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.

Delayed delay…

Was going to post something else today, but as I managed to finish something that includes software (which happens very rarely) I had to show that instead🙂

It’s a small delay-circuit, useable for amplifier muting etc. via external relays. Nothing new in that as such, but unlike many other such circuits this one is based around an Arduino-enabled ATTiny85 microcontroller. This means that in addition to basic mute-on-startup functonality there’s room for expansion as well, including connecting external sensors etc. to the board.

The (laughably) basic Arduino sketch that I have just made to do mute-on-startup and read a manual mute-switch for control is less than 1kB in size, so even with just 8kB of memory on the ATTiny there’s still quite a bit of room to add software-based features to suit any particular application.

In terms of hardware, the board includes FETs for driving the relays, a separate indicator LED attached to one if the pins on the ATTiny and also a 5V power supply. The board is wired so that the relays are driven from the raw input voltage with the FETs acting as level shifters. In the standard configuration there is two I/O-pins left for control purposes, but with a bit of hacking it’s easily possible to repurpose either the LED connection or one of the relay driver pins if required.

I have a few other ATTiny85-based projects where I have done the hardware ages ago, but now with a (modest) success under my belt I feel much more inclined to start developing software for those as well😀

Project files: ICEpower integrated amp board

What is it?
The project files for the “all-in-one” (nearly…) PCB for making integrated ICEpower amps shown in the previous post.

How big are the boards?
The board measures 2.65″ x 3.15″ (app. 67 x 80 mm.).

What is the status of the boards?
The board is version 2.1. As mentioned, it’s an old design that I have revised and updated to give it the 2.x version number. I’ve built my prototype on a v2.0 board and made some minor tweaks to that before publishing.
The changes in v2.1. are mostly mechanical (too little space for the input connectors etc.) and then minor touch-ups to the silk screen.

Does it use any special/expensive/hard-to-find parts?
No. The overall circuit is quite simple and only a few parts require a bit of attention.

  • The relays are standard mid-sized “2 form C” contact types. If you’re buying from scratch I’d recommend the Takamisawa RY-12W type, but there are app. 1 million equivalents with similar specs and footprint, so you may be able to get good surplus deals as well :). The coil voltage must be 12V.
  • The voltage regulators are standard 7812/7912 types but as they are mounted very close together I recommend the fully-insulated versions. I prefer the ones made by NJR as opposed to ST because the ST-ones seem to behave a bit strangely sometimes (and yes, I might be imagining this…).
  • See BoM-file for description of other parts and values.

Anything else I need to know?
A few things:

  • The on-board parts draw no current from the negative PSU rail. If you’re not using any external circuitry you can omit the negative rail (regulator etc.). If you build it anyway and get strange results, note that some regulators do not like a “no-load” condition and will give an weird unregulated output if not loaded. You can solder a 1-3k resistor on the bottom if you want for added peace of mind.
  • ASP/ASC-usage: It’s possible to use the board with ICEpower ASC and ASP modules. As these include a regulated +/- 12V AUX supply, you should jumper the regulators and the input resistors. The capacitors and remaining components can be left in.
  • Mute-header: The Mute-header simply brings the two pins required for the module’s mute or standby pins to work to a header at the from of the board to simplify wiring. Refer to the datasheet for the respective modules for details on how to use this, but in general you can switch using a mechanical switch.
  • Heat sinking: There is no heat sinking of the regulators as standard. With a simple preamp and no additional load this should not be necessary, but if you want to draw more power then use a small bit of metal as the heat sink. There is not much space in either direction, so using insulated regulators will once again be an advantage.
  • If you prefer a manual input switch, the board is just about ready and will be presented as part of another project post in a few weeks🙂

Download design files here

Related information:
Please read the FAQs in the original post as well. The picture below shows my “in progress” prototype amp with the Minipre and a 50ASX-module and gives an idea of the expected layout.

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



Simplifying ICEpower integrated amps…

Another old idea that I have resurrected and polished up a little🙂

Many people (and many of my readers) want to build small integrated amplifiers with ready-made amplifier modules, e.g. the ICEpower ASX-series. It’s not that difficult as-is, but what if there was a single board that could help to convert an ICEpower ASX-module into a proper integrated amp? Well, there is now😉

This module is basically made up of three parts bolted on to the same PCB.

– four single-ended inputs, switchable with relays
– a selector circuit that enables input switching with a single pushbutton (or with a rotary switch if you prefer)
– a power supply to utilise the on-board (but unregulated) AUX power supply on the ASX-modules as a power source

The only thing missing here is a pre-amp of some sort which must be a separate PCB, but can be powered from this board. The “Minipre” circuit was specifically made for this job but other circuits would certainly work as well – as long as they can run off +/-12VDC.

