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In Reply to: Re: okay, and the winner is...My own test posted by eagle1 on February 02, 2002 at 18:47:13:
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
Follow Ups:
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.
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