JLH Evo Update

All right, no more moaning about lack of build time (at least not for now😉 )

Managed to do a little work on the mechanics of my “JLH evo” concept allowing you to get an idea of what the end result will look like (when it’s eventually finished…).

I’m still figuring out a final chassis design so I may well leave it in this state for quite a while, but at least the mechanics seem to fit together as planned and there’s enough room to run the wires. The baseplate size is app. 170 x 230 mm per mono block.

The extra PCB is a CRC-regulator stage that I will add to reduce the noise and ripple from the switching PSU (a Mean Well EPP-150-27). The advantage here is that the ripple frequency from a switching power supply is very high (typically 65-100 kHz) so the attenuation is much, much greater than at the normal 100/120 Hz ripple from a linear supply – meaning in other words that it’s possible to get away with much smaller filtering caps than a usual class A amp.

This should therefore reduce the highish app. 240mV ripple that’s specified in the data sheet for the supply that I am using down to something much, much less. Any HF-noise on the output should be well attenuated as well. Not sure what effect it really has but that’s part of the experiment😀

April fools…

No, this isn’t really a joke as such. However, there’s something strangely appropriate about posting this today I think😀

It’s an “extended” version of my ZenHP amp, but I went a little overboard and added the gigantic polypropylene caps I purchased on my last trip to Japan as the output caps. As mentioned then, I’d want to test if using film capacitors on the output made any sonic difference compared to the electrolytics that are normally used. We shall see how that works out later on….

The downside of this (perceived) audiophile greatness (…) is that in order to make everything fit in a 2U/350mm enclosure I basically had to cheat a bit on the PSU. It’s either going to be an internal IRM20 switching type from Mean Well as shown or a very simple linear one that can be fed from an external transformer. Obviously having an amp as big as this requiring an external PSU is a bit stupid, but hey – it’s an experiment!😀

Also, since it’s an experiment I’m not going to order fancy front and rear panels for this amp yet. Once I’m through travelling for work in a couple of weeks I’ll have to do a bit of metalwork of my own instead. Not much else missing before it’s ready to play though, but with my current workload it might still take a while to do.

PS: I’ve you see any good audiophile April fools jokes online, feel free to post a link in the comments section.


Project files: A bal. driver with the THAT1646

Still busy at work, but being home for (most of) the weekend and I have time to dig in the back catalogue a bit – hope this is useful for someone:-)

What is it?
A simple SE/BAL line driver board using the THAT1646 line driver IC. This should make it compatible with the DRV134 from TI and the – now obsolete – SSM2142 from AD as well. The board can be used as a pure line driver to feed a balanced input or of course also to bridge two suitable power amps.
The THAT-chip is combined with an on-board opamp, partly to ensure that it is driven by a low-impedance source as per the datasheet recommendation, partly to increase the versatility as the opamp can provide more gain if required.

How big are the boards?
The board measures just 1.6” x 1.9” (app. 41 x 48 mm.) The boards can be placed side-by-side or stacked. I originally had this as a stereo board with two channels on the same board, but decided that the mono-version was probably more versatile overall. If you disagree feel free to let me know😀

What is the status of the boards?
The board is v1.0. I’ve built a single prototype and tested it (I needed one channel for a test setup) and it sounds fine as far as I can tell. No further sound impressions yet I am afraid.

Does it use any special/expensive/hard-to-find parts?
None. I am not actually aware of a source for the THAT-chip in Europe, but Mouser has them and that should work for most people I guess:-)

Anything else I need to know?
A few things:

  • Protection circuitry: I’ve omitted the protection circuitry described in the data sheet for the THAT1646, mainly because I only expect to use it in home applications where there is no risk of a phantom power supply being present. If you are using it with PA gear that (potentially) has a phantom power supply on the inputs then you might need to look into this.
  • Grounding: I have connected the ground pin of the output connector on the PCB to GND on the board, which is actually a no-no. Connecting all three pins to the XLR would (potentially) give you “pin 1-problem”.
    As I understand it, the proper way of wiring an XLR is therefore to only connect “hot” and “cold” from the PCB connector to the XLR out connector and then connect  PIN 1 on the XLR connector to the chassis ground via as short a wire as possible.
  • Preamp-mode: Given that the THAT1646 already has an opamp onboard to drive it, if you use 100k-220k input impedance (R1) it should be possible to put a 10k-20k log pot in front of the input capacitor and convert the board (well, two of them…) to a stand-alone preamp with SE in and Balanced out. I haven’t tested this, but I see a couple of potential applications here:)
  • Chip substitution: The DRV134 has the same pin connections as the THAT1646. The only thing I can see that makes them different is that the DRV134 data sheet specifies 1uF decoupling caps on the supply pins rather than the 100nF for the THAT1646.
    Note that the DRV134 also has a reputation (at least in some DIY-circles) for sounding pretty unspectacular. I have no personal experience to offer here, so try for yourself if you want😀

Download design files here

Edit 14th april 2016: Link has been updated to point to the correct file:-)

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

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


Just read over on Innerfidelity that the founder of the Headwize site and namesake of the CMoy headphone amplifier, Chu Moy, has passed away recently.

As a relatively early member of Headwize, I can remember discovering a site with an active discussion forum and a lot of inspiration for a novice audio diy’er like myself. Apart from the direct contribution of the Headwize forum (including the projects gallery that I have mentioned several times in the past), Headwize of course also spawned head-fi.org and many other international and local headphone forums that still run today.

