[elmer_dudd]

i did do a search.... but i got sidetracked and then forgot what i was doing.
so anyway, will any old opamp serve well as an audio buffer? or will i need something more specialized?

specifically, i'm interested in applying something like this to my eardrums:
http://www6.head-fi.org/forums/showt...=&threadid=703

 

[error401]

Buffers, by definition, are unity-gain devices. Many opamps, especially high bandwidth types and many of the 'preferred' audio opamps, are not stable in unity gain. You want a high current output device with high impedance (FET) inputs. Just going through a list of your 'favourites' and paring it down by removing those that don't fit the conditions above should give you a pretty decent list of suitable devices. Looking at the specs of BUF634 which is pretty popular around here, suitable alternates might include LM6171, OPA551 (relative to BUF634 and LM6171 quite slow), AD8397, etc. Pretty much any high-current, unity-gain stable opamp should technically work. As with opamps used in amplifiers, their sonic signature is going to be quite different. The information available about selecting amplifier opamps probably applies to using them as buffers as well, though with less pronounced effects as the situation is pretty much 'ideal', especially if the buffer is inside the feedback loop. Either grab one of the tried-and-true buffer opamps like the OPA551 or roll them like you might in an amp.

 

[pddjsteve]

One chip that seems to be great as a buf634 alternative is the LMH6321. I've used them in my PPAS. Once my latest mouser order gets here I'll have everything for a Pimeta and can start rolling opamps and buffers and can post some results with it with more than the AD8620/AD8610 I used in my PPAS.

The intersil HA5002 is the buffer that was used in the PPAv1. I plan on trying out that as well using a homemade adapter.

You might want to check some of the posts Andrea made about opamp rolling in the Xenos amp, I think there were some opamps that got used in a buffer role.

 

[amb]

error401, I wouldn't call the AD8397 "unity gain stable". While the datasheet doesn't say it isn't stable at unity gain, practical experience with this chip has shown that it's marginal at best. I would not recommend using this chip as a "roll in" substitute for any circuit that isn't specifically engineered for it.

 

[error401]

Quote:

Originally Posted by amb error401, I wouldn't call the AD8397 "unity gain stable". While the datasheet doesn't say it isn't stable at unity gain, practical experience with this chip has shown that it's marginal at best. I would not recommend using this chip as a "roll in" substitute for any circuit that isn't specifically engineered for it.

Thank you. I didn't check the specs on these too closely and haven't used any of them in this application myself. The datasheet claims it's unity-gain capable and I saw a reference elsewhere to it being used as a buffer IC so I mentioned it.

 

[tomb]

Isn't the AD8397 a BJT chip? It won't work in any of the prevalent designs except the withdrawn PINT and the never-released Mini3.

I'm surprised Amb didn't mention the OPA551, a favorite alternative for the buffers on the Millett Hybrid, and pretty much anywhere BUF634's are used, if the jumper is used on the pins. It's reported as a pretty decent opamp for the SOHA, too. You can't stack 'em, though, which is why I stick with the BUF's. Although, we've been having quite a conversation lately about stacking the Intersil's pddjsteve mentions.