NE5532 NOT a compatible upgrade for a TL072??

[sweetbeats]

**DISCLAIMER: I do realize that a particular opamp is one link in an audio path...that it is not a magic bullet nor a coffin nail...an audio circuit is a complex entity. My inquiry below is coming from the vantage point of fun experimentation not a grand delusion.

Okay.

I have a couple pieces of gear that use the 5532 chip in the audio path. In those particular pieces of gear I like how they sound.

I have some other similar gear that uses the TL072 and there is a character that is missing.

I'd like to try the 5532 in the 072 gear to see if that is part of the character.

I was always under the impression that the 072 could be subsituted with a 5532.

I read something in a gearslutz thread yesterday that challenged this, basically saying they are not compatible. The particulars are pretty well over my head and therefore not something I would have picked up or recognized on my own but they stem around the 5532's BJT design in contrast to the 072's JFET design.

So, I thought to ask here...I don't like the "well DUH you idiot" responses I might get elsewhere. Doesn't mean you can't/won't say that here, but its different coming from people with whom I'm relatively acquainted.

 

[mshilarious]

The particulars are pretty well over my head and therefore not something I would have picked up or recognized on my own but they stem around the 5532's BJT design in contrast to the 072's JFET design.

So, I thought to ask here...I don't like the "well DUH you idiot" responses I might get elsewhere. Doesn't mean you can't/won't say that here, but its different coming from people with whom I'm relatively acquainted.

They are correct, you don't want to swap a BJT input for a FET input opamp, unless you really know that FET input is not required. FETs are much higher input impedance than BJTs, so you see them used places like DI inputs.

On the other hand, if it's a plain-vanilla mic pre, a BJT input opamp should work fine.

You can usually go the other way, FET for BJT, but be careful because sometimes the FET part is noisier, or maybe lower output current or something (note that generally only the input is FET, much of the rest and nearly always the output is BJT). So there is no substitute for reading the datasheets.

OPA2134 is a more common upgrade for TL072; lower noise, lower distortion, higher speed, slightly higher current draw.

 

[sweetbeats]

Hey, msh, thanks for the info.

Yeah...I'm not sure about the line amp applications so I'm either going to leave them as is or fiddle with a 2134...I have some laying around.

BUT, there IS a mic pre application in which it would actually make more sense to try a 5532 since that is more of a "color" application anyway. Not sure if this would be considered "garden variety" or not...it is U101...ignore the fact that there are two "U101 (1/2)"...heheh...

 

[sweetbeats]

Hm...

I'm looking at a mic pre from the same manuafacturer that uses the 5532 and it is VERY different than the one posted above with the 072...

 

[mshilarious]

I can't see what the left U101 is doing, need to see the components at its input. Based on the feedback loop, which includes the gain trim pot, it's a noninverting gain stage. It is probably not differential input, which means if this is a mic amp, there should be an earlier differential stage (should be discrete with TL072, otherwise input noise would not be acceptable), or maybe a transformer?

Right U101 is an inverting amp with gain of 3.2, that is fed by left U101, which is low output impedance. Therefore, Right U101 (and U102 for that matter) could be 5532s. Given the low gain of Right U101, if you used low offset parts you might be able to dispense with C113. I don't really get the C117/L101 filter. That's a resonant filter, so it filters only a narrow frequency band, ~100KHz I think. Normally after an opamp you just chuck all the RF you don't need with a cap only--actually C114 helps there too.

U102 is what's known as a voltage follower, it just puts the same voltage on its output as its input, so it's really just another buffer stage after the selector switch.

Anyway, I doubt based on the schemo that this is a super hi-fi mic amp, so just do whatever you like really.

 

[sweetbeats]

https://www.torridheatstudios.com/documents/Tascam/Tascam 388/Tascam 388 Mixer Input Schematic.pdf

Right...sorry about that...was trying to keep the attached image from getting too shrinky/illegible.

This is the full sheet. This is the mixer strip from the Tascam 388:

https://www.torridheatstudios.com/documents/Tascam/Tascam%20388/Tascam%20388%20Mixer%20Input%20Schematic.pdf

if this is a mic amp, there should be an earlier differential stage (should be discrete with TL072, otherwise input noise would not be acceptable), or maybe a transformer?

As you can see, discrete transformerless.

Right U101 is an inverting amp with gain of 3.2, that is fed by left U101, which is low output impedance.

• How do you determine the gain of that feedback loop?
• And do you consider low output impedance because of the value of R135?
• What would classify it as high impedance?

Given the low gain of Right U101, if you used low offset parts you might be able to dispense with C113.

• What would classify it as high gain?
• How do you determine the DC offset? Is it the sum of the offsets of the individual components and is that typically found in a component's spec sheet?
• C113 is a...coupling cap? Blocks DC?

I don't really get the C117/L101 filter. That's a resonant filter, so it filters only a narrow frequency band, ~100KHz I think. Normally after an opamp you just chuck all the RF you don't need with a cap only--actually C114 helps there too.

This is beyond me. Not asking for a lesson or explaination on it...its just not in my comprehension at this point.

Anyway, I doubt based on the schemo that this is a super hi-fi mic amp, so just do whatever you like really.

Well, right. Tascam 388. They sound just fine. At this point I'm not likely to mess with it BUT any information you're willing to help with from an educational standpoint would be great.

