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PPAS Build Thread. - Page 14

post #196 of 254
Quote:
Originally Posted by el_matt0 View Post
alright, what about my second to last post about the opamps. would the ones i have in mind be an appropriate choice? and if so, which of the various different ones should i get? tx i appreciate the help guys

Can't see the link. I don't have much experience with different opamp sound, so i can't comment on the that. but you can check this.
post #197 of 254
Quote:
Originally Posted by NelsonVandal View Post
Please help me choose opamps! I have 3 LMH6321's which seem to sound amazing (tried them without opamps, but they started to oscillate), and I don't want crap in front of them. Since the LMH's are 12 V max, and since I'm planning on using 7 x AAA = 8,4 V and fit everything in a Hammond C801, my choices are limited. At first I was aiming at AD744's but I don't think they'll sound good at that voltage (I haven't heard them, only AD746, and it doesn't sound good at 9 V). Neither will OPA2701. AD8058 lacks "body". OPA2132 and AD823 are just not good enough.

Maybe I'll go for LM4562 or AD8066, but what opamp will sound good in the ground position? I'm not fond of AD8610 (too harsh). Maybe I should remove the ground LMH6321 and use LMH6654 or AD8045 or some other high current opamp alone?
aalmost IDENTICAL situation!! 3 lmh6321 and i want to use the AD8066...two things, can someone link me to the corect p/n via digikey for that, theres several versions and im a little unsure. and secondly, which opamp should i go for in the ground position?? thanks!
post #198 of 254
^^ anyone??
post #199 of 254
One of the members here claims that LT1363/64 are very good opamps, spec'd for 5 - 30 V and unity gain stable. They're quite expensive, and PPAS is very small so it will be hell to desolder them and roll in a new opamp if they aren't to my taste. I'm thinking that one of those high current/high speed opamps will be the best choice - AD9631, AD8045, OPA690, LMH6654 etc (all unity gain stable), and drop the ground channel LMH6321.
post #200 of 254
arent the LMH6321s the 3 buffers? from my current limited understanding, i need 3 buffers (my 3 lmh6321s) and 2 opamps, one OPALR and one OPAG right? would the ad8066 not be a great choice for my OPALR, with something like the LM6171 as my OPAG? please clarify!!
post #201 of 254
hi el_matt0
what nelsonvandal is suggesting is that you drop the lmh6321 for the ground channel, and use a high current opamp instead. kind of like a chip with both features built in.
post #202 of 254
Quote:
Originally Posted by balou View Post
hi el_matt0
what nelsonvandal is suggesting is that you drop the lmh6321 for the ground channel, and use a high current opamp instead. kind of like a chip with both features built in.
Yes.

Of the high current opamps I've only heard LMH6642 and LMH6654. The 6654 sounds very good, better than most of the "normal" opamps. AD9631 is claimed to be even better. OPA690 is probably very good as well, since it's going to be used in the Mini3. The problem is DC-offset, which isn't a problem in the ground position. And since it has enough output current, why use a buffer.

This will take some tweaking, to bypass the buffer and get the feedback loop and output right. Because of the size, PPAS isn't easily tweaked. It would be easier to just put it in front of the LMH6321, but then you have two amps adding to coloration.

I have used LMH6654 "stand-alone" in Xenos, and I liked it more than AD8620, AD8058, OPA2134, LM4562, AD823 (DC-offset was as far as I remember about 15mV). I've used it as ground channel amp in a PINT configuration and my buffer-only amps with great result. I've never used it in front of a buffer though, so I'm not sure how that would work out.
post #203 of 254
so what hes saying is use a high current opamp like lmh6654 in the OPAG position, and it wont need a buffer in the BUGF position (BUFG is empty?, or is it the other way around, chip goes in BUFG, OPAG is empty?) and then with whatever opamp i decided on, id have two LMH6321s in my BUFL and BUFR positions?
1) is LMH6654MA the one i want?
2) will AD8066ARZ be suitable for my OPALR position, or can someone suggest something that might be a better option?

