A good idea…

Like many people, I use running and walking as a way to try and stay in shape (yes I admit, you can’t really see it ;)) and also to take my mind off work and daily life in general. I also very often use this time as a way of solving problems and generating new ideas. Some of the ideas are definitely good, some are probably not so good and some of them just turn out to be very expensive :D

A couple of months ago while out, I had the idea for a way to build a balanced Beta22 headphone amp from AMB. I didn’t technically need that, but since I have a pair of balanced headphones I thought I’d give it a go.

The B22 is not a cheap project by any means, especially not in the balanced configuration – and when you then start adding a few custom-fabricated enclosure parts and transformers then it is really starting to hurt! But hey, I am not into DIY audio to save money (definitely not…) so here we are :D

Still quite a bit of work left to go as you can see, but even the electricals are coming along nicely. And while I am confident that the result will end up being worth it, I have to admit it was a pretty expensive run I went for that day :D

Project files: Little helpers – Connectors

The second part of my “little helpers” project series consists of a few connector boards amplifiers or for testing/lab use.

What is it?
Three boards for various connectors and purposes:

  • An XLR/TRS-board which is a small breakout-board for a Neutrik NC6FI-H XLR/TRS combo connector that means you can then use bare wires or a three-pin connector to wire up the socket.
  • An XLR I/O board which is intended for XLR in and loop out with “standard” PCB-mounted Neutrik D-series XLR connectors.
  • An RCA I/O board which is designed for some board mounted RCA connectors. I don’t actually know who makes these but they are pretty much the only decent-quality style PCB mounted RCAs that I know of. There are a couple of of internet sources for them (ebay, audiophonics, Rapid electronics, ) and I think they are identical (if nothing else then in size/dimensions) to the ones sold by Vampire at a more “audiophile” price ;) If anyone knows the “true” source of these then I’d like to know?

How big are the boards?
Small… I don’t want to list them all here :)

What is the status of the boards?
The boards are in v1.0 which means they have been tested and are working.

Does it use any special/expensive/hard-to-find parts?
Mostly there’s only one real part on the board and that is the connector itself which can be a bit expensive, so yes, I guess so :D

Anything else I need to know?

  • Note that although the XLR/TRS sockets do fit into a standard Neutrik D-series hole, for reasons I don’t quite understand the board will not sit completely straight if mounted that way. For most uses that will not be a problem, but if you want to use these in a 1U enclosure you need to be a bit careful or mount the board upside down. To avoid this, make your panel holes exactly as it is shown on the drawing.
  • On the XLR-boards there is an onboard jumper to connect pin 1 to ground, so depending on usage (SE or BAL) and grounding scheme of your build, this is an easy way to manage ground loops. There is also a jumper to connect the chassis to ground which should not ever be necessary if everything you connect is made properly. If it isn’t, then that jumper is here to save the day :D
  • The “XLR loop” boards are included in a “right” and a “left” version which are mirrored. If you only need one version and don’t really care which one, I’d recommend the one marked “left” as it has the nicest routing (unbroken ground plane).

Downloads:
Download design files here

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

As usual, please remember to consult the manufacturer’s datasheets as well and ensure that you verify the connector part numbers before hitting the “buy” button on anything :).

Standby-PSU & Controller board

For many of my amplifier builds, I have needed the ability to control and switch a mains connection for a transformer or SMPS with a low-current switch. I also frequently need a “stand-by” voltage for LEDs, fans and other circuitry outside of the main amplifier voltages. Some pre-made soft starts include both of these features, but they are mostly either fairly expensive or very low quality ebay-stuff (I have a few of those that work well, but I have also blown up a couple in the process of finding the good ones…).

One potential alternative is AMBs epsilon24 “switch driver” circuit. This was partly what I needed, but not quite. Firstly I wanted to use a latching switch (so you can easily see if the damn thing is on or off :D ) and secondly I wanted to integrate the mains switching part of the circuit as well, in order to eliminate as much clumsy mains wiring as possible. The end results (at least for now) are what you see here. I say “results” because actually I ended up with two versions of the board :D.