 

[sweetbeats]

Would the whole JFET/BIFET compatability issue be less so in a line amp vs a mic amp?

I'm just confused because there was a guy some time back that swapped out all the 072's in his Tascam 388 for 5532's...I guess that's why I'm befuddled by the reality that the two IC's aren't considered "compatible".

 

[mshilarious]

Yes, not a big issue for a line input. Note that it's BJT: "bipolar junction transistor", not BiFET, "bipolar field effect transistor", which is something so sexy I don't know much about it Something used in very high frequency power amplifiers . . .

 

[sweetbeats]

BJT...Right...thanks...

So, msh et al, bottom line here, and again this is all just for funsies when I "have nothing else to do", with a spare channel card in-hand I'm not setting myself up for immense harm even in trying the 5532 out in the mic amp correct? It would be a matter of putting them in maybe one at a time, popping the card into the unit, put a scope on it and see if there is anything oscillatory/freaky with some tone and if that looks good then try it out and see how it sounds yes?

 

[mshilarious]

Yes, you can stick them in the mic amp, nothing is going to explode and oscillation is highly unlikely.

 

[snatchman]

The TLE-2072 is a decent step up for the TLO-72.. I actually swapped some of the TLE-20XX for TLO-7Xs in my DDA console.. Had a slight improvement in definition/clairity..The 5532/4s are not bad sounding chips at all..Actually for driving outputs they perform really good..!

 

[sweetbeats]

Soundtracs used TL074's almost entirely in my MX desk...I think they used them well, but they did use 5532's for the channel output stage...I just really have a thing for the 5532's. Personal preference based on a number of different units I have heard and liked only to find there are 5532's dwelling inside so...creature of habit.

Thanks for the input, folks. Now to find myself having nothing to do...

 

[snatchman]

I actually tried swapping out the 5534s in my mixbuss of the DDA..I tried the BB OP-627s in there ( $18.00 a pop...)..To my ears, the 627s sounded " dull". I preferred the 5534s.I then switched the 5534s out for the LME-47910s..Game over..!...

 

[mshilarious]

OPA627 is one of those that's fast enough to have to worry about oscillation, although it's not a video opamp or anything really crazy. It's also a touch noisier than 5534 and it uses a bit more current, so you'd have to be careful about swapping a couple dozen in a mixer.

 

[Demolitionman]

I think I'll throw in my 2 cents worth here,....mshilarious has basically explained the difference between TL072 & NE5532 very well and...adding further,the biggest difference would be biasing these 2 chips! If you look at the the data sheets for these 2 devices,you'll notice, that while TL072 requires only 1.4mA (quescient current) the NE5532 needs 6mA,hence the resistors too are calculated accordingly.The original circuit would have taken " gain " requirement also into consideration in their design.

TL072 is a very high input impedance device > 10*4 Mohm to that of NE5532 which is in Kohm range! The noise spec too is quite different of these two,not to mention GBW.
So,a OPA2134 would be the best alternative to TL072 IMHO. I've been using TL072,NE5532 & OPA2134 exclusively in most of my design projects,& the improvement from TL072 to OPAxxxx is remarkable indeed. Mr.Douglas Page the brain behind many of of Soundcraft mixers has written a series of excellent articles on this subject,which I would recommend to anyone interested in opamp circuit designs.

I always use BJFT (LFxxx,TL072,OPA2134 etc) devices for very high impedance inputs & BJT's (NExxxx,LMxxx etc for low to medium impedance requirements as a rule of thumb!

 

[mshilarious]

I think I'll throw in my 2 cents worth here,....mshilarious has basically explained the difference between TL072 & NE5532 very well and...adding further,the biggest difference would be biasing these 2 chips! If you look at the the data sheets for these 2 devices,you'll notice, that while TL072 requires only 1.4mA (quescient current) the NE5532 needs 6mA,hence the resistors too are calculated accordingly.The original circuit would have taken " gain " requirement also into consideration in their design.

TL072 is a very high input impedance device > 10*4 Mohm to that of NE5532 which is in Kohm range! The noise spec too is quite different of these two,not to mention GBW.
So,a OPA2134 would be the best alternative to TL072 IMHO. I've been using TL072,NE5532 & OPA2134 exclusively in most of my design projects,& the improvement from TL072 to OPAxxxx is remarkable indeed. Mr.Douglas Page the brain behind many of of Soundcraft mixers has written a series of excellent articles on this subject,which I would recommend to anyone interested in opamp circuit designs.

I always use BJFT (LFxxx,TL072,OPA2134 etc) devices for very high impedance inputs & BJT's (NExxxx,LMxxx etc for low to medium impedance requirements as a rule of thumb!

Sorry but your post is a mess. Input bias current and supply quiescent current are completely different things. Iq runs from V+ to V-; input bias current goes into inverting and noninverting inputs. That is in the nanoamp range for NE5532 and picoamp for a FET-input opamp like TL072.

The resistor values chosen for a particular topology may be influenced by input impedance, but have nothing to do with supply current.

There is no such thing as a "BJFT", there are bipolar junction transistors (BJT) and field effect transistors (FET). I already briefly mentioned BiFETs, which are not relevant for this discussion.

"LM" is a prefix mainly used by National. Such a part may or may not be a BJT-input opamp. It might not be an opamp at all.