[Thraex]

Hi,
 
I want to upgrade the Texas Instruments TL071CP (JFET Input Op Amp) inside my SPL Volume 2 preamp.
Is it possible to use OPA604AP or the even better OPA627 without ANY problem?
Any other suggestion of a perfectly compatible/replacement upgrade in  the FET input Op Amp category?
 
Thanks

 

[agdr]

Quote:

Any other suggestion of a perfectly compatible/replacement upgrade in  the FET input Op Amp category?
 

 
The TLE2071CP.

 
At Mouser: http://www.mouser.com/ProductDetail/Texas-Instruments/TLE2071CP/?qs=sGAEpiMZZMtCHixnSjNA6I%2fK8QDhU1zCjAREOV9Gks8%3d
 
Datasheet: http://www.ti.com/lit/gpn/tle2071
 
From the datasheet: "Direct upgrades to TL07x". 
 
For $0.20 USD more the ""A" grade (TLE2071ACP) has even better input offset voltage numbers:
 
http://www.mouser.com/ProductDetail/Texas-Instruments/TLE2071ACP/?qs=sGAEpiMZZMtCHixnSjNA6P3Ssczg4flJx6OxKKD1WOg%3d

 

[Thraex]

Thanks agdr!
 
I'll order it so I'll be sure I can upgrade safely.
 
But I've already ordered OPA604AP and OPA627BP (highest grade).
Do you think I can damage the preamp using those? I've read a few successful use of OPA604AP in the SPL Volume 2 preamp.

 

[Thraex]

Reading the data sheet of TLA2071 it's stated:
 
"Because BiFET operational amplifiers are designed for use with dual power supplies, care must be taken to
observe common-mode input voltage limits and output swing when operating from a single supply. DC biasing
of the input signal is required and loads should be terminated to a virtual ground node at mid-supply. Texas
Instruments TLE2426 integrated virtual ground generator is useful when operating BiFET amplifiers from single
supplies."
 
I don't know if I've a single or dual power supply so to be able to use it safely, do you have any clue which psu type uses the SPL Volume 2 preamp watching the inside pic here :
http://www.6moons.com/audioreviews/spl/open_big.jpg ?
 
Thanks

 

[agdr]

Quote:

I don't know if I've a single or dual power supply so to be able to use it safely, do you have any clue which psu type uses the SPL Volume 2 preamp watching the inside pic here :
http://www.6moons.com/audioreviews/spl/open_big.jpg ?
 

 
It is dual.  In the lower right corner of that photo there is a dual rail +/-15Vdc setup (7815 and 7915 voltage regulators).   So no worries about single supply issues with the chip (common mode voltage, biasing, etc. )  No, you are not likely to damage your amp with the OPA604 or OPA627. The pinouts are the same and both run fine at +/-15Vdc.  Just be very very sure you are getting the chips in the right way, with the "dot" in the corner the same as the existing one.  Getting the new chip in 180 degrees reversed could very well damage some things, including popping the chip.
 
The TLE2071 is likely going to be the most "compatible" with the TL071 simply because TI has designed it that way.  The TLE2071 is intended to be an upgrade to the TL071, and the first rule of thumb for the chip manufacturers with this kind of thing is "first do no/little harm" in terms of incompatibilites with the old chip, then improve a few things slightly with new technology.   But the key word here is "slightly".

  From the data sheet the TLE2071 seems to trade off some distortion (THD is slightly worse) to improve the slew rate and unity gain bandwidth.  The TL071 slew rate of 8 to 13V/uS is already fine for most audio related things.  Depends on how large of a voltage you are swinging.  The TL071 unity gain bandwidth is a bit thin though at 3Mhz.  The 10mHz number of the TLE2071 would allow more distortion-cancelling negative feedback.  And the TLE2071 noise numbers are a hair better.  Long story short, I would guess that you probably won't hear any audible differences between your existing TL071 and the TLE2071.  But chips are cheap, give it a try for some DIY fun.

 
As for the other two chips, things are not as they seem.  In my original reply to your post I had more written up suggesting the OPA604AP as a better audio chip, based on its data sheet specifications.  But then I remembered this set of EE Times articles last year by Douglas Self which reviews all 3 of these JFET chips. Definitely worth the time for a read-through if you haven't already.  There are 3 pages, click the page link at the bottom to get the other two pages:
 
http://www.eetimes.com/design/audio-design/4219253/Op-amps-in-small-signal-audio-design---Part-4--Selecting-the-right-op-amp--JFET-input-types-reviewed-
 
From his comments the real-world performance of the OPA604 and what is in the data sheet are a complete miss.  From his comments and the data sheet the OPA627 would be good for DC servos, strain gauge sensors, instrumentation amplifiers, and other things that require some really good DC parameters.  As for audio the distortion numbers are a bit less than the TL071 and TLE2071.  Again I doubt you would actually hear much difference, and in this case your wallet would feel some pain with that pricey chip. But you could certainly give it a try!
 
So long story short, there may not be much you can do just in terms of (JFET input) op amp rolling to produce any major audible improvement.  If you were doing a completely re-design, just as a thought experiment, going to a bipolar input chip like the LME49710 or even the older NE5532 would probably produce improvements on sensitive measuring equipment like an audio precision, but still may not be audible improvements.  Take a look at the LME49710 data sheet and compare each line item vs. the same on the TL071 sheet.  Much better in terms of audio parameters:
 
http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=snas376b&fileType=pdf
 
http://www.ti.com/lit/ds/symlink/tl071a.pdf

 

[Thraex]

Thank you very much for the detailed infos.
 
