Best Op amp for transparent boost?

[12Bass]

I've had an Ampeg SVP-PRO bass preamp for many years.  Apart from the DI and the defeatable graphic EQ section, the signal path is all tube... except for one TL072 which is used as a buffer in the effects loop.  Out of curiosity regarding its sonic impact, I decided to replace the TL072 with a pair of high performance OPA827s.

The difference between them is dramatic through my K702 headphones.  The OPA827s sound much bigger and more open overall, while the TL072 sounds midrangey and one dimensional.  I was surprised, as I didn't expect a huge change.  

Of course, naysayers will likely bring up 'confirmation bias' and 'audiophools'... but the effects are real, and not at all subtle to my ears.

[Mark Hammer]

Well that's just it.

The value of selecting the semiconductor one uses for buffer will depend on what you're sending that signal to.  If we're talking about the usual guitar-amp-with-clipping-circuits-along-the-way, then semiconductor choice will, in all likelihood, be pretty moot.  Headphones and a DI, on the other hand, are going to provide a higher fidelity rendition of the input signal, and any changes to bandwidth or general spectral distribution, are going to show themselves.

A buddy of mine is a bass player who operates a very busy and well-respected studio in town.  He also makes mic preamps, discrete replacement modules for obsolete op-amps used in older exotic mixing boards, and a bass DI.  He goes to great lengths to identify which FETs to use in the DI.  Plugging it into an amp, I can't tell the difference, but he approaches it from the perspective of someone doing mixdowns and masters, where the ability of a DI'd bass to be identifiable in the midst of a surfeit of other sound sources is the basis for his judgment.

[Digital Larry]

I've had an Ampeg SVP-PRO bass preamp for many years.  Apart from the DI and the defeatable graphic EQ section, the signal path is all tube... except for one TL072 which is used as a buffer in the effects loop.  Out of curiosity regarding its sonic impact, I decided to replace the TL072 with a pair of high performance OPA827s.

The difference between them is dramatic through my K702 headphones.  The OPA827s sound much bigger and more open overall, while the TL072 sounds midrangey and one dimensional.  I was surprised, as I didn't expect a huge change.  

Of course, naysayers will likely bring up 'confirmation bias' and 'audiophools'... but the effects are real, and not at all subtle to my ears.

Well I'd like to be open minded in spite of those things.  You dropped in the newer one, so the overall gain is the same?  Would seem so.  Just a unity gain buffer or some other arrangement?

What could cause such a noticeable difference?  (sorry I'm not up to date on my op amp specs and stuff)...  I'd start by asking about:

Frequency response
S/N
THD or some other measurement of D
slew rate and if it's anywhere near doing that
phase margin
gain margin

You know, the typical "measurable" stuff. 

[FiveseveN]

the effects are real, and not at all subtle to my ears.

Bandwidth is trivial to measure, right? So it wouldn't take much to prove the "naysayers" wrong.

[karbomusic]

No naysayer here... Typically I go at it like this...

1. If one say's they hear a difference and the math agrees, we're done, all good.

2. If one say's the difference is "night and day" and the math does not agree, I need something more than "sunspots" or "sounds 3d".  

If one can't take the steps to properly evaluate it (for whatever reason), we simply can't remove bias because we haven't taken the steps to remove it that's all. I love hifi stuff, I've just learned to be careful about what I hear or  think I hear so I can make good, solid decisions. Remember, I just used 3 OPA2134s in my modified TS design, I can say thus far that it is likely quieter but won't make any other claims until I can properly make them. Or I'll just keep them and see if I notice something over time, no biggie, it's all good fun.

[12Bass]

FWIW, I did use RMAA to make analog loop-back measurements of the changes when I modded my Echo Gina 24 soundcard.  It originally came with some cheap JRC op amps which were replaced with LM4562s, then later OPA2211As.  There was a significant decrease in THD and IMD with the high performance op amps, and the result was a noticeably clearer sound.  However, it may be a bit more difficult to make accurate measurements with the SVP-PRO, because the five tubes add enough THD and noise that it would likely swamp the measurable impact of a high performance op amp.

[Haze13]

Somehow, people do hear the difference between BJT's and JFET's and do not forget Ge's for FUZZes... People do Hear the difference between audio grade BJT's and General Purpose BJT's too! In WHA's for example... (MPSA18 and BC108/BC109)
Op-amps made from these transistors (similar, smaller), so it's just complete nonsense to say that there is no difference between them. Some of them use Jfet's as differential pair as an input, more current sources, cascodes to reduce input capacitance and laser trimmed resistors for low DC offsets,  Laser trimmed capacitors with tolerance 0.5% (UAF42 from analog devices) and more. BUT, 741 and 4558 still sound and perform the same as new made Op-Amps! Very interesting... More than 40-years after and there is no progress, except in marketing...
Similar designs perform similar, different designs perform different. Mathematics and Physics still works! 

[FiveseveN]

What exactly makes a BJT "audio grade"?

More than 40-years after and there is no progress

Uhm... what?!

[12Bass]

Yeah.... not sure what to say about that.  Recent op amps vastly outperform the old 741.

[Haze13]

Fiveseven
Noise performanse,  linear HFe or Gm?
"Applications" from datasheet of 2sc2240 covers most of those critical "points".

What you quoted was a sarcasm.

[FiveseveN]

Noise performanse,  linear HFe or Gm?

OK, and are these things only relevant in audio applications? Aren't these "generic" objectives?
Isn't it funny how we can make 300 MHz GBP op amps (priced quite modestly, mind you) but it's the audio stuff that's supposedly harder to figure out?

[karbomusic]

so it's just complete nonsense to say that there is no difference between them.

Did someone say that there is no difference? I don't know, but since you said so, it made me curious.

[Haze13]

Well... actually yes. Every now and than I hear that 4558 is no better than average audio op-amp.
Fiveseven, HighBandwidth op-amps are audio-grade. It's what they do, amplify the incoming signal with very low total harmonic distortions and all that goes with this stuff... Audio applications is one of many other places where you can use them. Sonars, dacs, low distortion filters, spectrum analyzers, ultrasound preamps and more...

[karbomusic]

Well... actually yes. Every now and than I hear that 4558 is no better than average audio op-amp.
Fiveseven, HighBandwidth op-amps are audio-grade. It's what they do, amplify the incoming signal with very low total harmonic distortions and all that goes with this stuff... Audio applications is one of many other places where you can use them. Sonars, dacs, low distortion filters, spectrum analyzers, ultrasound preamps and more...

The quote of yours that caused me to post was referencing differences between actual physical transistors and opamps (or is how I read it), so I was specifically referring to the assumption that people were saying those were the same, sorry for the confusion since I may have read it wrong.

Somehow, people do hear the difference between BJT's and JFET's and do not forget Ge's for FUZZes... People do Hear the difference between audio grade BJT's and General Purpose BJT's too! In WHA's for example... (MPSA18 and BC108/BC109)
Op-amps made from these transistors (similar, smaller), so it's just complete nonsense to say that there is no difference between them.

[Haze13]

It's Ok. Nevermind... May be it's because of my poor language. My 3'd by the way, so it's some times really hard to choose a right word or to compose a sentence in the right way.