Woodface…

Yes, I know it’s the title of a classic album from Australian group Crowded House but it is also an occasionally very popular way of finishing hifi products :D

European (or at least Scandinavian) readers may recall the now-defunct Danish “Holfi” brand from a decade or so ago. Here, thick cherrywood fronts were the norm and as usual with these things, that made the opinion of the brand more based on looks and perception than on sound quality (comments along the lines of “I don’t want something I have to paint every year to keep it from rotting” were frequent…).

However, wood also has a number of benefits, mainly that it is easier than metal to work with for most average diy’ers, and so when I stumbled upon some suitable wooden panels I started planning to give it a go as well. The wood is an unknown “exotic” (for a Scandinavian at least) species that I purchased in Japan last year. The boards are cut to 5mm by 50mm dimensions that are perfect for front panels for Modushop cases and that is honestly why I bought them**.

What am I doing with them? Good question and I am not quite ready to show that yet, but it will be a small pre- and power amp combination (because I definitely need more of those – groan! :D)

**Sidenote: I am sure many of the readers here recognise the feeling of looking at something and realising that it can be used for an audio project – if that rings a bell, I can only warn you against going to Tokyu Hands (especially their main branches in Shibuya and Shinjuku) and visiting the DIY-supplies section :D

One amp to rule them all?

After years of experimenting I am slowly getting an idea of what the “perfect” power amp for me looks like. Not so much in terms of sound because that will always be an issue of system matching, especially to the speakers, but more in terms of feature set. So, for the last couple of months I have been planning a new amp design that when finished could be the only one I need – maybe it should be called “The Ring”? :D

The power amp section is comprised of two ICEpower 250ASX modules in BTL-mode which should make them good for around 600W output. I have never tried the 250ASX-modules before so it is a bit of a gamble that I like them better than the 125ASXs, but worst case the mounting plate design means I can make them fit anyway without having to drill into the enclosure again. The power is provided via an ICExtend-board – another first for me – but it looks very useful.

There’s input switching which comes courtesy of a 3-way version of my relay selector board. This should make it possible to use a stereo analogue setup with a RIAA and preamp, a stereo digital setup with separate DAC and also a surround-setup with the main speakers acting as fronts – without having to switch any cables around. Since the switching happens after the volume control stages there should be less risk of equipment or ear damage.

The relay selectors are powered by the AUX-supply on the ICExtend board that also distributes power to the ASX-modules and enables having both 12V- and 3-5V logic level trigger inputs on the back.

To facilitate some experimentation with the sound, the input section will be able to use a few different designs, namely the discrete Alpha20 buffers from AMB, my own simple op-amp buffer, AMBs new fully-differential Alpha24 or a slightly modified version of my BUF03-design. I am honestly not sure I need that much choice, but since the mounting holes are the same size they all fit :)

In addition to the input switching and buffer options I have included a “Power Out” option that could potentially be used to power a source and/or a preamp. Since I don’t know what is required here the power board has universal hole pattern and will fit anything from a standard 30-40VA toroid though a board-mounted transformer to a single board-mounted Mean Well IRM-series SMPS. The rear panel output for the power out is a Neutrik D-series hole that is fairly universal in itself and most likely I’ll start off with a 5p female XLR to ensure nothing is plugged into the power out by accident.

A couple of things missing obviously: I need new boards for the modified BUF03-stage which I’d like to try first, but due to Chinese new year it’ll be a couple of weeks before I can order boards and then another couple of weeks before they actually show up. I also need to assemble and test the PSU boards and while I already have the rear panel, I am missing some of the connectors etc. so we’re not quite there yet :D

Oh, and just in case any regular readers were wondering: No, I don’t really believe I can settle for having just one amp at my disposal but it is a nice thought, right? :D

Project files: Relay-based attenuator

What is it?
This is the board files for my relay attenuator described here.

How big are the boards?
The board measures 3.85″ x 2.4″ (app. 98 x 61 mm.)

What is the status of the boards?
This board is version 1.0. It has been built and tested and I haven’t really found it necessary to make any changes based on the prototype.

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

• The relays must be the specified Omron G6K 5V version and the ULN and MCP ICs should be in the right packages (SO-IC). All these parts should be available from the usual sources, i.e. Reichelt in Europe and Mouser/Digikey in the US and worldwide.
• The resistors should be 1% tolerance or better and some of the values are from the E96 range which might not be available in the shop around the corner but should be available from most of the mail order companies.

Anything else I need to know?

• Refer to the original build article (link) for some additional information and helpful links to Arduino code samples etc.

