Best sounding op-amp

I have a stock Music-Hall CD-25 that I'm planning on doing some 'easy' tweaks on. One of tweaks I had in mind was changing the op-amps. It currently has a pair of Burr-Brown OPA2134PA's, but I was curious if anyone had any experience/suggestions on other op-amps that might produce a little 'warmer' sound. Possibly considering one of the Analog Devices op-amps like the AD823 or AD827. Any feedback or recommendations would be appreciated.

The little differential small signal amplifiers, packaged as integrated circuits, and commonly called "Op Amps" are called that because they are not often designed or used as linear amplification devices. The important characteristics of an op amp are very (absurdly) high open loop gain and very high slew rate. Linearity is of no importance. The op amp drives its output so as to match its input and follow changes of the input. The "signal" that drives the op amp is not the signal that you feed into the circuit. The signal that drives the op amp is the difference between the op amp output and what you are feeding in. The high gain makes sure that this difference is driven down to zero, and the high slew rate makes sure that rapid changes of the input can be followed closely. The characteristics of the op amp circuit are overwhelmingly determined by the design of the feedback loop within which the op amp works, and the electrical components of this loop. In most cases substitution of an op amp with superior specs will have no effect on how the circuit performs.

As always, there are some exceptions. Soime op amp ICs are more noisy than others. In some high gain applications, such as a phono preamp, the op amp may play a significant part in overall circuit performance. (The practical solution to this problem is not to use op amps, even $50 items, in high gain phono preamp stages).

So, don't waste money replacing all the op amps, when few, if any, will have any effect. Make a review of the circuit before you "upgrade" op amps.
Well, I've 'rolled' the opamps in my headphone amplifier, and came to the following conclusion after a few days to a week with each one:

OPA2134 - flat and lacking soundstage, but decent overall since it didn't do anything wrong in particular, just failed to come through in those areas.
OPA2227 - similar, but warmer overall, slightly larger soundstage
OPA2604 - more detailed than either of the two but slightly cold sounding. Very wide soundstage though.
AD823 - punchy bass, but so detailed in the highs it sounds grainy. Constricted soundstage at times.
AD8066 - comparitively warm and lush, and not as detailed as the 823, but still very good. However had distortion when the input or volume as above a certain leve, like there was a 'step' in the volume knob - I don't think the voltage supply was correct. Upon going back to it the second time it let out a faint stream of smoke and was dead, maybe I plugged it in wrong though...
OPA627 - had to wire pair of these to work as a dual-channel, but by far the cleanest, richest sounding of them all, with the largest soundstage. Details are all there, but not offensive. It's staying.

Another one I may try: AD825.. and of course the AD8620 - I've heard some prefer it to the OP627.
Hi, I'm having Brice @ Sound Odyssey(phone717-846-6043 or e-mail ads on Audiogon) put the warm sounding AD825 op amps in my cdp(they just snap in)along with the (9) upgraded diodes, Cardas RCA's and damping sheet. He is very reasonably priced for the service and value minded. I'll update when I get the player back. Jerry
Op-amps do vary a lot in sound, particularly because of the power delivery on-die and on-package. Some parts are power starved from the get-go and need a lot of decoupling capacitance very close. Others are designed well for power delivery and need very little decoupling cap. These tend to be more dynamic and clean-sounding. OPA627 is my personal favorite. Packaging also has a big effect.
I'm currently using AD8620 on my Marantz 67SE and love it.
I also upgraded the clock board too.
After done much research, I found the AD8620 has the best spec.
Thanks for everyone's input... I'm leaning towards trying out the AD8620... does anyone know the difference between the AD8620-AR and AD8620-BR? The BR version is about double the price.

If op amps influence sound as much as people are saying, then op amps are being used in circuits where they don't belong. The headphone amp cited by Chillysalsa is probably a prime example. Op amps, even "good" ones are a lot cheaper than circuitry implemented with discrete transistors, so I suppose that widespread use is inevitable. Tubes anyone?
Here is the link to the product date sheet:

The only difference between the AD8620A vs AD8620B is the voltage drift per changing temperature ( 0.8 to 3.5 uV/C vs 0.5 to 1.5 uV/C) If that's critical then it is worth the price. Temperature range from -40C to +125C
S23Chang wrote:
"After done much research, I found the AD8620 has the best spec."

Specs don't tell all. The on-die power delivery is what makes a great op-amp.
Agree spec is not always the best gauge. However, I read many postings that majority of them prefer the AD8610/AD8620 over OPA627 from their setup. I'm not sure it has to do with spec or how they setup the Op-amp. I know the decoupling cap choice can also vary the sound. I've tried many different values and got very different results. Instead of paying the super high price to test, I got the AD8620 to start. I'm not expert here. You should really check diyaudio website. There are thousands of postings regarding to op-amp choice in the gain card type amp to cd players.