Concerto AD797A for AD797B

The AD797 is one of the best opamp You can get. I wouldn't bother replacing it. (maybe with LME49900 but get a browndog then)

you forgot a 9, the chip is lme49990 and yes its the only chip to have displaced my long standing favorite ad797. i wouldnt bother changing to the b version, you do realize the psrr is already far beyond your ability to hear it?

Oh, those are a lot's of 9s :-D Anyway, I already have a Prodigy HD2 with AD979Bs and I have samples of LME49990s so I will try it soon too. First I need the proper adapters for them. Does anyone have a suggestion?

ADA4627-1B 

OPA827 

yes opa827 is a superb chip also, but it was never able to displace the ad797 long term like the lme49990 has. i havent tried the ada4627, i meant to, but i just dont see it making the cut against these things. wrt dropping them in, it really depends on what they are doing with the rest of the circuit, the 797 has a distortion cancellation pin that is missing on the national chip (it doesnt have any to cancel), so without a schematic i cant really tell you

Quote:

Originally Posted by thegr8brian 

Quote:

Originally Posted by qusp 

you forgot a 9, the chip is lme49990 and yes its the only chip to have displaced my long standing favorite ad797. i wouldnt bother changing to the b version, you do realize the psrr is already far beyond your ability to hear it?

How would you describe the differences between the ad797 and the lme49990 datasheets aside. Any clue if this would work as a drop in replacement in the concerto?

well you probably know yourself by now, but i found that as fantastic and impressive as the ad797 is and it really is, it still has a sound sig, the lme just doesnt, i find it difficult to describe, it just vanishes

Quote:

Originally Posted by qusp 

yes opa827 is a superb chip also, but it was never able to displace the ad797 long term like the lme49990 has. i havent tried the ada4627, i meant to, but i just dont see it making the cut against these things. wrt dropping them in, it really depends on what they are doing with the rest of the circuit, the 797 has a distortion cancellation pin that is missing on the national chip (it doesnt have any to cancel), so without a schematic i cant really tell you

Then you are in for a real surprise if you ever get around to 4627, and get the B version.

Quote:

Originally Posted by thegr8brian 

I sent an e-mail to Jan Meier and he says that the pin 8 distortion cancellation is used in his design.  So it looks like it would probably be best to not tamper with it.  Oh well 

well you could simply leave pin 8 unconnected on the adapter for the lme, remove the pin on the adapter or something, pin 8 is 'not connected' internally and usually tied to ground if anything, so you probably could just drop it in without ill effect. every time i look at that datasheet it blows me away, nevermind the sound, which does the same. thats the impressive thing about it too, no special tricks past standard good supply decoupling arew required to produce performance that is not measurable with the highest end analyzers without constructing a special circuit to amplify the noise.

so in short after double checking the datasheet for you, i cant see any reason why you cant drop it in, it only has the 2 supply pins, the output and the non-inverting and inverting input/feedback pins, all others are NC

plus, unlike the ad797, audio was more than a passing interest taken into account when producing this chip, normally audio is a secondary consideration, but national has produced this not solely for audio obviously, but it was a strong focus
 

the opamp doesnt know what ground IS, let alone whether its passive or active ground. as with pretty much all opamps i know of, there is no ground connection, the inputs are floating and ground currents are referenced/returned to a point half way between the voltages on the supply pins. in essence it creates its own internal virtual ground anyway

So... did you ever try this, or do I have to be the guinea pig? Where can I buy them?