The first type is the one with the transformer. It includes the transformer (which is an EI-30 core type, so power is limited to around 3VA maximum) with a small rectifier and 78xx regulator to generate a regulated standby voltage – normally either 5V or 12V. The standby voltage is available for powering external circuitry and it also switches an on-board SSR (solid-state relay) to control a larger, mains-powered transformer or SMPS. The switch can be either a simple latching type and/or an input from a logic circuit such as a flip-flop or a microcontroller. There is also an onboard fuse for the load and the SSR is protected from transients by a snubber circuit and a varistor (MOV).

On the second board version I have replaced the transformer + the regulation stage with an integrated MeanWell IRM-series power module. I also added a second mains output, removed the fuse which should be placed off-board instead and thus managed to shrink the board by a few mm. in the process. Although a bit more expensive than the transformer, on paper there are several advantages of the integrated power module: More power (up to 10W instead of less than 3W), universal mains input, very low standby consumption (so easily compliant with the < 0.5W standby regulations), simpler and takes up less board space than transformer and regulator etc. However, the output voltage seems to fluctuate a bit more than I would like. If you’re just powering fans, LEDs or relays this is most likely not an issue, but the idea was that it could power logic circuitry as well and then I am suddenly not so sure it will work – we’ll see once I manage to do some more detailed testing.

So, even with two board versions that both work I am not sure it is really “mission accomplished” just yet: The transformer version might be a bit underpowered for what I would like (especially at 12V) and the SMPS version might not be stable enough for powering digital logic. If so, I might go for a rev. 3 of this idea and see if I can squeeze a bigger transformer on there to make just “one board to rule them all” :D

EDIT 07-09-2014: I have now done some more testing on the v2.0 board and it seems I was wrong about the output of the IRM module. At least now I can’t replicate the unstable output I saw last time any more. With both my normal multimeter and the more expensive Fluke, the output is now a rock solid 5.00VDC. I have also measured another IRM module (a 12V version) and that also shows a very accurate and completely stable output voltage. So, I guess it is “mission accomplished” after all and I I’ve shelved the plans to make another transformer version – at least for now :)

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 :D

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: Little helpers – Alps PCBs

These “little helpers” are small supporting boards I have developed for my various audio projects. I have a few different ones and I don’t think they are really “big” and sophisticated enough to warrant a post for each one so I’ve decided to lump them together in a few groups instead.

What is it?
The first collection is PCBs for mounting Alps (and a few other types, including the Noble I have used in some of the pictures :) ). Included are boards for different types of potentiometers namely stereo without motor and quad with and without motor (i.e. Alps types RK27112 and RK27114/RK27114MC).

For the unmotorised version there are two variants: “Preamp” groups input and output terminals together and “Breakout” groups the individual decks of the pot together. The “preamp” version is used when you want the signal to flow through the pot (such as in a pre-amp), whereas the “breakout” version is used when you want to insert the pot into an existing circuit, i.e. for wiring an off board pot to an amplifier PCB that has onboard space for it. This distinction is mainly to help simplify wiring – unless the circuit has a really strange design with respect to grounding, you can of course use the boards interchangeably.

How big are the boards?
Small… I don’t want to list them all here. The biggest board is the quad motorised which measures 3.5″ x 1.75″ (app. 89 x 45 mm).

What is the status of the boards?
The boards have been tested in v1.0 and for a couple I made some cosmetic changes, including changes to the footprint of the motorised quad pot, to upgrade them to v1.1.

Does it use any special/expensive/hard-to-find parts?
Mostly there’s only one real part on the board and that is the pot itself which can be a bit expensive, so yes, I guess so :D

Anything else I need to know?

