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I'm using an old CABRE AS45 two way active crossover.It uses (i'm quoting the booklet) "1% high precision metal film resistors, high stability and great precision 2% capacitors, j-fet input opamps with high slew-rate and low noise"
It does, however, bring a certain roughness to the treble, some kind of "dirtyness" that's very obvious on compression drivers.
It sounds a bit like my REVOX B226 did before I recapped it and swapped the old opamps for LM4562.
The "magical" recipe on the B226 was: Nichicon KW caps in the PSU, Elna Silmic II everywhere else, LM4562 in gold-plated sockets with local decoupling added close to the legs (replacing NE5532).
These small mods really made a night and day difference!
Checking the guts of the CABRE AS45 I can already see that:- the lytics are nothing special (Nippon Chemicon SM series) and might be old (I bought this device second-hand and while they still produce it, it dates from the eighties);
- the opamps are TL082
I guess a recap with Elna Silmic II or Nichicon Muse cannot hurt anything, but would I get improvements by changing the four TL082 for LM4562? My intuition says yes, but desoldering opamps and installing sockets + possibly local decoupling isn't as straightforward as changing a few caps.
Anybody has any opinion regarding the TL082 opamp?
Edits: 10/13/16 10/13/16Follow Ups:
"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.
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 :)
Well, I just did search on TL082 and it looks like it's a "general purpose" opamp. I guess replacing those with a widely "audio-approved" opamp such as LM4562 (I love them, I don't see the point going BurrBrown) could bring very interesting results.
The TL082 is nasty in comparison to modern op amps. Getting rid of them should make the improvements you desire. If the circuit impedances are > 5K ohms, the OPA2134 could be a better (less noisy) choice. Decoupling per the datasheet is not optional. And most of all, have fun!
Dark energy? Ridiculous!
We live in an electric universe.
Edits: 10/13/16 10/13/16
I don't have the board under my eyes right now, and i don't have any schematics, but i guess each opamp has two 10uF lytics about 1,5inch distance from it, and a couple small value ceramic (?) caps, so it looks like opamp decoupling would be enough for OPA2134?...
If there are small ceramics on the power supply pins very close to the op amps, you should be good to go. In all my travels, I have never seen vintage gear so equipped but it is possible.
Dark energy? Ridiculous!
We live in an electric universe.
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