**im looking at P/N's via digi-key btw
post #204 of 254
BUFG will be empty with this config

1.) depends if you want a single opamp or a buffered opamp in your ground
2.) yup, this will be an option. after some listening to the ad8066 (in a cmoy driving grado phones), I must say it has nice bass. not boomy, not to much, but well defined and nice. but I was quite used to agressive highs, the ad8066 is almost a bit to less agressive there in comparison. overall detail is good, much better than opa2132, a bit better than ad823
I wonder how the lm4562 sounds, it should arrive soon
post #205 of 254
any way to get those discrete buffer boards for this? I may have snagged a ppas board, and I'd be interesting in building it
post #206 of 254
LMH6654 has relative high output current (asymmetrical 80mA source, 120mA sink), but not in the same league as OPA690, AD8010 (200mA) or BUF634 (250mA). Also, the max voltage rating of the LMH6654, OPA690 and AD8010 are all +-6V, so can't use two 9V batteries.

Btw, DC offset does matter in the ground channel, just as it does with the other two channels.
post #207 of 254
k so, can someone take a quick look at the parts im about to order and just double check im not doing something silly.
1) AD8066ARZ for my OPALR
2) LMH6654MA in the OPAG (maybe someone can suggest an alternative, if i want to use 3 buffers)
3) LMH6321MR x3 in all the buffer positions
or should i stick with what ive got planned and just drop off one of the buffers for the BUFG and use the LMH6654 un buffered? im planning to power this with a single NiMh 9V, if that changes anything.
post #208 of 254
Quote:
Originally Posted by amb View Post
Btw, DC offset does matter in the ground channel, just as it does with the other two channels.
In my PINT-clone using LMH6654 as ground channel, I have 2/3 mV DC-offset at max volume. With LM4562 as LR there's only 0.4/0.7 mV. It doesn't add more offset than using passive ground. In what way does it matter?

What do you say about this, using just e.g. OPA690 and not the LMH6321 buffer in the ground channel? Is there anything to gain using the buffer as well?

Our "problem" is we are going for 9 V since we're using LMH6321, otherwise AD744 would have been an easy choice for me.
post #209 of 254
Quote:
Originally Posted by NelsonVandal View Post
In my PINT-clone using LMH6654 as ground channel, I have 2/3 mV DC-offset at max volume. With LM4562 as LR there's only 0.4/0.7 mV. It doesn't add more offset than using passive ground. In what way does it matter?
Your DC offset figures are good. When I say "it does matter" it's simply to point out that DC offset is as important on the ground channel as it is on the left and right channels.

Quote:
What do you say about this, using just e.g. OPA690 and not the LMH6321 buffer in the ground channel? Is there anything to gain using the buffer as well?
Since those two have only 50mA difference in output current, and both are high, then the difference isn't big. There are advantages to either scheme. A separate buffer eliminates thermal coupling between the output and input stages. But a separate buffer may give rise to instability when the buffer is wrapped in the feedback loop (depends largely on the characteristics of the opamp and the buffer). On the other hand taking the buffer outside the feedback loop loses the DC offset control and low output impedance characteristics. I have not tested a OPA690 + LMH6321 combo so I couldn't tell you if it would work well.
post #210 of 254
Quote:
Originally Posted by el_matt0 View Post
k so, can someone take a quick look at the parts im about to order and just double check im not doing something silly.
1) AD8066ARZ for my OPALR
2) LMH6654MA in the OPAG (maybe someone can suggest an alternative, if i want to use 3 buffers)
3) LMH6321MR x3 in all the buffer positions
or should i stick with what ive got planned and just drop off one of the buffers for the BUFG and use the LMH6654 un buffered? im planning to power this with a single NiMh 9V, if that changes anything.
anyone please? confirm this for me so i can order?
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