Temperature concerns are not with out reason, but the heat generated by the DAC1 is not a problem: it is well within the thermal budget for this product.
Heat can be trouble for electronic equipment. It can be particularly troublesome with electrolytic capacitors, by drying out the electrolyte, reducing the devices capacitance value and therefore its effectiveness. Capacitor design changes over the last couple of decades have provided for a potential increase in the operating temperatures – moving from 85 degrees C to 105 degrees C for the same operating life. Therefore, given the same operating temperature, the life of the electrolytic capacitor is significantly extended. Most other electronic parts are typically not as sensitive to high temperatures as are aluminum electrolytics.
When designing for ultra low noise audio, however, we face an additional issue. Ultra low noise in our products, by definition, means designing for increased power dissipation. Understand that noise is present in all circuits and resistances whether internal to an amplifier or external to it. For a given low noise amplifier, (the lower its noise the higher the current drawn), the circuit resistances around the amplifier determine the circuit’s noise. The lower the resistance, the lower the noise.
So the challenge is this. If we want to have a state-of-the-art noise floor from our boxes, we must use low values of resistance in our circuit design, and here’s the catch, when we use low values of resistance we also, by Ohm’s law, increase the power dissipation within our circuits. And now we see the limitation: what is the maximum power that we can get out of a box and still operate at reasonable internal temperature levels compatible with the parts limitations? Also, what will a customer consider unacceptable in terms of box temperatures?
Specifically, with the DAC1, having an external ambient room temperature of 74 degrees F, 23.3 degrees C, the following DAC1 temperatures were measured:
1. An output op-amp sits at 129.6 degrees F, 54.2 degrees C, well below the manufacturers maximum recommended operating temperature of 85 degrees C, 168 degrees F.
2. The high current headphone amp buffer is at 126.0 degrees F, 52.2 degrees C (will increase with load)
3. The power transformer is at a cool 103.4 degrees F, 39.8 degrees C
4. The internal ambient temperature is 99.2 degrees F, 37.3 degrees C
5. The outside top of the chassis temperature is 90.8 degrees F, 32.7 degrees C
Of course, if the chassis is located in a place where air flow is restricted or if it is setting on another piece of equipment that is a relative hot-plate, and the room ambient temperature is higher that 74 degrees, these temperatures will go higher. Personally, I have found that I can just keep my hand or finger on a surface that has a temperature of 130 degrees F, about 55 degrees C. If you cannot keep your hand on the DAC1’s chassis, it is too hot. That does not necessarily mean that there is a problem with the unit. It may simply mean that you need to relocate it for better air flow. Orienting equipment for the lowest possible heat buildup is a good thing.
So the tradeoffs a designer faces are these: noise, power dissipated, number of features (circuits) desired, maximum box power dissipation, and acceptable box temperatures.
Sometimes it comes out as: Ultra low noise = high current = power dissipated = higher than (customer) expected box temperatures = customer concern. Did someone say the word fan? Huh, I guess not.
It is true, those little electrons are working up a bit of a sweat in there, making that awesome audio for us. But thankfully, it’s comfortably within their capability.
