OPA 627BP VS OPA 637BP

[Squeek]

Hi All,

I was hoping someone could shed some light on these to opamps. I have SuperMacro on the way, and I'll be expiramenting with these two as well as OPA627AP.

What are the characteristics of all of these?

 

[Akku]

Quote:

Originally Posted by Squeek Hi All, I was hoping someone could shed some light on these to opamps. I have SuperMacro on the way, and I'll be expiramenting with these two as well as OPA627AP. What are the characteristics of all of these?

The "BP" selection has better DC spec. and I doubt you will be able to notice differences soundwise. 637 is the uncompensated version of the 627 (not stable at unity gain). I never tried the 637 but I don't think it should be so dramatically different from its compensated brother. If you want to taste different flavours why not trying other op-amps? Like 8610 for instance.

 

[bg4533]

Read Tangents Notes on Opamps if you havent already.

Personally I prefer the OPA627 over the OPA637. I keep trying the OPA637 and sometimes it seems like a nice change over the OPA627. However, everytime I end up back back with the OPA627, it just sounds more natural to me.

 

[Shosta]

Quote:

Originally Posted by bg4533 Personally I prefer the OPA627 over the OPA637. I keep trying the OPA637 and sometimes it seems like a nice change over the OPA627. However, everytime I end up back back with the OPA627, it just sounds more natural to me.

Could you explain more your impressions about these OpAmps? I'm in process of building a self made PIMETA and i'm in doubt.
I was almost decided to use the OPA637 after reading at tangent and other threads.
I heared only to the OPA134 which i have in my current cmoy. Is't the same sound signature?
Thanks in advance.

 

[bg4533]

The OPA627 is similar to the OPA134, but they are very noticably different. The OPA627 sounds a lot better in my opinion. More balanced bass and realistic highs.

The OPA627 and OPA637 sound extremely similar. It would probably take me a little while to tell if I didn't know which I was listening to. The OPA637 sounds a little more lively and active to me. This is most noticable in the high end. I think the upper midrange of the OPA637 has a slightly off sound.

It seems I am in the minority who prefer the OPA627 over the OPA637. Take that into account when you make your decision.

 

[Shosta]

Quote:

Originally Posted by bg4533 It seems I am in the minority who prefer the OPA627 over the OPA637. Take that into account when you make your decision.

Thanks for the information.
It seems that the generalized opinion is that the OPA637 sounds better just because it's uncompensated.

In my portable rig I use a headphone out and I turn the knob of my cmoy more than 3/4 (11 gain) but if i use the cmoy with that gain with my home cd player the knob it's almost at 1/10 (which makes very difficult to select a good volume).
So I think that my gain will be under eight because i want the pimeta for that cd player. So if you say that it's difficult to tell the differences i feel more confident using the OPA627 because everybody say that it's more stable at lower gains.

 

[JJ3810]

Actually there IS a difference and it's very real. I was auditioning a friend's SONY CDP-X77ES CD player via the headphone jack in the player and through my PPA that was installed with OPA 637BPs (627s in the center channel) at Gain of 11. The sound was noticably better through the Sony's headphone jack. I'm using Senn 650s for this test. I was surprised, to say the least. On a hunch, I swapped in the 627BPs and then there was no discernable difference (using my ears anyway) between the player and running through the PPA. Needless to say, the 627s have remained in the amp.
By the way, this old Sony drives the Senns just fine. I'm just above "mid point" on the volume level adjust for most CDs.

 

[Shosta]

Quote:

Originally Posted by JJ3810 Needless to say, the 627s have remained in the amp. By the way, this old Sony drives the Senns just fine. I'm just above "mid point" on the volume level adjust for most CDs.

In the end I made something like a PIMETA (in a protoboard)http://www6.head-fi.org/forums/showp...&postcount=531

Use two BUF634 per channel and 627s.
The sound it's the best i listened with my senns HD600s. Better than with my cmoys-opa134 and a lot of better than the standard headphone jack of the marantz (bloated).

It's detailed, extended, fast, airy but not cold (i think hd600s deserve part of the merit in this).

I'm thinking now in a RA.1 clone for my SR225s.

 

[saturnine]

I too prefer the 627s over the 637s. The 637s are more lively and fun sounding, but the highs are boosted just a bit more than the 627s. The 627s sound much more natural to me (in my rig).

 

[tradja]

After some very careful A/B-ing in two different and excellent PIMETA's -- the one in my sig, and one of yours, Brian!

, I found that I prefer the 627 to the 637.

I generally like a bright sound (I love my V6's), so I expected to prefer the 637. The 637 was indeed brighter, but the midrange seemed hollow, cold, and unconvincing compared to the relatively richer, fuller sound of the 627. Many people seem to prefer the 637 to the 627, though, so as with all of this, YMMV. It should be noted that I found both opamps beautifully detailed and crisp.

I was surprised on two counts: that there was a difference, and that I could really tell.

 

[labrat]

Deleted.

 

[bg4533]

Labrat,
What is the gain in your SuperMacro?

The OPA637 requires a minimum gain of 5, but may need a gain much higher depending on the circuit. The OPA637 is spec'd to have the same Iq as the OPA627, so battery life should be the same or close to it. I am going to guess your OPA637 was oscillating. That would explain the hiss and battery life. The sound might be better if the opamp was stable too. Also, be careful using the opamp if it is oscillating, it could be putting out a lot of DC.

 

[labrat]

Deleted.