Downloads:
Download design files here

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

Mini-stack (part 1)

Not exactly the most challenging builds ever undertaken, but still…

More or less since I originally built my passive preamps I have wanted to build more components in the same form factor. Here is the beginning of a “mini-stack”, namely a USB DAC and a passive pre, which should then be supplemented later by (at least) a power amp in the same small chassis (a GX143 from modushop.biz, so 124x40x73mm). That isn’t ready yet, but I do have a few ideas for what to do :D As for what is ready:

The passive pre is based on a Noble 10k pot that I happened to have lying around – not much more to say about that really :-)

The DAC is based on an “off-shelf” module from ebay. It uses the SA9023 USB receiver/ES9023 DAC chipset so that it can accept up to 24/96 input signals. The module is powered from the USB connection. It is possible (and possibly recommended) to use an external supply instead, but since the preamp is passive I wanted to keep the design “cordless” except for the USB. Obviously that won’t work for the power amp… My only little piece of hacking here was to wire an “USB on” LED on the front panel instead of relying on the on-board SMD one.

The ES9023 DAC chip from ESStech is a highly respected performer and used in quite a few designs such as the AudioQuest DragonFly (albeit there with a more complicated/advanced USB front-end) and quite a few others. It is voltage output with a built-in charge pump to avoid capacitors in the signal path and it is actually capable of driving headphones directly, so the 10k load here isn’t really an issue.

The sound quality of the board is quite a bit ahead of the older PCM27xx-based designs as well. The sound from this little combo is actually quite good and the fact that no external power suppliers are required makes it a bit more interesting.

My idea for the power amp is to use a class D chip powered from an off-board switching supply. I have looked at both the TPA311x and the TDA749x chips but I am still exploring options here so nothing definite yet…let’s see what happens :)

Happy 2015!!

Another year gone, another time to make a quick status :)

As I have written about a couple of times during the year, I am still a bit overwhelmed with the number of people clicking their way here. The number of page views passed 64k a few days ago which is quite a big step up from the 15k at the end of last year. The download count for the project files is now well over 1300 as well and I really hope to continue this trend in 2015 – workload and bank manager permitting of course :D

Now, things are probably going to be a bit quiet here for the next couple of weeks as I head to China on Friday. Mostly just a sightseeing holiday, but hopefully with a chance to do some audio-related shopping as well. Fortunately my X-mas break did give me a chance to (nearly) finish some builds that I will be showing over the next weeks/months. A big milestone was reached when I finally managed to case one of my RIAAs, which means I go into 2015 with a working vinyl rig – very nice!

In other news I received my first custom-machined Modushop front panels from Schaeffer/FPX last week. They turned out very well, so it seems my favourite hobby has found yet another way of ruining me which I will show soon. Also, as you have probably noticed from the last few month’s updates I still have plenty of half-finished projects to carry on into 2015, so in case you were worried there’s no real shortage of content for the blog :)

For now, thanks a lot for reading and all the best for 2015 to everyone of you :)

Project files: SLA battery charger

What is it?
For one of my work-in-progress builds I needed a simple charging circuit for an SLA (sealed lead-acid) 12V battery. So, good excuse for another project :)

Compared to the Li-Ion or LIPo-batteries used in most applications today, charging an SLA is extremely simple. You use a fixed voltage and then set a limited charge current of around 1/10C or a trickle-charge current of around 1/20C and off you go. (“C” is the nominal capacity of the battery, so 1/10C for a 7Ah battery is 700mA).

A bit of searching online turned up a few suggestions but one appealed more to me than the others, mainly because of its simplicity. The circuit is built around the L200 voltage regulator which features programmable voltage- and current limits, which is exactly what this application calls for. I believe the original circuit is from Elektor, but I am unable to find it so I relied on the web versions here and here instead.

How big are the boards?
The board measures 1.95″ x 1.6″ (app. 50 x 41 mm) without the heat sink.

What is the status of the boards?
The published version of the board is 1.1. Changes from the prototype v1.0 that I built are fixes for some misprinted LED-labels (doh!) and some minor touch-ups to the silkscreen – nothing major.

Does it use any special/expensive/hard-to-find parts?
Not really. Just be a bit careful checking component dimensions against board footprints because there isn’t much space left over.

Anything else I need to know?

• The PCB is meant for currents smaller than 1A due to the limitations of the rectifier and protection diodes. With a bit of searching it is possible to get 2A components that fit, however whether this is a good idea from a thermal POV remains to be seen.
• The component values are normally meant for 12V batteries (and a 13.8V charging voltage). A few of the articles have component values for 6V battery use as well, but if anyone can easily recalculate for 24V (2 batteries in series) please let me know.
• The L200 regulator must be heat sinked, but how much depends on charging current and input/output voltages. The one on my picture was the only one I had with pre-drilled holes, so don’t take that as a recommendation/indication in any way :)
• Although not shown, fuses should always be used in series with the charging battery. An SLA battery is capable of some truly terrifying short-circuit currents, so there should always be a fuse to protect the circuit from damage.

