What is wrong with op-amps?

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After using mainly tubes I am now looking for high performance low gain (about x4) from solid state, and hence looking at op-amps.

There seems to be some bad sentiment towards them for some reason.

So what is actually wrong with op-amps?


(If you say ‘they don’t sound good’ please give a technical reason why you think that might be).
 
As far as I know, intelligent application of op amps results in superior performance. Of course there are hundreds of types so you need to select judiciously, although for mundane audio work many will do.

If you drive from a high impedance source you need to stick with low bias current units. If you want wideband operation you need a high speed unit. Not all op amps will be stable at a given gain.

But over all, they are terrific devices and won't let you down if you treat them right. Much, much easier to apply than tubes.
 
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Hi Gordy... try something like the OPA604 or OPA2604 if you have been used to valves. OpAmps do have their own sound, the fact that we seem able to pick up on these tiny differences always amazes me, but we do. The 604 has the "right" kind of distortion spectrum to sound pleasing I find.

Edit... whats wrong with opamps ? Nothing, it's the way they are implemented that's often wrong :)
 
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There seems to be some bad sentiment towards them for some reason.

I don't use OPAMP's of two reasons:
1. They have a very low open loop bandwidth. The implication is that the distortion is rising 6dB/octave, resulting in a complete alteration of the overtone spectrum of musical instruments (You may argue that the distortion level is too low to make this effect audible, I am not sure that this argument holds)
2. I never know if they work in class A, normally the output stage work in class A/B; in some of them even the input stage is working in class B. Just look at the power consumption. Power amplifiers in class B is bad enough, small signal amplifiers in class B is magnitudes worse.
 
(If you say ‘they don’t sound good’ please give a technical reason why you think that might be).



Have you missed all the numerous polemics about NFB, solid state vs tube transfer functions, open loop bandwidth, etc, or do you just want all these thousands of opinions and claims repeated yet once again?

At the end it all boils down to: do you know how well can you actually hear? Or would you rather take someone else's word for it?

IME it's easy to build a poor sounding tube circuit and quite possible to build a surprisingly good sounding opamp circuit. When maximum effort is made, tube circuits do sound better than opamps to my ears (or else i would not use tubes at all) but i doubt there is a simple single reason for that.
 
They sound fine when properly implemented - but unlike tubes they're really susceptible to RF and this I think is responsible for much of their 'poor sound' reputation. People give them poor power supplies and decouple them in such a way (as shown in many textbooks and app notes) as to couple noise into them then complain about the 'solid state glare'.
 
After using mainly tubes I am now looking for high performance low gain (about x4) from solid state, and hence looking at op-amps.
There seems to be some bad sentiment towards them for some reason.
So what is actually wrong with op-amps?
(If you say ‘they don’t sound good’ please give a technical reason why you think that might be).

Each OP-Amp type has it's own THD/IM spectrum, strongly independend from the layout and load conditions so as the quality of power supply (mostly the badest solution with 7815/7915 or LM317/337 in use and hence the bad reputation by some music lover's)
For you an good solution could be this discrete and very easy topology:
http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp.html
If you want also deal with various OP-Amps for the aim of compare, prefer the types AD797, OPA604, OPA134, NE5534 oder LME49710. Avoid in all cases dual or quad OP-Amps (no perfect ground management possible) and use for each op-amp a complete independend power supply and independend power supply transformer. This means for a line stage two power supplies and if there is RIAA head amp integrated, six power supplies.
A good power supply solution is that one from the RIAA head amp NAD model PP-2, schema to find anywhere here on the forum.

I don't use OPAMP's of two reasons:
1. They have a very low open loop bandwidth. The implication is that the distortion is rising 6dB/octave, resulting in a complete alteration of the overtone spectrum of musical instruments (You may argue that the distortion level is too low to make this effect audible, I am not sure that this argument holds)
2. I never know if they work in class A, normally the output stage work in class A/B; in some of them even the input stage is working in class B. Just look at the power consumption. Power amplifiers in class B is bad enough, small signal amplifiers in class B is magnitudes worse.

I agree, especially if there are high parasitic capacitances by large and long signal leads to the power amp. The AD797 and the NE5534 are op amps with highest idle current in the normal DIP-8/SO-8 outline - as I know.
 
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Maybe, it's down to voltage and current overheads when higher level signals are passing through along with transients. These transients could be in the music or interference.

I am a great believer in ensuring that a power amp can deliver adequate current.
I see the opamp as powering what comes after it.
I cannot see why the same current capability rules should not be applied to opamps.
Just look at what an opamp feeds and what parasitics it might have to drive.
Then see what current overhead capability is left to spare.

That's part of the reason I started looking at discrete opamps. One can choose the level of ClassA output and the level of ClassAB output.

Have a read of Walt Jung's papers on composite opamps. He recognises the problem of high current demands on the output stage affecting the sensitive/delicate devices in the front end. So separate them.
 
What is wrong is that some people think that their
ears are accurate enough to measure -100db THD ratios
as soon as an op amp is involved in the sound chain..
Yet, a tube amp that produce 2% of THD will sound
distorsionless for the same pundits..

Yes, and this is still again to observe in a hifi shop by demonstrations of commercial preamp devices, if classic and acoustical/vocal jazz CD's/records was used. But what is the actually reason therefore?
 
