oh for sure it would, but not really workable for a kit unless you get the ok from everyone beforehand. regardless i've mounted these very same regs exactly how you are suggesting more than once, they wont be giving off much heat at all, the quiescent current is quite low and the amp will take most of the brunt as its always connected.
if levels are slightly out, we can do as we did with the D1 and use a small piece of pcb material to wedge under the 'front' of the reg between the reg and the bottom of the pcb if its not at the same level as the other parts and then pinch them down with the main mounting arrangements without the need for further arrangements. or mount it flush underneath and use a thick thermal washer. i think the main concern is the caps and transformer
regardless its going to be neat anyway, even without the custom case its neat as, can always do better with hindsight
if levels are slightly out, we can do as we did with the D1 and use a small piece of pcb material to wedge under the 'front' of the reg between the reg and the bottom of the pcb if its not at the same level as the other parts and then pinch them down with the main mounting arrangements without the need for further arrangements. or mount it flush underneath and use a thick thermal washer. i think the main concern is the caps and transformer
regardless its going to be neat anyway, even without the custom case its neat as, can always do better with hindsight
Hi Guys,
Several people have asked about the output impedance on the LPUHP amps and the other headphone amps so I took some time to measure them.
I used the dV/dI method to measure this which is the most accurate method I know of. You basically set the output voltage to a known level with no load, then connect a load and measure the difference in voltage at the output. This is then divided by the difference in current between no load and load, and that gives you the output impedance of the amplifier.
This method is most accurate when more voltage and more current is used, but it's also important not to clip or current limit the amplifier. In this case, I used an output voltage of 8 VRMS into an 8 ohm load. It's also important to measure the actual current and not just calculate it based on the voltage and resistance. Here are the results:
V (open load) = 8.004 VRMS (measured with AP and a calibrated Agilent meter)
V (8 ohm load) = 8.001 VRMS (measured with AP and a calibrated Agilent meter)
I (open load) = 0A
I (8 ohm load) = 0.9985A RMS (measured with a calibrated Agilent meter)
So we have 3mV of voltage delta and 0.9985A of current delta. This gives:
output impedance = dV/dI = 0.003V/0.9985A = 3.00 milliohms.
That gives a corresponding damping factor of 2667 with an 8 ohm load.
All measurements were done at the actual output terminals of the amplifier. To get the damping factor with an actual loudspeaker attached, you would need to account for the DCR of the cables and connectors in series with the output impedance.
Now... if you use a captive power cable as Ian suggests, I would expect the output impedance to drop down to at least -1 ohms
Cheers,
Owen
Several people have asked about the output impedance on the LPUHP amps and the other headphone amps so I took some time to measure them.
I used the dV/dI method to measure this which is the most accurate method I know of. You basically set the output voltage to a known level with no load, then connect a load and measure the difference in voltage at the output. This is then divided by the difference in current between no load and load, and that gives you the output impedance of the amplifier.
This method is most accurate when more voltage and more current is used, but it's also important not to clip or current limit the amplifier. In this case, I used an output voltage of 8 VRMS into an 8 ohm load. It's also important to measure the actual current and not just calculate it based on the voltage and resistance. Here are the results:
V (open load) = 8.004 VRMS (measured with AP and a calibrated Agilent meter)
V (8 ohm load) = 8.001 VRMS (measured with AP and a calibrated Agilent meter)
I (open load) = 0A
I (8 ohm load) = 0.9985A RMS (measured with a calibrated Agilent meter)
So we have 3mV of voltage delta and 0.9985A of current delta. This gives:
output impedance = dV/dI = 0.003V/0.9985A = 3.00 milliohms.
That gives a corresponding damping factor of 2667 with an 8 ohm load.
All measurements were done at the actual output terminals of the amplifier. To get the damping factor with an actual loudspeaker attached, you would need to account for the DCR of the cables and connectors in series with the output impedance.
Now... if you use a captive power cable as Ian suggests, I would expect the output impedance to drop down to at least -1 ohms
Cheers,
Owen
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output impedance = dV/dI = 0.003V/0.9985A = 3.00 milliohms.
That gives a corresponding damping factor of 2667 with an 8 ohm load.
All measurements were done at the actual output terminals of the amplifier. To get the damping factor with an actual loudspeaker attached, you would need to account for the DCR of the cables and connectors in series with the output impedance.
Now... if you use a captive power cable as Ian suggests, I would expect the output impedance to drop down to at least -1 ohms
Cheers,
Owen
Thanks for the measurements! That is very low for a real world amplifier
Hi Ian,
I very much doubt it. To put it into perspective, a standard headphone cable using 24AWG wire and being 3 ft long will have a resistance of over 150 milliohms, so reducing the amplifier from 12 to 3 milliohms doesn't even present a significant reduction is overall damping factor. That's also ignoring the connector resistance and the wire from the connector to the amp itself.
Using heavier gauge wire is also a bad idea since it will likely result in something that is not very comfortable and will probably have higher microphonics caused by the large stiff wires connected to the small drive in the headphone itself.
Overall I don't really believe that damping factor is that big of a thing to focus on. Certainly there will be a difference between an amplifier that has a damping factor of 1 or less and one that has a damping factor of over 100, but going from 100 to 1000 or to 10,000 doesn't really buy you much. When you factor in all the other resistances in the chain, and arguably the voice coil itself, then it really isn't all that relevant. Certainly not with headphones which are generally much higher impedance anyhow.
I also did get around to measuring the BAL-BAL version and it's output impedance is 6.2 milliohms, which is more than low enough for even the most absurd headphones.
