[quote author="radiance"]Ok, let's get one step further.
How can we thoroughly test an DOA?
For example, I've some (30 :shock: ) 990 kits comming my way. I've also bought 2 John Hardy 990's for comparison.
Is there a simple test set up to see whether my DIY 990's are in the same league as the John Hardy ones?[/quote]
That's a nice move, getting two JH's for comparison !
Maybe you should define the goal you're aiming at.
They obviously should be biased fine, don't overheat, realize adequate DC- & AC-specs etc, but I'm not sure how many 'special details' are considered during assembly & part selection. And of course also dunno how much a present day JH-990 differs from the original DJ-incarnations of the 990.
The various remarks & details in this thread got me thinking about the very same thing:
http://www.groupdiy.com/index.php?topic=8888&highlight=990c
... as in: OK, fine, we have those kits now, but how close will we be getting ? We might be missing out on those inside-info tweaks etc, but I'd want to add right away that we'd probably better not worry too much about this. If we want the official 990's let's buy these then. Life's too short to worry whether our DIY's will be exactly identical. I mean, I might have gone great lengths to accomplish that but won't longer do so; there's simply too much of that stuff going on that can get you sidetracked. But OK, that was about getting or not a perfect 'clone'. I don't know how far you would want to go. You stated 'simple test'. I wouldn't think a simple test would be able to reveal the subtle differences. Or who know you might just compare by listening. Or by comparing in the way Wayne recently described when swapping out opamps in a desk (IIRIC it was checking/listening for the residue when two channels are subtracted)
About getting a nice DOA whether it's a 990 or not is another topic though. I recall a thread that Samuel has started about an opamp-test-jig. You might find more details there.
And there are various articles around about opamp testing.
Enjoy,
Peter