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| Lincht Joined: N/A |  Message [#1] posted on: 11-26-2001 05:07 AM CST (US).   |  |  Is OPA62/37 far better than OPA132/4? I have this idea since they have a far difference in price. |
Tomo Headphone Council Joined: May 4, 1999 | Message [#2] posted on: 11-26-2001 06:09 AM CST (US). | | Hello, I believe OPA627 was designed for precision instruments which require high reliability. This makes the opamp much more expensive. However this does not indicate the sound quality when used in audio amplifiers. What I mean to say is that the sound quality does not necessarily related to the prices of the parts. I can't direct you to what opamps are good since I have very very strange tastes and prefer to use very strange things for audio. I am sure Apheared, Ppl, and several other HeadWizers will be able to tell you more about specific opamp models. Good luck, Tomo |
| Daniel Pumphrey Headphone Council Joined: N/A | Message [#3] posted on: 11-26-2001 11:33 AM CST (US). | | Just do a search of the 627 here. It is a wonderful opamp which requires +-15V and cannot be easily powered by batteries if that is a concern. My most recent amp uses this with the buff 634 and is the best sounding amp I have ever heard. I am messing with a battery powered version using 4 9V batteries for +-18V which I will change to 15V per rail. So this is one expensive amp including the parts and the batteries to operate but I think it is worth it sound wise. The Breadboarded version I assembled operated with a small BB +-15V regulated supply quite nicely but I think batteries will be cleaner. Obviously a well regulated low noise supply is essential for proper operation. There are suggestions for it's use in the BB data sheets for the 634 as a Headphone amp. This amp has the 634 in the same feedback loop as the 627. PPL and others think a multi-loop topology is best though. There is a nice multi-loop or composite design amp using the 627 with the 603 Current feedback opamp in one BB publication, although I think many of the designs in these articles are intended for VHF and UHF Amps and test equipment amps with very high gain operating well beyond the audio region. Not standard audio gear as some here suggest. The data sheet recommending three buf 634's is such a case. This is not a circuit for an audio preamp as some have suggested but is intended for a high speed probe capable of higher currents in the high frequency spectrum. Headroom used this chip (627)in one of it's high end amps until this year. I don't know what they are using in this year's new amps. Don't try to use this chip in a standard Cmoy as it likes high speed design with a real ground plane, etc. Many say it has a tendency to oscillate but I have had no problems. Dan [Edited by Daniel Pumphrey on 11-26-2001 at 03:59 PM.] |
ppl Headphone Council Joined: Jul. 28, 2000 | Message [#4] posted on: 11-27-2001 01:33 AM CST (US). | | LOL: comparing the 627 to the 134 is like comparing High end to Mid-Fi. The 627 is great with the exception of it's Prominent Midrange.As dan sed Dont Drive Headphones Direct from the 627 it will sound slightly grainy. This OPA hates reative loads. Slow opamps like the OPA-134 are mutch more tolerent of these kinds of loads. Matted to the BUF-634 is a match for the foward mids of the 627.as far as stability gose the 627 is as stable as the 134 in all the design's i have used. In fact i have a hard time getting the faster 637 to be unstable, although i managed this by operating the BUF-634 in the Low bandwith mode and using low Closed loop gains. Gains of 10 (20dB) is about right with the 637. However in the Wide-bandwidth mode an OPA637/BUF-634 sing a nice tune.Verry articulate. To obtain the best out of the 637 mate it with the Elantec EL-2002.The El-2001 is only marginaly stable with the OPA-637. My fav Opamp is The AD-843. This opamp flat Rocks But at 13 Ma Current drain it is not a battery opamp. My favorite battery operated Opamp is the AD-825.The AD825 accentuates Silbelence on some recordings But I think this a Recording Issue and Not the fault of the 825. On Lp records this is totaly a Non issue.Other opamps i like alot and i think are on par with the 627 & 637 with as you might gess different sonics are The AD-744 when used correctly the SMOOTHEST opamp i have heared and verry Musical.The AD-744 gives up some detail and soundstage over the 825,637,843 but not alot. if your source is less than state of the art the 744 is the one. the 744 also dose not like to drive Headphones without a Buffer only 20 Ma output current. Use the comp pin on the 744 to drive the buffer rather than the 744's normal out put pin. The LT-1122 is also another great Opamp verry similar in sound to the 627 evean hav the Foward mids but not as mutch. |
peranders HeadWizer Joined: Aug. 31, 2001 | Message [#5] posted on: 11-28-2001 06:32 AM CST (US). | | OPA627 is a precision JFET-input AND it has rather low noice. Those parameters makes this chip expensive. It's much easier to make precision bipolar opams. I have used OPA627 in my "DAC project" with excellent results. P-A [Edited by peranders on 11-28-2001 at 10:33 AM.] |
| ppl Headphone Council Joined: Jul. 28, 2000 | Message [#6] posted on: 11-30-2001 02:48 AM CST (US). | | The OPA-627 is indeed one of the Better Opamps for Audio. Precision is just one reason for the High cost> Diealectric isolation is the main reason as well as Greed. Lost of Precision opamps are reasonable in costThe Better grades of the OP-132 are considered Presision. The BB App note about using the 627/603 in a composit opamp configuation is different from jungs Multiloop in that unlike Jungs method the Feedback is not constant across the Audio bandwidth. The BB App note just combines the gain of Both Opamps to Hot-rod the Slower 627 into the Speed of the 603. This is a standard Composit opamp and every semiconductor manufacture has a version of this same thing. The Advantage of the BB composit opamp method is when High Speed as well as DC precision is required. [Edited by ppl on 11-30-2001 at 06:55 AM.] |
| jphone Member Joined: May 26, 2001 | Message [#7] posted on: 12-01-2001 09:34 AM CST (US). | | For a good analysis on opamps from a no-nonsense guy (Douglas Self) check the following http://www.dself.demon.co.uk/webbop/opamp.htm makes for great reading |
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