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Old 20th Feb 2018, 12:56 am   #1
bikerhifinut
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Default Difference between a TL072 and NE5532?

Until today I had more or less thought that these audio op amps were more or less interchangeable.
What started this off was building up one of the velleman kit magnetic cartridge preamps based on a TL072 with the EQ in the feedback network.
Everything seemed fine on the initial build. The only mods i made were to use polypropylene capacitors on the EQ instead of ceramics (ugh!) and polyesters instead of electrolytics for the 1uF DC blockers on input and output. And 150pF across the input to give a bit of capacitive loading for my mag cartridge.
As built it was a bit weedy for my power amps that need over half a volt to drive to full power (I use either a "passive" volume control or a unity gain cathode follower buffer, or a rega preamp set to unity gain.)
In fact it was struggling to drive the old Leak Stereo20 and that only needs 125mV.
So after a bit of advice and thought, I altered the feedback resistors R8 and R9 to roughly 770 ohms by the expedient of a 1k in parallel with the existing 3.3k.
Now I know that best practice would be to use a 2 gain stage circuit but the purpose of this exercise was to see if I could get an ACCEPTABLE result for a less demanding application, such as perhaps replacing a ceramic cartridge for a magnetic in an older Gramophone that had a deck up to using a heavy ish tracking mag cartridge, (Some DJ stuff is good for 5g tracking weights).
Anyway, first impressions have been very favourable and I am getting a nice sound via my reasonably decent stereo system, certainly good enough for many people.
The issue occurred when out of curiosity I swapped the TL072 for a NE5532, straight away I am getting a distorted sound, the sound is ok on first switch on then rapidly fades away to a tinny distorted tone and is much quieter. I swapped in another NE5532 and got the same result. Now prior to altering the gain the NE5532 worked fine.
I'm powering it with a pair of PP3 in series for 18V, it does seem to perform ok with 9V but velleman recommend 10V to 30V supply. I guess to provide a bit of headroom on the output.
So can anyone shed some light on this? In theory the NE5532 should be a shade better on noise levels but perhaps I pushed it out of its specification with the extra gain, I must be running pretty much on the edge squeezing this much out of a single op amp.
link to circuit here:
https://www.velleman.eu/downloads/0/...nual_k2573.pdf

Gotta say though, with the standard TL072 it's fine and with the gain tweak it might be worth considering as a means of keeping an older music centre or Record player going. These days a decent mag cartridge seems to cost less than a dodgy far eastern ceramic, and the used market can chuck up some bargains.

Andy.
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Old 20th Feb 2018, 5:00 am   #2
Radio Wrangler
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Default Re: difference between a TL072 and NE5532?

The NE5534 is a quite different beast to the TL072.

The audiophile sort of tube-rolling world tries swapping anything which has the same pinout, and has a sort of hit parade of what order of preference the parts fit into.

The nerdy engineering design sort of world says that these parts have quite dramatic differences in some of their parameters and not only will each work best in circuits designed around them, they may not work at all satisfactorily in some circuits the other will thrive in.

The TL072 is a surprisingly good opamp for audio applications, meaning it was designed to be a general purpose part with plenty of gain, and better than average bandwidth, but its big selling point was its high impedance JFET input stage, giving verly low bias currents. It was sold as a step up on the old 741 bread and butter opamps. Its weak point is the input offset voltage which isn't particularly low and is a bit temperature sensitive. It has its compensation capacitor inside, made on the silicon.

The NE5534 is also an 'improved' part compared to the 741 benchmark, but it's been improved in the opposite direction. It's big selling point was a very low noise bipolar input stage, and a lot of bandwidth. So the bandwidth can be tailored, its compensation capacitor has to be added externally to the chip, so the user can choose where to pitch the dominant pole, or can even go for more complex (bad pun) compensation schemes. It has an output stage which can source a lot more current than the 741 and TL072 families. Its big weak point is that the low noise/wide bandwidth features were achieved by running moderate gain bipolar transistors in the input stage at significant DC currents. So the bias currents flowing in its input pins are very large as opamps go.

The TL072 gives its best noise performance with higher impedance sources, and its low bias currents allow circuit design with high resistor values and low currents. It's a good choice for piezo-electric transducers. Ceramic and crystal cartridges will go well with a TL072 in the right circuit. You can drop a TL072 in place of most general purpose opamps without circuit changes and expect no surprises. You can also use it in high impedance circuits where a 741 wouldn't work.

The NE5534 shines at low noise performance with low impedance sources. It has to have lower impedance feedback circuits or else that big bias current will upset things. It really does have to have that external compensation capacitor connected for stability. Noise-wise, the NE5534 makes a good choice for a RIAA input stage for moving magnet or moving iron cartridges, though yo'd want to add a discrete stage if moving coils are your weapon of choice.