Yes, and this is still again to observe in a hifi shop by demonstrations of commercial preamp devices, if classic and acoustical/vocal jazz CD's/records was used. But what is the actually reason therefore?

Hi , Tief

As musician , i obseved 20 years ago that using what
was called an Aural Exciter changed a cold digital sound
in something that sounded warm and live , since
the principle of this accessory is to add EVEN harmonics
to the original sound.
A tube amp has almost the same effect, so when one
listen to a transistorized clean sound, he seems to him
that something that was there with a tube audio chain
is suddenly missing.
Of course, adding a tone control to a solid state amp
will not produce the same effect, since the tone control
increase both originals even and odd harmonics.
This, with the fact that a tube amp has a low damping factor,
modifying even more the original sound , is the reason why
some see a superiority of the tube things over the SS siblings !!

That it to say, they prefer an enhanced sound , yet, they
call those wave shapers "Hi fi" items !!...

cheers,

Wahab
 
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Each OP-Amp type has it's own THD/IM spectrum, strongly independend from the layout and load conditions so as the quality of power supply (mostly the badest solution with 7815/7915 or LM317/337 in use and hence the bad reputation by some music lover's)
For you an good solution could be this discrete and very easy topology:
http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp.html
If you want also deal with various OP-Amps for the aim of compare, prefer the types AD797, OPA604, OPA134, NE5534 oder LME49710. Avoid in all cases dual or quad OP-Amps (no perfect ground management possible) and use for each op-amp a complete independend power supply and independend power supply transformer. This means for a line stage two power supplies and if there is RIAA head amp integrated, six power supplies.
A good power supply solution is that one from the RIAA head amp NAD model PP-2, schema to find anywhere here on the forum.



I agree, especially if there are high parasitic capacitances by large and long signal leads to the power amp. The AD797 and the NE5534 are op amps with highest idle current in the normal DIP-8/SO-8 outline - as I know.

This is also the way I see it except that I would like to add OPA627 and LME49860 (a dual opamp) to the list of good devices. Since most of the commercial gear uses dual opamps the single versions are useless unless one wants to use pink cat adapter PCB's etc. which can make things worse.

As usual a non-technical opinion from me: in all cases where I replaced already tweaked opamp circuits (with even very good types) for an open loop discrete design with all its disadvantages it still sounded better. And no I did not listen to added distortion. The standard disadvantages with discrete circuits are :high offset/drift, channel differences etc. in a way larger magnitude than with opamps.

My experiences are with I/V converters in DACs and preamps. But it often is poor implementation of the opamps in question that defines the results. Proper decoupling the power supply lines is such an example where things go wrong.

Opamps are quite easy to work with when you know their limitations but a simple discrete circuit often sounds better but only so after a lot more work.

Despite all excellent explanations from true experts I simplified matters by avoiding designs around opamps as I think the feedback is what causes the disadvantages.

Yeah, "I think" is not the best of reasoning. And I too leave opamp circuits sometimes as they are and replace the devices for better types and decouple them as it is far less work than redesigning. The point is to think carefully especially with high speed high bandwidth opamps. An input filter around 100 khz can be a good remedy when it picks up high frequency signals.

BTW the original power supply of NAD PP-2 is an example of how not to do it !!
 
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Yet, a tube amp that produce 2% of THD will sound
distorsionless for the same pundits..


I would never defend or use any type of amplification with thd above 0.1%. If for no other reason, then at least because it's so easy to achieve.

Otoh, if 2% sounds distorlionless to someone it may simply mean they are not sensitive to what is quite likely a dominant 2nd harmonic. Is steady state thd, unless totally gross, at all relevant to music?
 
I've come from the 'tube' only camp and after years of that, recently got into solid-state (thank you Mr. Pass). Just last week I finished building an Audio Sector Phono Stage using OPA627 op-amps. Honestly, it is the most revealing, quiet and cleanest phono preamps I've ever heard. It has certainly changed my mind about op-amps! Like any other active device, if they are done right then the results will be good.
 
EVEN harmonics to the original sound
Even or odd just a pure math that comes from FFT. I've heard nice sound that comes from an organ or a grand piano but never directly from a spectrum analyzer.

a transistorized clean sound
It means that all transistor gear sounds exactly the same equally perfect, iPOD+LM3886 = MarkLevinson=TV set

However in real life every sample of audiogear has it own sound signature. Otherwise one clean (perfect) sounding opamp would be sufficient for the entire audio market forever.
 
Even or odd just a pure math that comes from FFT. I've heard nice sound that comes from an organ or a grand piano but never directly from a spectrum analyzer.

QUOTE]


Not at all....

musically speaking :

H2 is an octave and doesn tchange the harmony of the music
H3 is a fifth one octave higher and can be dissonnat if a chord
is played with an altered fifth.
H4 is the same as the fundamental, but two octave higher.
H5 is a major third, and can be dissonant if the musical piece
is played in minor mode.
H6 is a fifth again.
H7 is dissonnant musically speaking, having no relevance with
the musical scales.
H8 is the fundamental three octave higher.

So it s not about some FFT analysis, but about
musicality of the distorsions.

About the rest of your sayings, you are strtching my words
to fit your own sayings.
Did i said that a ipod + clone amp is perfect ?..
With such an imagination , you should have guessed
that i was talking about properly designed transistorized
items...and yes, a gainclone can be a good amp !!
For the ipod, it s another story, of course.
 
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