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ppl  Headphone Council Joined: Jul. 28, 2000 |  Message [#1] posted on: 04-07-2001 10:51 AM CST (US).   |  |  As most people hear know i am not a big fan of the OPA-627. I think the AD-825 is alot Better and for a fraction of the Price. However Certin qualities about the OPA-627 i find unique to this Opamp. One being the Delineation of midrange detail as i think Dan put it a presence in the midrange. The top octave is also choped off. In addition there is a slight grain to the reproduction. Well i have thought of trying the OPA-637's in my amp but was reluctent due to the rather poor phase margin of the OPA-637 over the more stable OPA-627. Well i got brave and installed a set of 637's to see what would happen. and no problems Compleatly stable. After allowing the devices to break in for about 24 hours i listened to Two amps that are the same except for the OPA-627 in one and the 637 in the other. Well the OPA-637 sure has alot more going for it than the OPA-627. The 637's top octave extention is quite noticable and strangly enought most of the Grain in the Midrange was also reduced by an order of magnatude over the OPA-627. The Air thaat the 627 only slightly Displays! is in full Bloom in the 637.In coclusion i Highly Recomend the OPA-637 over the OPA-627 for circuits with moderate amounts of gain. Do not use the OPA-637 in a unity gain Buffer application.Due to the fact that Both of these Opamps are the same with the exception of Compensation capacitors on the OPA-627 resulting in less Slew Rate and Bandwidth than the OPA-637,Futher adds to by Belief in High speed and Wide open-loop Bandwidth Princibles. |
| Pan Headphone Council Joined: N/A | Message [#2] posted on: 04-07-2001 11:31 AM CST (US). | | Love to read your posts, keep up your good work, saves time for us less "talanted". BTW, have you tried the AD846? |
| Ben HeadWize Fanatic Joined: Nov. 10, 2000 | Message [#3] posted on: 04-08-2001 05:29 AM CST (US). | | ppl, does the 637 have any more bass punch than the 627? One of the reasons I am using the AD825 instead of the OPA627 in my own system is that the 627 seems lacking in bass dynamics. What gain are you using the 637 at? |
| Daniel Pumphrey HeadWize Fanatic Joined: N/A | Message [#4] posted on: 04-08-2001 11:01 AM CST (US). | | PPL, Thanks for the information. All this testing and research is great for amp buiders to know. I do wish your amp designs were posted in the DIY library too. Dan |
| shinew HeadWize Fanatic Joined: N/A | Message [#5] posted on: 04-08-2001 12:31 PM CST (US). | | uhm... last time when I tried to put OPD637's in my amp instead of 627s, they gave me some very noisy buzz. I don't know why but my amp works fine with 627s. Well, I'll try them again sometime soon. |
| ThingyNess HeadWize Fanatic Joined: N/A | Message [#6] posted on: 04-08-2001 04:25 PM CST (US). | | Shinew: they were probably oscillating. :) The decompensated OPA637's have a smaller phase margin than the OPA627 (by virtue of being decompensated), so even at gains > 5 the OPA627 will be less prone to oscillate. If your design/layout was marginal in terms of stability, replacing an OPA627 with an OPA637 can and would be more than enough to make it oscillate, even with a gain > 5. (of course if your gain was less than 5 then you're in real problems while using the OPA637, regardless of layout. :) - Thingy |
| ppl Headphone Council Joined: Jul. 28, 2000 | Message [#7] posted on: 04-08-2001 05:40 PM CST (US). | | ThingyNess is Right the OPA-637 is to be used at High Gains. My Amp uses this at a gain of 11 and the layout is good. But evean still the Phase Margin Was the main reason i havent tried it befor. But it did work fine. I selected another pair of OPA-637's to see if it was just those individule OPA's but (3) other pairs also worked fine. No the OPA-637 dose not have any more punch and Bass than the OPA-627 and this is one of the reasons i do not like these parts over the Better sounding and alot less costly AD-825. in fact all Analog Devices OPA's seem to have more Bass Dynamics that any BB OPA i have used. The main gains of the OPA-637 over the OPA627 is in the Midrange and High frequencies, In these ranges the OPA-637 is the Clear Choice.for the BB line. |
| Vigier Headphone Council Joined: N/A | Message [#8] posted on: 04-08-2001 11:37 PM CST (US). | | Hi, I still have about 50 OPA627AP and 50 OPA637AP and 637BP! Grtz |
| ppl Headphone Council Joined: Jul. 28, 2000 | Message [#9] posted on: 04-14-2001 12:35 AM CST (US). | | After extensive listening to the OPA-627 vs the OPA-637 i like the 637 alot Better The 627 has some grain in the Midrange and the 637 is smooth as silk. So smooth that Tube lovers might be able to tolerate the sound. With the 627 the prominent midrange along with the slight grain and Choped off highs and Low's result in a sound that's thin and Gutless with No Bass or Upper octave extention combined with the Grain makes the 627 not a great sounding opa. and for the price down rite overpriced for the sound you get. The OPA-637 on the other hand is extended in the treble, Not a trace of grain and overall Verry Nice. The 637 still lackes the Bite of the AD-825 throughout the spectrum and is still an octive short in apparent Bass extention vs the AD-825, AD-744, AD-845. So i will leave the AD-825 in my reference amp and use the 637 in the other for mellow Music. |
| CBMC Headphone Council Joined: N/A | Message [#10] posted on: 06-07-2004 08:06 PM CST (US). | | still got any of those amps for sale? |
