Here comes another nice HiFiBerry DAC installation. Jens from Germany doesn’t like switching mode power supplies for audio. Therefore he created a HiFiBerry setup with a huge linear power supply. Note that the power supply needs to provide at least 5V/1A for a stable operation of the Raspberry Pi. Depending on the input voltage this means heat. He uses a large heat sink and a small ventilator to get rid of the heat.
Our next project will use an external 12-18V power supply. It will be again a Raspberry Pi powered device. Having an additional 5V/1A power supply in addition to the main 18V power supply is not really a nice solution. Therefore we want to create this 5V power supply from the 18V supply. As the Raspberry draws 500-1000mA current, a simple linear regulator is not an option. It has to be a switching regulator. The LMR12010 from Texas Instruments (formerly National Semiconductors) seems to be an interesting chip. It does not need many external components, but still has an acceptable efficiency. There are chips with better efficiency, however these usually need external switches. Today we tested the chip using the Evaluation kit from TI. Interestingly, the Eval kit still has the National Semiconductor logo on it. The result looks promising. The efficiency is good enough, no additional heat sinks or cooling for the switching regulator is needed.
Here are some noise and distortion measurements of the HiFiBerry Mini DAC. Without the ethernet connected, noise is practically non-existing. But also distortions look good. D2 has the highest level and higher-order noise is decreasing with each order. This is really a nice chip.
At 1kHz we see 0.0037% THD+N (distortions alone only 0.003%). However, the measurement equipment itself (an EMU0404) itself has a THD+N level of 0.002% at this frequency (in- and output together). Therefore the real noise and distortion figure might even be a bit smaller.
We also did tests at other frequencies and they look similar:
Note, that these measurements are a bit flawed, because at higher frequencies there are less harmonics within the measurement frequency range than at lower frequencies. Therefore the distortions go down. Unfortunately I was not able the extract the D2 and D3 levels alone.
There are more good news. The voltage regulation on the board works great. Even with the worst power supply I could find (a Nokia charger), the figures did not change much. THD+N went up from 0.0037% to 0.004% at 1kHz. That means there is no urgent need to upgrade the power supply of your Raspberry Pi.
Update 1.12.2013: We did some THD+N measurements of our production version. They were even lover than the values show here.
Some customers asked how to connect the shunt regulator board to the rectification board and other circuits. Unfortunately, some connectors on the PCB have no labels on it. Check out this page or the following picture:
Are you waiting for the comfortINA? We’re still working on it. There are still some components that have to be tested. To do this in a real-world setting we started the DigiPot project. The name is a bit misleading. DigiPot can be used as a digital potentiometer, but also for many other use cases. You want to switch the input capacitance of your MM phono preamplifier remote? DigiPot is the solution! You want to create a variable gain amplifier? Use DigiPot in the feedback loop! With some tricks you can even use it to use it as a input switch in a line preamplifier.
Do you already own a platINA and want to upgrade it with some remote-controlled features? Guess what you can use to do this: DigiPot!
The ingredients: A shift register and low resistance analog switches. Initially I had planned to use a LDO voltage regulator from AD (you still see it in the design above), but I’m gonna test this device independently and stay with old-fashion LM317L/LM317L for this project. This makes it easy to solder the circuit even for beginners. PSSR is very high for the analog switches and power consumption is extremely low. Therefore there is no real need for regulators with better specs.
Does this sound interesting? Stay tuned for more information.
The LM317/LM337 is one of the most used circuits for low power audio applications. The performance is good. For most applications, these integrated circuits work really well. But sometimes you may want something better and more modern. There are two interesting ICs for audio applications:
LT1963/LT3015: These ICs from Linear technologies are relatively expensive in low volumes. It looks like an interesting device for do-it-yourself use, because it is even available in TO220 packages.
TPS49xx/TPS30xx: This pair can be a nice replacement for the 150mA LM317T/LM337T. They are not too expensive, therefore you may even use more multiple devices of you need more than the 150mA. One specific use case is using them as regulators after a switched mode power supply. However there is one disadvantage for DIY use: They come in a 0.65mm pitch MSOP package. But even these devices can be soldered without a reflow oven. Check out Daves EEVBlog for a tutorial how to do this.