner, for example, designs oscillators with vanishingly low distortion. That is necessary when using said oscillator to measure other equipment. |
| David Hess:
Consider what the LF411 and LF412 are. This is not quite straightforward because the two parts are not directly related. The LF411 is a single version of the LF353 dual and the LF412 is a dual version of the LF351 single. So: LF351(S)/LF412(D) 4MHz 13V/us 25nV/SqrtHz@1kHz LF411(S)/LF353(D) 3MHz 15V/us 18nV/SqrtHz@1kHz 1.8mA/ch The only thing which makes these parts suitable for audio is the low transconductance of their JFET differential inputs which allows higher bandwidth and slew rate while maintaining unity gain stability. So replacements will need JFET inputs with class-AB outputs. Modern jelly bean replacements are the TL051/TL071/TL081 and TL052/TL072/TL082. The TL05x series has better precision. The TL07x series used to be the noise tested versions of the TL08x series but today they are the same. JFET Singles: LF351 SO only from STM, Eww LF356 $0.83 5MHz 12V/us LF411 $1.29 3MHz 13V/us TL051 $0.60 3MHz 20V/us 18nV/SqrtHz@1kHz Improved TL071/TL081 Higher Precision TL071 $0.55 3MHz 13V/us 18nV/SqrtHz@1kHz Noise Tested TL081 TL081 $0.52 3MHz 13V/us 18nV/SqrtHz@1kHz JFET Duals: LF353 $0.60 3MHz 13V/us LF412 Discontinued TL052 $0.70 3MHz 20V/us 18nV/SqrtHz@1kHz Improved TL072/TL082 Higher Precision TL072 $0.68 3MHz 13V/us 18nV/SqrtHz@1kHz Noise Tested TL082 TL082 $0.75 3MHz 13V/us 18nV/SqrtHz@1kHz JFET Quads: TL054 $2.62 3MHz 20V/us 18nV/SqrtHz@1kHz Improved TL074/TL084 Higher Precision TL074 $0.64 3MHz 13V/us 18nV/SqrtHz@1kHz Noise Tested TL084 TL084 $0.60 3MHz 13V/us 18nV/SqrtHz@1kHz Somewhat improved replacements for these: AD711/AD712/AD713 LT1792/LT1793 Single only but lower noise, lower distortion, and lower input capacitance. In his book, Douglas Self discusses a bunch of more modern JFET parts: OPA134/OPA2134 Not much of an improvement. OPA604/OPA2604 Not much of an improvement. OP627 Great improvement. |
| Marco:
A great improvement towards what exactly? When even the venerable AES needs to do something extremely silly like making the circuit amplify the distortion by 80 dB to do a listening test you can easily see HiFi kinda lost the plot. |
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