New AKGs are in…

It’s been a while since I last added to my already sizeable (and frankly unnecessary) collection of headphones, but now was the time.

Although new models come on the market regularly, the one “top of the line” model that I really wanted to get was the AKG K812. Up until a few months ago they have been very expensive and were only sold at RRP, but as they have started appearing at discounted prices I’ve renewed my interest. Although I’ve been eyeing them for a while now, it wasn’t until last week the stars finally aligned (or at least the combination of bank balance and foreign exchange rates🙂 ) and I could finally press the “buy” button.

When it came on the market some of the first reviews of the K812 mentioned harsh treble, but on the few occasions I’ve demoed them it didn’t sound particularly harsh to me. To be on the safe side I’ve bought one of the later-model “Made in Slovakia” ones, mainly on an assumption that any treble issues might have been teething problems in the first production runs of the original “Made in Austria” series.

I’m quite a big fan of the AKG house sound – and I have been since I first bought the K501 model when it was “flavour of the month” on head-fi a little over 15 years ago (yes, time flies…). I also own the K701, K550, K495NC and a few others and just as I expected my initial impressions of the K812 are that they are “more of the same” but better. As is the case with most other large AKG models (at least for me) the K812s are very, very comfortable once properly adjusted and I think I can wear them for a long time before they start being uncomfotable. For someone who wears glasses, this is definitely not a given when you buy a high-end headphone.

Obviously this purchase impacts the audio-related budget for my next big trip (in a couple of weeks) a little bit, but that’s ok – I’m sure it’ll be worth it once I get to spend a bit more time with these new AKGs😀


More ATtiny experiments…

Since I managed to breathe life into my ATtiny-based speaker delay project I’ve been working on more ATtiny-based boards. There are many potential applications I can see (if I look hard enough…) for a small SW-based controller and that is what I’ve tried to build. The hardware was done a while ago, but the software was lagging (and still is somewhat).

I also received my TinyLoadr programmer a few weeks ago and it was definitely worth the wait. I’ve mounted the board to a piece of aluminium to keep it stable and now its more or less a perfect tool – very highly recommended if you want to play with ATtinys!!

To speed up my development cycle I’ve build a prototyping setup with a ZIF-socket and a solderless breadboard. I’m not a fan of solderless breadboards in general, but they do have their occasional uses and this would be one of them. I bought a few small ZIF-sockets from ebay and together with the tinyloadr programmer they make up an excellent prototyping platform. Swapping ICs from one ZIF to the other is still a bit of an annoyance, but it’s far more flexible than the alternative🙂

If you need more memory space (or more I/O-pins) than the ATTinys can provide then I am also working on an update of my AmpDuino-concept. This will be a fully-fledged controller based on a stand-alone ATmega-chip that can do the same as the old version AmpDuino, but in a more optimised way. Connections etc. will be laid out for what I consider to be typical audio applications. ETA is, as always when there is software involved, unknown😀

VFET progress…

Well, not that much progress on the Pass VFET boards themselves – hopefully this weekend something will happen – but I have managed to make a PSU-board for them. Plenty of those around already of course, but being a) particular about dimensions and b) a bit particular about PCB colour matching I decided to roll my own instead🙂

The design is a pi-filtered CC-R-C type with space for 35mm electrolytics, which at the VFET-voltage are available up to 27-33mF. As I plan to use the boards in mono-mode (one per channel) that’s actually enough energy storage to be a bit frightening. The Pi-resistors can dissipate up to 12W per channel which should be plenty (at least I don’t plan to go that high).

Also included are a polyester decoupling cap, a bleeder resistor for the two first electrolytics and a pair of LEDs which, apart from indicating power, also bleeds the last pair of caps.

