# Beginner: does ordering matter, of components from the voltage source?

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#### nyoo

##### Member
Two very basic questions.

Are there two ways to solder this?
Apologies for an absolutely basic question. See two circuits attached. Are these circuits equivalent? My beginner's reading of Kirchoff's Current Law would lead me to believe these two are the same. (Needless to say, I'm laying out the components on a perf board, and version B fits better, but version A was specified.)

A general replacement for the UA741?
The op amp for most simple "hobby" circuits seems to be the UA741 or LM741. The LM741IP (good below freezing, DIP-8 package) version, is now beginning to be scarce.
For 5-18V supply,
in a DIP-8 package
with low risk of ESD,
where slew rate is not important,
but temperature range is important,
and priced economically,

Does the TL071IN make the running?

And which electrical characteristic on the datasheet is key to this comparison? Is it Output Current?

Thanks very much.

#### Attachments

• phototransistor A.JPG
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• phototransistor B.JPG
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#### Hero999

##### Banned
Use a comparator, like the LM311 or LM393 for those circuits.

For general purpose audio stuff use the TL071.

#### DigiTan

##### New Member
Are there two ways to solder this?
In this case, they're identical. If you were working with frequencies in the UHF range or higher, the self-inductance of the wire would start to come into play and make component placement more critical. And if the wire were hundreds of meters long, you'd have to worry about noise pickup as well. But in this case, both circuits will behave exactly the same.

A general replacement for the UA741?
For low-end general purpose op-amps, you have the Texas Instruments TL08X and TL07X series. The TL07X is pretty much a low-noise version of the TL08X chips, but both have trouble driving loads under 300 ohms. There's also the Signetics NE5532 and National Semiconductor LF355, which are both in the same performance "tier" as the Texas Instruments amps.

If you need to drive loads under 300 ohms and you want higher slew rates, basic Burr-Brown devices like the OPA132 and OPA143 might be worth looking into. Out of all of these, I'll agree with Hero that a TL071 is a good starting point. It's got a lot of improvements over the 741 and a very low cost.

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#### Speakerguy

##### Active Member
The NE5532 can both push some current and handle high rail voltages. It's my general purpose opamp unless DC accuracy matters. In that case I would use something like a TL07x series chip that uses FET inputs (actually I have a lot of OPA2132's laying around and I would use those, but for someone buying something the TL07x is a good recommendation).

#### audioguru

##### Well-Known Member
The lousy old 741 opamp is 40 years old this year.

#### crutschow

##### Well-Known Member
The lousy old 741 opamp is 40 years old this year.
I know it's not the greatest but it's old like me so I have fond memories of it. It was the first IC op amp to have internal compensation for a closed loop gain of 1, output current limit, and tolerant of input voltage to the supply rails.

#### Mikebits

##### Well-Known Member
Could be worse, like the K2-W.

#### audioguru

##### Well-Known Member
The lousy old 741 opamp was made for plus and minus supplies totalling 30V. It is not spec'd at lower supply voltages. Some do not work if the total supply is less than 10V.

Every opamp is tolerant of inputs to each supply but the 741 inputs do not work properly if they are within 3V ftom a supply voltage. Newer opamps work fine with the inputs at the negative supply (ground), others at the positive supply and others are rail-to-rail.

Its full-power bandwidth is to only 9kHz while newer opamps go up to 100kHz.
it is noisy (hissss).

May it rest in pieces.

#### nyoo

##### Member
In this case, they're identical. If you were working with frequencies in the UHF range or higher, the self-inductance of the wire would start to come into play and make component placement more critical.

For the next year, I'll probably be building circuits that control relays based on sunlight, heat, rain, wind velocity. You're talking about radio, correct?

For low-end general purpose op-amps, you have the Texas Instruments TL08X and TL07X series. The TL07X is pretty much a low-noise version of the TL08X chips, but both have trouble driving loads under 300 ohms. There's also the Signetics NE5532 and National Semiconductor LF355, which are both in the same performance "tier" as the Texas Instruments amps.

By low-end, do you mean low voltage or low price?