I've arlready the OPA627 in hand but I'm not sure if I'll try it:
SPL told me it's not compatible, another person told me to try it, worst thing it could do is osclillating and cause distortion, but it'll not damage the circuit.
 
Do you think I can try it safely?
If I try it, do I understand by ear if it's osclillating?
 
Thanks

 

[tangent]

Quote:

worst thing it could do is osclillating and cause distortion, but it'll not damage the circuit.

 
That's almost certainly true. I can imagine circuits where the wrong op-amp will cause physical damage, but it's hard to believe someone would design an audio circuit that way.
 
The circuit is in far more danger of physical damage by you doing the op-amp swap than from the op-amp itself. If the job requires desoldering and resoldering, you could damage the PCB, for example. If the existing op-amp is socketed (unlikely) you're still not out of danger; you might static-zap a chip, or bend a pin, or...
 
 

Do you think I can try it safely?

 
You can try any op-amp safely. It might not work, but you can always replace the old one, if you haven't damaged it.
 
 

If I try it, do I understand by ear if it's osclillating?

 
No, not really. Swapping an op-amp is not like changing a Lego brick.
 
While it is true that oscillation usually results in audible problems, it also often causes high DC offset voltages, or high AC voltages. Putting that across a headphone driver will damage it.
 
You must be capable of measuring the circuit's performance before and after to safely do this swap. At the very least, you need to measure DC voltage at the output of the amplifier between each stereo channel and ground, and the idle current of the amplifier. You must do both before plugging headphones in, and you must test first with headphones you can afford to destroy, in case the chip starts oscillating once you put a load on the amplifier.

 

[Thraex]

Ok, thank you.
I tought op-amp swapping should be fun, but too many variables to check I'm no more confident to swap.
 
I'll try only the OPA134 which SPL told me it's safe.
 
btw: the SPL Volume 2 is a preamp.

 

[tangent]

Quote:

I tought op-amp swapping should be fun, but too many variables to check I'm no more confident to swap.

 
 
The only equipment you need to do the tests I mentioned is a decent DMM, and some idea of how to use it.
 

btw: the SPL Volume 2 is a preamp.

 
In that case, you have even more reason to be careful. Bad output from a preamp becomes very bad output when you run it through a power amp. 

 

[agdr]

Quote:

I've arlready the OPA627 in hand but I'm not sure if I'll try it:
SPL told me it's not compatible, another person told me to try it, worst thing it could do is osclillating and cause distortion, but it'll not damage the circuit.

 
I'm curious - did the manufacturer say why the OPA627 wasn't compatible?   Nothing jumps out at me on the datasheet, with the exception of the offset trim circuit (anything connected to pins 1 and 5 to null out the DC offset).  They both (TL071 and OPA627) use 100k pots between pins 1 and 5 on the datasheet circuits, but the TL071 returns the wiper to -Vee while the OPA626 returns it to +Vcc.  I hadn't noticed that before.  The trim 100K on the OPA604 datasheet application circuit returns to -Vee like the TL071.  Those offset trim pins don't have to be used though - often are not.  I'm not seeing a stability graph vs. load capacitance for either chip (what often causes oscillation), so that may be the issue too.
 
EDIT: nevermind, I believe I found it.  The gain/phase plots of the two chips have very different phase shift characteristics.  Too much phase shift around the feedback loop = oscillation.  The OPA627 would likely require different compensation in the feedback loop to be stable.  Interesting to note that TI left the phase shift graph vs. frequency of the TLE2071 very similar to the TL071 - likely would not require any compensation changes.  The offset trim 100k wiper on the TLE2071 also returns to -Vee, like the TL071.
 
 
Quote:

The circuit is in far more danger of physical damage by you doing the op-amp swap than from the op-amp itself. If the job requires desoldering and resoldering, you could damage the PCB, for example. If the existing op-amp is socketed (unlikely) you're still not out of danger; you might static-zap a chip, or bend a pin, or...

How true! 

 

[KWS]

ADA4627 for sure!

 

[Thraex]

I've safely tested the TLE2071 and OPA134, given initial listening it seems the SPL Volume 2 could be upgraded with an op-amp swap. I'll post more precise impression in the following days so to be sure the results are consistent.
There isn't a night and day difference but my system is able to detect the changes, maybe lower systems are not capable.

 

[Thraex]

Hi agdr, it seems you're the only one who understand the chips differences and compatibility do you mind to suggest me a better opamp than the OPA134 or TLE2071?
The OPA134 has better specs but I greately prefer the TLE2071, maybe the design of the entire circuit is optimized for some parameters (unknown to me) which the TLE2071 do better.

 

[duncan1]

It may be be worthwhile to note that the values chosen by D .Self are "worst case" scenarios.
I never use more than 2X gain and output load [into a load] I keep to a high value .When you  check the graphs for lower situations you will see they perform well.
For example my own build mono-buffers look into a load of the Stax-727-11 of 50K OHMS.
Some of these chips have been used by Audio design engineers to produce test equipment reading to extremely low distortion.
Not all ADEs agree with  each other as the pages of Electronic World/Wireless World over the last 30YRS will back up .
Especially  between 1980-2006.
Very big arguments. I take  my lead from JLH [john Lindsay hood] of whom DS has had large differences of opinion with.
Its all down to actual-Reproduced sound. In other words -Subjectivism- a "nasty" word in EE circles.
But tell me what human being on this planet /animal/bird/insect/fish-that can make a sound and hear-DOESNT listen -subjectively ??