As the pictures show, I’m still missing some parts but this project was never going to be a rush-job anyway so that’s just fine. The days in Scandinavia are getting noticeably shorter now, so saving projects for winter will not be a problem :-)

Project files: THAT1646 in stereo…

What is it?
A stereo version of my THAT1646 balanced converter/preamp shown here. I wanted to build a small controller/pre for some active monitors and while the stacked mono boards were probably a good idea in princple, I decided to resurrect the stereo layout instead🙂

How big are the boards?
The board measure 2.7″ x 1.9″ (app. 69 x 48 mm.).

What is the status of the boards?
There are two board versions which differ only slightly. One is 100% through-hole and basically a stereo version of the mono-board shown earlier. The other has the R4 gain resistor replaced with a 1206 SMD type and mounted on the top of the board (under the IC socket). This means the feedback loop area is much smaller and the routing is a bit neater. Both boards are otherwise the same size and electrically identical. If you want to change the gain after building the through-hole version is probably easier to work with, but otherwise the SMD-version should be the best design. Both boards are labelled as version 1.0 although I’ve only prototyped the SMD-version in stereo.

Does it use any special/expensive/hard-to-find parts?
As usual, not much. Maybe the THAT IC itself. Mouser has it though, so that should work for most people I guess.

Anything else I need to know?
A few things:

  • Gain: You can tweak the gain of the circuit as you wish using the resistors for the pampas, but remember that the THAT1646 should add 6dB gain on its own when you go from SE to BAL.
  • Opamp selection: You should be able to use pretty much any single opamp here. if you don’t have a favourite already I’d once again recommend that you start with either the OPA134 or the LME49710 and then experiment from there.
  • SMD resistor: If you are using the board version with the SMD gain resistor, remember to solder R4 on the board before you fit the IC sockets (otherwise some swearing may ensue when you discover it… :D)
  • BW limiting capacitors: There is no space on the board for BW-limiting capacitors for the opamp. Not sure why really, but with the opamp only driving a very short trace with a fixed load at the end (the THAT1646) I felt quite sure most opamps will behave. If not, soldering some small ceramics on the bottom of the board should be easy🙂

Download design files here

Related information:
As usual, RTFD! (= read the f’ing datasheets :D)

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

Project files: ATtiny-based power delay

As the PCBs for my next ATtiny-based designs have landed over the weekend and I am back from my holidays, now seems to be an appropriate time to post this🙂

What is it?
It’s my ATtiny85-based power delay controller which can be used for speaker protection etc. as described here. In addition to the controller board itself are also a couple of relay boards to do the actual signal switching. One board is stereo and based on 10A relays, the other is mono and based on a 30A relay.

The controller board includes an on-board 5V regulator, an LED coupled directly to the ATtiny to indicate when the relay is engaged (or another purpose) and two FET-switched outputs. The last two ATtiny I/O pins can be used to trigger the chip with buttons, sensors etc. which gives tremendous versatility.

How big are the boards?
All three boards are my “industry-standard” 2”x2” (app. 51 x 51 mm.) in size, meaning they can be stacked on top of each other if needed.

What is the status of the boards?
All three boards are version 1.0 and the prototype boards looked and worked as expected.

Does it use any special/expensive/hard-to-find parts?
Nothing serious this time either🙂

  • The small heat sink for the regulator is a Fischer type SK95 with an M3 hole in the bottom, but if you’re having trouble finding this there should be plenty of other small heat sinks that will fit. In any case, the heat sink isn’t always required, it depends on your input voltage and current draw from the 5V line.
  • The relays are standard types, either Omron G5LE (small board) or Omron G8P (large board). I’ve quoted Omron part numbers to give you something to go on, but there should be plenty of identical replacements from other manufacturers available.

Anything else I need to know?

