Going to CanJam!

I am off to the European leg of the “CanJam” headphone meets/shows which runs this weekend in the middle of one of my favourite cities – London!

I have been to a couple of industry trade shows before but never to one where the focus is so much on the consumer and the community, so I am not really sure what to expect. Hopefully, there will be plenty of stuff to see, plenty of people that you know but have never actually met ( :) ) and of course – since it is in London -I will also have the opportunity to do a bit of shopping.

If you are joining us in London, feel free to drop me a line and let’s meet for a “hello” and a quick chat – I would love to get the chance to speak to any readers and fellow audio enthusiasts :)

…and yes, even the most exciting journey often starts with a long wait in a boring airport lounge – so guess where I am now? :D

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… :D ), 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.

ICEpower 200AC Amplifier

A while ago I realised I still had a single pair of ICEpower 200AC modules left over as well as a suitable transformer – and why miss an obvious opportunity to make another power amplifier I don’t really need? :D

The 200AC module is exactly the same amplifier section as the better-known ICEpower 200ASC only without the onboard power supply. The 200AC board is very compact at app. 55 x 107 mm per channel but will still put out over 200W into 4 ohms and because I had the transformer available I opted for a linear power supply. The transformer is a custom one I got from ebay (I think) with a 32VAC winding and a single 12VAC winding. This makes it perfect for the ICEpower modules as the dual-rail low-voltage supply can easily be generated via a voltage doubler. The main power rail is a bit lower power than I might have wished for (160VA), but not overly so, and the transformer is made by what I consider a quality manufacturer so it should be OK. 160VA is still more than 1/3 of the peak power which should work as a rule of thumb (yes, I know it is a bit more more complex than that but a good starting point as far as I am concerned).

The power supply board is a variation/update of a design I first made nearly ten years ago (when I started building with the ICEpower modules) and quite simple. I will publish the board files shortly as it might be useful for other users of the ICEpower AC-series and A-series modules without switching PSUs. I’ve used a dual-mono setup with separate PSUs mainly to be able to add a bit more capacitance to the mail supply rail (2 x 10000uF per channel) which shouldn’t hurt. The capacitors are very audiophile-approved “Gold Tune” types from Nichicon, not because I think it is audible per se, but because I like the look (yes I know, I shouldn’t admit to such things :D)

Apart from the amplifier boards and the power supplies I have added fuses on both the primary and the secondary sides of the transformer via a couple of my supporting PCBs. The secondary-side fuse board is the one I published here and the primary side fuse board is somewhere in the pipeline :). Obviously using these boards aren’t strictly required, but I wanted the fuses in the amp and especially the secondary-side board also makes for much neater wiring than would otherwise be possible for me to achieve.

I also wanted this amp to be fairly compact and unfortunately that took a few bits of custom metal work to achieve, namely a mounting plate for the modules and PSUs, another for the transformer and a small one for the primary fuse board (not fitted yet in the picture below). That obviously pushes the cost up a bit, but fortunately I have decided to ignore that part ;)

The back panel sketch is done and will be included in my next order with Schaeffer/FPX. Still to do is a front panel and some wiring, although I might actually hold off doing the front panel until later. That way I can match the looks of this power amp to an as-yet unspecified DAC/preamp/whatever to make a matching set :D


Building an Electronic Load

One of the tools that I sometimes need but haven’t bought yet is an electronic load for testing circuits such as power supplies. Of course you can make do with fixed resistors (and I have so far), but you practically never have the right value/wattage to hand when you need to test something (in my case, usually on a Sunday afternoon…grr!).

The solution is a programmable electronic load, or basically an adjustable current sink (or a “reverse power supply” as some people call it) that can simulate the load from any fixed resistor within reason. I haven’t bought one of these yet, partly because I didn’t feel I needed it enough to justify the expense, and partly because I am rapidly running out of space to store instruments that are only used occasionally.

Some weeks ago I started toying with the idea of building one myself to at least get started. I’d seen some nice designs on Tindie, but wanted something that was capable of higher power and something which I could more easily tweak for myself. A bit of googling turned up a few promising pages, most notably this one on Kerry Wong’s (excellent) blog.

I liked Kerry’s design as a starting point, mostly because it is relatively well documented and the control code is Arduino (which I can work with). I therefore started revising the circuit to suit my needs and laying out a PCB for it as well.

Key changes from the original:

  • I’ve scaled it down from three pairs of MOS-FETs to two because that is what I could fit on the Eagle board (being constrained by the freeware version).
  • I’ve replaced the parallel LCD connections with I2C to simplify the PCB layout and free up Arduino pins.
  • I’ve mounted the controller (an Arduino Nano v3) onboard. That wasn’t the original plan, but the space was there so why not?
  • I’ve broken out a pair of analogue Arduino pins, a pair of digital Arduino pins plus a second I2C-connection that can be used for other purposes. Top of the list for me would be a real-time clock (RTC) module for data logging purposes and some sort of thermal sensing and fan control, but I am sure there are many other potential uses (web-interface anyone? :D ).
  • plus a bunch of other minor tweaks :)

This is still work in progress, but I have received the prototype boards in hand and I have started the assembly as you can see from the pictures. Still to do:

  • Do the mechanical work on the heat sink (in progress)
  • Rewrite the software to work with the I2C-display (also in progress, but might take me a while)
  • Test whether the damn thing works! :)

PCB Layouts Part 1 – Workflow

I get asked (surprisingly) often about my PCB layouts and how I do them. Flattering obviously, but also a bit strange as I don’t really consider myself an expert on PCB layout at all. However, I can share are some “workflow” tips on laying out a board in the most effective way based on my experience.

