Hi everybody... I was hoping to get opinions of the community on the importance of op amp selection in an active preamp.
It is well known that in the construction of a headphone amplifier, the choice of the op amp can have a meaningful impact on the tone of the amplifier, however, it is less clear to me that there exists some consensus as to whether or not op amp choice makes as much of a difference when constructing a preamp which need only drive the input stage of a power amp rather than a pair of headphones.
Bottom line: Should I bother putting my opa627s in a preamp? or would a more mainstream chip work just as well?
It is well known that in the construction of a headphone amplifier, the choice of the op amp can have a meaningful impact on the tone of the amplifier, however, it is less clear to me that there exists some consensus as to whether or not op amp choice makes as much of a difference when constructing a preamp which need only drive the input stage of a power amp rather than a pair of headphones.
Bottom line: Should I bother putting my opa627s in a preamp? or would a more mainstream chip work just as well?
You can't speak about tone of opamps without specifying strictly conditions of usage. The same opamp will have very different tones depending on signal source resistance, output load, gain, inverting/non-inverting connection.
For example, I use very ancient JRC4558 opamps in my console, all of them are used according to their properties, and all of them are asymmetrically biased by resistors. In one model of power amp I use also ancient CA3140 opamps, but again they are used according to their unique properties. But 3140 would "sound bad" in console instead of 4558, while 4558 will "sound bad" in the power amp.
And so on...
For example, I use very ancient JRC4558 opamps in my console, all of them are used according to their properties, and all of them are asymmetrically biased by resistors. In one model of power amp I use also ancient CA3140 opamps, but again they are used according to their unique properties. But 3140 would "sound bad" in console instead of 4558, while 4558 will "sound bad" in the power amp.
And so on...
...so the application of the op amp is an important factor... This much I intuited... However, for the application of a preamp... taking the line level output of a cd player... feeding a tripath amp... which presents a pretty easy load... will the selection of the type of opamp (which will be used as a zero gain buffer stage) be as important as it is when designing a headphone amp? what sort of opamp is best to use? or is it better to use a discreet approach?
If you're building a preamp with an opamp, the opamp is the single most important part. Nothing else come close. Make sure to have it on socket so you can try different ones. OPA627 is an excellent choice. National's LME49xxx are cheap and good. The new OPA(2)211 from TI is probably very good as well. If you want reviews of how different opamps sound, do a search here or at head-fi.org
GratefulTony said:
Op-amps are not designed for audio use exclusively and therefor not just a question of inserting some gain block into the system. Most op-amps operate in class B, thus you have cross-over distortion from the onset. Applying bias to pull the output into class AB causes so off-set which has to be counteracted. Counteracting the off-set causes non symmetrical response and so, and so on.
As a tool, an op-amp is a very useful device in many signal conditioning applications, but as a pre-amplifier feeding your $100 000 power amp, I think I would give it a miss.
Op-amps are great building block needing few components strung around them to get a very good effect - so how easy ut us to make a filter of kinds, compare one level to another, etc,
You can do worse of course, but it would be interesting to evaluate your results with different devices provided all else remains the same.
Kind Regards
Nico
Each transistor, resistance, capacitor will distort
If you can install a transistor to do the job of pré amplification it is not very good to install a chip that has an entire power amplifier in a mini version,.... inside the chip case you have the input differential, the VAS, the drivers and the output...and usually they use more than that...a lot of parts contributing to a final big mess.
Despite beautifull specifications, they use to sound different, this means they "sound"..they have a character, a sonic signature.... so, gonna be alike to win a lottery to find the one will sound good to your ears...asking people, they will sugest you several different units, and i think only few of them have made A to B testings.... in other words...they do not really know the one sounds good..also this is subjective, personal, good to guy "x" does not means good to guy "y"
In my point of view we do not need even pré amplifiers.... or we can do it using just a potentiometer to control volume...this way, not introducing stages between the audio source and the power amplifier you will have, as a result, superior sonics.
I have never used pré amplifiers..... the tone is adjusted into my speakers, i use to adjust them to be flat (or something i think it is flat...or something nice to my years) using resistances, inductors and capacitors (avoiding inductors).