| Garbz Headphone Council Joined: Nov. 14, 2003 | Message [#11] posted on: 06-07-2004 08:43 PM CST (US). | | Id just like to add to what's already said the opa637 needs a lot more then a gain greater than 5 to work properly. My board layout is attrocious i'll agree to that, but still there's a capacitor at every leg, and the feedback loop is about 3 cm long. This is not good enough for this opamp and as soon as the volume goes below about 1/4 of the turn i get hit with noise and 500mV of DC nastiness. The main problem with my board is that there's no real ground channel as such. Just a ground trace which probably adds to the problem. If the amp doesn't work and ur gain is > 5 check: - Size of feedback loop - Distance parts are form the opamp - decoupling capacitors - ground channel how it's laid out etc. After addressing thoes it worked fine, pity the amp wasn't for me :( |
| sanaka Member Joined: Aug. 7, 2003 | Message [#12] posted on: 06-10-2004 05:08 AM CST (US). | | If using the 637 In a multi loop configuration, which gain value applies? I.e. if I have inner loop gain of >100, but overall amp gain of <5, will the 637 be happy? I asked this before but didn't get anything that felt like a 'definitive' answer. Peace, |
peranders HeadWizer Joined: Aug. 31, 2001 | Message [#13] posted on: 06-10-2004 05:19 AM CST (US). | | If the total gain is less than 5 you can't use the 637. You can't snap with your fingers and improve the phase characteristics of the opamp. I would recommend 637 for gains more than 10. [Edited by peranders on 06-10-2004 at 05:21 AM.] |
aos HeadWizer Joined: Jun. 15, 2008 | Message [#14] posted on: 06-10-2004 01:10 PM CST (US). | | Guys, this is gotta be a record. You revived a 3 year old thread, no less! |
| Garbz Headphone Council Joined: Nov. 14, 2003 | Message [#15] posted on: 06-11-2004 02:13 AM CST (US). | | lol i didn't even notice  I don't read dates and i didn't check for any necromancers either |
tangent Headphone Council Joined: Aug. 27, 2001 | Message [#16] posted on: 06-11-2004 02:40 AM CST (US). | | I've gotten an OPA637 in a multiloop amp to function at g=2, but peranders is right: it could easily blow up in your face instead. |
| ppl Headphone Council Joined: Jul. 28, 2000 | Message [#17] posted on: 06-16-2004 09:56 AM CST (US). | | add a 1-5K resistorbetween the volume control center wiper and the op amps input. make sure that other matters are attented to like resistor on op amp output isolating the load be it another device like a Buffer or a passive network like a headphone |
| MERTON Headphone Council Joined: Aug. 12, 2003 | Message [#18] posted on: 06-16-2004 08:09 PM CST (US). | | does this mean my 627 based meta sucks? |
| ppl Headphone Council Joined: Jul. 28, 2000 | Message [#19] posted on: 06-20-2004 09:50 AM CST (US). | | MERTON NO the OPA627 is a great device and alot more stable than the OPA-637, However the 637 sounds better to me. While some users report as tangent did that the OPA=637 in his amp is stable and lots of folks have used this chip at gains of less than 10 and it worked quite well, However some people have had stability issues at low gains. so i think the best answer is to say stability can not be a given with the OPA637 at any gain in any application. It may work for you and it may not. If you want safe then my answer is no!if you are advernurious and want to try it for yourself then there is a 50% chance it will work fine if attention is given to alot of other stability issues. No two Amp Builders or designers ever get the same results from the same part numbers YMMV [Edited by ppl on 06-20-2004 at 09:56 AM.] |
| fwh1599 Headphone Council Joined: N/A | Message [#20] posted on: 06-26-2004 12:39 PM CST (US). | | I no more Headamp,but I have Twinkle(Test version) only,it's a OP+DB,Gain=8.15(RF is 7K15 vs 1K00),a little like PPA's DB version,but it's 2ch no VG,no muilt feedback. I can't used OPA637 in my Twinkle before two hour ago.Because it always bring DC offset more 600mV or hit with noise,as Garbz. Just now,I can listen it very stably,Cool.So I can tell How to tame OPA637,along this way OPA637 sing in other muilt feedback amp---maybe. AS PPA is a muilt feedback loop,inner loop gain >100,and overall amp gain=11,seem satisfy OPA637 gain>5. But gain=11 is include buffers,a very long loop feedback,not OP's pin6 to OP's pin2(local loop),can you sure "gain>5,OPA637 will stably"? I think no. How to do?try to charge for inner loop gain and overall loop gain,let inner loop gain =11(gain>5 and local loop feedback,OPA637 was steady),and hold some feedback for overall amp(for no high offset). If you do so,you must measure offset of Output. My test for Twinkle(Tese version) (in the "muilt" Rf1 from op's pin6 to op's pin 2 is 7K15,Rf2 from Output to op's pin 2 is 100K,Output stage Iq=20mA)as follows: NOTE:Twinkle(test ver) no the resistance for blance souce impedance, as R5 of PPA,so local gain is (7K15+1K)/1K.if your amp have blance souce resistance,you must calculate it.for example,R6=10*(R5+R3); I don't know can I help you and my english is very poor. [Edited by fwh1599 on 06-26-2004 at 02:47 PM.] |
| fwh1599 Headphone Council Joined: N/A | Message [#21] posted on: 06-27-2004 10:24 AM CST (US). | | I find bias(+/-) of DB isn't symmetry,I fixed it. New data: ┈OP┈┈┈┈┈┈┈muilt AD8610┈┈┈┈2.3mV/3.6mV(stably) NE5534┈┈┈┈1.7mV/3.8mV(stably) OPA627┈┈┈┈3.6mV/3.7mV(stably) OPA637┈┈┈┈1.1mV/6.4mV(stably) |
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