what, if anything, distinguishes OPA637 from OPA627?

[ChicagoPhil]

I am interested in ordering the SuperMacro 3. On his site, Xin recommends the OPA627 if the added cost isn't an issue. The opamp section of his Selection
Guide also mentions the 637 saying that the "637 has no compensation and thus faster and slightly better benchmarks" relative to the 627.

Can anyone elaborate on the difference between the 627 and 637? What is
"compensation" in the context of opamps? Does Xin offer the 637 directly, or must it be sourced by the end user?

Thanks for your assistance,
Phil

 

[amb]

Without going too deep into techno-babble, opamp internal compensation is the presence of a capacitor inside of the opamp to restrict the high frequency bandwidth a bit (and in the process provide more phase margin) for stable operation at low voltage gains (or in this case, unity gain). The OPA627 has such a compensation cap, and the OPA637 does not. The opamps are otherwise identical. The compensation cap allows the OPA627 to operate at unity gain but the OPA637 is specified to be stable only at gains greater than 5. However, due to the compensation cap, the OPA627 has a gain-bandwidth product of 16MHz and slew rate of 55V/uS whereas the OPA637 is 80MHz and 135V/uS.

Both opamps can be purchased from Digikey, amongst other places.

 

[ChicagoPhil]

Quote:

Originally Posted by amb Without going too deep into techno-babble, opamp internal compensation is the presence of a capacitor inside of the opamp to restrict the high frequency bandwidth a bit (and in the process provide more phase margin) for stable operation at low voltage gains (or in this case, unity gain). The OPA627 has such a compensation cap, and the OPA637 does not. The opamps are otherwise identical. The compensation cap allows the OPA627 to operate at unity gain but the OPA637 is specified to be stable only at gains greater than 5. However, due to the compensation cap, the OPA627 has a gain-bandwidth product of 16MHz and slew rate of 55V/uS whereas the OPA637 is 80MHz and 135V/uS. Both opamps can be purchased from Digikey, amongst other places.

Thanks for that, much of which is still beyond me. What do those gain-bandwidth and slew rates really translate to in terms of musical performance?

I assume Xin builds the SuperMacro, or would if I asked, to a gain greater than 5 if using the 637? However, if I'm using my UE-10s, will a gain setting of 5 with the 637s be too loud? Because there is no capacitor to limit high frequency bandwidth, would it sound too bright? Or might the 627s seem too dull?

Thanks again,
Phil

 

[crypt@]

At the time of my order, only 627s were offered as an option. While ordering I queried if 637s could be installed instead. Unfortunately, that was at a time when Xin experienced some e-commerce issues. Because of the delay in communication I decided it might be quicker/easier to just stick with 627s and order some samples from TI instead. And this way I can roll the OPAMPs later.

So it was a delightful surprise when the amp arrived with 637s installed, plus Xin bundled in some assorted OPAMPS and an interconnect as well.

Xin in his communication with me stated that SM-3 is default with gain of 5 and the 637 will run stably in this configuration, which I can attest to with mine.

 

[iamdone]

Soundwize I find the 637 to be just a touch brighter w/out as much texture, slightly thinner mids, and the bass doesn't seem as deep. It presents more detail than the 627 but doesn't sound as natural after extended listening. All very minor differences. The 637 sounded closer to the ad8610. I think I prefer the ad8610 between the two because it was more dynamic and had better bass. The 627 just sounds more natural than all the opamps I've tried. It's all very subjective and depends on source, cables, and headphones.

I haven't done any real comparision with ue10 since this is used mostly on the SR-71. I did find the sensaphonics sounded much better on the 637 because of the highroll and enhanced bass. They sounded a little muddy with the 627. I'd imagine the ue10 would work better with the 627 since it would give them more warmth and they don't suffer from high rolloff.

With 637 you also have to have the gain above 5 and that can be a problem with the sm because of the gain switch. I believe he recommended not using the 637 with the gain switch installed. This may have changed.

 

[jlingo]

Hey Iamdone,

Have you had a listened to Supermacro 3, 627? It's giving me a 3D soundstage, and even better high. It's very very good with Sensaphonics compared to SM V1 in my opinion.

 

[Welly Wu]

I have the Ue-10 PRO and a Ray Samuels Emmeline HR-2. I reviewed the OPA627BP and OPA637 op-amps in the amplification review archive. I can attest to you that the OPA627BP and Ue-10 PRO sound so musical and so natural that it is unheard of. I also have the AD8620 (the dual version of the AD8610 op-amps) installed in my ModWright LLC Pioneer Elite DV-59AVi and the synergy between those and the OPA627BP keeps me up to 5 o'clock AM EST just listening to pure music bliss...while surfing Head-Fi, of course!

 

[iamdone]

Quote:

Originally Posted by jlingo Hey Iamdone, Have you had a listened to Supermacro 3, 627? It's giving me a 3D soundstage, and even better high. It's very very good with Sensaphonics compared to SM V1 in my opinion.

I haven't heard any of the supermacros. I just tested the sensas on my PPA w/diamond buffers. I was testing the hd650/zu at the time. With the 627, the hd650 sounded perfect but the sensas were lacking in comparison. When I put the 637 in, the sensas sounded much better but the hd650 seemed to be missing the texture and lowend.

I also just tested my RS-1 with the 627, 637, lt1028, and lt1122, and the 627 came out the winner. I couldn't test the ad8610 because two of the opamp had a pin fall out.

I find the 627 in my PPA w/diamond buffer anything but grating. It's very warm, organic, and liquidy with the RS-1. I've only listened to the ue10 just a little bit on this amp because I find the RS-1 sound far better in ever way to my ears. I have never heard the SinglePower MPX3 so I can't compare but it sounds like a great amp they way you describe it.