Note that the below is based on using the freeware version of Eagle, but much of it should translate to other software packages without much difference.

The first step is to draw the schematic in the schematic editor. If I start from someone else’s published schematic I’ll normally print a copy on paper and mark on that which parts sizes I expect to use. This then becomes the reference for drawing the schematic in the editor. Once the schematic is drawn in it’s basic form I’ll check it, rename the parts and then run an electrical check to verify that nothing has been missed. If I am going from a published schematic I normally stick to the part names from the original schematic (because that makes for much easier troubleshooting if something’s amiss later on), otherwise I will make up something that is logical to me, usually going from input to output.

Then it is time to switch to the board editor. Most of my PCB layouts start out with mounting holes placed in the four corners (because that’s normally where I want them) and a ground plane drawn in the top layer. If I have a specific board size in mind I’ll restrict it straight away, otherwise I will keep the full area and then reduce the size as the layout progresses. I will also load my own standard design rules and tweak the parameters (mainly clearance) if required before I start, because then I will not make something that I have to revise later when the DRC (design rule check) fails.

I generally then start the actual layout process by placing the key components as I want them. Key components usually mean:

  • Power and control devices (transistors/ICs and potentiometers/switches) that must extend over the edge of the board
  • Power devices that need an onboard heat sink (heat sink is placed as well of course)
  • Other ICs plus their associated decoupling parts as close to the IC as possible
  • Key connectors (if they need to be in a certain position I fix that, otherwise I put them on the specific board edge where I believe it makes most sense to have them).

After this, the fun (or frustration) starts. Using the schematic on one side and the “ratsnest” command in Eagle to recalculate wires I start moving first the major and then the minor parts of the circuit around and positioning them to yield as short and as neat traces as possible. This requires several iterations and usually also putting the board away and coming back to it later because I tend to “go blind” after staring at the layout for too long at a time. Other tips that I use to simplify the layout process include:

  • Every time I make a major change, I save the board as a different file version with a new revision number, because sometimes layout changes turn out to be “dead ends” and then it’s easier to return without having to do massive amounts of rework. Some of my more complex designs have 10-15 file revisions before getting to the final layout.
  • I normally do the basic layout using one trace width, generally the smallest width I expect to use in the circuit. Once I have a layout I am reasonably happy with mechanically, I can enlarge key traces without having to do a lot of fiddly rework and without risking that I miss something. In general I also stick to using a few standard trace widths which makes it easier to quality check the layout later on in the process.
  • I normally start with 45 degree trace angles for simple and consistent routing, and the in the last round of tweaks I may change some traces to be “odd” angles instead if it significantly helps the layout.

Once the layout is beginning to shape up and all traces are routed, I will start the actual layout screening process. This usually involves generating gerber files for the circuit and rendering them with circuitpeople.com and looking at each layer in isolation. For the copper layers I mainly try to look at a) whether the individual traces follow the most unbroken and logical path and b) whether the individual signals will flow through consistent trace widths. If not, i go back and make corrections accordingly. Once I start checking Gerbers, I also start adding text elements to the board because I now have a reasonable idea of where there is space for them.

I then pretty much repeat this process over and over again until I believe I can’t make any more improvements. Again, putting the board away for a day or more often helps and I often find that even a short break from something I am happy with means that when I come back I can make bigger optimisations than I though possible when I left it. Often during these breaks I also think up new features that may be worth including, such as multiple footprints for key components, additional labelling for connectors etc.

Eventually I get to a point that I am happy with the layout and then it is mainly the last checks of both the individual layers (using gerber renderings from circuitpeople) and the full board (using renderings from gerber-viewer.com, which allows displaying of multiple layers at the same time) plus the last tweaks to the silk screen. The last step is usually confirming that ERC and DRC are still error-free, and then printing off a sample of the board layout at 100% to check the final size. Seeing the board printed in actual size gives me a better impression of the size, even if I already know how big e.g. a 2” x 2” board is.

I will then place the PCB order and mark the last Gerber version with a tag in my Eagle project folder so that I can see later that this was the file version I sent off for manufacturing.

Project files: Little helpers – Ground Loop Breaker

One more little helper for you guys :) Once again, not exactly a major effort with this one, but I hope it is still useful.

What is it?
It’s a Ground Loop Breaker as described in this article by Rod Elliot on grounding/earthing of audio equipment.