The need of pré amplifier remains when you use turntable..then you cannot avoid to use, at least, 2 stages to each channel...unavoidable...but, other audio sources, alike CD or DVD line output, or satelite receivers, or computers line out, all them have enougth audio level to drive power amplifiers.
Also, power amplifiers have adjustable gain into the feedback loop...into the second differential transistor.... a patch to ground starts into the second differential transistor base..there you have a resistance in series with a capacitor to ground... that resistance, when decreased, increase you gain..... and of course, this same resistance when increased, goes reducing, decreasing, your gain, your sensitivity... this means you can make your amplifier sensitive to any kind of source...not needing to install stages between the audio source and the power amplifier input.
Try it my dear, the day you do that, will be the last day you gonna use pré amplifiers.
Sound is absolutelly better, more clear, less distorted.,, even the impedance is not an issue..the source output impedance use to be around 47K..... the power amplifier input impedance also use to be 47K, so, no need to match anything using circuits.
The best pré amplifier you can have in your life will be NO pre amplifier... test that, and then return here to thank uncle Charlie.
regards,
Carlos
If you can install a transistor to do the job of pré amplification it is not very good to install a chip that has an entire power amplifier in a mini version,.... inside the chip case you have the input differential, the VAS, the drivers and the output...and usually they use more than that...a lot of parts contributing to a final big mess.
Despite beautifull specifications, they use to sound different, this means they "sound"..they have a character, a sonic signature.... so, gonna be alike to win a lottery to find the one will sound good to your ears...asking people, they will sugest you several different units, and i think only few of them have made A to B testings.... in other words...they do not really know the one sounds good..also this is subjective, personal, good to guy "x" does not means good to guy "y"
In my point of view we do not need even pré amplifiers.... or we can do it using just a potentiometer to control volume...this way, not introducing stages between the audio source and the power amplifier you will have, as a result, superior sonics.
I have never used pré amplifiers..... the tone is adjusted into my speakers, i use to adjust them to be flat (or something i think it is flat...or something nice to my years) using resistances, inductors and capacitors (avoiding inductors).
The need of pré amplifier remains when you use turntable..then you cannot avoid to use, at least, 2 stages to each channel...unavoidable...but, other audio sources, alike CD or DVD line output, or satelite receivers, or computers line out, all them have enougth audio level to drive power amplifiers.
Also, power amplifiers have adjustable gain into the feedback loop...into the second differential transistor.... a patch to ground starts into the second differential transistor base..there you have a resistance in series with a capacitor to ground... that resistance, when decreased, increase you gain..... and of course, this same resistance when increased, goes reducing, decreasing, your gain, your sensitivity... this means you can make your amplifier sensitive to any kind of source...not needing to install stages between the audio source and the power amplifier input.
Try it my dear, the day you do that, will be the last day you gonna use pré amplifiers.
Sound is absolutelly better, more clear, less distorted.,, even the impedance is not an issue..the source output impedance use to be around 47K..... the power amplifier input impedance also use to be 47K, so, no need to match anything using circuits.
The best pré amplifier you can have in your life will be NO pre amplifier... test that, and then return here to thank uncle Charlie.
regards,
Carlos
Attachments
What function is this "preamp" serving?
MC phono cart pre benefits from low noise where discrete designs can best op amps
at higher signal levels you can find very good op amps such as the OPA627 you mention
for general line driving composite op amps as described by Jung in his Op Amp Applications book can match low noise input op amps with high current drive op amps such as those developed for DSL for a composite amp with superior performance to any single chip implementation - some of the DSL op amps have several mA output Q bias current - enough for Class A operation into any audio power amp input I can think of just now
MC phono cart pre benefits from low noise where discrete designs can best op amps
at higher signal levels you can find very good op amps such as the OPA627 you mention
for general line driving composite op amps as described by Jung in his Op Amp Applications book can match low noise input op amps with high current drive op amps such as those developed for DSL for a composite amp with superior performance to any single chip implementation - some of the DSL op amps have several mA output Q bias current - enough for Class A operation into any audio power amp input I can think of just now
Incorrect. Some are.Nico Ras said:
http://www.national.com/pf/LM/LME49710.html
"LME49710 - High Performance, High Fidelity Audio Operational Amplifier"
There are many others.
