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In Reply to: okay, and the winner is... posted by Ehien on January 31, 2002 at 01:42:40:
Hi Ehien,It seem's that I'm not the only one playing with op-amp in phono stage these days. I first try NE5532 as input and OPA2604 as output. Then change the 5532 for an OPA2134. Then split the input for two OPA134. Change the 2604 to 2134. Put back the 2604. Change the 2604 for an AD826. The AD826 is clearly above all those. I still have some LT1364 to try as output amp.
This takes me more than an year. Right now, I'm comparing OPA134 to OPA227 to LT1115 for the input stage. After I settle on one of them, I'll do a match between it and the OPA627. I can't use OPA637 because at HF, the gain go under 5, so instability can happend.
Regards,
Daniel Trudeau
Follow Ups:
Hi all,From replies, I see that's a important topic! A great way to learn BTW.
Ok, as Ehien state, the 627-637 is a warm op-amp, even warmer than the OPA134, wich I dislike. So the OPA627 as input op-amp for my RIAA is out. 40$ worth of useless op-amp, at least for that application.
The 604 being to veiled for my taste, I tried OPA227 and LT1115. The 227 remind me of the 604 but with less HF and midrange edge. It stills manage to give me that "kick ass" bass and midrange speed I like and that I miss in warm sounding op-amp. The proplem is that subjective speed is detrimental to midrange transparency and grain-free highs.
Came in the LT1115. I didn't read enough the datasheet at first so I was wondering why I did get some weird noise in HF, like someone searching to lock on a channel on short-wave radio. After reading back, I discovered that this op-amp don't like to see unity-gain i.e. like the OPA637. But I think: I got these for an year without listening to them, so I tried them anywhay. Wouha, the bass and the midrange became really good. The focus was great and I experienced the right balance of speed and transparency. The LT1115 is a bit warmer than the OPA227 but achieve what the BB can't: absolutely no edge in voice, er...for an op-amp, that's it. The Linear offer my enough speed to enjoy rock, be-bop and massive classics. In the same time, the more delicate music is not trashed as with the 227. I get lost in the sound and finally listen music without A.N. The only problem is that f... trouble with treble. As it can't handled them right, cymbals lost some sharpness and bite.
That experience trouble me. I was thinking that the erratic behaviour at HF should destroy completely the sound, it doesn't append. Now, I think that the best I can do is to swap to passive filtering with a LT1115 as input and any high-speed op-amp at output.
Regards,
Daniel Trudeau
Daniel,Thanks for the inside scoop. I think your preference on LT1115 over other opamps has a lot to do with application. In the preamp part of a phono amp, LT1115 seems to be an ideal device due to its exceptionaly low noise, low distortion, and moderate slew rate. But it might not be a good choice (just speculation as I've not used LT1115) for output stage of a phono stage in driving cables.
I've not touched the preamps (AD SSM2017) used in my Black Cube as they are in the RIAA circuitry. Maybe there are even more rooms to improve, if I can identify a proper replacement (such as LT1115?).
Cheers.
Ehien
Dan:Have you had a chance to read about or actually try the new AD8610?
The datasheet has some interesting charts and info, especially the shootouts with the OPA627.Michael
This opamp and its comparison to OPA627 are very interesting. But this is another damn surface mount component. Look like I'll one day have to design and build a header to accept these ever-popular SMT opamps.
Well, I did worry a little bit about stability before installing 637's. However, as it will take me longer to study the feedback arrangement of Black Cube than soldering the 637's, I simply went ahead and tried them out. Obviously, so far so good. I'll try 627's when I get the time.Look to me AD825/826 have the potential to be very good. However I have no chance to try them. The SMT single 825 is available from LC Audio as dual configured opamps. Maybe you can report back after comparing 627/637 with 825/826.
By the way, I seem to prefer BB (now part of TI) over AD equivalents. For instance AD746 was listed as OPA637 dual equivalent; and AD823 was listed as OPA2604 equ. on AD's cross reference list. However, in my system these two AD's were no match to their counterparts.
Just my thoughts...
-Ehien
Hello again Ehien,I'll try AD826 against 627, but it will take some times. I'll built a newer phono stage soon to incorporate the 50KHz pole and will go full monoblock, batteries PSU too. And no, I wouldn't buy the LC Audio soon, I have enough of op-amp here, there's no way I will pay someone to do a job I can do. But for begginer, the LC Audio solution is easy.
Me too, I prefer BB over AD equivalent. And I've only seen one BB chip going bad so far. AD is not bad, but doesn't give the same MTBF as BB.
Stability have more to do with PS lines than feedback. In my basic design, the OPA627 oscillate. I will fix that today and include it in the match.
Regards,
Daniel Trudeau
no decent op-amp should fail in any decent application! MTBF is a parameter that makes sense in the digital world!unless you are talking about how often a circuit that is on the fringe of oscillation will really oscillate. but this is more a question of design errors rather than op-amp quality
Hi Capslock,Like any digital device, it's a matter of alot of things. You should know that some manufacturers clearly annonce that there products isn't appropriate for life support. Of course, brand new, they should work OK. But because they know that they can't specify enough reliability in rough conditions and the way IC fails, they protect themself. BB products can be use in critical application, even if not in life support. That's what I mean by MTBF for op-amp.
Regards,
Daniel Trudeau
> Stability have more to do with PS lines than feedback. In my basic design, the OPA627 oscillate. I will fix that today and include it in the match.You meant only for OPA627, right? Otherwise for OPA637 since it's not unity-gain stable one has to take care of both feedback (thus gain) and PS to ensure stability.
nt
Hi,> I can't use OPA637 because at HF, the gain go under 5, so
> instability can happend.Well, first insert the missing 50KHz breakpoint in the active RIAA and you will find in most cases, the gain is sufficient for guaranteeing stability.
Ciao T
Hello T,Yes, I'll have to check that. I have a new circuit that take care of this breakpoint, I just need the time to try it. I still not fully understand why a 50KHz pole change so much things. Maybe it's most a phase behaviour than a relative voltage attenuation. Getting the phase right makes the soundstage real.
Regards,
Daniel Trudeau
take a look at the AD797 data sheets for ways to degrade op-amp bandwidththen, there used to be a pretty instructive BB app note called "op-amp stabilility and gettings things right for a change"
Enjoy!
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