Old hobbies die hard. It’s been several years since I’ve actually done any audio related projects at home and have been quite happy with my living room listening setup. Somehow – I think mainly thanks belong to my ex-colleague who was constantly building some amps or speakers – I’ve found the spark again in audio reproduction and things related. Perhaps more on this side of home improvement later…
I recently ended up buying a new set of headphones, as my awful, old and (t)rusty Philips headset from 90’s was finally giving up and my wireless AKG set is way too noisy to really enjoy music with. I haven’t ever had anything that could be considered as a high-end headphones but now I do. I was already aiming for roughly 100 euros price range, but after trying out various models at local store, I ended up with Sennheiser HD-598. Both for how the set sounded and how it was built. Feels and looks like something that is meant to last for years to come. After listening through few records at home I also found out that none of my listening equipment had decent enough headphone output, so I had to build an amp to drive these.
So to the amplifier section. First and simplest choice is single-ended Class-A MOSFET design. These are all over the internet for many decades now, so nothing new invented with this wheel but I’ll share it anyway. For something that is constructed from handful of surplus parts in hand without too much effort for the design, result sounds very good. It has flaws (or points for improvement!) but I very much like the simplicity of this thing. Judged by listening, it is much better than what my amp or CD player has (not to even mention my computer audio card phones output.)
For the design, I had planar FQD1N80 MOSFETs laying around, so this was obvious choice. It’s a planar construction, so it’s well suited for linear operation mode. It has quite high on resistance so it seemed like a perfect and very balanced match for single-ended headphone amplification. For sake of simplicity and low part count (and perhaps lower overall noise!), this incarnation uses resistor instead of current sink.
Tested this through with signal generator and oscilloscope, everything seemed fine from 10Hz – 100kHz sweep. Not too much added harmonics, waveshapes were symmetrical and seemed to match the input amplitude for whole frequency range. Channel amplitudes were even with each other level-wise over whole frequency range without any additional fine-tuning.
Quickly drafted schematic of one channel and AC analysis result in LTSPice. FET model isn’t same as I couldn’t find any close(r) matches from the library. Despite the model, results agree with the quick measurements I made.
Obviously it can be improved in many areas, but this shall serve now as a reference to which I can compare when I try something different. Also a thing to note is that simulation is run into a nice resistive load so real situation is a bit more complicated and even more complicated when extended into SPL’s from those non-ideal headphones. But that’s a different story, Mr. Linkwitz has made some nice notes on modeling speakers. When I have time, I’ll try to craft a spice model of these headphones to play around.
To feed the amp, I’ve also acquired couple of DAC boards based on Asahi Kasei AK4393 chip. First complete amp setup was paired with 24bit/96kHz USB audio card for hassle-free digital out from any PC, AK4393 DAC board and this single-ended amp design. I really do enjoy how it sounds – It’s super silent noise wise and is more than capable of driving my headphones (SPL levels upto painful). Amount of new detail from my records with this setup is overwhelming. So improvement (or change atleast 🙂 is well noticeable.
What I’ve read from various sources, these DACs by Asahi Kasei should be superb for the price. I myself don’t yet have anything else on the matter other than initial listening impressions, but based on that, it’s very well worth the price! But look here for some serious stuff on the AK4393 DAC – Lampizator and Behringer Ultramatch. The site has also plenty of other interesting reading if you’re into Audio and things related, so take a look.
To continue this project, my next target is to build couple of different kind of headphone amp designs (perhaps one push-pull discrete and some nice tube amp design) to test those side by side and perhaps find some differences in how they sound and decide my favorite. One of the DAC boards will also get all unnecessary stuff removed from signal path, so that is also interesting to hear if changes are audible and can it be considered improvement or not.
Aihearkisto: Electronics
Electronics circuits, design ideas, other interesting stuff
How about a coilgun?
Project idea(s) for this year. I’ve been fiddling lately a lot with electromagnetism and solenoid structures at work – but how to do something more entertaining with electromagnetism? One of the first things I can think of would be by shooting projectiles. Of course, there’s nothing new in creating a coilgun – besides the fact that I’ve never built one myself. But what I’m actually interested about in this, is to make it more efficient and not to waste any unnecessary energy to heat. Typical approach seems to be single stage coilgun where awful energy storage is converted to heat with every shooted projectile. That’s just silly.
