[djbob]

Greetings,

I'm searching for the best available alternative for the Buf634p for a Pimeta build. I'm currently purchasing all of the parts and the 634 seems to be eluding me.

Thanks in advance for your assistance.

 

[slowpogo]

The LMH6321 is a good alternative to the BUF634P. It is SOIC, but put it on a Browndog adapter and it's a drop-in replacement--you just need to snip pin 1 (top left).

I actually like the sound better. It's a little firmer and more lively, more impact, but nicely detailed.

 

[MisterX]

Quote:

put it on a Browndog adapter

For why?

 

[slowpogo]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif For why?

Yeah, the Pimeta has SOIC pads on it. But it's more or less permanent if you solder a chip in. Better to use a DIP adapter, and be able to try other things down the road, IMO.

 

[user18]

I have a couple of spares (DIP8). if you need them, pm me.

 

[aamefford]

I want to build the Pimeta, but the BUF634's are eluding me as well. I've found them for US$17.97 ea, which is just not reasonable to me. I just looked at the LMH6321 at digikey, at a reasonable $5.88 ea. The package is listed as 8-PSOP. I don't know what this means. I am not yet experienced in the various IC packaging options. My understanding is that the BUF634P that is spec'd for the pimeta is DIP8. The BUF534U is an SO-8 package, and that a brown dog adapter is required.

As I stated, I really don't know the difference between DIP8 and SO-8. I also don't know if 8-PSOP is equivalent to SO-8, DIP8 or is different from both. Can someone help me out or point me to appropriate resources?

Will the LMH6321 fit on the bottom pads?

Is there any advantage to putting them into adapters and mounting them in sockets? It seems that buffers for this amp are hard enough to find that "buffer rolling" is not practical, so soldering them to the bottom of the board is reasonable?

Also, multiple searching here and at headwise reveals a difference of opinion as to whether the LMH6321 is a good choice in the pimeta, and whether or not it is a good idea to use browndogs, as oscillation may result. Comments?

How do I diagnose oscillation without an O-scope and signal generator? I've got a decent DMM (Fluke 179) but no O-scope.

Here is the link to the digikey listing for the LMH6321:

Digi-Key - LMH6321MR-ND (National Semiconductor - LMH6321MR/NOPB)

and the digikey part number: LMH6321MR-ND

Thanks everyone! I think this is all that eludes me for this build. I've got a pair of HD 580's crying out for a break from the iPod headphone jack!

 

[FallenAngel]

Quote:

Originally Posted by aamefford /img/forum/go_quote.gif I want to build the Pimeta, but the BUF634's are eluding me as well. I've found them for US$17.97 ea, which is just not reasonable to me. I just looked at the LMH6321 at digikey, at a reasonable $5.88 ea. The package is listed as 8-PSOP. I don't know what this means. I am not yet experienced in the various IC packaging options. My understanding is that the BUF634P that is spec'd for the pimeta is DIP8. The BUF534U is an SO-8 package, and that a brown dog adapter is required. As I stated, I really don't know the difference between DIP8 and SO-8. I also don't know if 8-PSOP is equivalent to SO-8, DIP8 or is different from both. Can someone help me out or point me to appropriate resources? Will the LMH6321 fit on the bottom pads? Is there any advantage to putting them into adapters and mounting them in sockets? It seems that buffers for this amp are hard enough to find that "buffer rolling" is not practical, so soldering them to the bottom of the board is reasonable? Also, multiple searching here and at headwise reveals a difference of opinion as to whether the LMH6321 is a good choice in the pimeta, and whether or not it is a good idea to use browndogs, as oscillation may result. Comments? How do I diagnose oscillation without an O-scope and signal generator? I've got a decent DMM (Fluke 179) but no O-scope. Here is the link to the digikey listing for the LMH6321: Digi-Key - LMH6321MR-ND (National Semiconductor - LMH6321MR/NOPB) and the digikey part number: LMH6321MR-ND Thanks everyone! I think this is all that eludes me for this build. I've got a pair of HD 580's crying out for a break from the iPod headphone jack!

Yes, the LMH6321MR should fit on the bottom of the board, it's PSOP, so it's small surface mount. DIP is the one with pins. Since it's a high speed buffer, it's not recommended to be on an adapter. This is a precaution so that it doesn't oscillate. It might, it might not in Pimeta, I'm not sure, but why not be on the safe side.

