Trial and errors….

Like most blogs, social media showcases etc. this page is to some extent a massive display of selection bias – you only see the stuff that works, and only when it works. You never (or at least rarely) see the things that don’t work. Because of that, I just thought it would be funny to at least give you a few examples of the memorable mistakes I’ve made during the life time of this blog – along with the lessons I’ve (hopefully) learned from them.

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Experimenting with ESPs… (part 1)

…ESP8266’s that is (if you hadn’t guessed that 🙂 ).

Although I am not directly involved with it, I have several colleagues at work that are looking at Industrial IoT applications for various use-cases. Quite a few of them have built personal home-automation systems of one sort or another, and as I would actually like to do a ittle bit of monitoring/control around my house as well I started looking at options a while back.

My old Ampduino project was of course a big inspiration, but the Arduino lacks onboard wifi which is a big drawback, even for “IoT” at home, and so the ESP8266 was a very logical step up. The original plan was to build from scratch using “raw” ESP-12 modules, but after a bit more research I stumbled upon the Wemos D1 mini. I then decided to go back to the original “Ampduino” approach of building a baseboard for a ready-made module instead. This gives a good amount of flexibility while at the same time ensuring that USB, programming and all other standard functions work as they should.

For once, I decided that I was going to get started on the software-part of this immediately (that’s usually my weak spot) and since I have had to wait three weeks for the fist PCBs to arrive I’ve made very good progress. Two things helped me along though: Firstly that I found a basic sketch at RNT that did a rudimentary version of exactly what I wanted, namely control via a web-UI. Secondly, I had a standard NodeMCU-board which I could pop in a protoboard immediately. That made it feasible to start getting individual pieces of the code together as soon as the PCB-order was submitted and then subsequently assembling the pieces of code into the “real” thing later on. My prototyping efforts while the v1.0 boards were in the mail also gave me input to v1.1 boards, so I can actually start placing those orders in a couple of weeks (no point doing it now because all the PCB factories are closed for Chinese New Year).

As usual for this type of project I’ve ended up making several versions of the board. The “original” version is USB- or DC-powered and has an onboard relay and an onboard DHT22 temperature/humidity sensor in addition to a couple of spare in/outs (analog/digital). The smaller version shown here ditches the onboard relay and instead breaks out a full set of SPI-pins. This allows connecting an SD-card adapter so that data from either the onboard DHT22 sensor or any of the other inputs is saved to a local card as well as being displayed on a web interface and a local LCD/OLED display (via I2C).

The original plan was to do a mains-powered version but I couldn’t get a good design together at the time and so I went DC-powered instead. However, I think I’ve cracked it now so the next run is going to include a mains-powered version as well. Other changes for v1.1 will be some routing improvements and (most likely) doing away with the onboard DHT22-sensor and replacing it with the option of one or more offboard sensors based on the BME280 and/or the DS18B20 sensors.

Board sizes are from app. 50-75mm squared, so these are quite compact and versatile. More updates and also some code samples later on 🙂

Power-delay timer for 5/12V triggers

This small design is actually a solution to a problem I have, but as it’s also one I’ve seen others describe from time to time I still find it worth sharing.

My current preamp is discrete and has a 15-second delay before the output is turned on (to allow it to stabilise).  This means that the poweramps I use will turn on before the preamp and consequently I get a bit of a turn-on thump in the speakers when the preamp turns on. There is a 12V trigger output on the preamp, but even if there was a trigger input on the poweramps as well (and there isn’t) the 12V trigger is active immediately and so that doesn’t really help.

Of course you can solve this manually by waiting for the preamp to switch on fully, but 15 seconds feels like a long time when you’re just waiting and so I decided to do something to address this terrible hardship… 😉

The easiest way to fix it – introduce a longer delay before turning on the power amps – only required a modification of my previous delay circuit to power a bigger relay, so that’s what I did. The relay I’ve chosen is an Omron G5LE which is rated app. 5A with a reactive load, so that should be fine for most amps in the power range that I normally use. Not all manufacturers publish the specs of their 12V triggers, but those that do generally state a max. current capability of 100-150mA. As a single 12V board draws app. 45mA with the relay engaged powering one board should be fine and even adding a second should be trouble-free as well.

When I made the board I only really could see the point of a 12V version, but afterwards I realized that a 5V version would be able to work with USB-power and that might be worthwhile as well. On 5V the current consumption should be just under 100mA, which pretty much any (non-portable) USB source should be able to provide.

