Op Amp substitutes

mosfetti

Member
2007-12-06 10:26 am
I swapped a couple JRC 2043D Op Amps from my integrated amp. One was for the phono stage and the other in the line stage. I replaced them with Analog Devices AD712's and believe me the only reason I chose those is because I had a Parasound pre amp that used them for the same functions. I made sure both were used for the same purpose, etc. and I got lucky, the AD712's work fine. As for sound quality the AD's are great for the phono stage as it warmed up and added low end boost that was missing with the JRC's. The jury's still out in regard for the line stage, maybe a bit too warm but I'm still listening. I understand BurrBrown, recently bought out by Texas Instruments, has similar offerings for my application. Searching for is however MIND-BOGGLING. Is anyone familiar with the BurrBrown in question or know of shortcuts for Op Amp substitutes.
 
The NJM2043 is roughly equivalent to a National LM833. Its strength is its OK bandwidth and noise, and a very low price.

For the phono stage, the AD712 seems like a poor choice because of its limited GBW and high voltage noise. Either the Burr-Brown OPA2228 or Linear Technology LT1126 should be a good choice. They're both low noise, decompensated bipolar op amps with good GBW and modest current demand. The LT1126 is faster but requires higher closed loop gains for stability. Don't use either in line stages because they're not unity gain stable. LM4562 is also a candidate here.

For the line stages, drop in your favorite unity gain stable chip. The NJM2043 should be adequate here. Bipolar candidates include the LM4562 or LT1469, either of which is IMHO overkill for a line stage. The LM4562 is quieter with low-Z sources, but the LT1469 is faster and draws less current. FET fans can go for the OPA2134. Video op amp fetishists should consider the LM6172 or LT1358. The AD712 would be acceptable but is slower than most of the alternatives, including the NJM2043!
 

mosfetti

Member
2007-12-06 10:26 am
Thanks much Chuck I appreciate the info. I've read a lot of good things about BB Op Amps for audio so I think I'll pick up a OPA2134 for the line stage and hear how it sounds. As far as the phono stage is concerned to me the AD712 sounds better than the original NJM2043 which to me sounded a bit bright with a lack of low end.
 

mosfetti

Member
2007-12-06 10:26 am
Well John I'm sure you had a hand in the design of the Parasound pre amp I discovered the AD712's in because of your past designs from said company. And more than likely the design parameters for the P/HP-850 pre amp are quite different than my integrated but they sound fine in my amp. I don't go by specs. Chucko suggested that the 712 didn't seem like a good choice for the phono stage by the specs. But the sound is what I'm looking for and the 712 sounds good to me for the phono section. The line stage of the P/HP-850 is definitely more sophisticated than the one in my integrated so I'll probably experiment some more.
 
No disrespect intended to Mr. Wurcer, but the AD712's specs are typical of FET input op amps of the '80s, in fact at first glance it looks very similar to the TL072. If someone likes the sound, I can't argue with that. But it certainly wouldn't be on my list of candidates for a phono stage!

The AD797 is another story entirely. It's clearly intended for high gain stages driven by a low source impedance. I don't think I'd use it in a line stage, but again, if you can make it stable and you like the sound, who am I to complain?