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In Reply to: RE: Upgrading the CABRE AS45 active crossover posted by KanedaK on October 13, 2016 at 06:02:48
"bring a certain roughness to the treble, some kind of "dirtyness" that's very obvious on compression drivers."
"the opamps are TL082"
Probably the source of your problem, as long as there are no series electrolytics (if there are, bypass them with 0.1µF film types).
There may be a DC off-set problem switching from FET input opamps to bipolar.
OPA2134, 2604 (FET types)always sounded good to me.
Follow Ups:
Tonight I removed the board to have a look at the under side of it. I found out what I thought were local decoupling 10uF lytics are in fact output coupling caps. so all the signal goes trough basic electrolytic caps before reaching the output cinchs.
I had a few SilmicII caps laying around so I did the following: two 47uF in back to back position (-cap++cap-) to simulate a bipolar capacitor on the high pass outputs; a single 100uF on the low pass.
This is just trial and I didn't have enough caps of each value to use the same everywhere, but this arrangement seems logical to me.
I also cleaned all four pots and various connectors with deoxit.
It's late here and I cannot crank it up, but low level Purcell - Funeral of Queen Mary seems to go trough with more ease and transparency.
I didn't deal with the two input coupling caps yet, I'd like to use this back to back configuration, but I'm not sure space will allow; a film cap would be nice (of course) but I tried this back to back config on my B226 and to my ears it sounds really great.
Would you recommend OPA2134 or OPA2604? Is one of them more sensitive to circuit layout, or is it just a matter of taste?
For the 470uF filtering caps I was thinking Nichicon KZ.
Looks like the best option (as in "safest") would be OPA2134. I'll give those a try, then! This is going to be fun :)
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