Is 4x stacked buffers worth it on the PIMETA?

[Porksoda]

Hey guys

I've ordered parts for a pimeta and I bought enough buffers to stack them 4-2-4. I'm having second thoughts about whether it is worth it to use all those buffers on what is essentially a mid-grade amp. I'm certain if I don't use them all I will find another project for them, so I'm not worried about wasting them. OTOH, I do anticipate using Grados with them, so the stacking might help with the low impedance cans.

Just for reference, my other components include:
Alps Blue Pot
VD RN55D resistors throughout
4x 470 uF Cerafine power caps
~1000uF additional Pana FC caps in the battery board
Either AD8620 or 2xOPA634 op-amp
8x AA NiMH batteries @ 2000mAh

I've got enough batteries to still get good battery life with all 10 buffers, I'm just concerned that there is no appreciable gain, and 10 buffers represents a fairly good chunk of change to throw at a single project that could otherwise be enough for two projects.

Any thoughts on this? Anyone that uses a PIMETA/Grado combo that would care to comment?

 

[Earwax]

I ended up actually taking out the extra buffers and going back to 1-1-1

I find the sound to be fuller & smoother this way. I previously tried 2-1-2 and 2-3-2 configurations, which seemed to have a more detailed and refined sound, but it was somehow unsatisfying, perhaps just a bit thin. I also thought 2-3-2 was very slightly better than 2-1-2.

If you're careful, you can test the buffer stacks without soldering them together, just pressed in place. Although there'd be the risk of a buffer coming loose and shorting something out if the amp gets moved around like that.

 

[bg4533]

I built a similar Pimeta with Cerafines, OPA627, 4 buffers l/r and 2g. I can hear very little difference between that Pimeta and a more basic one with 2 buf l/r 1g, Panasonic caps and an Alps. The nicer Pimeta is a tiny bit smoother, but it seems this is more due to the Alps and/or Cerafines. This has been tested with MS2s, HD650s and DT770s.

The OPA627 is a good choice with Grados. The AD8610 can be fun at times, but can also be quite irritating.

I shouldn't say this since you already ordered parts, but it seems a basic PPA is significantly better than a maxed out Pimeta. Probably similar priced too.

 

[Syzygies]

Quote:

Originally Posted by Earwax I ended up actually taking out the extra buffers and going back to 1-1-1 I find the sound to be fuller & smoother this way.

Whoa! That's interesting. What is your op amp preference ordering? (I'm trying to calibrate your judgement call here, from power use perspective 1-1-1 is appealing.)

 

[bg4533]

The thin sound is actually my biggest complaint about the Pimeta. The PPA just sounds so much fuller. I have never really listened to a Pimeta with 1 buffer/channel. Maybe I will give it a shot.

 

[Earwax]

I rank 637LR/627G slightly ahead of AD843s. I wasn't happy with 627s on all three channels. For power stingy portable use I think I'd pick the OPA2228/227.

And I also ended up running the buffers in low bandwidth mode after trying a few variations for R11.

(I'm probably really a tube person at heart. Warm and lush usually wins my heart, but I do like the gilmore dynamic too.)

I use HD600, HD555(50 Ohm), Sony CD780(60 Ohm) and Shure E3c(26 Ohm), gain is around 5.

 

[Porksoda]

Thanks for all the replies guys!!

As to the PPA vs PIMETA arguement, I am making this sucker SMALL and very portable; the PPA board wouldn't fit in the case I am using.

As for buffer stacks, I suppose I could make a few different stacks and try several different combinations. By my figurings I could test 1-1-1, 2-1-2, 1-2-1, 1-3-1, and 2-3-2 if I were to solder together two 2x stacks, 1 3x stack, and leave 3 separate.

I guess given my musical leanings I would probably take a more agressive sound over a smoother sound, but of course perfectly neutral is always the ideal

Of course with 1-1-1, my amp would have like 35 hours of battery life!!