Linear PSUs are better…

…aren’t they? 😀

No, I don’t really want to start up that discussion here because in my opinion it’s much more complex subject than most audiophiles believe. However, one thing that is obvious is that as more and more small audio components run on single DC rails from an external PSU (streamers, DACs, headphone amps etc.), a fairly large market for aftermarket “upgrade” PSUs has opened up. Some manufacturers (e.g. Auralic) even offer separate PSUs as upgrades themselves. Well, a linear PSU is normally a relatively simple thing so why not DIY it?

Since I now have a DAC, a preamp, a streamer and quite a few other things that run on single-rail DC this seems a worthwhile project and it’s actually been on the drawing board for a while. I did have a bit of trouble getting started on the circuit and layout though, and I didn’t manage to really break the deadlock until remembered a design called STEPS by headwize/head-fi user Tangent from (many) years ago. The design isn’t up anymore, but thankfully I managed to locate it on the wayback-machine.

It’s basically a standard LM317-based PSU, but with a few tweaks added to tease as much performance as is possible out of the LM317 regulator (or one of its many derivatives). My version isn’t a straightforward copy of the STEPS, but I owe a big thanks to the the STEPS all the same. Compared to a “normal” LM317-based circuit this one includes:

  • A simple mains filter on the primary side of the transformer.
  • A snubber circuit on the secondary side of the transformer.
  • Space for high-speed/soft recovery diodes and snubber caps.
  • Space for 2+2 18mm filter capacitors in C-R-C (pi-filter) configuration before the regulator.

Everything else looks like the “high-performance” circuit variation from the data sheet of any LM317-type regulator. The onboard transformer is a 25VA Talema PCB-mounted toroid type meaning the design should be good for most applications requiring less than app. 20W power. The 15VA type transformer will fit as well and allow for mounting in a 1U enclosure, but the constraints on heat sinking and capacitor height might then be an issue.

The pictures show the completed 12V prototype for my Arcam IRdac as well as a partially completed 16V board for an Auralic Aries Mini (a recent purchase) – I’m waiting for a transformer in the mail before I can finish that and test it 🙂

Project files: VFET PSU

What is it?
In response to a reader request, the project files for my V-FET PSU board shown here. Of course, this will also work for any other class A design you might think of, as it is a fairly standard CC-R-C configuration with onboard rectifiers and space for three 35mm snap-in capacitors per rail. On typical class A voltages that means you’ll be able to use capacitors in the 22-33mF range and the the onboard rectifiers are 15-25A plastic SIP types, which should be just fine for most applications.

Input and output connections are via FAST-ON tabs and there are two sets of output connections. Since we’re paying for the copper on the boards anyway, I’ve tried to keep as much of it as possible  with a top-side ground plane and the supply rails on the bottom. 🙂

How big are the boards?
The board measures 3.1” x 6.675” (app. 78 x 170 mm).

What is the status of the boards?
Since the prototypes worked fine I haven’t made any changes and the board is therefore version 1.0.

Does it use any special/expensive/hard-to-find parts?
Nothing worth worrying about really. The only possible exception is only really the rectifier which is in a small GBU-package. However, Mouser has them up to 25A (p/n 750-GBU2510-G) and they are available from many other sources in 10-15A variants as well.

Anything else I need to know?

  • If you want to use off-board bridges, bridge the AC and the DC-connections with as thick a wire as you can get through the holes. That should allow you to use offboard metal-cased rectifiers up to 50A. Since the average current draw of most class A amps is quite low and the surge ratings aren’t that different between package types I don’t see the need to use anything else than the plastic ones, but by all means complicate matters with offboard bridges if you must 😀
  • The four series resistors can be 3-5W types in parallel which should be plenty, even if you want to burn off a bit of voltage in them.
  • The (optional) 3W bleeder resistor discharges the two first capacitors while the LEDs will discharge the last ones. The series resistor for the LED can be a 1/2W or 1W type.
  • Last, but not least: Electrolytic capacitors in this sort of size aren’t to be trifled with, so make sure you mount them correctly and test the board properly before mounting it in your amplifier chassis.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

vfetpsupcb-2

Project files: Amplifier PSUs

Digging in the back catalogue a bit again here.…and found some of my power supply boards that I haven’t published yet 🙂