Put a TL072 in a circuit designed for an NE5534, and it won't see impedances conducive to its best noise performance. If the circuit exploited the NE5534's driving ability to drive 600 Ohm lines or headphones, the TL072 will be left gasping.

Put an NE5534 in a circuit designed for a TL072 and it will miss its compensation capacitor. Stability will be an issue. It will be presented, most probably, with AC impedances well away from where it gives its best noise behaviour. If the circuit has exploited the TL072's very low bias current, that of the NE5534 could offset the output DC voltage close to a rail. You might hear distortion caused by either HF oscillation or a big DC offset, or both.

Both ought to be able to drive the input of a Leak valve power amp.

If you want an RIAA stage using an NE5534, Peter Baxendall, no less, published an excellent one in Wireless World.

Quad used the TL072 family in their later preamps. They could probably have got a bit better performance designing around the NE5534 or NE5532, but they did not deem the difference worth the added cost.

David
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Old 20th Feb 2018, 7:17 am   #3
Diabolical Artificer
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Default Re: difference between a TL072 and NE5532?

Being of the "chuck a different opamp at the job, see if that works" persuasion I've found the 5532/4 works less often than the TL072/4, probably for the reasons David points out. It's easy to think of all opamps as triangles spewing out gain, I see though, that we have to look at datasheets and use our brains ...groan.

"So the bias currents flowing in its input pins are very large as opamps go." I thought no current flows into or out of the input of opamps - rule # 2, but thinking about it some has to if there are Q's in there for base current.

Tother Andy .
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Old 20th Feb 2018, 9:25 am   #4
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Default Re: difference between a TL072 and NE5532?

Yes, It's the base currents of the input bipolars.

One other difference I forgot to mention, overdrive can reverse-bias the b-e junction of one input transistor. And more than a few volts of reverse b-e is the most efficient way known of dispatching a bipolar transistor to the afterlife, so the NE5534 fixes this vulnerability by having a pair of diodes across the + and - inputs. The NE5534 therefore wont work in a lot of cookbook opamp circuits where they get used as voltage comparators... It's limited to +/- one diode drop on its input. Try more and you get a lot of current flowing..

Other opamps may use other forms of input protection but the shunt diodes suit the NE5534's target applications where overdrive should not happen, and other methods like series diodes spoil the noise and bandwidth performance.

Horses for courses, and this one was made to be a good audio amp. It turned out to be a great audio amp. It's been out for 40+ years and there are some a little better in various ways, but not that much better.

Signetics done good!

David
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Old 20th Feb 2018, 10:37 am   #5
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Default Re: Difference between a TL072 and NE5532?

A minor point, but worth remembering: the NE5534, which is a single opamp, needs an external compensation capacitor. The NE5532, its dual counterpart, has internal compensation capacitors. The TL072 is also a dual opamp.

Having had a quick glance at the Velleman circuit, there's nothing about it which suggests to me that it wouldn't work with an NE5532. The potential divider R1/R3 at 22k each is a bit higher than I'd instinctively go for, but it ought to be OK. If the sound is fading away via distortion to nothingness, that suggests that either the DC conditions are going wrong or it's oscillating. If both channels are fading in the same way, it may be the DC conditions that are the problem, because both channels share the R1/R3 bias network.

If you feel like investigating the problem, it would be instructive to know what the voltages on the opamp's pins are when the problem occurs.

Many opamps are also very unhappy driving capacitative loads and tend to go unstable. I can't remember whether the NE5532 is one of them, but it's another thing that may differ between the it and the TL072. I don't know what your power amplifier input looks like, or whether you have long cables, but adding resistors of a few hundred ohms in series with each opamp output coupling capacitor should stop oscillation if it's present.

Chris
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Old 20th Feb 2018, 10:58 am   #6
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Default Re: difference between a TL072 and NE5532?

Quote:
Originally Posted by Radio Wrangler View Post
Yes, It's the base currents of the input transistors.............

......Horses for courses, and this one was made to be a good audio amp. It turned out to be a great audio amp. It's been out for 40+ years and there are some a little better in various ways, but not that much better.

Signetics done good!

David
AFAIK the NE5534 in its original incarnation as the Mullard TDA1034 was yet another innovative Philips creation, designed primarily for professional (studio) audio applications. The clue lies in its 600 ohm output load specification. Back in 1976 at Neve Electronics, we were starting the design of what turned out to be the highly successful '54' series of mixers, beginning with the portable 5422 'suitcase' mixer. Before then, our amplifiers had been discrete, but ICs were beginning to make a great deal of sense.

