Yeah sure but how do you decide they are exactly the same? Do you overlay them on the scope and eyeball them? That seems rather inaccurate.
BTW What's the pulse level you use? Maybe you mentioned it, and if so I apologize for missing it. Are you driving the amps to a sizeable fraction of max output, or do you do this at small signal levels?
jan didden
That's interesting, there are dozens of high speed op-amps that will reproduce a 24KHz band limited pulse to almost an unmeasurable difference. Conclusion...
Isn't an IC opamp a discrete circuit all put on a single substrate, with the advantages of very small connections between the components, plus that all the components are at the same temperature, plus that components are as a rule well matched?
I have never been able to hear a difference that I could not relate to a measurement. However, I have measured numerous differences that were inaudible. So, I lean towards to position that if two IC's measure identically, they will sound the same.
Pano, are you shooting at Luigi's measurements & suggesting that he could just as easily have seen "different harmonic spectra" - no need for his type of temporal test at all?
I think you even asked him for a good test of attack in music. What, it doesn't show up in harmonic spectra? So are you saying that you can measure transient performance of an amp by "different harmonic spectra"?
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I hear differences between different IC's, yet their data sheet specifications are similar. You know; noise, slew rate, distortion, etc.
I have to be able to hear these differences, if I am going to make a successful audio product. I just won an award for my first IC based phono stage. I attribute it to listening to differences between IC's and other factors, and insisting on getting the design 'right' before putting it into the marketplace. Had I just let the measurements do the evaluation, I would have had a product failure. I am sure of this. I have made that mistake in the past, on occasion, and introduced products, even with my name attached, that failed both with the reviewers and the public, and were soon removed from the marketplace.
I have to be able to hear these differences, if I am going to make a successful audio product. I just won an award for my first IC based phono stage. I attribute it to listening to differences between IC's and other factors, and insisting on getting the design 'right' before putting it into the marketplace. Had I just let the measurements do the evaluation, I would have had a product failure. I am sure of this. I have made that mistake in the past, on occasion, and introduced products, even with my name attached, that failed both with the reviewers and the public, and were soon removed from the marketplace.
Jan,
I use to make the difference between the 2 channels with both an analog or a digital scope: this difference signal can be displayed with a higher sensitivity scale.
Levels: if a make a measurement of a power amp, I connect it to the loudspeakers that I will use for listening, so I use both the maximum comfortable and listenable level in my room (I will use the amp exclusively for my listening: I don't have to sell my devices, so I don't need to check at the maximum level) and progressive lower levels. In case of a pre-amp I use the maximum output level less 3 dB, -6 dB, -10 dB, -20 dB and 40 dB (BTW I didn't notice any differences with pre-amps at different levels).
NO. That is not what I said.
JC. I was asking because from many people we often read or hear the refrain "I hear differences between devices that measure the same (or similar)". Well, I do too - depending on what is measured. So I look for measurements that will reliably show me the differences that I hear. Nothing new in that.
But what I find odd is that lvigone says that he can match the sound of amps when he gets the pulses to match by measuring them - then you say that you hear differences between devices with the similar spec. Would that also apply to a similar pulse response? I.E., they measure the same, but still sound different.
Or is the pulse response a "good enough" measurement to characterize the sound of an amp?
That's interesting, there are dozens of high speed op-amps that will reproduce a 24KHz band limited pulse to almost an unmeasurable difference. Conclusion...
They will sound the same, for sure!! But, unfortunately, this can be done only for low level pre-amps, not for power amps.
Scott, please, could you build a real circuit with one of these op-amps that will have the same ligh blue pulse response I showed some posts ago? I'm very interested. Really!! I tried many times, but I had to surrender myself, it's my fault.
I could send you the .wav of the test pulse I use.
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