I’ve tested the circuit and it works as expected, so apart from still being on the lookout for suitable case it’s more or less “mission accomplished” for this one 🙂

Desktop DAC with a cheap ES9038-board…

Last year I mentioned that I had bought a cheap ES9038 DAC-board and now that’s starting to come together. This will be used as a controller to feed a pair of active monitors on my desk (that’s the “need” I mentioned in the original post) where it will save me a box as I currently have a separate USB DAC and passive pre). To make the box a bit more versatile (and to use some of that empty space inside…) I am thinking about including a Raspberry Pi Zero W in the box and connecting it to the I2S-input of the DAC plus add a potentiometer for volume control (digital on the DAC via an onboard uC). The ES9038Q2M DAC is asynchronous with its own clock so perfect for use with the RPi and this combination would give a Volumio-based source with two additional digital inputs and a volume control. That means that can be connected directly to a power amplifier input or active speakers – perfect for the desktop or a second system!.

The slightly unusual power arrangement with 5V input to a DC-DC converter is to support this setup. It will allow the RPi to be powered on constantly while the DAC power can then be switched on and off. I bought an early (”first generation”) of the ES9038 board with a slightly different power setup than the current version and crucially no DC input connector that I did not need (of course the newer versions of the DAC board can be used as well). Check the diyaudio-thread for the board for loads more examples of how people have been hacking this by the way – some of them are close to unrecognisable.

The original idea was basically to allow the power source to be a cheap 2A USB-charger, but reality seems to have thrown a spanner in the works here – none of the chargers I have tried will actually let the DC-converter start properly because of the high inrush-current it draws. Using a slightly more beefy 5V supply fixes the problem though, so the concept is more or less intact anyway 😀

Part of what drew me to this DAC-board originally were the on-board connectors, but as I couldn’t find any mechanical drawings having to make the back panel by hand seemed a bit of a risk. Using my own measurements and the datasheets of the connectors I managed to trace it out and with judicious use of paper printouts from Frontpanel Express to check the dimensions against the physical board it actually fits well for a first time attempts – although this is definitely an occasion where I would wish for a 3D-printer or a laser cutter to make prototypes before betting my money on ordering “the real thing” from Schaeffer/FPX (they are becoming quite expensive I think).

Soundwise this seems quite close to the other ESS-based DACs that I have tried. I am not sure that is such a good thing to be honest, but I am prepared to compromise a little bit on my desk where convenience is important and the differences aren’t night and day anyway 🙂

Happy New Year!

My New Year’s travels are a recent, but by now well-established tradition. This year I am a little closer to home than last year, which is to say in London. It’s one of my favourite cities to visit – much to the surprise of many of the locals I have to say – but there’s tons of stuff to see and do and I really like the vibe of the place (again, to the surprise of many 😉 ).

I’m here for another couple of days and I have absolutely nothing audio-related planned but that is on purpose. That said, I am of course keeping an eye on the local sales ads just in case there is something on sale that I did not know I needed, but that’s about it 😀

Best wishes for a happy new year to all my readers and I hope to be able to bring you more interesting posts in 2019 🙂

A gem for Christmas…

The other of Richard Murdeys “gem” designs (the first one was here) that I have worked on is the Sapphire headphone/line amplifier. Now in version 4, I’ve looked at it before but I didn’t have a compelling reason to start building anything. However, when Richard “upgraded” it to version 4 before the summer it caught my eye again (through here) and so I finally decided to start my own version. This was a while ago now, but due to some problems with my board orders (the first one didn’t show up at all and the second one just took nearly two months to arrive…) it’s been a lot longer than I expected.

The Sapphire is a current feedback design which can be built to drive low- or high-impedance loads, meaning it can be used as both a line preamplifier and a headphone amplifier. It’s fully-discrete circuit but uses standard parts that are easy to find and it’s actually a fairly simple build. Once again, for “my” version I set out from the published Eagle-files (v4.1) with a view to make minor changes but just like the Emerald it didn’t really hold. My board is smaller than the original and some of the routing is different because I used a “splayed-pin” footprint for all the transistors (I try to buy all my TO92s on tape, so the inline pins footprint makes everything much easier).

The only real changes I’ve made to the electrical design is the addition of a couple of indicator LEDs to show that the board is powered on. I find this quite useful for troubleshooting, it looks nice and there was space on the board for them 🙂 While I’ve been faffing around with PCB orders from China, Richard has made small tweaks and released v4.2, but that’s of course fine – if you want guaranteed boards with support etc. you should be buying his anyway 🙂

My prototypes are one of the “high-bias” configurations because I mainly have low-impedance headphones. That’s probably fine, but the small heatsinks get seriously hot (app. 65 degrees C) and the offset is also higher than I would have liked. However, I think that’s more to do with my iffy transistor-matching that any serious issues with the board layout itself. I’ll probably give it one more go in January and see if I can get the amp to behave as I want them to and then post the board files in case anyone wants to do more tweaking 🙂

An early Christmas present…

I generally make a point of buying myself a Christmas present every year and this year it came a little early 🙂 While I was looking for the Hypex Ncore module I wrote about a couple of weeks ago, a stereo ICEpower700AS2 popped up as well – so I bought that 🙂 This is going to be a “little brother” to my 700ASC-monoblocks but whereas the monoblocks (which I also hope to finish over this Xmas break) have added buffers and dual-input switching, this is just going to be made into a simple and no-frills power amp.

