Op-amps, more than volume?

A

Atech

2[H]4U
Joined
Jul 14, 2007
Messages
3,946
Quick question:
Anyone got any data/measurements that shows if chaning op-amps does anything, but change the sound up in volume, causing a pseudo-subjective altering of the sound...like turning the volume knob on the amp up a notch or two?


I don't care about what you THINK you hear, I wan't hard data not subjective views thanks.
 
Sure, there's all kinds of things they can change. How much of it makes a difference in the sound is up for debate, but that the change happens is not, you can see it on a scope.

One would be current handling ability. If your opamp is directly driving the output, and if you put headphones on that output, the opamp is going to be expected to handle a good amount of current. Depending on the opamp will depend on how gracefully it does that. Some can deal with the low impedance loads fairly well, some can't and their performance suffers in a big way.

Rise and settling time would be another. An ideal opamp would go right to the correct voltage and stay there. In reality, it isn't so clean. There is an amount of time that passes as the opamp bring its voltage up. It will overshoot the target slightly, then fluctuate as it settles. How long this takes and how much error there is can depend on the quality of opamp you've got.

Noise would be another one. If you look at data sheets you'll notice one of the things a better opamp buys you is lower noise in all forms. Cheaper opamps can have more inherent noise, let in more noise from the power rails, have more cross talk, and so on.

Now how much any of this matters to sound is a matter of debate. That is when you do get in to some subjective testing and so on. Also, it is dependant on what your setup is like. If the opamp is driving a power amplifier that has a high impedance input, it isn't going to have to work as hard as an opamp that is driving 32 ohm headphones. Thus an opamp that sounds just fine in the first case might not in the second.
 
I'll tell you what I know then :)

It does depend on what op amps you have and what you change them to whether you will notice a difference.
Burr Brown make some excellent op amps that have been reviewed with the new Auzentech X-Fi processor card. I'm thinking this is what you have in mind?

If you replace the op amps, you can get less distortion so might be able to turn the volume up higher.
The gain is normally configured in the external circuitry (on the card) so its doubtful it will be louder at the same volume setting.

The sound quality can be improved substantially which is the main reason I would upgrade them.
The comments on this page are typical of the experiences being reported.
http://forum.ncixus.com/forums/inde...01&product_id=20812&msgcount=20&overclockid=0

Are you wanting to see data sheets?
 
This is not what I requsted, I want data, technical sheets ect.
Not user "opnions", sorry.

I have heard a lot about op-amps, but I have never seen any data to suggest the magnitude and the relative difference between op-amps, all I hear is "I think..."
 
Are you interested in anything in particular like
Total Harmonic Distortion (THD)
Noise floor
Phase Response
Frequency response
Transient response

If so you need to specify which device you want the data for.
 
Ummm, while you keep saying you want data, I don't think you really know what you want. If you want technical data on opamps, just go get it. Opamps are marketed to electronics professionals so the amount of technical data the manufacturers provide is extreme. Just go to their website and look it up. For example the TI (who now owns Burr Brown) sheets include things including, but not limited to offset voltage, open loop gain vs frequency, phase vs frequency, CMMR vs frequency, GBW and slew rate vs temperature, settling time vs closed loop gain, and so on. There is a massive table full of minimum/typical/maximum values for various things, and pages of graphs showing how one characteristic affects another.

Now if you don't understand these specs, well then perhaps the specs really aren't what you are interested in. They provide every relevant spec to the opamp's performance, it is up to you to sift through those and determine what matters.

As I said, for audio this isn't the easiest thing in the world. It's questionable how much some of this matters, if it all. It also is variable depending on the setup.

So if you want data, go hit up the websites for Texas Instruments, Analog Devices, and National Semiconductor. There you will find the opamp datasheets you seem to be interested in. However, if you aren't an electrical engineer, don't be surprised if it is a little above your head. They don't sum up things in one or two "this is how good it is" numbers as that isn't possible.

Also opamp specs aren't necessairily as simple as the finished circuit specs. With a final circuit, you can measure the frequency response and graph it. You can't do that with an opamp as the response will depend on other factors like the gain. Any frequency response information has to be graphed against another factor. Only when you've decided on the final design can you actually estimate what it'll be, and only once it is built can you actually measure it to see what it is.
 
Like others have said, just go get a data sheet. The LM741 is a venerable (if ancient!) op amp. Its data sheet includes values most of the parameters that have been described to you.

You'll want data sheets for other parts in your project, as well, like the capacitors, resistors, and FETs. They'll help you understand how the circuit's components have error, imbalance, and noise. You can use a simulation program like pSpice, or some bench-top testing of a prototype, to show how those problems introduce measurable harmonic distortion and noise.

Over the years, Jerald Graeme has written a bunch of articles in EDN about measuring op amp performance characteristics, and how some of the data sheet numbers are a little less than intuitive. If you can't find back issues of EDN, you might try Graeme's book, Optimizing Op Amp Performance, ISBN 0070245223.

Jung's Op Amp Applications Handbook ISBN 0750678445 is also another good reference.
 
You must log in or register to reply here.
Back
Top