J-Fet vs regular type OP=AMP

[Stevo]

Would using a 741 type op amp inplace of a J-fet type op amp create any problems? Should work maybe noise :cry: .. They use the same type pinouts...Thanks

[Eric H]

Would using a 741 type op amp inplace of a J-fet type op amp create any problems? Should work maybe noise :cry: .. They use the same type pinouts...Thanks

impossible to say if you don't tell us the application.

-Eric

[niftydog]

depends on the application, but considering that the LM741 is one of the oldest and worst performing op amps thats still widely available, just about ANYTHING would be better than it!

[petemoore]

It'll probly work, as long as the pinouts are correct for the type of OA [Single not to be confused with Dual].
 Fuzz ?

[Stevo]

I was going to build the gargletron that uses a TL062 dual low power j-fet...I have a NTE dual low power op-amp 928M dual low power integrated op-amp, would that work?.. that is what I am going to see?? Or I will have to find a TL062..Thanks

[petemoore]

Every cross reference NTE substitution I've tried, worked.
 I wouldn't make a habit of buying NTE Chips unless I could get some kind of 'discount' going.
 If your NTE Says it's a low current Jfet Input OA, then that's what it is and you'll find only small tonal differences between that and a TL062.

[Stevo]

My NTE subsitution is not a J-fet amp it is a integrated op-amp, not a j-fet that is what I wanted to know if it could be used? Thanks

[Joe Kramer]

the LM741 is one of the oldest and worst performing op amps thats still widely available, just about ANYTHING would be better than it!

THIS IS VERY SUBJECTIVE!  (Although, paradoxically,  true by TECHNICAL STANDARDS.)  I wouldn't use a 741 for complex program material (full frequency, high fidelity music, ), but musical INSTRUMENT applications are totally different.   In that respect, generally speaking, your ears don't give a damn about technical standards.  The only rule that matters in a musical instrument effect is this: IF IT SOUNDS GOOD, IT IS GOOD.   One of the qualities that makes the 741 technically bad, namely low slew rate, makes it very nice for guitar IMHO.  Besides, it has lower noise, lower current consumption, and better ouput drive than the TL0XX series!    The best way to go is to put in a socket and try 'em all.  Use the one that SOUNDS good to you!

Regards,
Joe

[Eric H]

My NTE subsitution is not a J-fet amp it is a integrated op-amp, not a j-fet that is what I wanted to know if it could be used? Thanks

When you ask technical questions about specific devices it's helpful to provide a link to the schematic. Sometimes you get lucky and someone with recent knowledge of (for instance)  the gargletron can help you. I have only read the name, myself, and still can't answer your question.

-Eric

[Stevo]

http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html                                 Here is the link to the gargletron a envelope filter type!!!

[brett]

Hi.
Regarding

One of the qualities that makes the 741 technically bad, namely low slew rate, makes it very nice for guitar IMHO. Besides, it has lower noise, lower current consumption, and better ouput drive than the TL0XX series!

I'm not aware that the 741 has lower noise than the TL0XX series.  In fact, I thought the latter has better specs.  A TL071 has certainly sounded quieter than a 741 in the circuits where I've tried both.  (and a TL072 is certainly quieter than a 4558).
Also, given that the load on most of these chips is multi kohms, does the "output drive" really make a difference?  I assume that you're talking about output current capacity.  The 741 would be out-performed by the TL series in terms of voltage swing.

Are there any examples of circuits where the 741 really shines??  

cheers

[niftydog]

your ears don't give a damn about technical standards.

well, speak for yourself. But I do take your point. However, being an engineer I only know one language - techno gargle!  

now, to stick up for me and my kind (like brett!);

the supply current difference according to my info is 0.1mA in FAVOUR of the TL074 which is a QUAD op amp!!!

the noise spec is rarely given for the LM741 (because it's so awful) and there's no way that I would ever accept that the LM741 outperformed a TL0XX in this regard.

and I have no idea how you could make the assertion that the LM741 drives more current than the TL0XX, but the TL0XX series allow a greater voltage swing at the output which is more desireable in a well designed circuit (with high input impedances).

[Eric H]

http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html                                 Here is the link to the gargletron a envelope filter type!!!

