DC-DC converter experiments…

A while ago I started looking at DC-DC converters for powering some of my audio circuits. I am not quite sure what triggered this to be honest, but mainly it was because I wanted to be able to make some more compact headphone amps and preamps than what the usual linear supplies can provide. At least around here there are very few external dual supplies available and so building a preamp or a headphone amp with an external PSU can be a bit tricky. Another option is a single-rail amplifier design, but they are often compromised because they need big input and output caps, so what do you do then?

Enter the DC-DC converter, a switching device that chops up a DC voltage and then transforms it up or down as needed. Most types include regulation of the output and galvanic isolation as well. The DC-DC converter gives tremendous flexibility because instead of needing a 2×12-15V PSU with a transformer, rectifier/caps and a wasteful linear regulator that must be heat sinked, you get a very small PCB that only needs a single DC input from a wall adapter or other DC source to work.  Some, like the Traco THN-series I have used offer a 4:1 input range and up to 20W output from a 1″x1″ brick, meaning you can get a fairly powerful regulated +/- 15V PSU in a tiny form factor and with just a single 9-36VDC input  – that’s pretty impressive I think!.

Another useful feature is that many of the converters have a remote on/off feature to put the converter into standby-mode. This means that if you are using a circuit that already has a micro-controller built in you can turn the converter (and the circuit it powers) on and off using the uC or even by a simple low-voltage mechanical switch.

The downsides of this power and versatility are mainly that DC-DC converters can be quite expensive and then that they (like most switching supplies) have rather a poor reputation for audio use. In some cases that is probably well-deserved, but I don’t like ruling out a whole technology just because of a few poor examples – in my world there are very few absolutes like that in audio. However, using switching technologies of any kind doesn’t really eliminate problems, it just replaces one set of well-known problems (heat, space, weight etc.) with another, perhaps less common set (EMI, high-frequency noise, inrush currents etc.). Depending on the application these “new” problems may be significantly harder or easier to deal with than the “traditional” ones.

So, after a bit more digging, reading datasheets and application notes etc. I have built some prototype boards for various DC-DC converters. Below are some pictures of my prototype boards, using industry standard footprints for 1”x1” and 1”x2” converters (more versions in the works). I’ve followed the application information from a few different Traco and Recom application notes but the boards will generally fit converters from a variety of manufacturers – one of those pictured are some old Tyco ones I bought a few years ago without really being sure what I wanted to use them for.

As for audio quality I can’t really say anything just yet, but as one of the pictures below show I have tried to power my universal preamp/headamp from a +/- 12V converter and I think it sounds pretty good. There are no audible artifacts such as hum or noise from the converter and the remote on/off feature works great as well. So while more testing is definitely needed, I am already starting to look at look at some of my current projects in a new way 😀 If anyone has used standard DC-DC converters to power audio circuits I’d love to see some examples 🙂


7 Responses to DC-DC converter experiments…

  1. awjlogan says:

    Any more impressions on these? I’ve had pretty mixed results designing from scratch. Generally I can get a single inverter or boost converter to work, but never off the one control chip. These look considerably easier to use, and much cheaper considering PCB and chip costs…

  2. theslowdiyer says:

    Apologies for the late reply 🙂

    I haven’t really done any further testing, but I just tried again with the small 15W Traco DC-DC converter feeding my BUF+OPA headamp (same setup as shown in the pictures in the post). With the inputs shorted I hear no noise or hum on the output, even with the volume control at maximum. This is with my lab supply as a power source and regardless of the input voltage (within the converter’s limit of course). The gain of the amp is only app. 3 but it still sounds very promising (hopeless pun intended 🙂 )

    I got the last of my PCB prototypes (for 2”x2” converters) last week so I will post the PCB files here shortly.

  3. Pingback: Project files: DC-DC converter boards | theslowdiyer

  4. awjlogan says:

    Nice – may give one a try…

  5. Pingback: Minipre in a box… | theslowdiyer

  6. Bill Mack says:

    I’m a fan of DC-DC converters and have studied them with the same audio intent as you have. Sony used a Torex DC-DC IC in the PCM-D1 for the split-supply. You’ve already successfully outlined the set of issues one needs to address i.e. RFI/EMI, inrush current, etc. Those issues can be worked out with careful layout. A few years back I looked at the newer X2Y SMD MLCCs specifically designed to shunt switching noise. Ever work with those?


    Then there is an old appnote from Linear (written by Jim Williams?) that focuses on the Linear LT3439 used for a low-noise 5v to +/-15VDC supply with post LDOs. Seems that the circuit in Design Note 316 might be ideal for the minipre and other micpre circuits.


    • theslowdiyer says:

      Thanks for those links Bill 🙂 Part of the attraction for me was honestly that it’s possible to get pre-made modules which immensely simplifies the sometimes complex problem of power supplies. However, there’s no doubt that it’s possible to squeeze much more audio performance out of the basic technology than the pre-made modules will provide if you roll your own, so I’ll definitely look at that last link a bit more closely 🙂

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