Rupert Neve himself was involved in that project and I recall that he called Alex Balster, then head of Philips Studios, asking his opinion of the performance of the TDA1034. Alex was enthusiastic, so that clinched our decision and the start of the progressive transformation of Neve circuits from discrete to IC.

We did soon also start to introduce the TL072 family for input circuitry because everything got rather warm with lots of NE5534/TDA1034s in the channel strip!

Martin
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Old 20th Feb 2018, 1:31 pm   #7
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Default Re: Difference between a TL072 and NE5532?

One interesting thing about OP amps, despite the data sheets, you don't really get to see how they perform at various frequencies for both large and small signal conditions until you wire them up for the application.

A lot of it depends more on the OP amp's output stage design, than input stage unless you are running the inputs close to the supply rails.

Many op amps produce terrible results for audio, like an LM358, most specimens of which display cross over distortion. Other types, if you want at least 3/5 of the peak to peak output voltage, compared to the power supply, give distorted and asymmetrical outputs.

Interesting you should mention the TL072, because this is one of the few common garden op amps which has a very good low Z output stage and it can produce distortion free output swing closer than most to the supply rail limits and has a slew rate suitable for audio work. Another similar type you might like to try, just as good, is the TLC272.

One way you find out what the output stage impedance is, looking into it, is when you use an op amp to create a virtual earth or an artificial central rail for a power supply and you try to drive currents into its output stage.

For high frequency/RF work I would recommend the AD8056.
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Old 20th Feb 2018, 1:51 pm   #8
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Default Re: difference between a TL072 and NE5532?

Another fantastic post from Radio Wrangler, explaining the development of the TL072 and NE5532 being optimised for different things!

Quote:
Originally Posted by Diabolical Artificer View Post
"So the bias currents flowing in its input pins are very large as opamps go." I thought no current flows into or out of the input of opamps - rule # 2, but thinking about it some has to if there are Q's in there for base current.
Not quite correct - the input has NEGLIGIBLE current flowing in or out. Whether it's negligible depends on whether you can neglect the effects of 1 femtoamp, 1 picoamp, 1 nanoamp, 1 microamp, etc.

Using medium-range resistors, you can generally ignore 1 microamp, true, hence the success of the 741 years ago. But if you are trying to connect to a pH meter electrode, you'll be stuffed and you need op-amps with input currents measured in sub-picoamps.
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Old 20th Feb 2018, 2:49 pm   #9
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Default Re: Difference between a TL072 and NE5532?

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Originally Posted by Argus25 View Post
Many op amps produce terrible results for audio, like an LM358, most specimens of which display cross over distortion.
It's possible to design LM358 circuits to reduce the distortion, but I agree it's a poor choice for audio circuits given that audio specific chips like the TL072 cost no more. It's odd that there are so many preamp circuits on the web using the LM358 - presumably there was a significant cost advantage at some stage in the past.
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Old 20th Feb 2018, 3:34 pm   #10
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Default Re: Difference between a TL072 and NE5532?

Perhaps because the LM358 (and related cousins) has the advantage of being "rail to rail" and works at significantly lower supply voltages then the others? It's a handy little op-amp and I use them a lot, but in no way is it an "audio" op-amp.

One drawback of the NE5532/4 opamps is the 4mA per op-amp section current drain - the dual 5532 runs rather toasty when you want to maximise headroom by running it from higher supply rails.

If you need an op-amp that has nearly as good distortion performance, but without the problems of high DC input currents, the OPA134 is a good choice. The dual is the OPA2134. I've used them extensively, but they've got a bit pricey in recent times, so use the 5532 wherever I can. The NJM2114 is another worthy choice - that's used in a lot of Arcam gear, for example. The TL072 is fine for non-critical stuff, as is the LM833. But a lot of the time, the surrounding circuit conditions dominate the overall performance, as has already been alluded to...

I'm always amused by this quote from Douglas Self:

Quote:
With horrible inevitability, the very popularity and excellent technical performance of the 5532 has led to it being criticized by subjectivists who have contrived to convince themselves that they can tell op-amps apart by listening to music played through them.
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Old 20th Feb 2018, 3:39 pm   #11
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Default Re: Difference between a TL072 and NE5532?

Interesting stuff. So much op-amp theory is devoted to 'Ideal' ones so it's nice to have some real world information.

I've made a couple of amplifiers with 741 gain stages (one feeding BD transistors and the other an EL84) and been very happy with them. I tried swapping these for NE5532s and couldn't tell any difference.
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Old 20th Feb 2018, 5:20 pm   #12
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Default Re: Difference between a TL072 and NE5532?