Cheers,
Owen
I very much doubt it. To put it into perspective, a standard headphone cable using 24AWG wire and being 3 ft long will have a resistance of over 150 milliohms, so reducing the amplifier from 12 to 3 milliohms doesn't even present a significant reduction is overall damping factor. That's also ignoring the connector resistance and the wire from the connector to the amp itself.
Using heavier gauge wire is also a bad idea since it will likely result in something that is not very comfortable and will probably have higher microphonics caused by the large stiff wires connected to the small drive in the headphone itself.
Overall I don't really believe that damping factor is that big of a thing to focus on. Certainly there will be a difference between an amplifier that has a damping factor of 1 or less and one that has a damping factor of over 100, but going from 100 to 1000 or to 10,000 doesn't really buy you much. When you factor in all the other resistances in the chain, and arguably the voice coil itself, then it really isn't all that relevant. Certainly not with headphones which are generally much higher impedance anyhow.
I also did get around to measuring the BAL-BAL version and it's output impedance is 6.2 milliohms, which is more than low enough for even the most absurd headphones.
Cheers,
Owen
I like the TDK @ 0.80 each or 6.70 for 10 2 people could throw in for 100 and get them for 0.42, but the Taiyo Yuden is cheaper.
the TDK i mention above actually appears to be identical to the one in the BOM right down to the price
the TDK i mention above actually appears to be identical to the one in the BOM right down to the price
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hehe
me neither, i'm a chef/graphic designer, well thats my field of qualification anyway, i work with electronics more and more these days.
but yeah you can go with the 10% if you are willing to blow the extra cash which wont be much once you get the bulk discount most likely, but i'd say owen was just being his usual self and going OTT with the spec to make sure all was above board. when its only 0.08 the difference why not i guess. but for bulk decoupling i dont see any harm in going with the 20% if need be. resistors i wouldnt change at all.
now of course now i've said that, Owen is going to pop in and mention some effect i havent thought of, or dont know the existence of
me neither, i'm a chef/graphic designer, well thats my field of qualification anyway, i work with electronics more and more these days.
but yeah you can go with the 10% if you are willing to blow the extra cash which wont be much once you get the bulk discount most likely, but i'd say owen was just being his usual self and going OTT with the spec to make sure all was above board. when its only 0.08 the difference why not i guess. but for bulk decoupling i dont see any harm in going with the 20% if need be. resistors i wouldnt change at all.
now of course now i've said that, Owen is going to pop in and mention some effect i havent thought of, or dont know the existence of
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Attached is the updated BOM with a little resistor matrix to help people decide what values of resistors eveyone needs for thier desired setup. Here are the options:
1. SE input with 15dB of gain (clips with 2VRMS input)
2. SE input with 21dB of gain (clips with 1VRMS input)
3. BAL input with 15dB of gain (clips with 2VRMS input)
4. BAL input with 21dB of gain (clips with 1VRMS input)
For the SE input type, you only need to buy one LME49990 per channel, so please account for this if you're building that version.
You are, of course, welcome to change the suggested values to whatever you want to get different gains, but keep in mind that higher gains will have higher levels of noise, and higher resistance values will also have higher noise.
The measurements posted on the first page were done at 18dB of gain, and so represent a middle ground between the two suggested gain levels. You can expect the 21dB version to have slightly higher noise, and the 15dB version to have slightly lower noise. You should always use the lowest gain possible for your given setup, and in the case of mating to a DAC, you should plan to have the LPUHP amplifier just below clipping with a 0dBFS input to the DAC in order to get the lowest noise and highest possible dynamic range.
If you're using these on the output of a Behringer DCX2496 for example, you would only want a gain of about 2dB since the Behringer outputs over 9VRMS at 0dBFS input, and needs almost no gain whatsoever from the power amp. Setting the gain of the amp in this scenario to 21dB does nothing but increase your noise floor by 19dB. It's important to carefully consider your system gain if you want the best possible performance (this applies to any amp, but is of particular importance if you want to reap the benefits of the low noise floor of this amp)
Cheers,
Owen
1. SE input with 15dB of gain (clips with 2VRMS input)
2. SE input with 21dB of gain (clips with 1VRMS input)
3. BAL input with 15dB of gain (clips with 2VRMS input)
4. BAL input with 21dB of gain (clips with 1VRMS input)
For the SE input type, you only need to buy one LME49990 per channel, so please account for this if you're building that version.
You are, of course, welcome to change the suggested values to whatever you want to get different gains, but keep in mind that higher gains will have higher levels of noise, and higher resistance values will also have higher noise.
The measurements posted on the first page were done at 18dB of gain, and so represent a middle ground between the two suggested gain levels. You can expect the 21dB version to have slightly higher noise, and the 15dB version to have slightly lower noise. You should always use the lowest gain possible for your given setup, and in the case of mating to a DAC, you should plan to have the LPUHP amplifier just below clipping with a 0dBFS input to the DAC in order to get the lowest noise and highest possible dynamic range.
If you're using these on the output of a Behringer DCX2496 for example, you would only want a gain of about 2dB since the Behringer outputs over 9VRMS at 0dBFS input, and needs almost no gain whatsoever from the power amp. Setting the gain of the amp in this scenario to 21dB does nothing but increase your noise floor by 19dB. It's important to carefully consider your system gain if you want the best possible performance (this applies to any amp, but is of particular importance if you want to reap the benefits of the low noise floor of this amp)
Cheers,
Owen
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