I LOVE my PPAS

[bhjazz]

Nice work oz. I have two PPAS boards waiting myself. I like the case. So small and unassuming...bwa-ha-ha-ha.....so evil!

 

[Andrea]

Quote:

Originally Posted by pddjsteve The only thing I've ever used it in was the PPAS, since it has almost the same pinout as the Buf634, and it does a good job there. I'd say it is maybe a little harsh on the highs, but that could be the AD8620 coloring it rather than the buffer. We had to lift the "CL" pin off the board to use it in the PPAS circuit, and comparing the datasheet to the Buf634 the "GND" pin on the LMH is a "NC" on the BUF. So neither of those were connected. I probably can't give too good of an impression because right now, I don't have any other PPAS to compare it to. I've actually been meaning to make a "test" amp to play with some extra ones, I've got a couple LMH6321 and a couple HA5002 to play with. I also wanted to check out a few of the chips you and filbert have been talking about.

Thanks! I really want to give this buffer a try.

 

[Filburt]

Hmm, if you can use bipolars with the PPAS I'd try the AD8058/57.

 

[ATAT]

Filburt, I'm waiting for the new set of resistors to arrive so I can try the LM6172 and the AD8058s

impressions in the next week or so.

 

[Andrea]

Quote:

Originally Posted by ATAT Filburt, I'm waiting for the new set of resistors to arrive so I can try the LM6172 and the AD8058s impressions in the next week or so.

Aren't they too fast, particularly the LM's, to be buffered by the BUF634-like buffers (at audio frequencies & with a headphone load) ? For the BUF634 I'd personally prefer a chip with, say, no more than 150-200 V/us slew rate.

 

[Filburt]

Quote:

Originally Posted by Andrea Aren't they too fast, particularly the LM's, to be buffered by the BUF634-like buffers (at audio frequencies & with a headphone load) ? For the BUF634 I'd personally prefer a chip with, say, no more than 150-200 V/us slew rate.

Hmm, I think both the 634 and 6321 could probably handle the 8058.

 

[ATAT]

634 - max bandwith 180Mhz

LMH - bandwith 110Mhz

LM6172 - GBP = 100Mhz

 

[els0rz]

Quote:

Originally Posted by ATAT pddj - I like the AD8066/OPA132 combo (yes i know this is a weird combination) so far.. The LMH as far as I remember is a bit brighter and punchier than the BUFs, so that should help tame the highs.. hopefully, my search will be over once I build the LM6172/1 PPAS Andrea - both CL and GND are needed only for current control, if that's not needed, then leave both of them open.

hey what values are you using for your resistors in this setup? can i get away with the defaults? (i'm still waiting for my opamps in the mail)

 

[Tedro]

I have built a few PPAS with either a OPA2107/OPA121Ku and AD8620/AD8610 both with the LMH6321 buffer. They both sound nice and have not been able to pick a favorite yet.

Fake Edit:
That is all.

 

[Andrea]

Quote:

Originally Posted by ATAT 634 - max bandwith 180Mhz LMH - bandwith 110Mhz LM6172 - GBP = 100Mhz

Have you heard Jan Meier's warning about "DIY projects where the controlling op-amp is much faster than the buffer at audio frequencies" ...I have no means to prove it, but it sounds reasonable. LM6172 = 3000 V/us ; BUF634 = ideally, (and if I understand correctly, unrealistically) 2000 V/us. The result being, again in Jan Meier's words, an "increase of distortion".

 

[ATAT]

Andrea - not sure why slew rate matters, what should matter is the -3db bandwith of the opamp and the buffer. As long as buffer bandwith > opamp bandwith, then you have nice, stabilizing negative feedback across the opamp bandwith.

Also, what in the "audio" range slews at 3kv/us?

or even the 2kv/us limit of the BUF634. That's approaching high-sped digital circuits there... I guess if the input signal was at 3kv/us, you'd get some issues (slew-limited clipping perhaps) but otherwise, in the sane-audio range I see no problems.

(especially since none of my sources can slew at even 1kv/us)

 

[Andrea]

Jan said in some thread recently that the BUF634's bandwidth driving a headphone, considering a typical headphone cable's 300pf or so capacitive load, is limited to about 25 MHz (configured for widest bandwidth).

The slew rate thing, well... my bad, likely. I thought the same (it's just a theoretical limit) but Jan's argument has confused me. I don't know if a faster driver op-amp than the buffer might cause the IMD to raise, even when the real life slew rate of a digital signal (I read somewhere) can't go over about 0.7 V/us.

 

[nysulli]

anyone have experience with both the pint and the ppas, i've got some ppas boards i haven't built yet, i've just been happy with my pint, but still curious to see if i want to build a ppas, or just jump into an M^3

 

[ATAT]

http://www6.head-fi.org/forums/showp...1&postcount=95

 

[ozshadow]

I can confirm, a opa2107 sounds noticably brighter with a AD8610 in ground than a opa627. Bass is more neutral, probably due to perception of hearing a brighter sound. I prefer the opa627 in ground with Grados.