Quote:
Originally Posted by cmjones01 View Post
Many opamps are also very unhappy driving capacitative loads and tend to go unstable. I can't remember whether the NE5532 is one of them, but it's another thing that may differ between the it and the TL072. I don't know what your power amplifier input looks like, or whether you have long cables, but adding resistors of a few hundred ohms in series with each opamp output coupling capacitor should stop oscillation if it's present.

Chris
5532's do have a tendency to oscillate in some circuits and output stages generally need a series resistor. I have successfully used 100 ohms on single-ended outputs.
I'm just looking at the circuit diagrams of a well-respected mixing console (but not one of Hartley118's) - it used 56 ohms on each leg of the 5532 balanced output stages.
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Old 20th Feb 2018, 7:36 pm   #13
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Default Re: Difference between a TL072 and NE5532?

Quote:
Originally Posted by ThePillenwerfer View Post
Interesting stuff. So much op-amp theory is devoted to 'Ideal' ones so it's nice to have some real world information.

I've made a couple of amplifiers with 741 gain stages (one feeding BD transistors and the other an EL84) and been very happy with them. I tried swapping these for NE5532s and couldn't tell any difference.
Out of interest, we once carried out listening tests on a live source in a major recording studio comparing a channel with the standard NE5534s with one where they'd been replaced with 741s. None of the 'golden ears' could detect a difference!

Martin
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Old 20th Feb 2018, 8:43 pm   #14
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Default Re: Difference between a TL072 and NE5532?

Thanks for the explanations chaps, I did some late night homework last night and the light bulb did start to glimmer.
I consider the experience to have been a useful learning experience.
As stated earlier, I had tweaked the feedback to give a bit more gain and until that point the NE5532 worked just the same as the TL072. Which now I understand
Anyway it's not as bad as I expected, it makes a jolly pleasing sound. yes it's a bit rough round the edges but all in all it ain't half bad.
If I was to make a serious RIAA stage for my own or a more critical use, then I would always have gone down the 2 gain stage route and used the 5532 in an appropriate manner.
Many thanks for the enlightenment folks.

Andy
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Old 20th Feb 2018, 11:24 pm   #15
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Default Re: Difference between a TL072 and NE5532?

I think the old 741 is a very good OP amp if it is used in the appropriate circuit where the input voltages are kept sensibly within the recommended range and you don't want or expect high level output voltages, or high frequency capability, expect to amplify very low level signals or are too worried that the OP amp's open loop gain is not high enough to get the circuit to behave as though the OP amp was an "ideal OP amp" in closed loop conditions.

So the performance of a 741 is more of a mix of the external circuit design and the OP amp performance, rather than the external circuit alone, which as noted, ideally it should be. Maybe it is almost sad & ironic that the more ideal or perfect an OP amp is, the less contribution its performance limitations make to the actual circuit it is used in. So in the end, there is little to pick between many types for audio, especially under the RF spectrum.

I have some military spec 741's and they are the most reliable and robust and beautifully made OP amps ever, despite the low specs by modern standards. Low slew rate OP amps can be handy to for high frequency immunity, so it is not always a bad thing. I used this feature of an OP295 OP amp once to create ramp signals from square waves as in slew rate mode they make beautifully linear integrators.

One thing I heard from the audiophile industry, I still do not know if it is a real problem, or not, but it is plausible;

The claim is that when an amplifier is switched on & off the coupling capacitors charge & discharge into the inputs of OP amps, considering ones with bjt inputs. This zeners the input junctions relentlessly over time, degrading the OP amp performance.This has caused some people to re-populate their entire pre amps with new OP amps.

I set up a series of experiments zenering the B-E junction of signal transistors, it definitely does lower the hfe (there is an interesting paper from Motorola on this effect which is ill understood). But I don't know if this is a real or practical problem in HiFi preamps with OP amps.

Last edited by Argus25; 20th Feb 2018 at 11:36 pm.
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Old 21st Feb 2018, 12:28 am   #16
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Default Re: Difference between a TL072 and NE5532?

Quote:
Originally Posted by Argus25 View Post
I set up a series of experiments zenering the B-E junction of signal transistors, it definitely does lower the hfe (there is an interesting paper from Motorola on this effect which is ill understood). But I don't know if this is a real or practical problem in HiFi preamps with OP amps.
The effect is real. During zener action there is migration of dopants in the semiconductor layers. Hfe is degraded, Ft is degraded, and noise figure too. These things are measurable.

The back-to-back diodes in the NE5534 protect the input stage, and the diodes should have no effect in an operating preamp.

The sequencing of multiple supply rails is a classic problem. If you try to sequence the supplies, you can never find an acceptable sequence to suit all the devices being powered. The escape route is to forget sequencing, and instead to design the circuitry so it can survive unscathed any and all combinations of supply voltages. This way if a single rail fails, you only have the power supply to fix, and you don't lose sleep worrying about transients.

David
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