Trying to decide on which of these to have put into a Maxi Moy from Shellbrook, and have read that the 627 is a great opamp, possibly more stable than the 637 in some applications, but also has less high end extension. The 637, on the other hand, is said to have more treble extension and more bass.

Which would be a better choice in an amp if I want to have a nice warm, yet detailed, almost analog-ish sound, paired with some Beyer DT770/80's? I'm torn and can't decide... last I left it with Drew, I said 627's and I'm wondering if that's really the best choice-- and I hate PM'ing him and changing my mind...

All I know is that the 637 is a faster op amp than the 627, but it's unstable below a gain of 6. This is what Norm from Headsave told me. I don't know what gain you'd set the 770s to, though, so I can't really comment on that.

Also, I asked Norm what he'd recommend for the DT770/80 (as I was considering them to pair with the Classic that will be purchasing soon) and he said the AD8620 was his recommendation for almost all Beyers.

If you want to go in the 627/637 direction, then don't let my comments discourage you, but I thought you might like to know what Norm thinks.

yeah, I definitely would trust his opinion on things... the AD8620 has more of a slightly boosted high end and a firm low end, so they tend to fit more of a hifi-ish sound with the Beyers... I'm leaning more towards "comfy pair of shoes" sound out of the DT770's... I'll probably go with the 627's, unless the price is too high, and then I'll just stick with the stock OPA2227's that Drew uses (which sound great too).

thanks!

i thought there was no diffrence between the two, other than the 627 for low-gain application, and the 637 for higher-gain applications. that's why i chose the 627bp for the xp-7. can someone elaborate the diffrences between the two op-amps, if any?

The 627/37AP and BP will be the same for audio purposes, the only difference is DC specs. You don't really hear DC and both chips have excellent DC specs.

For low ohm headphones the gain required for the OPA637 will probably be too high. I have tried both with my Alessandro MS-2s and I strongly prefer the OPA627. The OPA637 does sound faster, but the OPA627 sounds more natural. I currently use the OPA627.

I will have a pair of DT-770-250s by Tuesday. I can test the OPA627,637 and 2227 in my Pimeta if you want. The OPA627/637AP cost about $18/chip and you need 2. You can always upgrade to them later for not much more.

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Maybe for a Pimeta, but some other amps (like the PPA) need 3 opamps (left, right, ground).

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In his first post he says he is getting a Maxi Moy and I was going off this. When using single channel chips like the OPA627 the Pimeta needs 3 as well.

OPA627 are nice but what about LM6171? those things are as fast as lightning

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Hey Pinkie,
Are the Lm6171 available in a pdip package? i would like to give this a try in my xp-7.

The OPA627/637 is a great opamp -- the 637, from what I've read, sounds a touch better than the 627 (probably because it's not internally compensated like the 627 is, and has a higher bandwith) but it is not stable in gains less than ~6. I've heard some people say it's not really happy until you have a gain of ~10. I don't build my amps with gains that high, so I haven't had a chance to play with it yet. The 627 is stable no matter what your gain, and sounds really good.

It does have a warmer, darker sound to it than the 86x0 opamp; I like that one too but it does not pair well with brighter headphones (a bit of a glare, really), while I find the 627 good with my Grados, Allesandros, and Senns. Haven't heard the Beyers, so no comment there.

As a general note, the 627/637 is a single channel opamp, so you'll need one per stereo channel (depending on your amp you may need an adapter to fit two chips on the one channel) and, if you have an active ground channel, one there too. Do not get a 637 for the ground channel in an amp like a PPA or Pimeta, since the ground channel is set to a gain of 1 -- use a 637/627 combo for that.