  • The intention is that the ATtiny chip should be programmed using the Arduino IDE. That means you need to have either a dedicated programming shield for ATtinys or wire up the chip to an Arduino board that is used as an ISP. You also need to have the ATtiny cores installed in your Arduino IDE (see explanation here) and you have to burn the Arduino bootloader onto the ATtiny yourself before filling it with the actual program.
  • For programming, I highly recommend something with a ZIF-socket because it will make the whole thing much easier. I’ve got one of these on order (which recently came back in stock) because that looks brilliant, but there are shields on ebay that can be used as well. I’ve been working with this one so far and it works well, but of course you need a dedicated Arduino board to run it.
  • As you can see from the schematic, the intention is that the controller board is fed from a higher voltage (9-24V) than the ATTiny requires, in order to be able to use relays that draw less current. The onboard regulator will provide the 5V that the ATtiny requires.  If you are using the big mono relay boards, be aware that the worst-case power draw for these is around 1.2W each. This means that if you are using a pair of 9-12V relays here you’ll need to be sure that your power supply can handle that.
  • The second output is intended as just that – a secondary switch – but since it’s connected to one of the ATtiny pins that provide a PWM-output, you could probably do something clever and use this for controlling a variable-speed fan fed from the same voltage as the relays. If anyone does that I would love to steal, ehm…. borrow your code😀
  • Although the relay boards have on-board protection diodes across the coils, there is also space for optional SMD diodes on the bottom of the controller PCB. Use these if you’re driving off-board relays etc.
  • There is a sample sketch included in the download file, but please don’t laugh (too loudly) at my pitiful attempts to code – it’s just an example🙂

Download design files here

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

Most of the complexity here is around the coding. There are tons of links available around the web for how to use ATtinys with Arduino, so I’ll not list them here. Start from the link to the official Arduino page and then do your own search from there.

Pass V-FET kits are here!

Forgot to post this a week ago when they arrived, but I managed to secure a couple of the Nelson Pass V-FET kits which I am quite excited about.

In short, this is a low-power class A amplifier based on some complementary Sony V-FET (SIT) transistors that have been out of production more or less since before I was born. The actual devices were bought as NOS (new old stock) by Nelson Pass himself and offered to the diyaudio community through the diyaudio store as a (more or less) one-off opportunity. I was lucky enough to register my interest early on and so managed to secure a couple of kits to keep me busy on those long Scandinavian winter nights when they come around😀

There’s a big discussion thread on diyaudio and also an article on the FirstWatt website about the design, in addition to the information in Nelsons previous articles on SITs (also on the FW website). As usual, I don’t really need these and the class A heat is a bit impractical in a small apartment, but a limited-edition amplifier kit with unobtanium transistors that was developed by Nelson Pass himself was an opportunity I simply could not pass up (pardon the stupid pun🙂 ).

The Firstwatt F5 is still one of the best amplifiers I’ve heard in my system so I have very high expectations for this new design. The lower power of the VFET could be an issue, but I’ll have to build it and try I guess – with my current speakers it should be OK and if not, I can always get a pair of very inefficient planar magnetic headphones instead😀.


The plot thickens….

Bit of a pause here lately as I’ve been away on holiday. I just have a few days left at home before work starts again, so time to get some building in🙂

Some progress on my “mystery” project – hence the post title – with most of the mechanics now ready. And no, I’m still not revealing what it is yet😀

More ATtiny-powered stuff in the pipeline as well, but unfortunately the weather is too good to be sitting inside doing SW, so that will have to wait a bit longer (maybe😉 ).


Tripath TK2050 monos…

Well, it’s been a while since I posted a project that was actually finished…. and this one isn’t either😀

It’s a pair of monoblock amplifiers based on Arjen Helder’s Tripath TK2050-boards. Arjen Helder is/was a Dutch guy living in China who around 5 years ago sold some great DIY boards based on the Tripath class D ICs. He’s probably mostly known in the DIY-community for the low-power TA2020-based amps, but he did make a few designs based on the more powerful TK2050 chipset as well. I bought a couple of the TA2020 boards when they were available because they were cheap and sounded great, but I managed to stay away from the TK2050 boards back then because I did not have anything to use them for (come to think of it, I don’t now either…🙂 ).