What is it?
Power supplies for amplifiers, d’oh! 😀 Two basic variants, namely a “class AB” type and a “class A” type. The “class A” type is intended to be used in a CxC configuration with resistors onboard for CRC and pads for a choke to make it CLC. The “class AB” one is a standard unregulated design for class AB or D amplifiers that allows using both small 16/18mm radial capacitors and large snap-in types (up to 35mm). Here there are two versions, one for 2 off 35mm caps (or 8 smaller caps) per rail and one for 3/12.

The picture below is of the large class AB board. It’s actually the board from the previous post that has had some caps mounted in the mean time 🙂

How big are the boards?
The AB board measures 3.55” x 3.9” (app. 90 x 99 mm.) for the standard version and 3.05” x 6.1” (app. 77 x 155 mm.) for the XL version. The CRC board measures 3.15” x 3.95” (app. 80 x 100 mm).

What is the status of the boards?
Both of the “class AB” boards are in v1.0. The “class A” board is in v1.1 as I made a couple of tweaks (including the pads for off board R/L) to my original version. The original v1.0 is the board that I use in my “Green Monstre” amps.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. You can go overboard with expensive capacitors if you want, but even if you have the money to put NOS Black Gates in your power supplies I’d still suggest you spend them elsewhere in the circuit 😀

Anything else I need to know?

  • Unless you are building very small amplifiers I’d recommend that the CRC and the small AB boards are used in dual-mono configurations with one PSU per amplifier channel. The large AB board can be shared across channels for a medium power class AB or D amplifier (meaning anything with a rail voltage up to around 55V and 63V caps).
  • The boards all include LEDs that indicate power and bleed the capacitors when no load is connected (albeit very slowly). The corresponding resistor footprints should be large enough to allow fairly high LED currents but remember to calculate the power dissipation.
  • The CRC board has space for two resistors in parallel per rail, either axial types (up to around 3-5W will fit) or MPC7x radial types up to 5W.
  • The rectifiers are GBU-types which are available from Mouser up to a 25A rating.
  • Input connections for the Class AB “XL” board are via FAST-ON tabs. All other input/output connections are via 5mm spacing screw terminals.
  • The capacitors on the class A-board can be up to 30mm in diameter. Since class A amps tend to get hot, I’d recommend 105 degree types here. As mentioned above, the class AB boards use either snap-in caps up to 35mm diameter or 16/18mm  radial caps with 7.5mm pin spacing.
  • Needless to say, all capacitors should be rated appropriately for your amplifier’s rail voltage.

     

Downloads:
Download design files here

Related information:
These are very simple circuits, but there’s some god background on PSU design for amplifiers over on Rod Elliot’s pages (under “power”)

Note: Always read the “intro post” for additional important information about my designs.

Project files: ICEpower Linear PSU

What is it?
The project files for the linear ICEpower PSU board I showed here. The first version of this board concept was made around 10 years ago, but as I didn’t have any boards left over I updated the design and cleaned it up a bit in the process.
The basis of this is once again the GP-PSUs shown here and the same file that I also used in a triple-configuration here. I have simply added a single high-power rail with a rectifier, two main caps and the usual decoupling + discharge LED – absolutely nothing fancy 🙂

How big are the boards?
This is the “XL”-version for 35mm main caps and the board measures 4.4” x 3.45” (app. 112 x 88 mm.).

What is the status of the boards?
The design is called v2.0 as it is based on a previous idea. It’s been prototyped and I see no mechanical or electrical issues.

Does it use any special/expensive/hard-to-find parts?
Not really, unless you choose to go overboard with expensive boutique parts, such as premium capacitors and fast rectifiers for the low-voltage supply (which I kinda did…).

Anything else I need to know?

