| Electronics > Beginners |
| AB-class amplifier schematic analysis & optimization |
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| Alex Nikitin:
--- Quote from: Zero999 on May 24, 2019, 08:45:32 am ---Any measurements should be performed with the speaker or headphones connected to the amplifier, via a suitable length of cable. I'd say this is even more important when you're using an IC out of specification, as would be the case for the LM7171 driving headphones, rather than the purely resistive load it was designed for. Yes, different amplifier designs exist for different purposes, which is why using a video amplifier for audio is daft, even if some people like the colourful ringing and distortion it might add to the sound. --- Quote from: David Hess on May 24, 2019, 02:54:24 am ---Distortion and noise will be higher on the LM7171 because of lower open loop gain and lower common mode and power supply rejection. Perhaps more importantly, the output power is limited by limited output voltage range and limited power dissipation from a single 8 pin package. --- End quote --- Yes, the LM7171 isn't suitable for use as a headphone amplifier. There are much better alternatives. Just because it can be done, it doesn't mean it's the best way. :horse: --- End quote --- :palm: I personally find this amusing. I have shared some information which I consider valuable, as it is the result of many hours of work at the time I did that design. I am not trying to sell anything. I have a practical experience using that particular chip for that particular application in a production headphone amplifier which was produced for many years and in many thousands of units. And I get theoretical arguments from people who most likely never tried to work with that particular IC and not even read the data sheet carefully (as it clearly states the LM7171 can be used for driving ADSL lines and transformers for instance). ADSL drivers in general are not a bad choice for headphone amplification (low distortion, high output current and ability to work on difficult loads) and there are designs which use them*. Cheers Alex P.S. Worth noting that TI actually sells the THS6012 Dual Differential Line Driver as a "High Fidelity Headphone Amplifier" chip under a different name (TPA6120A2) ;) . |
| Alex Nikitin:
--- Quote from: magic on May 24, 2019, 08:53:03 am --- --- Quote from: Alex Nikitin on May 24, 2019, 07:51:09 am ---driving a speaker coil is not equivalent of driving a resistive load, that is one of reasons why amplifiers with similar traditional measurements could sound different in real life --- End quote --- True that, but after all those years of hearing about it I would like to finally see a demonstration of two amplifiers which both show no perceptible noise, 0.1dB gain flatness from 10Hz to 50kHz and some low THD figure, all measured into the actual demo speaker, and yet sound different enough that somebody (bonus: everybody) can tell them apart. I'm not aware of any instances of such demonstration actually being done. I suppose it would be all over the Internet if it happened, given the amount of controversy. --- End quote --- It is getting completely off-topic, however I will only ask a simple question: can you provide a link to an example of a statistically valid controlled DB listening test with a positive result? Cheers Alex |
| Zero999:
--- Quote from: Alex Nikitin on May 24, 2019, 09:07:58 am --- :palm: I personally find this amusing. I have shared some information which I consider valuable, as it is the result of many hours of work at the time I did that design. I am not trying to sell anything. I have a practical experience using that particular chip for that particular application in a production headphone amplifier which was produced for many years and in many thousands of units. And I get theoretical arguments from people who most likely never tried to work with that particular IC and not even read the data sheet carefully (as it clearly states the LM7171 can be used for driving ADSL lines and transformers for instance). ADSL drivers in general are not a bad choice for headphone amplification (low distortion, high output current and ability to work on difficult loads) and there are designs which use them*. Cheers Alex P.S. Worth noting that TI actually sells the THS6012 Dual Differential Line Driver as a "High Fidelity Headphone Amplifier" chip under a different name (TPA6120A2) ;) . --- End quote --- I don't doubt that it's possible to build a headphone amplifier with the LM7171, just that it'll make life harder, with no benefits, over ICs specifically designed for it. What "valuable information" have you posted? You've not posted any details of your design: schematic or layout. All you've done is said "I've used the LM7171, an IC which is not designed to be used as a headphone amp, as a headphone amp" and are wondering why people are questioning it. You haven't provided any solid reasons to use it, over the alternatives, in the face of valid arguments not to use it, as a headphone amp. This is not helpful, especially in the beginners section as someone with far less experience might try the LM7171 and wonder why it doesn't work! --- Quote from: Alex Nikitin on May 24, 2019, 09:12:23 am --- --- Quote from: magic on May 24, 2019, 08:53:03 am --- --- Quote from: Alex Nikitin on May 24, 2019, 07:51:09 am ---driving a speaker coil is not equivalent of driving a resistive load, that is one of reasons why amplifiers with similar traditional measurements could sound different in real life --- End quote --- True that, but after all those years of hearing about it I would like to finally see a demonstration of two amplifiers which both show no perceptible noise, 0.1dB gain flatness from 10Hz to 50kHz and some low THD figure, all measured into the actual demo speaker, and yet sound different enough that somebody (bonus: everybody) can tell them apart. I'm not aware of any instances of such demonstration actually being done. I suppose it would be all over the Internet if it happened, given the amount of controversy. --- End quote --- It is getting completely off-topic, however I will only ask a simple question: can you provide a link to an example of a statistically valid controlled DB listening test with a positive result? Cheers Alex --- End quote --- I'm not sure what you're asking? Double blind tests are a the gold standard for determining whether anything is detectable or effective. If your LM7171 amplifier is audibly transparent i.e. doesn't distort the sound, the difference between it and any other amplifier which is also audibly transparent, should be undetectable when subject to a double blind test. |
| Alex Nikitin:
--- Quote from: Zero999 on May 24, 2019, 10:15:05 am ---I'm not sure what you're asking? Double blind tests are a the gold standard for determining whether anything is detectable or effective. If your LM7171 amplifier is audibly transparent i.e. doesn't distort the sound, the difference between it and any other amplifier which is also audibly transparent, should be undetectable when subject to a double blind test. --- End quote --- So, you can not provide a link to a statistically valid DBT with a positive result (meaning that there is a difference in the sound confirmed in the test) ? So, you have a "gold standard" with negative results only, don't you think it is funny? Cheers Alex |
| Zero999:
--- Quote from: Alex Nikitin on May 24, 2019, 10:23:12 am --- --- Quote from: Zero999 on May 24, 2019, 10:15:05 am ---I'm not sure what you're asking? Double blind tests are a the gold standard for determining whether anything is detectable or effective. If your LM7171 amplifier is audibly transparent i.e. doesn't distort the sound, the difference between it and any other amplifier which is also audibly transparent, should be undetectable when subject to a double blind test. --- End quote --- So, you can not provide a link to a statistically valid DBT with a positive result (meaning that there is a difference in the sound confirmed in the test) ? So, you have a "gold standard" with negative results only, don't you think it is funny? Cheers Alex --- End quote --- I still don't know what you're going on about. Please provide a more detailed explanation of what you're asking. |
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