OK, due to the high resistances in the feedback loops, Id say the 741 types (or other bipolar input types) will be quite noisy. I would suggest using any of the specified opamp ==or another with jfet input.
I have no reference for the NTE part# 928m

-Eric

[Joe Kramer]

I'm not aware that the 741 has lower noise than the TL0XX series.  In fact, I thought the latter has better specs.  A TL071 has certainly sounded quieter than a 741 in the circuits where I've tried both.  (and a TL072 is certainly quieter than a 4558).
Also, given that the load on most of these chips is multi kohms, does the "output drive" really make a difference?  I assume that you're talking about output current capacity.  The 741 would be out-performed by the TL series in terms of voltage swing.

Are there any examples of circuits where the 741 really shines??  

Though 741 spec sheets don't quote noise figures, I don't think it's because the designers had something to hide.  I think it's because the chip was never specifically designed for audio.  However the Mitsubishi 5218, which the data sheet says has "virtually the same characteristics as the 741" gives a a noise spec of 2uVrms.  Usually noise specs are given in V/us  (EDIT: should be nV/Hz. :oops:  See later posts), but the equivalent noise spec for the TL072 gives 4uVrms, twice as high.   In standard noise spec terms, an 072 is about 18 V/us (s/b nV/Hz :oops:): not that great.

TL0XX series don't like to drive capacitive loads (ie cables) or they can oscillate and go into phase reversal--in other words, they crap out.  Not that this is a hugely practical problem for a couple of guitar cables or a buffer, but the 741 is stable in that regard and never exhibits these problems.

As for current draw, data sheets I've seen give about 1.5mA for 741s, and 3mA for 072.  The data sheets vary, but if you swap an 071 and a 741 in circuit and measure the current consumption, the 071 always hogs about twice the current in my experience.

As far as where the 741 shines, well, we're back to where we started: it's very subjective.  My whole point is that deriding (or advocating)  a particular op amp based on specs is sort of like assuming you know about a place because you've seen it on a map.  You should listen first, check specs for academic reasons later, if at all.   Personally, I happen to think the TL0 series is scratchy and thin for everything guitar related, and I happen to think 741/1458 has a nice round sound with solid midrange body to it.  This conclusion is due to swapping and swapping constantly to find the one that sounds best, regardless of specs.  For EQs, buffers, phasers, and just about anywhere you can use an op amp, I usually go for 741s and 1458s every time.  But that's just me!


Regards,
Joe

[niftydog]

well, confusion abounds in that post among the wildly different data sheets. Don't know where you pulled the rms noise spec for the TL072, but regardless I'd sooner go for 18nV/(SQRT)hz over 2µVrms anyday! (V/µs is slew rate.)

I'm definately anti-mojo. Flat ­Æ' response and I'm happy.

[puretube]

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(scroll down to pg.8 : ad on the right... only 25$)

[Joe Kramer]

well, confusion abounds in that post among the wildly different data sheets. Don't know where you pulled the rms noise spec for the TL072, but regardless I'd sooner go for 18nV/(SQRT)hz over 2µVrms anyday! (V/µs is slew rate.)

Oops!  My bad!  A slip of the fingertip.  Please forgive!   :oops:

You are correct: V/us is slew rate.  nV/Hz is voltage noise.  

RMS noise spec for TL072 here:

http://www.alldatasheet.com/datasheet-pdf/pdf/NJRC/NJM072.html

M5218 data here:

http://www.alldatasheet.com/datasheet-pdf/pdf/MITSUBISHI/M5218.html

Sorry for the "abounding confusion." :lol:  

Regards,
Joe

[R.G.]

JFET input opamps are technically better in every classical specification I can think of.

The 741 comes from a time when simply getting an operational amplifier inside a single IC package was a monumental task. it's too slow for high level audio, noisy, has a relatively high input bias, and poor (and asymetrical) slew rates.

There are a few applications where only a 741 will do. These are places where the circuit was designed to take advantage of the quirks of the 741, and a no-quirks opamp will not work.

The 741 was the best of its time - back in 1968, 37 years ago.

[Joe Kramer]

The 741 was the best of its time - back in 1968, 37 years ago.

Yet it's still in production today, PDIP as well as SMT. . . .  

[R.G.]

Yet it's still in production today, PDIP as well as SMT. . . .

Yeah - amazing!

I suspect that today's "741" is not the same as a 70's 741. For one thing, we no longer have semiconductor fabs that are crude enough to make them that bad.