The SA5532 has an Output Short Circuit Current, I(sc), of 38 mA.
The LM293 -- resistant to ESD -- has an I(sink) of 16 mA.
The TL071IN - also resistant to ESD- has an I(os) of 40 mA.
The the LM741's 20 mA.
If the opamp's output goes to, say, a 2N2222 or an IRF510, can I substitute the opamp without a second thought? Or do each of these opamps imply a different condition, requiring different or extra resistors, a different transistor, etc.?

#### audioguru

##### Well-Known Member
The minimum output current of an LM393 (and for an LM293)is only 6mA and its max saturation voltage at that low current is a horrible 1.5V. They are weak because they are "low power".

The max output current from opamps varies over a fairly wide range. The minimum output current of a TL071 could be much less than the max output current from a 741 opamp.

The output voltage of most opamps goes to about 1V higher than its negative supply voltage which is not low enough to turn off a transistor unless a voltage divider is added.

#### nyoo

##### Member
The output voltage of most opamps goes to about 1V higher than its negative supply voltage which is not low enough to turn off a transistor unless a voltage divider is added.

Maybe this is drifting away from my original questions, but it looks like the right time to ask....

One of Delton Horn's books had me thinking that
- if I connect +12VDC to pin7, and
- if I connect pin4 to ground,

then the output voltage (without feedback loops) for the LM741 would be
- the lesser of +12VDC or 20,000 x [V(in+) - V(in-)], if V(in+) is greater than V(in-), and
- zero VDC, if V(in+) is less than or equal to V(in-).

Please say again: in the case of "pin4 connected to ground", the output voltage from pin6 will not be higher than 1 VDC?

#### audioguru

##### Well-Known Member
On a lousy old 741 opamp, If pin 7 is +12V and pin 4 is 0V then the output pin 6 will go from +1.0V to +11V if there is no load current and will have less swing if there is load current.

A few opamps have outputs that will go close to 0V. The LM324, LM358, MC3317x and MC3407x opamps have outputs that go down to a few mV above 0V.

Most Cmos opamps have outputs that go to 0V if there is no load current.

#### nyoo

##### Member
On a lousy old 741 opamp, If pin 7 is +12V and pin 4 is 0V then the output pin 6 will go from +1.0V to +11V if there is no load current and will have less swing if there is load current.

A few opamps have outputs that will go close to 0V. The LM324, LM358, MC3317x and MC3407x opamps have outputs that go down to a few mV above 0V.

Most Cmos opamps have outputs that go to 0V if there is no load current.

Aha, thanks. Life is easier when Output Voltage Swing is less.

To revert.

"Does ordering matter?" The answer is: well of course, Yes. I'll move those components around, until they're in the right order. It's the right thing.

And "which electrical characteristic on the datasheet is key?" The answer is: several. But, in passing, TL071 and LM393 can substitute when LM741 becomes scarce.

Still a long way to go, but with constantly noting the multimeter's responses, peering over the datasheets as if they were ancient Babylonian, and with the occasional query to yourselves, I'm making progress.

#### audioguru

##### Well-Known Member
Motorola called their dual 741 the MC1458. Many other companies copy it.
Then Motorola made an MC1741S and an MC1458S that had 741 opamps with a high slew rate that had a good output beyond 20kHz.

#### DigiTan

##### New Member
Yeah, just radio. I mean, you would also have to take component placement into account in digital logic and microcontroller projects, but not really here.

By low-end, do you mean low voltage or low price?
Mostly price and audio quality. The TL071 is a good chip but you wouldn't really find one in a high-cost stereo, you know? But are they low cost, and very good for this kind of project.

#### Nigel Goodwin

##### Super Moderator
Mostly price and audio quality. The TL071 is a good chip but you wouldn't really find one in a high-cost stereo, you know?

Only because there's little need for an opamp in a stereo system, but the mixer that created the music you listen to probably had hundreds in it - and quite possibly lower quality devices as well.

#### audioguru

##### Well-Known Member
A TL072 has harmonic distortion rated at 0.003% and noise rated at 18nV. It costs $.50US. An OPA2134 is rated at 0.00008% and 8nV. It costs$2.43US.
An LM4562 is rated at 0.00003% and 2.7nV. It costs \$4.53US.

You might be able to hear distortion at 0.2% or more.

#### Nigel Goodwin

##### Super Moderator
You might be able to hear distortion at 0.2% or more.

If you've got really good hearing!

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