An “Autopower” Circuit…

This is another Rod Elliot circuit (from here) but as usual I have done my best to add my own personal touches to it.

Basically this is a signal-activated trigger circuit (such as you would expect to find on just about any active subwoofer). The board turns on the power when a signal is detected and switches it off again when no signal has been detected for a while (usually 10-30 mins). For schematic and details on how the circuit works I’d refer you to Rod’s original page.

What I have done to make my mark is partly to keep the relay offboard and make a matching relay board instead, and then of course to actually lay out a PCB for the design. Both the relay board and the main PCB are in my own industry-standard of 2” x 2” :D

The main connectors on the control board and the relay board line up so the boards stack perfectly on top of each other. The relay board also includes a separate regulator (mostly because there was a bit of space left :D), so the board can be powered from any DC voltage above app. 15V. If you have no suitable standby voltage available in the device, I have also made a small unregulated PSU that can provide power to the circuit using a small (app. 1.5-2.5VA) mains transformer.

I’ve done some basic testing on the prototypes and it seems to work fine as such. However, one potential issue needs further exploration: The time is set by an electrolytic discharging through a very large resistor (10M). This makes the delay time a bit unpredictable. Also because the “must-release” voltage of most relays is around 10% of the nominal coil voltage the relay doesn’t actually release until very late and the indicator LED is therefore slightly pointless.

Project files: LM1875 Gainclone

What is it?
The project files for my mini gain clone with the LM1875 IC as described here. The download file includes both the amplifier board and the matching PSU-board.

How big are the boards?
The amplifier boards measures 1.8” x 1.3” (app. 33 x 46 mm.)  and the PSU board measures 3.9” x 1.8” (app. 99 x 46 mm.)

What is the status of the boards?
Both boards are v1.0. I have built a working prototype, but detailed testing is on hold until I have build another set that I want to turn into a finished amplifier. All I know is that the design plays music just fine on the test bench :)

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. You can, but you don’t have to… :D

Anything else I need to know?

  • The boards are intended to be used in dual-mono configuration with one supply board per amplifier. Take the speaker output from the amplifier board and the speaker ground connection from the spare ground terminal on the PSU output connector. It is of course also possible for two amps to share a PSU, but you may struggle with wiring everything with reasonably thick cables.
  • If you want to mount the amplifier in a 1U/40mm heatsink you need to keep the capacitors on the PSU board below app. 30mm in height and the amplifier board mounted perpendicular to the heatsink. If you have more space it is possible to mount the boards directly to a 50mm heat sink (parallel to the heat sink with the IC mounted from the underside). This would however mean you have to bend the pins of the LM1875 to fit yourself, because there is no standard pin configuration that supports this way of mounting.
  • You can mount R4 either on the top or the bottom of the board. I’d recommend that you use the opposite side of where the amplifier IC is mounted for easiest access.
  • There are more versions of the LM1875 IC depending on how the leads are shaped (straight and two different bend patterns in both 90deg and 180deg versions). From the datasheet I honestly can’t determine the correct order code for this board, so you’re on your own here… ;)

Download design files here

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

Read the LM1875 datasheet for more information. I’d also recommended the kit manual as a good source of information.


Past projects: Old ICEpower Amps…

I’ve built quite a few ICEpower amplifiers over the years, but many of them were built and sold before I started this blog. Recently I actually saw an amp for sale that I am pretty sure I built and so I started looking to see if I had any pictures of these amplifiers. Mostly I don’t, but I did manage to find a few:

The first amp is a small amp based on a 200ASC-module with a 200AC hanger. Unlike the ASP and A-series, the amplifier sections on the AC/ASC are the same so it is possible to build a (deceptively compact) stereo amplifier this way. I used this amplifier in my office system before I eventually replaced it with the B1/125ASX combo.

The second amp is a full-size amp based on 2 pcs. 1000ASP-modules. At the time, this was intended to be my own reference amp, but firstly I preferred the sound of the 500ASPs I were using before and secondly I got a very good offer on it so I decided to sell it soon afterwards.

The last amp is a three-channel model with a single 500ASP and a pair of 200AC hangers. The amplifier I used for a couple of years to power the center and rear channels. As the front amplifier I had two stereo amplifiers with dual 500ASPs wired in bi-amp mode, which made for a very compact surround system with plenty of power – around 3kW into 4Ohms – on tap :D. I eventually sold all these amps and started using the 6-channel 50ASX instead.

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 :) ).

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.

Back from Canjam…

Yes, I have returned from the CanJam meet in London! (see previous post). Overall a very good experience – although it was my first show/meet of this type. I met quite a few interesting people and had some good discussions with fellow hifi-nuts. As always, the enthusiasm clearly shines through (as is the case with any hobby I guess?). I also thought (and that might just be me) that it looked like a more diverse crowd than what I typically see at audio shows – not surprising as such, but just enough to be noticeable :)

I brought the camera, but there were so many other people with cameras that I only managed a few shots before putting it away. If you want to see what went on, check out the official head-fi “meet-thread” for pictures etc. instead.

As expected there were quite a lot of interesting new products to see, touch and try, but I managed to get out with my credit cards (relatively) unharmed – at least for now :D Best sound of the show for me was definitely the combination of the Stax SR-009 electrostatic headphones and the Headamp “Blue Hawaii SE” tube amplifier as pictured below. This is a killer setup – unfortunately with an equally killer price tag.

The most annoying thing was probably that I’ve never listened to the SR-009s before and I was a bit surprised at how big a step up from the SR-007s that I own they represent. That does not bode well for whenever I decide to go to Japan again :D

Looking forward to next year’s CanJam because if my schedule allows I will definitely be there! :)

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 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 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, 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.


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