  • The stereo boards have a four-hole footprint to fit various pots that use that configuration, but the last set of pads isn’t connected to anything so will not work directly with a loudness tap.
  • The various quad boards have all holes in the same places so the motorised and unmotoriseed boards can use the same chassis footprint (even if of course the unmotorised board is smaller)
  • The “preamp” style boards have a ground plane and a ground pad that can be used if you grounding scheme requires the shaft of the pot to be grounded. Use a piece of wire connected from the ground pad to either one of the screws on the back of the pot or soldered to a ring terminal wedged between the pot and the chassis.
  • On the motorised quad pot the shaft is connected electrically to the solder pins for the motor housing, so if you want to ground one of these you only need to connect a small jumper on the underside of the board from one of the housing pins to the ground pad – no messy wiring needed.
  • The eagle footprints for the quad pots are not “official” but ones I made myself by chopping up the stereo footprint. They work fine, but they probably aren’t the last word in accuracy and the holes for the housing pins could have been done more elegantly…

Downloads:
Download design files here

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

As usual, please remember to consult the manufacturer’s datasheet as well.

 

EDIT July 28th 2014: Added pictures (which I stupidly forgot when I posted this…)

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 :D If anyone has used standard DC-DC converters to power audio circuits I’d love to see some examples :)

A comment on audio reviews

No, it’s not me making it….

I normally don’t just link to contents like this, but if you’ve ever read an audio review and been annoyed/frustrated/puzzled about how reviews are written then this post by Srajan Ebaen (the owner and founder of 6moons.com) is well worth a read. You may not agree with the man, but he does make some important points I think.

Incidentally, both 6moons and digitalaudioreview.net where the post is published are well worth following if you aren’t already :)

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.

Project files: Mini JLH1969

What is it?
This is the project files for my version of the JLH1969 amplifier as shown here. The files for the matching PSU will follow shortly.

How big are the boards?
The board measures 2.25″x2.3″ (app. 57x58mm).

What is the status of the boards?
The board is in version 1.0. I have built and tested a couple of prototypes (as described in the original post) and although they play music just fine, you should still consider this a “work-in-progress”. I would be especially concerned with confirming the thermal stability of the amp because of the compact dimensions, so if anyone decides to build this please share your results :)

Does it use any special/expensive/hard-to-find parts?
No. I have used MJL21196 output transistors because I had them, but versions of the MJE/TIP3055 should be OK as well as long as they are in suitable (meaning TO-247 or TO-264) packages. Do not be tempted to use faster transistors such as the MJL/NJL3281-types as the amp will most likely not be stable with these. Have a look at the TCAAS page on transistor substitutes for more info.

Anything else I need to know?

  • The only change I have done from the original schematic is to replace R5 with a 200k trimpot to make it easier to adjust the operating point. Oh, and I’ve made up designators for the parts that don’t have a number on the original schematic ;)
  • In my opinion the output cap should be 4700uF or larger, even with an 8 ohm load. Even if the supply voltage is 27V, I’d be comfortable with using a 25V cap in this position. All the other electrolytics should be 35V or higher.
  • Heat sink T3 as it might get hot. You’ll probably not be able to find a standard heat sink that fits. so my recommendation would be a small piece of bent aluminium or copper with a hole tapped in it for easy mounting.
  • Raise the R2 resistor 5-10 mm above the board for cooling (I haven’t done this in the prototype version but it gets quite hot).
  • The footprint for the input transistor is for a 2N3906 as described in the original BoM, but other types can be used as well. An easy to get choice is a BC560C which needs to be turned 180 deg. in order for the footprints to match.

Downloads:
Download design files here

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

As usual, both TCAAS and this diyaudio.com thread contains lots of worthwhile information.

minijlh1969pcb-1

JLH 1969 PSU

As promised, here is the matching PSU for the mini JLH1969 amp. Based (roughly) on the PSU designed for the JLH1996 amp, this is a single-rail regulated PSU based on an LM1084 (or LM338) regulator giving a 5A current limit. The board measures 5×10 cm and is intended to be used for one amplifier channel. The onboard heat sink is a Fischer SK68/50 which should be enough for an amp that draws app. 1.3A, especially if the low-drop LM1084 regulator and a suitable transformer is used.

The PSU works, but I haven’t had time to test it properly with the amp just yet (hopefully in the coming weekend). More pictures and information when that is done and I can post the project files :)

jlh1969psu-1

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