In contrast to the Ncore module the ICEpower amp has onboard heatsinks so mounting in a small(ish) enclosure should be fine – at least for home duties. As I already had a basic layout for both a bottom plate and a back panel, drawing them up was quite easy and the back panel order is already placed. The support PCB I did for the monos also works here which should mean that once I receive the back panel there should hopefully be very few blockers to wiring up the amp and getting it tested within the next weeks.

I have seen one comparison of the Ncore and the ICEpower module (although I can’t find the link at the moment) with the Ncore coming away as the clear winner, but I am looking forward to seeing if my own conclusions match that 🙂

(apologies for the poorly lit pictures, but winter in Scandinavia means no daylight when I get home from work :D)

Testing the F3 amplifier…

Earlier this year Nelson Pass graciously started distributing batches of the Lovoltech LU1014 Power-JFETs for free to diy’ers. You could get 4 pcs. and only pay for shipping and of course that offer was hard to turn down – all the more so since I had been looking at trying an F3 amplifier at some point. There are no “official” group buy boards for the F3 at the moment and the few redesign/group-buy initiatives I have seen have been false starts, so I picked up a set of amplifier boards from ebay instead.

The F3 amplifier is one of Nelson’s “unusual” First Watt amplifiers, in that it uses a Power JFET as the gain device. Power JFETs are rare, and as a result for those of us who were a bit slow on the uptake the LU1014 came and went without me buying any. Otherwise the F3 isn’t a very complicated design, but it’s got normal First Watt class A heat levels and even-lesss-than-First Watt levels of output and gain. As a result i am not sure whether I actually have any practical use for the finished amplifier, but as a listening experiment I am still going to give it a try 🙂

The F3 is also a single-rail amplifier, which quickly led me to the realisation that I didn’t really have a PSU board suitable for a single-rail power amp. When you have a good “back catalogue” of designs then that’s quite helpful and so taking one of my existing class A power supply boards and chopping it up to create a single-rail version wasn’t that hard. The end result should hopefully – at some point – end up as a (nearly) dual-mono F3 amplifier (meaning a single transformer is used).

Another complication is that for reasons I can’t really remember I decided to try using 3U heatsinks for this build which may end up being a mistake – they are going to get very hot I guess. Anyway, for now it is an experiment and hopefully I will have it (electrically) completed by the Christmas break so I can hear what it sounds like before I put time and money into finishing the mechanical design 🙂

Encore?

A quiet last few weeks here – at least on the surface. Two reasons for that really: 1) With an Xmas-break looming on the horizon the pace at work is picking up a bit and 2) for quite a lot of projects I am in the annoying phase where lots of important work is done, but it doesn’t really look like you are getting closer to a finished product and so it’s not really worth showing here. If nothing else though, it’s nice to have a good pipeline for next year 😉

However, one thing there is always time for is to buy new projects for the shelves 😀 As regular readers will know I have made lots of ICEpower-based projects, but practically nothing with the various Hypex-modules. However, recently one of the new Ncore NC502MP modules came up on ebay and so I pounced on that. The module looks very nice but I need to test it for a while to check the sound (waiting for proper cables at the moment) and then I’ll decide on a suitable enclosure for it. The original goal was to built a custom high-power integrated amp, but I may end up going in a different direction and do a pure power amp instead. One deciding factor will definitely be whether mounting the module on a simple aluminium bottom plate proves to be enough heat sinking, because if the module has to be on a “real” heat sink, then all my current enclosure ideas are definitely out the window!

Soundwise, I still expect that the benchmark for the Ncore to beat (at least in class D) is going to be my trusty 125ASX-based stereo amp and the 700ASC-monos (which incidentally are also among the designs that are I am currently inching closer to completion…)

Project files: The “MoFo” power follower

I did this version of the “MoFo”-design a while ago and also mentioned it briefly (here) but didn’t manage to complete it or even test the boards. In the mean time the “official” boards have become available from the diyaudio store, but since I now finally got round to testing my boards I still thought I’d share my version as well.

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