  • The board should work with the ICEpower 200AC/300AC and the 250A modules which require around a 50VDC Vp voltage. For the 500A and 1000A modules you might need to check and modify the board files to get enough high-voltage clearance for the higher supply voltages used (nominal 80VDC/120VDC respectively)
  • The high-power supply uses a pair of snap-in capacitors up to 35mm in diameter and a GBU-type rectifier (available up to 25A). The low-voltage supply uses 22mm snap-in or 18/16mm standard radial caps with 1N540x or similar rectifiers.
  • Due to the rectifier setup on the low voltage supply, it is possible to use it with both single (voltage-doubled) and dual AC connections. In that case you should connect the transformer to one side of the AC-connector and you need only fit the required pair of diodes (either DA/DB or DX/DY), although of course there is no harm in mounting both pairs.
  • If you have space, I would recommend that you run “dual-mono” with separate power supplies for each channel, mainly to ensure that there is a good amount of capacitance on the high-power rail. If, like me, you still want one box and avoid a true mono-block design, then the high-power rail can use separate windings on the same transformer and the low-voltage transformers can be separate or shared between the channels. The sharing can of course be done either as parallel-connected dual rectifiers or as separate voltage-doubled circuits with each board using one transformer winding (honestly not sure what would be better here 🙂 ).

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Read the ICEpower module datasheets carefully as well (and, if you can get your hands on them, the Designer’s Manuals as well).

Note: For once, I do actually have some spare boards left as I only needed the pair and I had to order 10 pcs. As you can see, they are green, HASL-plated and made with 2 oz. copper. If you are interested in boards, drop me a line.

A Smaller Gainclone…

I have already done a couple of “gainclone”-type chipamp designs with the LM3875 amplifier IC, mainly here and here. Now there is a new one, this time based on the smaller LM1875 IC.

The smaller IC obviously means less voltage and less power compared to the LM3875 and LM3886 but unless you have a big room and/or very inefficient speakers (or you are having a party… 😀 ), the 20W or so that you can squeeze out of the LM1875 should still go quite far.

The circuit I’ve used is exactly the same as the standard one in the datasheet and also the same as the one used by chipamp.com in their kit. Some people might recognise the schematic as more or less a textbook example of how to make a non-inverting amplifier from an op-amp. That isn’t surprising though, because that is what the LM1875 really is – a power op-amp.

I have made the amplifier PCB as small as I could to make it possible to fit the amplifier either in a 1U enclosure or directly to a 50mm heatsink. The form factor of the board is a bit different than I originally intended, but layout-wise it’s obviously much better now than I could have managed by sticking to the original plan so that’s no big issue. In addition to the amplifier board I made a matching PSU board. This is a simple unregulated supply which is fine for this kind of application, but actually the current requirements of the LM1875 are approaching the range where regulation starts to be possible, so maybe I’ll do that some other time (in the future…).

The boards shown here are the prototypes with the mostly standard components I had available (and yes, the heat sink is for testing purposes as well). In the works is a more “boutique” version with better parts which is probably also the one I’ll end up putting in an enclosure. Testing confirms that it does indeed play music, but real listening tests I’ll hold off until I have the other prototype ready.

Project files: GP-PSUs v2

What is it?
Two boards for general-purpose LM317/LM337 power supplies with two rails, useable for many low-power applications (preamps, buffers, filters etc.). There are two versions, one where the +/- voltage is derived from a single AC-voltage via a voltage-doubler and one where it comes from a traditional dual-AC, two-bridge rectifier circuit.
These boards are effectively an update on the old GP-PSUs and they are based on the triple-PSUs I posted a while ago. In fact they are just the three-rail designs with the third rail removed 😀

How big are the boards?
Both board versions measure 3.925″ x 1.8″ (app. 100 x 46 mm.) and they are mechanically interchangeable.

What is the status of the boards?
Both boards are in v1.0. I haven’t actually prototyped these in this format yet, but since they are the same as the three-rail version (which I have tested) I don’t mind publishing them.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires a higher performance PSU than this, you are probably better off looking at entirely different circuits and regulators anyway.

