PPA Requests (Next Revision) Thread
Apr 22, 2004 at 6:24 PM Post #78 of 93
Looks good, Morsel
smily_headphones1.gif
Thanks for your efforts (the rest of Team PPA included)
smily_headphones1.gif



/U.
 
Apr 23, 2004 at 7:09 AM Post #81 of 93
Quote:

Originally Posted by morsel
Tangent requested we sack the so8 pads to reduce parasitics. Does anyone take issue with this? Kurt would rather see them stay. I don't feel strongly either way.


Seriously, SO08 pads how much do they disturb? I say not much, fractions of pF. If you think really hard: The evolution is going towards SMD and your design gets much more flexible if you have this option. All my newer hole mounted designs has this option. Check especially my Gainclone pcb. Look how I have done with the DIL08/SOIC08 thing.
http://home.swipnet.se/~w-50719/hifi...gainclone.html

The opamps are in the center of the pcb.
 
Apr 23, 2004 at 7:49 AM Post #82 of 93
Peranders, it's a bit late to be discussing the sacking of the so8 pads. Personally, I was fine with them, but Tangent brought this up 2 months ago and only Kurt naysayed removing them. Since it was Tangent's request, I'll leave it to the two of you to have last words on the subject. I could toss them back in if there was a change of heart and Tangent has not ordered the boards already, but I think I'll shut up before I get shot.

HamPhones, R8 provides a bit more isolation for the opamp power. P=I²R so for 7mA of current (Iq of an OPA627, double that of an AD8610) through a 10 Ohm resistor that's about .5mW, way less than the power rating of a 1/8W resistor.
 
Apr 23, 2004 at 8:58 AM Post #83 of 93
Quote:

Originally Posted by morsel
Peranders, it's a bit late to be discussing the sacking of the so8 pads. Personally, I was fine with them, but Tangent brought this up 2 months ago and only Kurt naysayed removing them. Since it was Tangent's request, I'll leave it to the two of you to have last words on the subject. I could toss them back in if there was a change of heart and Tangent has not ordered the boards already, but I think I'll shut up before I get shot.


I see also what you mean. There is a Gainclone project in Sweden and also a couple of other amp projects and they never will come to "shoot" since there are too many opinions and wishes. At some time you must freeze the design and a very few people must be in charge.
 
Apr 23, 2004 at 3:10 PM Post #84 of 93
Quote:

Originally Posted by peranders
Seriously, SO08 pads how much do they disturb? I say not much, fractions of pF.


Quite possibly, but I also observe that I've only seen a few amps that have ever used this feature, and always with the AD8610. I may be wrong, but somehow I suspect the use of the SO-8 pads has been more about saving money by avoiding adapters than reducing parasitics by avoiding the DIP package. If reducing parasitics was the goal, we'd put the SO-8 pads on top and not on bottom in a tangled arrangement, and sack the DIP holes completely. No, the SO-8 pads are about saving money, and that's really counter to the whole idea of the PPA.

I've only heard half-hearted support for the SO-8 pads, and also half-hearted, "well, I guess if you want to" sort of support in favor of removing them. Since few seem to feel strongly either way, I'm going to remove them for at least this board run and see who screams. If it turns out to be an unpopular move, we can put them back in 1.1B.
 
Apr 23, 2004 at 3:35 PM Post #85 of 93
I dreamt about so8 pads in the wee hours of this morning. In my dream, all became clear. Parasitics are irrelevant. The lack of so8 pads strongly encourages the use of socketed opamps, which in turn keeps the door open for future upgrades when the next godly opamp comes out that clearly bests the AD8610.
 
Apr 23, 2004 at 4:00 PM Post #88 of 93
tangent, if you have to use SO08, it's better to have SO08 pads instead of a brown dog. Keeping parts close to the pcb are always a positive thing, especially for fast IC's. Long leads (inductance) are worse than more stray capacitance.

My point of view is only practical. If you have an easy option for SMD and DIL you can virtually choose any opamp as long as the electrical properties are OK.

morsel, it's not so hard to desolder a SO08 and if you happened to have two soldering irons it's real easy, just "burn" and move the IC aside. I admit though that if you want to upgrade often a socket is the best thing if you don't want to ruin the pcb.
 
Apr 23, 2004 at 4:19 PM Post #89 of 93
Quote:

Originally Posted by tangent
Quite possibly, but I also observe that I've only seen a few amps that have ever used this feature, and always with the AD8610.


When I designed my Gainclone I had AD8620 as first choice and an OPA2134 as second.

If you don't have already, test the AD8610/20 becuase they are nice and with extremely low offset voltage, less than 100 uV, infact 60-80 uV. They sound marvelous... but they come only in SO08....
 
Apr 23, 2004 at 4:38 PM Post #90 of 93
Is there any measurable difference in the performance of the PPA with soldered AD8610 vs. DIP socket and AD8610 on BrownDog? Despite possible theoretical advantages, I bet most builders prefer the convenience of the latter. I certainly do.
 
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