I made the first iteration of this board several years ago but managed to mess up the power supply arrangement so the original version didn’t really work (grr!). That I decided to get this circuit out of the drawer quite recently is no coincidence – I happened to find a single 50ASX module which I thought I had used already and so you can probably guess where this will eventually be going😉

PS: While I prepare the project files for publication, let’s take the most obvious Q&As straight away🙂

Q: Can it be used with other ICEpower modules, e.g. ASP/ASC-models?
A: Yes, but you’ll have to bypass the onboard power supply regulators etc. on the selector board as the ASP and ASC-modules have a regulated AUX-supply. Also, this board is intended for SE inputs and not balanced inputs (see below).

Q: Can the board be used as a standalone circuit or with other types of power amp modules?
A: Yes, but you’ll probably need a small unregulated dual power supply (15-18V) to power it. The current requirements will depend on which preamp-circuit you are using, but around 100-200 mA should be enough.

Q: Do I need to be able to program microcontrollers to build this?
A: No, the input switching is based on a 4017 counter IC so there is no code in this project at all.

Q: Can I use a rotary switch to select inputs?
A: Yes. Just connect the switch to the I/O header and omit the 4017 IC and its supporting components (a dedicated PCB for this is coming very soon).

Q: Can I stack two boards for balanced inputs?
A: Probably, although I haven’t tried it. Build a full “master” board and then a separate “slave” board without the PSU and selector components. Connect the I/O headers between master and slave for power/control and it should work (again, note the “should”-part…).

Good news from TI…

I’ve written a couple of times about components being discontinued, but sometimes it seems we’re in luck and things go the other way🙂

According to a recent post on diyaudio (and a TI PCN) it seems some of the TI parts I originally wrote about were being discontinued are now being reinstated. Among the 22 parts that are being restored to “active”-status are the LME49710 and the LME49720 in DIP-packages, as well as the LME49600 buffer. Note: I can’t really work out if this is temporary or permanent but even if its temporary the last delivery date is in 2017 so with luck there’ll be some more parts in the supply chain to stockpile🙂

Now I have no real illusions that TI’s decision is based on the desperate cries of audio diy’ers, but whatever the reason it’s nice to have more quality parts available😀

Project files: Universal Mini-preamp

A few weeks ago a reader was commenting on simple buffers/preamps and also asked about ebay-kits to use since I haven’t posted anything with a volume control yet. That got me searching to see what was actually out there and very quickly came the realisation – “I can do this better”😀 Not sure if I did, but I at least tried🙂

What is it?
A very simple opamp-based buffer/pre with an onboard volume control that can be used as a “buffered volume control” with a power amplifier module, a real preamp with or without gain or even a “CMoy”-style headphone amp. The board has space for a DIP-8 dual opamp, polypropylene input caps and a full-size Alps volume control and still manages to be very compact. I’m showing the board now as I already have a couple of applications for it in the pipeline myself which you will see later🙂

How big are the boards?
2″x2″ (app. 51×51 mm) – a theslowdiyer standard size (TM)😉

What is the status of the boards?
The board file is v1.0. I’ve built a prototype and everything seems to be fine.

Does it use any special/expensive/hard-to-find parts?
None, really. You can get what you need from Mouser/Reichelt and similar places and most of the component values aren’t that critical anyway.

Anything else I need to know?

  • The opamp should be a dual-type with standard pinout. My recommendations would be either the LME49720 (sadly discontinued in DIP) or the OPA2107 (still available but fairly expensive), but there are loads of other options. The board layout should be suitable for using adapters as well (for DIP/SO-8 singles or SO-8 duals) and if you want to go all-out there’s even a discrete option from Burson that should fit as well.
  • The only surface mount components are the optional (but recommended) 1206 bandwidth-limiting caps on the bottom – otherwise it’s through-hole all the way.
  • The PCB should be happy with just about any (regulated) dual power source – linear PSU, switching PSU or even a pair of 9V batteries.

Download design files here

Related information:
Even though this is a basic opamp circuit and I can just about draw the schematic and recite the parts values from memory, I went back to look at it once more to try and read up on the theory behind. If you aren’t very familiar with the basic schematic already I can absolutely recommend the old but still excellent articles from Headwize/Head-fi member Tangent here and here. Tangent’s pages also have a ton of other useful information and although the site isn’t updated any more (and it’s quite old) there’s still plenty of good stuff even for inexperienced diy’ers.

If you are more technically inclined then probably the best resource is the “Opamp Applications Handbook” from Analog Devices and edited by Walt Jung.

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


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