Opamp Replacement

Hello everyone.

I would like some advice on replacing the opamp in the headphone amplifier that you can find at this link:


My needs are:

Single channel

Possibly FET input or alternatively bipolar input with very low offset that can be used in this specific application without the need to create an offset adjustment circuit.

Power supply +- 18V or more.

Very transparent, open and linear sound, rich in detail, harmonics and spatiality, with solid, deep and damped basses. I don't like the veiled and soft sound on the high frequencies.

Thanks in advance for your suggestions.

NE 5532, TL072, and so on are quite competent enough for audio, I do not remember the voltage specs off hand.

2134 and so on also have fans.

+1 to above, the device is supposed to faithfully render the signal, or amplify it.

Would you drink water from a drain?
Because the drain is adding color to the water, among other things.

So if the op amp, or other device actually changes / distorts the signal, then it is not doing its job properly.
You can always use an equalizer to modify the sound to your taste.
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Badly explained myself. I don't mean that the opamp should add something that doesn't exist, but it shouldn't alter the sound message in any way. In this forum the sound signature of opamps is often discussed, and I would like to understand if there are more correct ones regarding the transparency characteristics which are the most important thing for my sound tastes. But beyond the dialectical subtleties, do you have any concrete suggestions about it, since I don't know the OPA134, which has been on the market for several years and may have been superseded by new models?
Semola, the attributes that you are looking for are totally subjective, and every person would have a different interpretation of such words. Numbers are objective and accurate. Linear is also one of the misconceptions. If three points are not in a straight line, it is a curve and linearity goes out the window.

"Very transparent, open and linear sound, rich in detail, harmonics and spatiality, with solid, deep and damped basses. I don't like the veiled and soft sound on the high frequencies."

In my humble opinion, you have learned a lot of words from a romantic authors (those cheesy ones) none of them really exist in that context. Her eyes were very transparent, and her open mouth produced a linear rich detail while whispering in my waxy ear (was she a guy?) With solid deep damped bass (maybe a Rottweiler).... goodness we can make a few stories along those lines. Audio Jargon never describes anything real, only a figment of the imagination. For anything sounding like that would be close to a very loud wet fart that rolls off gently toward the end when the little low distortion bubbles pop softly and gently while slightly soiling the underpants contains most of the attributes you mention.
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All competent Op Amps (any designed within the last 20 years) and available for way less than sandwich money will be WAY more linear and transparent than what human ears can detect.

Is flat within 0.1dB in the Audio band, less than 0.1% distortion, transparent enough?

Lots of Op Amps fit those specs, more than 50 years passed since uA741.
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You are not getting much sympathy because this "headphone amp" is a pile of expensive audiophile clichés that should give you good results but cost much more time and money than it's worth. The circuit is a single channel op-amp driving a diamond buffer using BD139/140. It's unlikely you want high quality mono, so why use two mono boards? Such op-amps come in duals and the diamond topology is not going to improve the drive from an op-amp. OPA134 are already too expensive for this job, and you want something more expensive? If you want something newer, go to the semiconductor web sites and see what they are selling. But as others have suggested, much older and cheaper parts will work fine in this application. If you are new to electronics, please forget astounding the world with your creation and be happy if you get it to work at all. You must learn to walk before you can run.
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Hi semola,
I have worked with diamond buffers quite a lot. They work extremely well, even in high power amplifiers. So a great starting point, it should be able to drive very low impedance headphones. The OPA134 is overkill, an NE5534 with compensation would work well also. But, it is designed with the OPA134 and you know that works - so use it. Faster op amps may only oscillate. The one they picked has excellent drive characteristics as well, so any reflected impedance changes to the output of the op amp probably won't matter.

They probably made the PCBs mono for ease of mounting in a case. Otherwise no advantage. Since it is designed that way, build it as intended. Now, with 18 V rails you can blow headphones. I don't know if you want to pay extra for a high voltage op amp that has relaxed signal performance just to get the voltage rating up. You do not need the higher voltage anyway. That and diamond buffers tend to run with higher bias currents and you do not need the extra heat either.

Looks like a good kit. Build as designed and enjoy. I would probably run it at 16 volt rails to be honest. That's also more than enough.

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See the first issue date of BD139/140..that tells you a lot about the seller!

We have a lot of jokes here about ordinary food being passed off as exotic, "idli chutney" (very common breakfast / evening food in South India) being called "rice cake and coconut crush" in fancy restaurants, and of course at least ten times the price.

There are many examples of head phone amps here on this site, some using the LM386 IC (IIRC), look at them, then decide what you want to do.