How big is the board?
The board measures 2.0″ x 2.0″ (app. 51 x 51 mm.) This is my new semi-official standard for modular circuits like this and will allow stacking of boards :)

What is the status of the boards?
The board is version 1.1 as I had to replace the original bridge rectifier with a different footprint.

Does it use any special/expensive/hard-to-find parts?

Anything else I need to know?

  • Read the article and follow the recommendations on connections.
  • The rectifier bridge should be in a so-called GBPC-W package with wire leads. The rating should be 25A or higher and both the bridge and the capacitor should be rated for at least the mains voltage where you live (so 250VAC/400VDC in 230V countries)
  • The connections on the “ground” side (input) are either via the screw clamp or a couple of FAST-ON tabs. Connections on the “earth” (output) side are either via FAST-ON tabs to a dedicated ground screw or a plated-through hole that can be used to make the chassis connection. The board mounting holes are isolated. Use cables that are as short and thick as possible for all connections.

Download design files here

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

Be careful with working with any mains wiring and be sure to ask questions if you are not sure about anything, either in an online forum or to a local electrician (preferred).

Project files: Little helpers – Capacitor boards

Another post in my “little helpers” project series consists of a couple of capacitor boards for mounting input/output capacitors that will not otherwise fit on an amplifier board.

What is it?
Universal boards for (input) capacitor mouting, either for testing purposes or for designs where there is no space to mount a decent-sized capacitor on the main PCB. I made the small board to supplement my P3A clone where adding a large input capacitor would have increased the overall board size quite a bit, so using an off board input cap gives more flexibility. The background for the ridiculously large “MegaMKP”-version you can read in my previous post.

How big are the boards?
This big :)

  • The “normal” board measures 2.0″ x 2.0″ (app. 51 x 51 mm.)
  • The “MegaMKP” board measures 3.95″ x 0.625″ (app. 100 x 16 mm.)

What is the status of the boards?
Both boards are in v1.0, meaning they have been tested and are working.

Does it use any special/expensive/hard-to-find parts?
Well, there’s really nothing on these boards except the capacitors :D

Anything else I need to know?

  • The small board has capacitor mounting for small caps on the top and for larger caps. Max dimensions are approximately:
    • Bottom side mounting: 25 x 38mm axial capacitor (with holes for 33mm long caps as well).
    • Top side mounting: 27mm lead spacing x 15mm thick box cap or app. 20 x 28 mm. axial capacitor.
  • If using the bottom side mounting points, either mount the board upside down on standoffs or don’t use the footprint for the terminal block but solder wires to the board instead.
  • The large board has holes for a various combinations of 2/3/4 large caps. There are screw holes that can be used to mount the boards to the chassis via standoffs so you can use caps as big as you like.

Download design files here

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

Audiophile or Idiot?

Some say there is a fine line in DIY audio between rational overengineering and then “audiophile overkill”. This is then on the next line out, between “audiophile overkill” and “plain stupidity” :D

More of less since I started building amplifiers I have been hearing that electrolytic capacitors in the signal path are bad and they sound bad – yet many successful (and great-sounding) amplifiers including the original JLH, the Zen v4, the J-Mo buffer and so on have electrolytics in the signal path, so what is up?

During my recent trip to Japan I found a way to perhaps try and clear up some of this “myth” – in the form of a good offer on some gigantic polypropylene capacitors that I had to jump on. “Cheap” is obviously a wonderfully relative term, but suffice to say that I did not pay anything like what I have seen similar sized caps advertised for elsewhere.

Obviously using these caps present some practical challenges – they are huge! Instead of trying to design a PCB for them, I designed a small PCB to use as the terminals and then mounted the PCB and the caps on an aluminium back plane. With a few different holes the terminal boards will support several different combinations of caps so although I don’t expect to need any more, it does make for a more versatile design.

The caps alone measure app. 63×115 mm (standard 330ml can for comparison below) and when assembled, each module is roughly 190x180x70mm high. This actually means that with these modules as the output caps, the amplifier circuit itself will have to be fairly compact in order to fit everything into a standard 2U chassis… :) The total capacitance per side is 990uF/250V meaning they should be suitable as output caps for headphone amps down to a load of app. 32 ohms.

Any good suggestions on what these should be used for? :D

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 :D

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.

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: The J-Mo Headphone Buffer

What is it?
The project files for my version of Richard Murdey’s  J-Mo mk. 2 buffer with gain.

How big are the boards?

  • Amp: 2.45” x 1.975” (app. 62 x 50 mm.)
  • PSU: 2.35” x 1.975” (app. 60 x 50 mm.)

What is the status of the boards?
Both boards are version 1.0, meaning I have prototyped them and they work. However, I am still waiting for some mechanical parts for my own build so this isn’t final yet which means I have only done very basic tests.

Does it use any special/expensive/hard-to-find parts?
Well, the J-FETs are getting harder and harder to find but it isn’t impossible yet.

Anything else I need to know?

  • Can’t really think of anything. Be sure to read through the article on Richards website though, that contains most of what you need to know.

Download design files here

Related information:
See the original post for some more information and links. There is also a big discussion thread on diyaudio that may be of help.

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


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