Anything else I need to know?
Yes, pretty much a repeat of what was mentioned for the three-rail circuits:

  • The diameter of the main filter capacitors is 18mm, but the dual footprint means that anything between 10mm and 18mm should be fine.
  • The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
  • Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
    • 1) Loosely assemble the regulator, the isolation components and the heatsink.
    • 2) Mount the combination on the PCB and solder the heatsink in place.
    • 3) Tighten the screw holding the regulator to the heatsink.
    • 4) Solder the regulator in place.

Downloads:
Download design files here

Related information:
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.

Note: Always read the “intro post” for additional important information about my designs.

Project files: Little helpers – Powerhelpers

What is it?
A few auxiliary boards to match the mainscontroller boards or for use one their own. More specifically, there are a couple of relay boards for use with the relay-less version of the Mainscontroller. The large relay board is intended for a “T90”-type relay which is typically rated 20/30A. The smaller board is using a Omron G5LE relay which is rated 6/10A.

There is also a simple softstart-board that can be used when powering transformers over app. 250-300VA. This is based on a very old (and frequently copied) circuit from Elektor that seems to work well, at least for medium-sized PSUs.

How big are the boards?
The Softstart board and the large relay board are both 2″ x 2″ (app. 51×51 mm.). The smaller relay board measures 1.5″ x 2″ (app. 38 x 51 mm.) As the pictures show, mounting holes and connectors line up so the boards can be stacked and cables routed neatly between them.

What is the status of the boards?
The softstart board is now in v1.5 as it is an improved version of one I did earlier. The large relay board is v1.1 as I have prototyped it and corrected the relay footprint which wasn’t perfect (my own design, obviously…). The small relay PCB is in v1.0. I haven’t actually received and tested the prototype boards yet, but as it is the exact same circuit as the large board and the footprint for the relay is an eagle standard one I am OK with releasing this design as well.

Does it use any special/expensive/hard-to-find parts?
Not really, but:

  • The T90 relays can commonly be found on ebay. There are name-brand equivalents as well from Omron, Finder and other manufacturers of relays.
  • The Omron G5LE can be puchased cheaply from Mouser or Reichelt. Alternatively there are equivalents available on ebay, usually marked with SRD-xxx designations.
  • The relay on the softstart is an Omron G2R-24V type which is also available from Mouser or Reichelt.
  • Note that the large 330nF capacitor on the soft start board must be an X2-rated type.

Anything else I need to know?

  • When in use, these boards may feature exposed mains parts (the softstart certainly will). One especially “problematic” thing is that the legs of the axial resistors are partly exposed so make sure that the board is protected from accidental touches. If you are stacking boards, I suggest putting the relay PCB on top as it has fewer exposed parts, but even so a cover** of some sort could be a good idea.
  • Whether used with the Mainscontroller board or on it’s own, be sure that you are aware of the current consumption of the mechanical relays. The T90 relay typically consumes app. 1W (1200 mW worst case) and the G5LE relay consumes app. 400mW, which for instance means they cannot be controlled directly by a micro controller.
  • I have never tested the softstart board on transformers larger than 500VA. I imagine it should be good up to around 800-1000VA, but anything more and I would be cautious and probably look for something with bigger relays and resistors. The same applies if you are using exceptionally large capacitor banks.
  • **The cover is based on an idea I had a while ago but didn’t test until now: I wanted to have an easy way to make covers to shield sensitive and hot/live parts from touches. I could use Front panel express to have 2mm acrylic sheets made but that is comparatively expensive, so I came up with another way: The Gerber files give me the board outline for each design and so by rendering the Gerbers e.g. with Circuitpeople I can get a true-size outline. Once that is scaled I can then import into a graphics program to add warning symbols, text or anything else. To get the cover I simply laminate the printout using a home laminating machine with the thickets foil type and then use a hole punch to cut out the mounting holes which are clearly marked. It’s obviously not a safety-approved material in any way, but it fits perfectly and it will protect against accidental touches which is bound to be better than nothing.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Project files: Little helpers – Fuseboards