It is far easier to design a high performance preamplifier with quality audio opamps than with discrete components.
Well, I agree, but I wouldn't be building my own preamp to drive a $100K power amp either. At that level, layout and build quality are of the utmost importance and a home constructor won't have access to the production and test equipment required.
Re: Each transistor, resistance, capacitor will distort
Doesn't a passive pre (just a pot basically) show potentially variable input impedance? isn't a little buffering/ matching good for the robustness of signal?
I used to use a passive pre, and indeed, I was pleased with the sound... however my fullrange speaker system requires a sub, and a sub requires a copy of the source signal... I don't think it is wise to simply "split" the input cables and send them to the power amp and to the sub... is there a way to do this with a passive main amp signal path? perhaps branch a pre channel off of the passive channel? Obviously, it is less important that the sub channel be crystal clear... I would almost be bold enough to use jellybean parts in the sub signal path.
can just exposing the signal to the uber high impedance load of an opamp color the signal?
destroyer X said:
Doesn't a passive pre (just a pot basically) show potentially variable input impedance? isn't a little buffering/ matching good for the robustness of signal?
I used to use a passive pre, and indeed, I was pleased with the sound... however my fullrange speaker system requires a sub, and a sub requires a copy of the source signal... I don't think it is wise to simply "split" the input cables and send them to the power amp and to the sub... is there a way to do this with a passive main amp signal path? perhaps branch a pre channel off of the passive channel? Obviously, it is less important that the sub channel be crystal clear... I would almost be bold enough to use jellybean parts in the sub signal path.
can just exposing the signal to the uber high impedance load of an opamp color the signal?
Attachments
Re: Re: Each transistor, resistance, capacitor will distort
Hi Tony!
I have 4 thoughts about this:
1). Perhaps using a pair of subwoofers in the traditional locations of woofers?
2). The quality of the signal sent to the subwoofer (a woofer) matters greatly because one doesn't want a miniature jukebox boom that could interfere with the quality of your music.
For extended range / realistic range bass, this is the root of discussions on NFB cap size and much of the reason that diy power supplies have so many large caps.
3). The JRC4560 (NJM4560) and its "high quality edition" JRC2121 (NJM2121) are featured in many good audio source devices (M-Audio Revo 5.1 uses 4560). They're known for providing a sturdy drive, as the documentation illustrates, and as demonstrated by their good dynamics. The 2060 is the quad version.
This series of op amps is designed to handle a very wide variety at its output. *plug "whatever" into the output*
4). I do know some friends who swear by a "fet input" as being able to cope with potentiometers--perform better during impedance mismatches at the input side. There are both op amps and discrete designs with fet inputs.
That's all I've got on it. Now I have to wonder if New Japan Radio doesn't happen to make "just like a 4560 but with a fet input added"???
GratefulTony said:
Hi Tony!
I have 4 thoughts about this:
1). Perhaps using a pair of subwoofers in the traditional locations of woofers?
2). The quality of the signal sent to the subwoofer (a woofer) matters greatly because one doesn't want a miniature jukebox boom that could interfere with the quality of your music.
For extended range / realistic range bass, this is the root of discussions on NFB cap size and much of the reason that diy power supplies have so many large caps.
3). The JRC4560 (NJM4560) and its "high quality edition" JRC2121 (NJM2121) are featured in many good audio source devices (M-Audio Revo 5.1 uses 4560). They're known for providing a sturdy drive, as the documentation illustrates, and as demonstrated by their good dynamics. The 2060 is the quad version.
This series of op amps is designed to handle a very wide variety at its output. *plug "whatever" into the output*
4). I do know some friends who swear by a "fet input" as being able to cope with potentiometers--perform better during impedance mismatches at the input side. There are both op amps and discrete designs with fet inputs.
That's all I've got on it. Now I have to wonder if New Japan Radio doesn't happen to make "just like a 4560 but with a fet input added"???
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