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PPAS Build Thread. - Page 15

post #211 of 254
Maybe you should go for OPA690, since it's used in Mini3, it's probably even better than LMH6654. Those people know what they're doing. It's very cheap, and hopefully it's as stable as the 6654.

I simply can't come up with a known good opamp to use in front of LMH6321.
post #212 of 254
Quote:
Originally Posted by NelsonVandal View Post
Maybe you should go for OPA690, since it's used in Mini3, it's probably even better than LMH6654. Those people know what they're doing. It's very cheap, and hopefully it's as stable as the 6654.
Actually, the OPA690 choice was based on KurtW's amp (he used AD8397s for left and right and OPA690 for ground, except that his amp's "ground" is a OPA690 acting as a rail-splitter, and no separate output ground channel). Kurt reported good sound and lower battery comsumption as compared to AD8010. I have yet to test any of this, pending the arrival of prototype PCBs. So, I am just operating on blind-faith here, and won't know whether the OPA690 would be the final recommendation until I build several prototypes with different chips and test them all.
post #213 of 254
should the OPA690 be used with a buffer like the lmh6321 or is it bufferless?
post #214 of 254
the purpose of the mini³ is to be bufferless, that's why it uses the high output ad8397 and the opa690.

so the opa690 is bufferless
post #215 of 254
k, well i ordered a 3rd lmh6321 ANYways just incase i end up needing it at some point. i should leave opa690 bufferless though, so leave BUFG just completely open?
post #216 of 254
or since i have one, should i put an lmh6321 in that spot?
post #217 of 254
no, that would just add unnecessary current draw and it'll degrade sound quality - it would be the distortion of the opamp plus distortion of the buffer.

you can jumper across the buffer with a short wire. I don't have the exact pinout in mind, just look at the datasheet and jumper from input to output
post #218 of 254
ok balou, thanks thats exactly what ill do then. on a different note, has anyone heard the ad8066 / opa690 / lmh6321 combo?? any thoughts?
post #219 of 254
Now I've listened to AD8066 in my Sijosae amp. I compared it to LM4562. I'm quite sure what opamps to use in my PPAS - LME49720/LME49710 (it's supposed to be the same as LM4562). AD8066 wasn't to my liking, too rough and sibilant. I liked the energy though, especially in the lower registers. I hope the slam of the LMH6321's compensate for the slightly sterile sound in the LM/LME's.

There will be some serious current draw. A single 9V is out of the question. It's going to be a tight fit to squeeze in 7 AAA's and a charger in a C801.

I forgot to order resistors, and I'm up to some other projects (and work, and family, and house, and garden...) so it will take some time I'm afraid.
post #220 of 254
amb, would you mind trying the ADA4899-1 on the Mini3. I'm curious as to how well it works for you. I wonder about the AD9631 as well, though the PSRR may be a bit too low.

I wish there had been some way to fit single channel for the L/R on the PPAS. Would be neat to try something like the OPA655.
post #221 of 254
Filburt, I've just built a platform to try AD8099 LR and AD8045 ground. I forgot to order resistors for this as well, and I don't know when I have time to finish it. ADA4899 sure looks more interesting. Specwise it seems to be the opamp for headphones. I wish I've heard about it before I ordered AD8099. If there are problems with AD8099/45, I'll go for ADA4899 (I'll probably go for it anyway sometime). Thanks for sharing the information. Have you tried it yourself?
post #222 of 254
if im using opa690 as my OPAG, i understand this is an un-buffered opamp, so i dont need a buffer in the BUFG position right next to it right. do i need to jumped across that pad somehow, or can it just be left empty? the jumper needs to go from pin 1 to the pin directly opposite it?
post #223 of 254
Quote:
Originally Posted by el_matt0 View Post
if im using opa690 as my OPAG, i understand this is an un-buffered opamp, so i dont need a buffer in the BUFG position right next to it right. do i need to jumped across that pad somehow, or can it just be left empty? the jumper needs to go from pin 1 to the pin directly opposite it?
I'd warn against using OPA690 in a circuit not designed to use it. This is a very wideband, fast opamp, and sensitive to capacitive loads. At the minimum you'll need a ferrite bead at its output to isolate such capacitance or the opamp could become unstable. Without proper instrumentation you may never know if it's not performing well.
post #224 of 254
OH..:P i actually only went with it on someones recommendation here. bummer. k so ill need to buy a ferrite bead somewhere, although i have no idea where? back to the bufg, do i just run a jumper from pin 1 to the pin directly opposite it?
post #225 of 254
in addition to my jumper question...this concept of the ferrite bead is totally new to me. what rating should i be looking for when i buy one? and i assume since i need to put it on the opa690s output, i would have to wire each of the 8 pins with a wire rather than have the opamp directly soldered to my board (and in which case the ferrite bead goes between pin 8 and the board?)? thanks guys...darn i wish someone coulda advised me against opa690 earlier
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