The third part of my “little helpers” project series consists of a few connector/fuse boards for power supplies or for testing/lab use. Not exactly the world’s most interesting PCBs, but still  – they can be quite useful so I decided to publish them anyway 🙂

What is it?
These are simple fuse-boards with LEDs to be used on the secondary side of a transformer or DC PSUs (such as switchers). There are two versions:

One version can be used to combine two AC or DC voltages to provide a center-tapped voltage. The circuit works on both AC and DC so can be used for example for wiring up two secondary windings on a transformer to provide a +/- voltage or for combining two DC power supplies to do the same.

The second type of board is more or less identical, except that the ground plane is split so they are “passthrough” for the input voltages. This is useful for instance if you want to put fuses between the transformer secondary and a PSU board that already has an onboard rectifier and does not need (or want) a center-tapped voltage.

The boards also include fuses for both rails as well as LEDs to indicate that power is applied. If connected in the “standard” way then the LEDs are connected to the input through the fuse, so if the fuse breaks the corresponding LED will turn off.

How big are the boards?
There are two sizes of both designs:

  • The “small” one measures 2.0″x1.95″ (app. 51x50mm)
  • The “normal” one measures 2.5″x1.95″ (app. 64x50mm)

The two versions are compatible, meaning the board size and hole spacing are the same for the two versions.

What is the status of the boards?
All boards are in v1.0, meaning they have been tested and are working. (Well, to be honest I haven’t received the prototype versions of the “passthrough” boards yet, but as they are made from the schematics to the other ones I expect no issues) 🙂

Does it use any special/expensive/hard-to-find parts?
Not really. The fuses are standard 5x20mm types with holders (22.5mm lead spacing). The LEDs, resistors and diodes are all “standard” types and the terminal blocks are 5.0/5.08mm types.

Anything else I need to know?

  • On the large boards it should be possible to use PCB-mounted FAST-ON tabs instead of the terminal blocks (not tested though).
  • Note: These boards are not intended for mains voltage use!

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Project files: DC-DC converter boards

What is it?
PCBs for DC-DC converters as described here. There are three sizes, for 1”x1”, 1”x2” and 2”x2” converters respectively. These footprints are industry-standard so you can use converters from a variety of manufacturers such as Traco, Recom, Murata and many others.

How big are the boards?

  • 1”x1” PCB: 1.875″ x 1.475″ (app. 48 x 38 mm)
  • 1”x2” PCB: 2.85″ x  1.475″ (app. 72 x 38 mm)
  • 2”x2” PCB: 2.85″ x 2.5″ (app. 72 x 64 mm)

What is the status of the boards?
All the boards are in version 1.1, meaning they have been prototyped and minor tweaks made to silkscreen etc.

Does it use any special/expensive/hard-to-find parts?
The ceramic caps between the primary and secondary sides should typically be rated for 2-3kV which can be a bit difficult to find. Mouser/Digi-key obviously have them but your local parts suppliers might not. Otherwise, apart from the converter itself, not really.

Anything else I need to know?

  • The external components are for EMI filtering and (usually) not required in order for the converter to work. All the caps on the primary side have 1812 SMT footprints.
  • The two component positions on the secondary side can be used for decoupling (required for stability with some converters) or for voltage trim if your converter supports that. These have 1206 SMT footprints.
  • Not all converters have enable-pins and some has the functionality, but wired as “always-off” instead of “always-on”. In this case you need to wire the enable-pin to the negative input voltage in order for the converter to turn on (you can of course also use the optocoupler here, but with the logic inverted).
  • If you use a 4:1 input range converter and you expect to actually use that input range, you need to be a bit careful with the value and power rating of the LED resistor, at least on the two small boards. Both the LED and the resistor are 1206 SMT here. On the 2”x2” board you can fit a 1/2W or 1W leaded resistor and then there should be no problems.
  • Many converters are sensitive to the capacitive loading on the output, so remember to check the datasheet for maximum allowed capacitance. If you exceed this limit it is possble that the converter will refuse to start up.
  • You can sometimes find DC-DC converters as cheap surplus items. Normally that is absolutely not a problem, but remember that even if the footprints are industry standard there can be quite a few differences between manufacturers. I recommend that you do not buy anything that is so obscure that you can’t google your way to a datasheet/application note for it 😀

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Always remember to refer to the manufacturer’s datasheet and application notes for specifics on pin connections, external component values etc.