Downloads:
Download design files here

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

Another Borbely clone – almost…

You may remember this post about a clone of one of Erno Borbely’s design. Now there’s another one! …but unlike the last one, which was green, this one is red! :D

It is actually a combo of amp and PSU from ebay seller jimsaudio. The amp is not really a pure Borbely design, but instead a Borbely JFET frontend mated to a (Walt Jung) diamond buffer output stage – which in itself doesn’t really matter if the sound is OK. Quite like the last one though, it is full of parts that are now pretty much impossible to find. However, 20 years of “collecting” parts can actually be helpful sometimes :D.

The power supply is also a “bastard” design – a tweaked version of Borbely’s take on the Sulzer regulator I think. However, Erno has definitely left his mark here as well – even the regulator uses some very hard to find transistors – and I can’t be the only one that winces a little at putting “unobtanium” devices like 2SK170BL/2SJ74BL JFETs in a power supply? OK, it was only one pair of each and I had an odd number anyway, but still it hurts a bit…. ( :) )

Anyway, if the results are worth it then I can live with it and initial impression is definitely that it is. The sound is smooth and detailed without any noise or hum, even from just a simple bench test. Now all that remains is the usual waiting period before I get around to making the rest of the mechanical stuff for the casing – shouldn’t be more than a year or two :D

PS: While looking around the internet I found another Borbely design for a tube/FET hybrid line stage running at just +/- 24VDC. It comes in two variations, one intended for line stage duty and the other one beefed up a little to drive headphones. The differences are small though, so it should be possible to put both variations on the same PCB. I am thinking that there could be a way to redesign this with transistors that are still available – maybe not 100% the same performance, but it would be worth a go I think :)

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.

Layout of “passthrough” board.

Layout of “combiner” board.

Panda Headphone Amp

Another half-arsed half-finished project… :D

This is a hifidiy.net HA-1 mk2 headphone amp, also known as the “Panda” amp. I bought the kit a few years ago when this amp was FOtM (“flavour of the month” – or as some would say “fad of the month” :D), but of course I don’t really need any more headamps and so it was just lying in my box of “may need at some point” unassembled kits. However, I few weeks ago I was cleaning looking through said box and found it again, and since I felt like soldering something that day I started working on it.

Unlike most “cheap” kits, this actually comes with decent components. I replaced a few components for cosmetic reasons and bought new main caps because the ones provided did look a bit worn, but other than that everything is what was provided. The amp is an all-discrete design with JFET input stage and a BJT output stage, so I had to do some matching to the input FETs, but other than that it is a straightforward build. Initial impression is that the sound is very good, but one of the reasons for the hype around this amp originally was that it is supposedly very good with AKGs and so I need to dig out my K501s and K701s to try that as well (they’re in another box..) :)

Now, I am still counting on the upcoming x-mas break to give me some time to finish some builds, but it’s unlikely that this will be one of them. When I started putting the board together I just wanted to do some soldering, but I didn’t have a case design in mind then. I still don’t to be honest, and since I’ve used 35mm tall heat sinks and capacitors the board is now too big to fit into a 1U modushop case – grr!

Maybe it is time to head to ebay for some “inspiration” instead then? :)

Amp Camp Amp

Here is another one of Nelson Pass’ brilliant designs, the “Amp Camp Amp” or ACA for short, that I managed to put together (halfway at least – as usual…).

First launched a couple of years ago, the ACA was developed by Nelson for an “amp camp”, an audio maker event and the schematic since posted as a project article on his website firstwatt.com. The ACA is a very simple and easy to build class A amplifier that produces around 5W (which goes surprisingly far in most “at-home” applications). To make the ACA more “beginner friendly” it is designed to work off a 19V switching adapter from a laptop computer. This makes it cheap to build and ensures that an inexperienced builder does not have to worry about mains wiring etc.

For this build, I have used the “official” boards from the diyaudio store. There is also a very sexy looking custom chassis for the ACA in the diyaudio store, but since they would be shipped from the US and I would be hit with well over 30% extra in VAT, import duty and brokerage fees I elected not to go that route.

Instead I found some special heat sinks from ebay to brighten up an otherwise black chassis :D The main argument for choosing these was otherwise that they are 80mm long as opposed to the more commonly available 75mm ones which would be just a tad small for the ACAs recommended mounting. The quality is decent although the colour washed off a bit while I was threading them (using lots of spirit for lubrication). The aluminium alloy is also a bit softer compared to the Fischer or Alutronic heat sinks I normally use, but that isn’t necessarily a problem.

As usual with the Pass designs, the components for the ACA are completely standard “off the shelf” types and the only part that could be difficult to obtain is the 2SK170 input JFET. There are a few alternatives though (the 2SK246, 2SK369 and LSK170 should all work if you just respect the pinout) so even that should not deter prospective builders.

The original ACA design used external switching supplies but I prefer to keep the PSU internally in the chassis, because the laptop supplies are a bit impractical. Instead, I have got a standard “industrial grade” 20V/100W SMPS from Mouser in a 3″x5″ open-frame format.

Looking forward to the Xmas holiday where I should be able to make some more progress on this one :)