[applegd]

After reading http://www.tangentsoft.net/audio/pimeta/tweaks.html, I am thinking about stacking BUF634 for each channel. But I have couple questions need help.

1. I plan to stack 2 buffers for R & L channel, also halve R11. Do I need to double buffer for G channel as well?
2. If I don't stack buffer, I will try to add discrete diamond buffer output stage. But I don't know where to buy professional PCB.

Please share your experience. Thanks!

 

[tangent]

Quote:

Originally Posted by applegd Do I need to double buffer for G channel as well?

No. In fact, experience shows that the benefit isn't as great here. If you're on wall power and have the money to burn, hey, why not -- it's not a worthless thing to do. But if the extra $6/buffer matters to you or you're on battery power, I definitely wouldn't do it.

 

[MisterX]

I got one tweak for you:
Don't install the class A bias stuffs or maybe socket the R10's so you can easily disable it.
Order a pair of AD744 DIP8 opamps from Digikey (or wherever), remove pin 6 from the op-amps and bend pin 5 over so it will fit in now vacant pin 6 holes of a browndog Single-to-dual Op-AMP Adapter.
Insert this into the left and right channel opamp socket.
You are going to love the results.

 

[Andrea]

Quote:

Originally Posted by MisterX I got one tweak for you: Don't install the class A bias stuffs or maybe socket the R10's so you can easily disable it. Order a pair of AD744 DIP8 opamps from Digikey (or wherever), remove pin 6 from the op-amps and bend pin 5 over so it will fit in now vacant pin 6 holes of a browndog Single-to-dual Op-AMP Adapter. Insert this into the left and right channel opamp socket. You are going to love the results.

Mmmmm, interesting... probably I'm going to love 'em too, for something I have in mind.

 

[setmenu]

My best tweak was to junk the 634 buffs and replace them with HA 5002's

Not a simple plug and play solution though, as they don't share the same pin out configurations.



.

 

[quicksilver96]

I also got rid of my BUF634s though I didn't use the HA500X series. The National LMH6321 is currently my prefered IC buffer solution and is pin compatible with the BUF634. Just cut off or lift pin 1. I believe this is connected to V- through the BW resistor the PIMETA board, but you want this pin left open or tied to ground when the error flag function is not in use. The LMH only comes in PSOP-8 so you can use a socket on the PIMETA and a browndog SOIC->DIP adapter so you can swap/compare with the BUF or other ouput stages; or you can just solder the LMH to the SOIC pads on the PIMETA.

I find the LMH to be more impactful and more transparent (opamp choices effect the sound more) than the BUF634. I had double stacks on originally, but they sit unused right now because I much prefer the LMH6321.

 

[nysulli]

Quote:

Originally Posted by applegd After reading http://www.tangentsoft.net/audio/pimeta/tweaks.html, I am thinking about stacking BUF634 for each channel. But I have couple questions need help. 1. I plan to stack 2 buffers for R & L channel, also halve R11. Do I need to double buffer for G channel as well? 2. If I don't stack buffer, I will try to add discrete diamond buffer output stage. But I don't know where to buy professional PCB. Please share your experience. Thanks!

http://www6.head-fi.org/forums/showthread.php?t=159959

n mahar put his diamond buffers in a pimeta a while back, theres a thread somewhere in the DIY forum with a picture i think, all he had to do was cut the board in half and put pins on it

 

[Pars]

You can also look at this, particularly the last page or 2 where mono took Sijosae's buffers and modified them a bit with amb's help to replace the BUF634s. I've built a few of these and do prefer them to BUF634 in BW-mode (even stacked, as I recall).

I'll have to try MisterX's suggestion tho...

 

[Andrea]

The LMH6321 has an input impedance of just 250K ohm. Can the AD744's pin 5 drive this impedance without any loss of performance?

 

[quicksilver96]

I'm not sure Andrea, I have never even tried what MisterX suggests, my DIP-8 opamp of choice is the AD843. From the simplified schematic it appears he is using the internally "class-a" biased front half of the 744 chip and not using the output transistor stage of the chip. I'll have to get some just to play with. The input resistance of the BUF634 is much higher (8M at the lowest) and I'm not sure of the current output capacity of the modified 744. MisterX can you fill us in?

 

[applegd]

Thanks very much for all the replies!!!

As my PIMETA is always on wall power, I plan to do following:

(Step 1)
I will try HA5002(SO8)x1/channel first as I have 8 chips in hand and my 5 SO8 to DIP8 adapters are on the way to my home. Then try HA5002x2/channel. I will stack 2 HA5002 together just as other people stack BUF634. Hope my PIMETA will not smoke.

(Step 2)
If I am not satisfied with the result of Step 1, I will buy additional BUF634s, try BUF634x2/RLchannel.

(Step 3)
When I buy BUF634s in step 2, I will also buy parts for discrete diamond buffer. I will take the Discrete diamond buffer output stage in PPAv2 as reference.

Maybe I can just skip step 2, go step 3 directly.

 

[tomb]

I recently tried stacks of the Intersil buffers on a Millett. They definitely have better transparency and dynamics that an equivalent stack of BUF634. The difference is not great enough that a single can compete with a stacked BUF634. However, stack-to-stack, the Intersils easily sound better.

One reason for that transparency is the lack of any output protection whatsoever. You may need to put real resistors in the PIMETA's R8 positions. Just the intermittent shorting that occurs when pluggin/unplugging a set of headphones could be enough to fry them instantly.

I would be afraid to use them otherwise. There are stories of a single slip with a meter's probe destroying them in an instant.

 

[luvdunhill]

so, what are the options for adapting the Intersil buffers in stacked configuration to the PIMETA DIP-8 format?

 

[kklee]

Quote:

Originally Posted by nysulli http://www6.head-fi.org/forums/showthread.php?t=159959 n mahar put his diamond buffers in a pimeta a while back, theres a thread somewhere in the DIY forum with a picture i think, all he had to do was cut the board in half and put pins on it

I've built a max'ed out Pimeta that's using the Millet diamond buffers. It definitely fits if you cut the board in half, although you may have to nudge a couple of the capacitors a bit to wedge the boards in. I get just under 2 hours of battery life running on a pair of 9V NiMH's.

 

[pddjsteve]

I'm kind of curious about stacking them, too. I just layed out and etched an adapter to convert the intersil pinout to the buf634 pinout. So can I just stack a pair of dip-8 intersil buffers on top of my adapter the way I would a pair of buf634, and then put it all in?

My goal is to be able to swap between LMH6321, Buf634, and the HA5002 along with swapping opamps so I can find the combo I like the best.