[MrMajestic2]

I want to try some new op-amps in my newly comleted Pimeta, but I have some questions to clear thing up for me.

Here are the op-amps I want to try:
AD843 on all channels
AD8066 on L/R and AD8610 on ground
AD744 on all channels
OPA2107 on L/R and AD744 on ground
OPA627 on all channels
OPA637 on L/R and OPA627 on ground

Is there anything I should know about these combos or are they just a drop in replacement? I know Im gonna need some Brown Doggies on some combos, but is there anything I need to change on the amp or op-amps before dropping them in? I know there is a compensation pin on the AD744, should I use that or the regular output when running on a buffered Pimeta? Is there any other op-amp beside OPA627 that I can use for ground with the OPA637 on L/R?

My configuration at the moment is exactly copied from Tangents Pimeta schematics except R11, which is 100ohm, since I have double stacked buffer. My gain is about 11 if Im not mistaken.

I know some of they questions have been asked before, but they usually involve sound quality of the op-amps, not the actual implentation.

 

[tomb]

Just my experience:


AD843 on all channels - Stay away from this - bad offset, oscillation, etc., stc. This is a nasty chip in the PIMETA.

AD8066 on L/R and AD8610 on ground - A little more detail than A8620/8610, but thinner with lighter bass

AD744 on all channels - Boring.

OPA2107 on L/R and AD744 on ground - waste of time if you try the 627/637.

OPA627 on all channels - As good as 8620/10, but different - super rich, luscious and huge sound, with adequate detail.

OPA637 on L/R and OPA627 on ground - Same, but better than previous, with more detail, more snap.

Quote:

Is there anything I should know about these combos or are they just a drop in replacement? I know Im gonna need some Brown Doggies on some combos, but is there anything I need to change on the amp or op-amps before dropping them in? I know there is a compensation pin on the AD744, should I use that or the regular output when running on a buffered Pimeta?

It may be wrong, I don't know - but I just plugged them in.
Quote:

Is there any other op-amp beside OPA627 that I can use for ground with the OPA637 on L/R?

AD744 seems to be an excellent all-around ground opamp.

Good luck - it's fun trying the different combinations and noticing the changes in sound quality. Everything I tried worked except that AD843 chip - also had oscillation with the AD8065 in ground when using the AD8066 in L/R. I had some issues with isolating my output jack for awhile that may have caused it, though.

 

[MrMajestic2]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Just my experience: AD843 on all channels - Stay away from this - bad offset, oscillation, etc., stc. This is a nasty chip in the PIMETA. AD8066 on L/R and AD8610 on ground - A little more detail than A8620/8610, but thinner with lighter bass AD744 on all channels - Boring. OPA2107 on L/R and AD744 on ground - waste of time if you try the 627/637. OPA627 on all channels - As good as 8620/10, but different - super rich, luscious and huge sound, with adequate detail. OPA637 on L/R and OPA627 on ground - Same, but better than previous, with more detail, more snap. It may be wrong, I don't know - but I just plugged them in. AD744 seems to be an excellent all-around ground opamp. Good luck - it's fun trying the different combinations and noticing the changes in sound quality. Everything I tried worked except that AD843 chip - also had oscillation with the AD8065 in ground when using the AD8066 in L/R. I had some issues with isolating my output jack for awhile that may have caused it, though.

Thanks for your reply. It kind of reinforces what I kinda knew already, that the OPA627/OPA637 are the best Pimeta op-amps. The OPA627 seems to be very hard to find, so I guess I will have to run AD744 on ground together with OPA637 on L/R. Too bad they are soo expensive, the OPA637 is $26.63 at Digikey

But considering the amount of money I've spent already, it wont matter

 

[tomb]

Don't neglect the AD8620/10 - after wrestling with many of these combinations, I actually prefer that pair best overall. The OPA637/27 is a bit slow - it depends on your headphones and your own preferences - there is certainly nothing richer.

 

[majkel]

Call me deaf because I here no snap whenever OPA627/637 appears in the amp. Not worth their price. Natural - yes, detailed - yes, warm/cold - nothing of these two, well extended - yes, soundstage - you can find better. What I see on this forum is people use almost exclusively the chips described by Tangent. AD825 is the best and nothing will change it. Not a word about this chip on Tnagentsoft website is a big mistake. AD843 is harsh and unpleasant, no competition for OPA637 in spite of the snap AD843 provides.
In addition AD825 is one of a few op-amps that truly respond to class A - it's neither worse nor better, just different. I think AD825 is great for ground channel. I don't use it for L/R channels because I've got there a dual channel chip providing 350mA peak per channel (100mA more than BUF634) I won't tell you the name of this chip because it's very nasty and if somebody doesn't know how to stabilize AD843 or AD8065, then should keep away from this one, however this chip kills AD8397 in terms of SQ, power consumption and maximal power. Maximum supply voltage is it's biggest flaw. Not for PIMETA, anyway.

 

[MrMajestic2]

Sorry, I forgot to mention that Im running the AD8620/AD8610 combo at the moment.

