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Old 12th January 2004, 05:31 PM   #1
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Default WTB: Something a little better than OPA2134s

Hi,

I'm looking for dual opamps to use in an active line level crossover. It'll have a passive autoformer linestage and a tube amp after it. My current XO was built with OPA2134s (and what I think are reasonably decent resistors and capacitors), and I think it made the sound slightly flatter and drier. Of course, maybe the missing bass boom is making me feel that way. I've been reading threads on opamps, and I'll check these for oscillations.

Anyway, so I need dual opamps that aren't too much more expensive than the OPA2134s (so OPA627s on adaptor boards are out). My PS rails are +/-12V, and I believe my filter circuits run the opamps at pretty low gain (probably close to 1). The source impedance criving the opamps will be pretty low, since it'll be the output impedance of my sources (SS DAC and phono stage) divided by the square of the turns ratio of my step-down autoformers. The load impedance is the 100K input impedance of my amps, and about 2-3' of coax interconnects.

Suggestions for opamps to try are welcome, and if anyone has a handful to sell me (say 5-10), that would be perfect.

Thanks,
Saurav
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Old 19th January 2004, 07:22 PM   #2
sma is offline sma  Indonesia
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older NE5532 from Philips with ceramic packing is better warm,i use opa2134 and found same problem like you,sound is too drier,better high but lost in mid and low bass....

opa2134 is nice for cut frequncy in active crossover application ,but if put in xo preamp section ,you will hear drier sound..
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Old 19th January 2004, 07:46 PM   #3
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Well, I have OPA2134s in the whole XO box, so that's an input buffer stage, the high pass and low pass stages, and a summing stage for the subwoofer. NE5532... ok, I'll take a look into that. If anyone has any other suggestions, they're most welcome. I don't want to start yet another opamp holy war though
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Old 19th January 2004, 08:11 PM   #4
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OP249
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Old 19th January 2004, 09:19 PM   #5
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Never heard of that one before, so I did a search. In one post, I found you recommending OPA2134 and OPA2604 over the OP249 So have you changed your mind since then? Or are you recommending this based on my comments of finding the OPA2134 too dry/cold?

And I assume this is what I want. It's the only OP249 I could find in a dual DIP (I think PDIP just stands for plastic DIP), so this *should* be a drop-in replacement for what I have, if I'm understanding this correctly.

Thanks,
Saurav
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Old 19th January 2004, 10:08 PM   #6
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Where is that post ? I found this to be my text:

Quote:
I would use the OPA2604 because they really sound OK. I also have good memories on the OP249. Think they are out of production now. Special thing about the OP249 was that they have a symmetrical slew rate. Not very common with opamps.
Quote:
Concerning opamps there is some choice. Better drop-in replacements for NJM2114 are : OPA275, OPA2134, OP249 or OPA2604. I have experience with all of them and for me the 2604 and 2134 are the better choices. YMMV.
OP249 is harder to get ( here it is anyway ) , hence my advice. Could have specified that more clearly. OP249 does not sound dry like OPA2134. I stopped using OPA2134 because in the end I preferred the others soundwise. OPA2604 is a good allrounder so to speak.

But you know how to use the Search function. It will give you the answers on a plate. PDIP is plastic DIP as you correctly assumed.

Please do check datasheets for max. power supply voltages etc. to determine what opamp suits best. OPA2604 can't go wrong IMO. Decouple them well ( as with all opamps/amps/electronics in general ).
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Old 19th January 2004, 10:38 PM   #7
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I have experience with all of them and for me the 2604 and 2134 are the better choices.
That's the one I read which I assumed to mean you preferred them to the OP249. I guess I misunderstood you.

Quote:
OP249 does not sound dry like OPA2134.
That's good to hear. I'm glad I'm not the only one who thinks it makes the sound drier

Thanks once again.
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Old 21st January 2004, 09:25 PM   #8
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OK, I just ordered a bunch of different opamps, based on reading posts here:

OP249
AD826
LM6172

I thought about the OPA2132 too, since many people said it's better than the 2134 that I currently use, but ultimately decided against it. Ditto for the OPA2604.

Anything I specificaly need to take care of with these opamps? One post said the LM6172 needed extra decoupling - what do I need to do for that? My supply is regulatred +/-12V, and I have small caps at both the opamp power supply legs. The circuits are Sallen-Key filters. Do I need to make any changes to the PS or signal circuitry?

Thanks,
Saurav
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Old 21st January 2004, 09:33 PM   #9
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Since you asked for a replacement for OPA2134 which is a FET input opamp I suggested FET input replacements.

AD826 is a fine sounding bipolar opamp, as is the excellent LM6172. Check the datasheets of the latter as IIRC its maximum voltage is +/- 12 V. They both are good choices if a bit higher noise and a little offset does not bother you or your device.
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Old 21st January 2004, 10:04 PM   #10
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Hmm... I wasn't really looking at BJT vs. FET, I didn't even notice the others are bipolar. I also saw that some said current feedback and some said voltage feedback, I'm not sure what the sonic implications of that are either.

Thanks for pointing that out, I'll see if I can find any common traits to BJT inputs vs. FET inputs. Though, with a sample size of 2 each, any conclusions I'll draw will be dubious at best.

Quote:
Check the datasheets of the latter as IIRC its maximum voltage is +/- 12 V.
That's my supply voltage, so I'm covered there I think.

Quote:
They both are good choices if a bit higher noise and a little offset does not bother you or your device.
It's an active line-level crossover. It's followed by a tube amp and I mostly listen to vinyl, so I think the noise in the rest of my system will swamp any noise from the opamp. Offset... you mean DC offset in the output, right? I think my amp should be able to handle that, I'll need to think about that.

Can you (or anyone else) characterize the sound of these opamps when compared to the OPA2134? If possible, in the type of circuit I'll be using them in?

Thanks for all the help so far.

Saurav
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