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Old 14th December 2013, 05:31 AM   #1
fap is offline fap  Australia
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Default Are all dual op amps of the same type 'the same'?

G'day all, my first post in this forum and I hope somebody can please give me some definitive information on this subject. I've been chasing a curious phono preamp 'hiss' problem that I've traced to my use of the OPA2134 dual op amp when high inductance moving magnet phono cartridges are used.

In my investigations I've been led back to older dual op amps like the LM833 and the venerable (but excellent) NE5532. Indeed in my particular application I find both the NE5532 and the LM833 much less noisy (hissy) than the supposedly premium OPA2134.

However reading the various forums around the internet it appears as though there are measurable differences between manufacturers of the same op amp type. For example I have read that the 'on semi' version of the LM833 is generally better than other manufacturers. Certainly the 'on semi' LM833's that I've used are excellent.

On the NE5532, I have several of the NE5532AP version. Does the 'AP' denote 'low noise'? I wonder. Regards, Felix.

Last edited by fap; 14th December 2013 at 05:46 AM. Reason: Spelling.
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Old 14th December 2013, 05:59 AM   #2
jcx is online now jcx  United States
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actually bjt inputs are expected to be worse with MM high Z at higher frequency due to noise current which is much higher than jfet input

but few fet input op amps Vnoise are as low as SA/NE5534A - the OPA2134 has 2x the Vnoise


OPA827 is pretty good on Vnoise for a fet input - but only available as singles in smt - so you need an adapter

AD743 is still the winner as far as I know for audio frequency Vnoise in fet input op amp - AD still makes them but would rather not - "not recommended for new design" - but they don't come close in a low Vnoise replacement yet
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Old 14th December 2013, 06:19 AM   #3
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The LME49720 is an excellent chip for phono preamps. Here:http://www.google.com/url?sa=t&rct=j...57967247,d.aWM

Mike
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Old 14th December 2013, 09:08 AM   #4
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NE5532AP: The A means selected for low noise and the P means DIP package.

Yes, I would expect different manufacturers of the same op-amp to perform slightly differently. Even if they used exactly the same design, the open-loop gain and noise performance depend on the fine details of the semiconductor fabrication process.

Indeed, with a high inductance source you should find that a BJT opamp is noisier than a FET one, and the noise has more of a high frequency character to it. The RIAA equalisation network might change this though.
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Old 6th January 2014, 11:32 PM   #5
rfj5106 is offline rfj5106  United States
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Can the OPA2134 directly replace the NE5532? Would an improvement/degradation in sound be expected?
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Old 7th January 2014, 01:27 AM   #6
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Quote:
Can the OPA2134 directly replace the NE5532? Would an improvement/degradation in sound be expected?
Sure, it "can". But the 5532 is BTJ input and 2134 is FET, so circuit impedance scaling and supply bypassing should be optimzed specifically for each type to achieve optimal results. If this isn't done it will usually result in more noise and distortion than would be had otherwise, and if supply bypassing isn't correct for the application it could allow the chip to oscillate.

Mike

Last edited by Michael Bean; 7th January 2014 at 01:32 AM.
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Old 7th January 2014, 04:14 AM   #7
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Originally Posted by Michael Bean View Post
.... But the 5532 is BTJ input and 2134 is FET, so circuit impedance scaling and supply bypassing should be optimzed specifically for each type to achieve optimal results.....
Which begs the question of what phono preamp design the OP is using or if it's a commercial product, what model so we can refer to specifics.
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Old 7th January 2014, 09:32 AM   #8
fap is offline fap  Australia
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G'day all, well this is interesting as my phono stage is a DIY design, the Elliott Sound Products P06/P99 sub bass filter combination.

According to the designer, Rod Elliott, any good quality dual op amp(s) can be used with essentially equivalent results.

I now have an NE5532AP in the first op amp position and an OPA2134 in the second (gain stage) position, with excellent low noise performance with my Shure M97xE phono cartridge installed. With an OPA2134 in the first position as used in the past, 'hiss' was all too apparent! Regards, Felix.

Last edited by fap; 7th January 2014 at 09:33 AM. Reason: Spelling.
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Old 7th January 2014, 07:30 PM   #9
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It is odd that you should find such a big difference between the two. The P06 could be used with a lowly 4558 opamp (or any other ~10 nV/sqrt(Hz) job) and only suffer a ~3 dB noise penalty over a noiseless one. Resistor values are a bit highish - I'd consider swapping R5 and R7 and dropping R2 to maybe 1k. Should give ~2 dB less noise.

Things become even more odd when considering that hiss usually denotes high-frequency noise, and up there source impedance climbs into the double-digit kOhms with typical cartridges, making high current noise more of a threat than voltage noise. A dominant inductive source should also benefit FET inputs in general when it comes to noise.

Possibly the OPA2134 previously used was ESD damaged or something. (Or it was oscillating. POAx134s have been noted to be more prone to oscillation than OPAx132s, and I can't see any (!) power supply bypass caps on the P06 PCB.)

BTW, different kinds of 5532s do in fact vary measurably. Samuel Groner ran both a TI part and an old Signetics (should be same as Philips) through his opamp tests, and while the latter seemed a touch worse in transfer linearity, common-mode linearity was ~10 dB better. If you still have Philips/Signetics parts, treasure them, they haven't been made for 10 years as a result of a fire in the French fab.

Last edited by sgrossklass; 7th January 2014 at 07:47 PM.
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Old 7th January 2014, 11:16 PM   #10
fap is offline fap  Australia
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G'day mate. I tried several known good new OPA2134's with totally identical results.

In email contact with Rod Elliott, he has agreed the altering some of the the RIAA component values will reduce op amp hiss, however changing the first op amp to an NE5532 has acheived the same result. Regards, Felix.
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