 

[MrMajestic2]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif Call me deaf because I here no snap whenever OPA627/637 appears in the amp. Not worth their price. Natural - yes, detailed - yes, warm/cold - nothing of these two, well extended - yes, soundstage - you can find better. What I see on this forum is people use almost exclusively the chips described by Tangent. AD825 is the best and nothing will change it. Not a word about this chip on Tnagentsoft website is a big mistake. AD843 is harsh and unpleasant, no competition for OPA637 in spite of the snap AD843 provides. In addition AD825 is one of a few op-amps that truly respond to class A - it's neither worse nor better, just different. I think AD825 is great for ground channel. I don't use it for L/R channels because I've got there a dual channel chip providing 350mA peak per channel (100mA more than BUF634) I won't tell you the name of this chip because it's very nasty and if somebody doesn't know how to stabilize AD843 or AD8065, then should keep away from this one, however this chip kills AD8397 in terms of SQ, power consumption and maximal power. Maximum supply voltage is it's biggest flaw. Not for PIMETA, anyway.

Well, the AD825 is certainly had a very nice price, thats for sure. Im gonna add that to my order. Thanks mate.

 

[majkel]

AD825 is like AD8610 with no harshness and no veil. Find a person who could describe AD825's sound signature, it's so damn transparent, with snap, space, good extension and warmth.

Any other op-amp I have tried has got it's unique sound signature that will make you bored and fed up with this someday, and push towards upgraditis. AD825 won't do that IMHO.
Second one you can call natural is AD744, but it's... yes, boring, however soundstage is outstanding. BTW, AD825.

 

[Soymilk]

mrmajestic, if you haven't bought them yet and can wait a few days (or maybe a week), i'm going to be getting a lot of different opamps to play with. i haven't constructed my amp yet though, and i'm pretty sure the opamps will arrive before i finish the amp, so if you'd pay for postage, i'd be willing to send you some opamps to play with so you dont need to spend as much money. i might get some extras of each just to build up a stockpile/stash to have around when the mood hits me to build something, so if there's a set you'd like to keep you could paypal me the cost of the opamps and send the rest back.

edit - i will have OPA627 and 637 for sure, not 100% on what else i'm getting yet, i'll let you know within a few days.

 

[balou]

It's interesting that the AD744 is recommended as a ground channel opamp - according to it's datasheet, it is not unity gain stable without additional compensation. This shows how important it is to not just listen to the datasheet, but to check things out yourself. Something I'll really have to consider in my new amp

 

[tomb]

Quote:

Originally Posted by balou /img/forum/go_quote.gif It's interesting that the AD744 is recommended as a ground channel opamp - according to it's datasheet, it is not unity gain stable without additional compensation. This shows how important it is to not just listen to the datasheet, but to check things out yourself. Something I'll really have to consider in my new amp

Hmm ... maybe I did more opamp rolling than I should have.

EDIT: As a matter of fact, I pulled that thing out and put in an 8065 (this one had 8066 in L/R). Sounds great - no light bottom end now - very strong, impactful with outrageous detail. I had always waffled between the 8066 and the 8620 as my favorite L/R chip. As mentioned earlier, I had problems with isolating the output jack on this particular PIMETA and fixed it some months back. That may explain my earlier problems with the 8065 in Ground, too.

It pays to try things again, too.

 

[MrMajestic2]

Quote:

Originally Posted by Soymilk /img/forum/go_quote.gif mrmajestic, if you haven't bought them yet and can wait a few days (or maybe a week), i'm going to be getting a lot of different opamps to play with. i haven't constructed my amp yet though, and i'm pretty sure the opamps will arrive before i finish the amp, so if you'd pay for postage, i'd be willing to send you some opamps to play with so you dont need to spend as much money. i might get some extras of each just to build up a stockpile/stash to have around when the mood hits me to build something, so if there's a set you'd like to keep you could paypal me the cost of the opamps and send the rest back. edit - i will have OPA627 and 637 for sure, not 100% on what else i'm getting yet, i'll let you know within a few days.

Thats a very generous offer but Im going to put in an order tomorrow. Not sure I want to go all out on the OPA637/AD744 combo, its really expensive. The AD825 sounds very promising though, will absolutely buy that one.

 

[MrMajestic2]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Hmm ... maybe I did more opamp rolling than I should have. EDIT: As a matter of fact, I pulled that thing out and put in an 8065 (this one had 8066 in L/R). Sounds great - no light bottom end now - very strong, impactful with outrageous detail. I had always waffled between the 8066 and the 8620 as my favorite L/R chip. As mentioned earlier, I had problems with isolating the output jack on this particular PIMETA and fixed it some months back. That may explain my earlier problems with the 8065 in Ground, too. It pays to try things again, too.

Wouldnt mind trying the AD8066/AD8065 combo, but the AD8065 is out of stock at Digikey.

 

[tomb]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif Wouldnt mind trying the AD8066/AD8065 combo, but the AD8065 is out of stock at Digikey.

Yeah, they're definitely the detail kings. Get one when you can. I think the conflicts arise when the ground chip is not fast enough to sink the bandwidth/slew rate from the L/R - or something like that, anyway - and the AD8066/65 are super-fast. No opamp expert here, although I do aspire to be a Millett Maestro.

 

[gates_2]

to be honest i think i may prefer 627's on all over the 627/637 combo... I guess its a matter of personal pref. tho