My first approach to this topic would be multi-stage coilgun with ”energy recovery”, so energy stored to magnetic field of coil will be stored and used again in further stages. At least couple of easy ways to do this come to mind at this instant, either charge the energy straight to a capacitor through the coil (and so on…) or use the coil-stage as boost generator for next phase.
So basically increasing efficiency would mean couple of things, coils cannot be very ”thick”, because we want to keep the magnetic flux path under control and airgaps short without sacrificing too much of the mechanical simplicity. Also resistance losses is something we want to avoid (heat), so this eventually leads to figuring out the optimal capacitance and finding semiconductors to survive the quite high current pulses… More on that when I have time to do some calculations 🙂
Anyway, this leads straight to another cool side-project. When you need lots of coils, hand-winding is awful and boring task, at least I don’t like the calculation part at all – you’ll lose it at some point anyway! There’ s ofcourse option just to measure the overall length of wire and use some approximation for nominal radius of coil, but I’ve found that this is way too inaccurate for inductors. And ofcourse there can be lot of other cool uses for this toy, how about custom-made guitar pick-ups? So my ”to be” winding machine would be uc controlled dc-motor with smooth speed control, winding round calculation and some sort of automatic spreading for the available core-area. Controller part will be piece of cake, but making this suitable for different kind and sizes of coils and wires will need some thinking on the mechanical construction. Meanwhile I had to do a number of similar hand-wound coils, so I built up a little helper for the task. This was constructed in couple of hours from scrap parts and it uses old pedometer for round calculator.
Not pretty, but it works as a charm!
All cool things come in small packages!
This is already quite aged product, but as I’ve used it before on various devices and stumbled across a killer deal at ebay for 10 units, so I couldn’t resist it. Now I’m already designing a multiple new solutions to use these in. The module in question is a small ARM7 based ethernet device by Digi International – and they also have an upgraded version of this, based on ARM9. I like these a lot, it has proven to be very solid design and the supplied Net+OS very stable and quite easy to understand.
And what to do with it? For example, ethernet-enabled lightning control and movement sensing unit. Easily timed and controlled remotely. Powering can be done with POE, so it’s all standard equipment and cabling needed to use it. More on this when I’ll have time to write some more code for it.
Here’s also a pic from my test setup for outdoor led-lightning. Would be nice if it was a bit warmer in tone, and picture again makes it seem colder than it is actually. Plan is to add ~6-8 of these units in a similar fashion to light up the front yard, so it would prove enough light to see at night time but not be too bright.
Let there be rock (or more noise at least)!
Long time no press, I’ve been busy finding a job and again noticed that doing things is generally much more fun than documenting the doings, but here we go again.
I’ve been planning for a sort of home studio for a long time. This is what I’ve come up with during past few weeks and well, studio is a bit too hi-fi expression for the current state, but it’s a start and it works. Equipment now includes couple of nice dynamic microphones for vocals, Korg D4 multitracker, basic mixing abilities, power amplifier and close-range monitor speakers. This can now serve for singing, synth (or multitrack) backings, karaoke – whatever the need.
And it wouldn’t be mine if it wasn’t something home-made. I built the amplifier enclosure from what was once a cd-tower, so it’s recycled! Amplifier is a Tripath chip based ”Class-T” module with stated power of 2 x 100W @ 4ohms. I bought it for testing earlier this year and it surprised me with both being quite clean and quiet sound-wise but also by delivering almost the specified wattage to a load. So I made a power supply for it and put it to good use. It’s actually impressively efficient too. Amp delivers pretty much the promised wattage per channel to 4ohms with very nice THD figures and generates very little heat, shoebox has no air-holes at the moment and I can still keep the volume cranked up for several hours with no problems.
This is how it looks.
No extra bells and whistles. Switch to turn it on, power and audio in and speakers out. All you really need 🙂
Audio processing is now only done with a small Behringer mixer I purchased second hand. It still needs some nicer preamp for mics and perhaps a dsp for mix-out, more on those later when I’ll find suitable device(s) to fill the needs.
Mixer has seen it’s better days for sure, but nothing a little cleaning up wouldn’t take care of. All the channels and features work and the best part is – no noticeable humm or hiss at the output – it’s quiet!