Checking for oscillation, simplest way is find out if there is any heat from the buffers/opamps, there should be none. Next is to measure current draw of the whole amp (connect V- to battery -, V+ to DMM - and DMM+ to battery +), count up how much current is used by the opamps and buffers, and if your meter says it's more, you've got problems.

Also, remember, do not populate R11 and you might need to lift Pin 2 on that buffer to avoid problems.

 

[Filburt]

You can probably use this buffer as an alternative. IMHO, it's actually the better buffer of the two; I avoid using the BUF634 for basically anything even though I have some on hand. I haven't tried it in the PIMETA, but I suspect it'll be OK. However, don't use an adaptor + socket; just solder it right onto the surface mount pads.

You'll probably need to lift/remove the EF and CL pins, though.

edit - I see Nelson already handled this

 

[joneeboi]

There was a recent thread on this sort of topic, though it covered discrete buffers. I'm not sure it's the best, but if you're having trouble finding the BUF634s, you might also want to try some relatively cheap and easy discrete buffer build. Check the second page for the one I built.

http://www.head-fi.org/forums/f6/dia...pimeta-247189/

 

[rjad]

Quote:

Originally Posted by Filburt /img/forum/go_quote.gif You can probably use this buffer as an alternative. IMHO, it's actually the better buffer of the two; I avoid using the BUF634 for basically anything even though I have some on hand. I haven't tried it in the PIMETA, but I suspect it'll be OK. However, don't use an adaptor + socket; just solder it right onto the surface mount pads.

I used one for the ground buffer in a pimeta, it worked fine, I think it sounds better but not sure. I soldered it straight in, so its there for good now. I didn't lift up any pins, but I didn't have R11 in.

 

[aamefford]

Thanks all. I've heard to lift the CF and EL pins, which I'm sure will be labeled on the data sheet. Also not to populate R11. Can anyone clarify this a bit? Do I lift pins and not populate R11 both, or is it one or the other? As for the discrete buffers, that is an option for the second Pimeta. First one is just to build and understand the circuit, second one will be to build a nice, tweaked one. I'll probably order parts this weekend or next.

aamefford

 

[MrMajestic2]

Does anyone have an answer for this? Im looking for parts for Pimeta that Im building for a friend and the BUF634 cost an arm and a leg here in Sweden, but it is in stock though. The LMH6321 would be a much cheaper alterntive, even if I have to order it from Digikey.

Quote:

Originally Posted by aamefford /img/forum/go_quote.gif Thanks all. I've heard to lift the CF and EL pins, which I'm sure will be labeled on the data sheet. Also not to populate R11. Can anyone clarify this a bit? Do I lift pins and not populate R11 both, or is it one or the other? As for the discrete buffers, that is an option for the second Pimeta. First one is just to build and understand the circuit, second one will be to build a nice, tweaked one. I'll probably order parts this weekend or next. aamefford

 

[aamefford]

I haven't gotten that far yet. I did elect to use the LMH6321's. From much reading around and correspondence with others here, that seems to be the best IC alternative. Tangent even sort of alluded to that when I ordered boards, Wima caps, tread, cross-feed and pots. I haven't gotten to exactly how to install the LMH6321's yet, though I've been told twice not to use R11. Hopefully tomb or MisterX or Tangent or someone else that has some experience will chime in and enlighten us!

 

[Pars]

Well, as usual, RTFM, or in this case, DS. It would probably help to have the pimeta schematic handy as well, so you can compare how the BUF is used vs. the pinout for the LMH. You'll also need to verify that an 8-PSOP package will fit a BrownDog in place of an 8-SOIC pkg. (I would guess it would, but ???).

 

[Marzie]

I used LMH6321 and did omit R11

Edit: A little more info, I put the chips on browndog adapters. The standard pinout one, not the one that changes the pinout. If you do elect to go this route, as I would suggest, I would also do it the way tangent suggests in one of his tutorials, that is solder one pin and bend/position it so all the pins make contact and are square on with their pads. I used the flow/suck method (think thats what its called) where I put a good deal of solder on the pins, then swipe the pins to get the excess off. But make sure you get all the pins! I had oscillation when I first hooked it up and felt the buffers (or it may have been the opamps, I used AD8620 and AD8610) and they were getting very hot. I couldn't be sure by looking but I slid a piece of paper between the pins and found the corner pins on one wasn't touching. Same thing happened the second time I powered up and I found another chip had a corner pin that was not touching. After that it has worked well (other than some grounding issues I just got worked out...)