Unfortunately I am nearly powerless to resist the temptation of an ebay-bargain so I snapped up this pair that I stumbled upon a couple of months ago without much hesitation. Originally, the plan was to mod the boards a bit replacing the stock capacitors, in/out connections etc. However, some of the traces seem to be very thin and as it isn’t possible to get a replacement board if I damage something I limited myself to just replacing the input caps.

The power supplies are a couple of Mean Well EPP-150s which were “left over” from my JLH-Evo build. They should be more or less spot-on for this when used in dual-mono mode and the small 4” x 2” size is an advantage as well.

The mechanics consist of pair of Chinese-made enclosures (selected because they were the right size for the job…) with custom rear-panels. I was going to use the stock rear panels, but a couple of stupid measurement-errors that I did not notice until after drilling made that a lost cause😉

What’s missing is only really a few cables, but that isn’t my favourite part of a build and so I might save it for a long dark winter’s night instead😉

Project files: Universal selectors (part 2)

This is the second part of my ”universal selector” series (the first one is here). This post includes the control boards designed to match the selector boards from the first post.

What is it?
Control boards for the relay-based selectors. The download file consists of three designs:

  • A “push-button” input selector based on the 4017 counter IC. This is more or less the same circuit as the selector-part of the ICE-int PCB.
  • A PCB for a rotary-switch based selector.
  • A simple PCB for a 4-LED input indicator that can be used with the above boards.

The last two boards are also suitable as “companions” for the ICE-int board.

How big are the boards?
The board sizes are as follows:

  • The 4017 button switch board measures 1.35″ x 1.35″ (app. 34 x 34 mm.)
  • The rotary switch board measures 2.0″ x 1.25″ (app. 51 x 32 mm.)
  • The LED indicator board measures 0.6″ x 1.3″ (app. 15 x 33 mm.)

What is the status of the boards?
The switch PCBs are both v1.5 because they are existing designs that I have revised to match the standard pinout for the selector boards. The LED PCB is v1.0 because I only realised I needed it after putting everything else together😉

Does it use any special/expensive/hard-to-find parts?
Nothing that’s worthy of any real concern: The rotary switch is a standard 3pole/4position rotary switch which is made by many different manufacturers (Lorlin, C&K etc.). I’ve tried a few and some seem to fit the PCB a little better than others but with a bit of lead-bending they should all work.

Anything else I need to know?
Some quick notes:

  • The connections between the boards carry power as well so under normal circumstances these boards do not need their own PSU (power is applied via the relay board).
  • 4017 PCB: This is basically the control circuit from the ICE-int PCB, separated from its companions and “spiced up” a bit. The selection is performed by operating the 4017 as a counter, triggered via a debounced mechanical switch. The “spice” consists mostly of a second control input via a PC817 optocoupler which can be connected to a microcontroller port if that suits the application better than a manual switch. The optocoupler then acts as a level shifter making it independent of the relay voltage.
    Most versions of the 4017 will run on power from app. 3V-18V, so as long as relay voltages are within that range it should be fine. For 24V relays, there is a resistor on the board that can be used to drop the supply voltage to within a safe range for the 4017. For 48V relays this solution isn’t really practical and the rotary switch selector should be used instead.
  • Switch board: The switch PCB uses two of the three decks of the switch. One side can be powered externally so it is e.g. possible to use 24V/48V relays and then a separate supply for the LED board which prevents having to drop a lot of power in the LED resistors. If you want to connect the two sides and use a single supply from the relay board, use the jumpers marked JG (for GND) and JV (for V+).
  • LED-board: The “normal” board has separate resistors for each LED so you can use different LED colours if needed. A simpler version with just one resistor is also included. The two boards are mechanically identical and made so they can be mounted vertically on a 1U enclosure front panel. The LEDs are spaced 0.35″ (9mm) apart and the mounting holes are 1″ (25.4 mm.) apart. The offset between the center lines of the LEDs and the center line for the mounting holes is 0.275″ (7mm.).

