This is a detailed look at temperature sensitivity of the ESS ES9038Pro DAC chip as used in SMSL USB DAC. In a separate thread it was shown that another unit had its performance improve with temperature/on time whereas my review sample performed the reversed. I purchased another M500 from Amazon Prime which means it was already in stock in US. It arrived today and I thought I create this separate thread on the performance of the two relative to temperature.
Taking out the PCB is a bit of a challenge but I managed to do so on both. Pulling the PCB out all the way disconnects ribbon cables form front panel which I have not figured out how to open yet! So I left the review sample (bottom) half out with cables still attached and the new retail version (top) fully removed:
Both PCBs look the same to me and both have the same version 1.2 indicated on them. The DAC has two boards but the top one is of interest to us since it has the ESS DAC chip and output stage.
Here is a higher resolution shot of the retail version (click for larger image):
Review Sample Thermal Analysis
Here is the performance of the original unit I received from SMSL as it warmed up (volume set to 34 which equals 4.2 volts output from XLR jacks):
Top set of lines are SINAD and bottom are THD+N (identical values, expressed in dB or percentage respectively). Sorry the SINAD scale got chopped off. A bug in AP software. So let's focus on the THD+N (red and blue lines). We can just convert the dB value to positive and get SINAD. We start with 117 dB SINAD which is what I reported in the original review. As the unit warms up we lose 3 dB to finish around SINAD of 113 dB.
Half-way through the test I touched the ESS DAC chip to see how warm it was. It was not hot at all but my touch was enough to cool it momentarily causing performance to improve. This pointed to very high sensitivity to temperature variation.
Next, I sprayed some component cooler on the ESS DAC. The results were dramatic:
Performance immediately shot back up to SINAD of 117 dB. So no question, my review sample likes to be cold to produce its best performance.
SMSL M500 Retail Sample Thermal Performance
I repeated the same warm up test on the retail version of M500. This time as we explored in the other thread, performance actually improved with warm up (first part of the graph to the left):
Next I pulled out the big guns literally in the form of my wife's hair dryer.
As soon as I warmed up the PCB performance suffered good bit (more than 3 dB). I stopped the hair dryer and as the unit cooled off performance started to improve.
What this means is terrible: there is a narrow temperature range where the ESS DAC in this implementation performs its best. We saw an attempt by Sabaj to deal with this in the D5 whereby they put a heatsink on the ESS DAC chip. This reduced power up performance but allowed temperature to stay low enough within the good performance range of the ESS DAC.
Sensitivity of other components
I cooled off the output OPamps and they made no difference whatsoever. So the sensitivity is definitely in the ESS DAC chip. Note however that this may be circuit dependent.
Conclusions
As with "ESS IMD Hump," ESS seems to be doing a terrible job of providing a stable reference design for designers to use. They are left to deal with these issues on their own. Having a chip lose 3 to 4 dB of performance with 10 to 20 degree temperature change is just unacceptable.
It remains a mystery why the sample I have works in reverse. It may be that it is a DAC chip that is working above its spec when cold and only degrades when it gets colder.
With respect to retail samples however, we collectively have tested three of them with similar performance. While I don't think the above changes are audible your DAC will perform better after a few minutes of warm up. Keep it away from other sources of heat however as that seems to have the reverse effect. If you live in Florida, I suggest you move somewhere colder!
I will have either my retail sample or the review sample for sale soon. Start a conversation with me if you are interested in either one. I don't like to return things to Amazon for such use.
--------
As always, questions, comments, corrections, etc. are welcome.
Taking out the PCB is a bit of a challenge but I managed to do so on both. Pulling the PCB out all the way disconnects ribbon cables form front panel which I have not figured out how to open yet! So I left the review sample (bottom) half out with cables still attached and the new retail version (top) fully removed:
Both PCBs look the same to me and both have the same version 1.2 indicated on them. The DAC has two boards but the top one is of interest to us since it has the ESS DAC chip and output stage.
Here is a higher resolution shot of the retail version (click for larger image):
Review Sample Thermal Analysis
Here is the performance of the original unit I received from SMSL as it warmed up (volume set to 34 which equals 4.2 volts output from XLR jacks):
Top set of lines are SINAD and bottom are THD+N (identical values, expressed in dB or percentage respectively). Sorry the SINAD scale got chopped off. A bug in AP software. So let's focus on the THD+N (red and blue lines). We can just convert the dB value to positive and get SINAD. We start with 117 dB SINAD which is what I reported in the original review. As the unit warms up we lose 3 dB to finish around SINAD of 113 dB.
Half-way through the test I touched the ESS DAC chip to see how warm it was. It was not hot at all but my touch was enough to cool it momentarily causing performance to improve. This pointed to very high sensitivity to temperature variation.
Next, I sprayed some component cooler on the ESS DAC. The results were dramatic:
Performance immediately shot back up to SINAD of 117 dB. So no question, my review sample likes to be cold to produce its best performance.
SMSL M500 Retail Sample Thermal Performance
I repeated the same warm up test on the retail version of M500. This time as we explored in the other thread, performance actually improved with warm up (first part of the graph to the left):
Next I pulled out the big guns literally in the form of my wife's hair dryer.
As soon as I warmed up the PCB performance suffered good bit (more than 3 dB). I stopped the hair dryer and as the unit cooled off performance started to improve.What this means is terrible: there is a narrow temperature range where the ESS DAC in this implementation performs its best. We saw an attempt by Sabaj to deal with this in the D5 whereby they put a heatsink on the ESS DAC chip. This reduced power up performance but allowed temperature to stay low enough within the good performance range of the ESS DAC.
Sensitivity of other components
I cooled off the output OPamps and they made no difference whatsoever. So the sensitivity is definitely in the ESS DAC chip. Note however that this may be circuit dependent.
Conclusions
As with "ESS IMD Hump," ESS seems to be doing a terrible job of providing a stable reference design for designers to use. They are left to deal with these issues on their own. Having a chip lose 3 to 4 dB of performance with 10 to 20 degree temperature change is just unacceptable.
It remains a mystery why the sample I have works in reverse. It may be that it is a DAC chip that is working above its spec when cold and only degrades when it gets colder.
With respect to retail samples however, we collectively have tested three of them with similar performance. While I don't think the above changes are audible your DAC will perform better after a few minutes of warm up. Keep it away from other sources of heat however as that seems to have the reverse effect. If you live in Florida, I suggest you move somewhere colder!
I will have either my retail sample or the review sample for sale soon. Start a conversation with me if you are interested in either one. I don't like to return things to Amazon for such use.
--------
As always, questions, comments, corrections, etc. are welcome.