And the microphones. Bought them based on some reviews to try them out. T-Bone MB-85Beta (Shure imitation) and Beyerdynamic Opus 29-S. I like them both for what they are, affordable dynamic microphones with solid build quality and natural sound reproduction (in my case the singer will be the main problem anyway 🙂
Last (and least) the speakers. They’re small Behringer passive close-range monitors I removed from my surround setup couple of years ago. I’ll propably upgrade these soon-ish, but as the room is quite small and they handle the available power well, result is actually quite good. Overall when considering how little money I spent on these components, this is a superb solution.
Tested this also as a karaoke setup last night, works very well indeed!
Let there be light
One of the things too long on my to-do list was some nicer night-lightning to my home and leds would be the perfect solution for that. They’re cheap and practically last forever. Like usually, I couldn’t find anything that would fit my purpose from stores, so I decided to make the led-strips myself. It’s made from triangle shaped wooden strip. Drilled the holes (by hand at this point, which is very visible :P), milled a groove for wiring in the back side and soldered the leds in place. Leds are 5mm, white, driven with constant current of up to 50mA. Lightning output was around 15000 mcd @ 20mA. Not very much in lumens, but it is enough for this sort of purpose.
And first installation of strips fitted in place, this is how it looks now in stairs. Photo is actually quite dark compared to what it is in reality. There’s well enough light now to see where you put your foot on.
EPROM data lost forever?
I got myself an interesting bit of museum-grade hardware last week from a friend of mine. Little (not in size, though) Z80-based industrial computer, four A4 sized cards on a back plane, 8KByte of battery-backed up SRAM. Device seemingly worked – one could read data (programs) from memory, but saving didn’t work correctly or at all. My first suspicion was of course software Eprom(s) as the computer originates from somewhere 1980’s. As I hadn’t instant access to a prommer, I first decided to check possible hardware-faults in address decoding logic of memory card as the fault was hinting to that sort of problem as well. I didn’t find any faults in there, couple of potentially hazardous design-flaws, but as the device had already worked 20+ years, those had perhaps been proved to work after all.
So I loaned a simple prommer from a friend and started verifying the eprom contents. One out of the three eproms was outputting random-ish bytes here and there. I could read out 4-5 different commonly repeating binary images out of the one Eprom, but none of these worked at the actual hardware. With any of the tried images the computer stays dead silent, with original supposedly-corrupted rom, it atleast starts up. As the prommer-software lacked any control parameters over the reading, I decided to do what I had planned to do for some time now, my own prommer (well, memory-reader at this point atleast). I was hoping that with settable read-speed, I could perhaps still salvage the lost contents somehow. On to the matter… few hours and roughly 100 lines of C later, I had Atmel mcu interfaced to eprom and could read it’s contents over serial port to PC.
Good news, after slowing down the read operations and precise control over the vcc, I could now get more consistent data out of the eprom. Bad news, none of these images was even close to the ones read with the commercial prommer. At this point I verified that my prommer was actually reading the data correctly and not outputting any garbage – it worked, so the fault was really the ROM itself. I read the contents for about 30 times, out of the results there can be found three commonly appearing binary patterns. Looking at these three patterns more closely, reveals there is difference between them only in three address locations, so I can now atleast get quite consistent garbage out of the chip.
Too bad for more testing, the commercial prommer decided to stop working at this point (what seems like timing problems with the PC, it’s one of those using programmed I/O through parallel port), so I couldn’t test all of the read images on the actual hardware. So I’ll propably have to continue with adding the write operations and some kind of terminal functions to my own prommer.
What troubles me at this point, is that despite the more consistent data, I can’t be sure if the the idea of slowing the read was correct at all or if I did end up with more garbage than with the commercial prommer anyway. Disassembling the rom contents doesn’t immediately reveal anything as there are no illegal opcodes or non-sane parameters at the differing address locations and digging through thousands of lines of disassembled code to understand it, is too much trouble to do for just plain curiosity. Anyway, should this test succeed, it would propably be a nice bit of information as the much used eproms are getting older every day in all kinds of equipment.
Long story short – if you have a car, refridgerator, tv or anything useful (and old) equipment you have containing eproms, back the data up before it’s too late. They’ll fail eventually to point of no repair.