[slowpogo]

I'm going to try this buffer in the ground channel of my PIMETA, soldered directly to the pads on the bottom, pin 1 clipped off.

1. Do I need to do anything with R11 -- remove it, or change its value? Right now there is a 110ohm resistor there, for doubled 634Ps.

2. Is it possible to stack the LMH6321 like it is with the 634P?

 

[balou]

1. Remove it. It's only a valid option pin on the buf634. But you might check if you should put a resistor on the current limit pin (pin 2) to ground. I don't know it either, looks like the LMH6321 could handle short time 700mA current, but if you plug out your phones, it may be a lot higher than this.

2. I think buffers are in general stackable. But I'm not 100% sure with this chip.

Have you ever thought about putting the LMH6321 in a DIP8 adapter? Might be helpful if the chip ever gets fried or if you want to try another one. You could use a brown dog adapter or one of Sijosaes DIY methods. See here and here.

I'm also interested if stacking really is possible - with the BUF634 nowhere available, this looks like a viable alternative

 

[beerad]

Quote:

Originally Posted by balou /img/forum/go_quote.gif I'm also interested if stacking really is possible - with the BUF634 nowhere available, this looks like a viable alternative

This is a bit off topic, but...

I believe Digikey has the BUF634P in stock. Their catalog pages have been acting a bit weird for a couple of weeks, but if you go to the product page for BUF634P-ND, it should show 50 in stock. (If I search for BUF634 the search result list show 0 in stock for me. If I click on BUF634P to go to the product page, I see 50 in stock. If I then go back to the search results list, it may or may not show 50 in stock. A shift-refresh usually shows 50 in stock. Weird.) OPA2107AU was doing this to me a week ago, but I tried ordering it, and received it, so it was in stock. If the part is not actually in stock, I think Digikey will not let you add it to your order, too.

Hope this long-winded explanation helps. (I would link to the Digikey pages, but the links seem to expire).

 

[balou]

Well, the 27$ intl shipping costs put me off a bit...
edit: 27-33$, plus customs

 

[pddjsteve]

I've got LMH6321 mounted on browndogs in my pimeta. I like it a lot. I haven't tried to stack them at all, though.

 

[slowpogo]

I tried stacking the LMH, and it works fine. I'm not sure if I can actually hear a significant difference in the sound, but the chips are not warm, offset is fine, etc.

I liked the sound I was getting from my Pimeta..it was really open and lush, but lacked much impact. For this reason classical sounded wonderful, but rock, while sounding great sonically, just wasn't much fun. With the LMH6321 in there (on ground channel only) it now has just a bit of zing to it, exactly what my amp needed (hoorah!). But again, I'm not sure if I can hear much difference with them double-stacked. I'm certainly not the golden-eared guru some of you are, though.

Here's another question: what about using *both* the BUF634P and LMH6321 simultaneously (the BUF in a socket on top of the Pimeta, the LMH soldered underneath)? I have a feeling this is an awful idea, but I'm curious..

 

[slowpogo]

OK, update, the chips are actually *hot* now that they're stacked. Offset is stable and low (0.5mv), and the amp sounds good, but the chips are not happy.

 

[slowpogo]

Just an update on this one...I finally tried putting two LMH6321s on a Browndog adapter. The legs of the top chip, even when clamped straight and bent down, are not long enough to make contact with the legs of the bottom chip. Before, I had just made a small solder bridge between the two (as in about 1mm).

This time I actually bridged the chips with resistor leads, making physical contact on both. The process was a real pain, honestly, but they ended up being a lot less warm that way. Still pretty warm (could leave finger on for about 7 seconds) but less than before (where I could only touch them for about 2-3 seconds).

The amp had sounded pretty good to my ears before, but with this new method it sounds even better. Just out of curiosity I stuck a memory chip heatsink on the LMHs, and the sound improved even more. My hunch is that the LMH6321 is just a warm chip in general, and when you stack two of them it becomes too hot. I don't think there's anything "wrong" with stacking them (with pin 1 clipped off) per se, as even when they were really hot they sounded as good or better than two stacked BUF634Ps.

Anyway when all is said and done, the Pimeta w/ AD744s all around (using comp. pin), Sjostrom QRV05s for L and R buffer and the above config. of LMH6231s for Gnd gives a VERY nice sound! It even makes my low-end AKG phones sound pretty nice.

 

[Soymilk]

so does this look to be better than the buf634? what would the recommended configuration for buffers be? L/R stacked buf, ground stacked lmh?

 

[slowpogo]

Well, in *my* amp I think the LMH sounds better without a doubt. I'm using discrete buffers for L and R, and I would have used a third QRV05 for Gnd but it looked like it would be quite a hassle to implement.

Two stacked BUFs sounded open and airy but mushy with no impact. Some music, especially lush orchestral stuff, sounded great, but almost everything else just wasn't enjoyable at all. It just lacked any zing whatsoever. The LMH adds a significant amount of impact without being slam-like, and is also more detailed and has a much more spacious, deep sound stage.

Just try it if you're interested...no guarantees it will sound this way for your amp or your ears, but I'm happy with it.