Download design files here

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

Project files: Universal selectors (part 1)

This is the first in a series of posts for relay-based input (or output) selector boards made to be as universal as I could reasonably make them. This is part one, the selector boards themselves. Part 2 (which is coming shortly) includes the matching control boards (button-based and rotary switch) and an LED indicator board. There might eventually be a part 3 (and 4) as well to cover some additional variants and accessories.

What is it?
A relay-based selector boards with four single-ended inputs (or outputs). There are four board sizes, distinguished mainly (well, only…) by the spacing between the relays and input connectors:

  • Size S: Input spacing 0.5” (12.7 mm). This is the minimum size I could reasonably make the board. The spacing is smaller than typical RCAs, but would be suitable if you are using different connectors e.g. mini-jacks or if you need to keep the selector board separated and run longer wires to the inputs. This is the same basic size as the ICE-int board.
  • Size M: Input spacing 0.75″ (19mm). This is the spacing of many integrated and/or low-cost RCA sockets.
  • Size L: Input spacing 0.95″ (24.1 mm). This is the standard size board size which gives a bit more space between connectors and thus allows using better-quality “premium” RCA sockets. It is also the biggest board that can be made to fit inside a 5×10 cm limit as imposed by many board manufacturers.
  • Size XL: Input spacing 1.1″ (28mm). This is the standard spacing for Neutrik D-series RCAs/XLRs and so the one that is best suited if you want to stack two selector boards for balanced inputs.

Note: There is no functional difference between these boards. The only reason for using a specific version would be to make the wiring between the board and the connectors as neat as possible.

All boards share the following features:

  • Standard “2-form-C” relays are used (Takamisawa RY-xxW series, Omron G5V-2 series or similar). Depending on how the boards are controlled, relay voltages between 3 and 48VDC are possible.
  • Universal in/out connectors.
  • Power connectors at both ends of the board.
  • Stackable for balanced configurations (or if you need more than 4 inputs)
  • Space for optional termination resistors on the bottom of the board (1206 SMD footprint), so that unused sources see a finite load instead of an open connection.

How big are the boards?
The board sizes are as follows:

  • Size S: 2.6” x 2.0” (app. 66 x 51 mm.)
  • Size M: 3.35” x 2.0” (app. 85 x 51 mm.)
  • Size L: 3.95” x 2.0” (app. 100 x 51 mm.)
  • Size XL: 4.4” x 2.0” (app. 112 x 51 mm.)

What is the status of the boards?
All the boards are labelled v2.5. I originally made a layout much like this back around 2006-2007 which I used as a starting point. Version 2.0 was the first attempt at cleaning up these and introducing more versions. Version 2.5 is because I’ve more recently cleaned up the silkscreen and standardised the control connector pinning to match the switch boards.
These boards were developed separately but should now be completely aligned and integrate without issues. I’ve prototyped v2.0 of all of them except the XL version where I have made the v2.5-version (as shown).

Does it use any special/expensive/hard-to-find parts?
None. The relays can be Takamisawa RY-xxWs or any one of the many similar parts. You should be able to buy these from ebay and any other source.

Anything else I need to know?
Some quick FAQs with answers:

  • Q: Can I use the boards to switch outputs instead of inputs?
    A: Yes, however in order to have more than one relay active at a time you will have to do the switching in a different way than what I have done.
  • Q: Can I use the boards to switch headphones?
    A: Probably. I haven’t tried it, but I expect it would work. Same caveat as above on multiple outputs though.
  • Q: Can I use the boards to switch digital/coax sources?
    A: Well, it’s definitely not designed for that purpose but better dacs might be able to survive the signal degradation. By all means try it, but no guarantees🙂
  • Q: When do I need to use the termination resistors?
    A: Not sure actually. Some sources are reportedly not happy with a no-load condition and in the spirit of versatility I decided to cater for that eventuality as well. If you do fit the resistors they will also serve as a discharge path for any source that has a capacitor-coupled output which might help. Values between 10k and 100k should be fine here.

Download design files here

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