EDIT 20-08-2014: Added comment on capacitive loading.

dcdc-3

Project files: High current regulators

What is it?
These are high-current regulators designed for LM/LT108x-type regulators with current limits up to 5A or 7.5A dependent on the package. There are two versions, one with an on-board heat sink (as used to power the JLH1969 here) and the other without an onboard heat sink. The PCB with heat sink is intended for regulators in TO-220 packages. This will give you up to 5 amp current capability with an LM338 or a LM/LT1084 reglator IC. The PCB without heat sink is intended to use a TO-247 packaged regulator (LM/LT108xCP – up to 7.5A output current) and should be mounted on a suitable heat sink instead. Whether you use one or the other board version, remember to always calculate the heat dissipated in the regulator – if you are expecting to draw a couple of amps or more, the heat dissipation in the regulator quickly becomes quite large.
Also included is a small DC-DC regulator that fits on top of both regulator PCBs and can be used to generate an additional DC voltage from the main rail to power auxillary circuitry. Depending on the voltage differential and current draw, the AUXreg can use either a standard 78xx regulator or a switching type like the Traco TSR-1 or the Recom R78xx. The compact size means it can also be used as a “voltage thief” in many other places where you have a main DC supply but need a small extra DC voltage for a fan, a microcontroller or similar.

How big are the boards?

  • Regulator with heatsink (onboard-HS): 3.925″ x 20″ (app. 100×51 mm)
  • Regulator without heatsink (non-HS): 2.0″ x 2.0″ (app. 51×51 mm)
  • AUXreg: 0.4375″x2.0″ (app. 11x51mm)

What is the status of the boards?
The onboard-HS board is in v1.1. I built v1.0 and made some small adjustments subsequently, including moving the regulator footprint a little forward because it was too close to the heat sink and also tweaked the silkscreen a bit.
The AUXreg and the non-HS regulator are both in v1.0. I have built the AUXreg and it seems to work well as-is. I haven’t built the non-HS regulator but it is electrically identical to the onboard version it should be fine.

Does it use any special/expensive/hard-to-find parts?
Not really. The only potential exception is if your application requires a switching regulator for the AUXreg board – they can be a bit expensive.

Anything else I need to know?

  • The output voltage on the main regulator can be variable within a certain interval. If R1 is 121R, R2 will set the minimum output voltage (use my spreadsheet to calculate) and using a 500R/1k trimpot for P1 will give app. a 5V/10V adjustment range on the output from the minimum voltage. Note that with R1 = 121R, then C3 should be at least 22uF.
  • For the small caps on the main regulator boards, I recommend types that are rated for a 105C operating temperature as these sit very close to the heat sink. A 105C rating will help improve the reliability and overall lifespan of the caps.
  • The on-board heat sink is a Fischer type SK68/50. It is possible to fit a 40mm fan to the slots on top for improved heat dissipation.
  • Mounting considerations: Mounting the regulator and the PCB to the SK68 heat sink requires a bit of manual support because the screws tend to “slip” sideways in the slots. Also, you’ll want to mount the C1 capacitor last as it obscures the access to the mounting screw for the regulator.
  • For the AUXreg: The cap values C1 and C2 should be 330nF and 100nF respectively (ceramic or film types) for an 78xx regulator. For a switching regulator normally only a small electrolytic is required at the C1 position, but please consult the datasheet for the specific regulator you are using to be sure.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Always read the manufacturer’s datasheets for regulators etc. to confirm component values are correct. Even for “generic” types there may be slight differences between each manufacturer’s recommendations.