Headwize was also the birthplace of the first community headphone amplifier build projects (like the ones from Tangent and AMB) that have helped others get started in this new hobby. I am sure there are quite a few people out there who first experienced the elation of playing music through a self-built amp via one of these projects:)

Although I never knew Chu Moy personally and he was out of the “spotlight” for many years, I am very grateful for his contribution to the audio hobby and of course for being one of the reasons why I am in this at all:)

Full story by Tyll Hertsens

High voltage…

Yes I am still here, but it’s another busy period for me at work so updates to the blog are correspondingly few and far between. As usual when I don’t have a lot of time for diy I still somehow manage to start up new projects. Even with less than 48 hours at home in a weekend, there’s still time to do a little soldering to relax and unwind😀

Among the overdue projects I’ve managed to start up lately are some amplifiers for my Stax electrostatic headphones. This is actually more than a little overdue, because I haven’t had a Stax amplifier for nearly a year now and so the headphones I have aren’t getting any use which is a shame really.

The pile of half-assembled boards in the picture actually consists of the following designs, all by Kevin Gilmore:

– A pair of KGST tube amp boards and matching 350V PSU

– A mini-version of the KGSSHV amp and matching 400V PSU

– A version of the KGSSIC/“Carbon” amp and matching 400/450V PSU

Most of the boards were all acquired through various group-buys on the head-case.org forums, but Kevin graciously keeps the Gerber files for all of his designs available for free download as well.

I’ve soldered more or less all the parts I have available, so still to do are:

1) Order remaining parts (working on that – since it’s also possible to do from hotels after work :D)

2) Figure out the mechanical stuff (mostly done, but still needs a bit of work – and some tools I don’t have regular access to)

3) Select and match a pile of semis (saving that one for a rainy day:-) )

4) Finish and test boards (as quickly as possible)

I’m not really used to high-voltage stuff so I am being extra careful with these boards. Just like when you move up in frequency, moving up in voltage means that things that were not previously issues suddenly become very important. Fortunately I have a working variac again (fixed after stupidly blowing a fuse in it a few weeks ago) which makes testing much easier – not to mention safer all round.

These aren’t the only Gilmore-designs I’m working at the moment by the way, but the rest involves much more pedestrian voltages😀


Project files: The Zen Headphone Amplifier

What is it?
The board files for my Zen Headphone Amplifier “remake” shown here.

How big are the boards?
The board measures 3.575” x 3.75” (app. 91 x 95 mm). This is obviously for a mono-channel.

What is the status of the boards?
The boards are version 1.0. The prototypes seem to work well and there wasn’t really anything that needed changing in my view.

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

Anything else I need to know?
A few things:

  • Heatsinks: The basic type for me here in Europe is the Fischer SK129, but there are many manufacturers of this profile. The board is designed for the heatsinks to be soldered in place with pins, but screw-mounted versions might work as well. You can use 1″/25mm heat sinks, but in that case I recommend to tune the bias a little lower. My prototype measured app. 240 mA of bias and the heat sinks seemed to stabilise at around 55C in free air, which probably is a bit too much when the board is cased. So, either turn the bias down a bit and/or use taller heat sinks if your case allows for it.
  • Adjustments: Space around R10 and R12 is quite tight, especially with heat sinks/output caps taller than 25mm. In order to easily be able to adjust bias and balance of the amp, my suggestion would be that you don’t trim the leads of the two resistors completely flush but leave enough of the resistor legs that you can connect crocodile clips to them on the underside.
  • Output capacitors: The recommended value is 2 x 470uF from the original schematic, but if you’re using low-impedance headphones I think you should consider 2 x 1000uF instead. This is one place where I think “audiophile” capacitors can’t hurt, so look for Nichicon Muse (KZ/KW, FG/FW, ES etc.), Elna Cerafine/Silmic capacitors or similar. Bypassing the electrolytics with small film capacitors is easily done on the underside of the board if you want to.
  • Transistors: The Q3 footprint on the board is for a BC550C, but the original ZTX450 from the schematic can be used as well if it’s turned 180 degrees. Remember also to match at least the two Q2 FETs between channels as described in the build article. If you buy 8-10 of the IRF610 FETs you should be able to get a couple of very tight matches and the leftovers can be used for the current source (Q1).

Download design files here

Related information:
See the original post for some more information and links to the build article for this design. After posting I actually also managed to find the original headwize article cached here – amazingly it seems that most of the headwize library has been kept intact there! :)

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


New Chinese miniamps…

A few weeks ago I stumbled across a post on diyaudio mentioning the latest in (the long line of) ultra-mini class D chipamps offered on eBay/Aliexpress. The boards looked interesting and so I “splurged” for a pair which turned up this past weekend. Although in all honesty “splurged” probably isn’t the right term here as I paid a grand total of 12.50 EUR for the pair – including shipping (!!).

Like many of the other small amp boards, this one uses the TPA3118d2 class D IC from TI. The TPA3118 chip has a fairly good reputation on diyaudio and it will give a reasonably high power level when used as a mono amplifier (called PBTL-mode). The chip has a thermal pad on the underside and so uses the PCB copper as the heatsink surface. Unlike many other similar boards though, these boards are pure poweramps (no onboard volume pot) which is fine for me. They are also tiny at 35 by 46 mm – which means even two channels side-by-side are still visibly smaller than a credit card (!!)

So, very small, very cheap, quite powerful, and decent sound quality – what’s not to like? Not a lot actually. It would have been nice if the chip had been the TPA3116 which has the thermal pad facing upwards. Even through there isn’t a lot of space, it would still have been possible to fit a small heatsink on top of the chip and thereby (probably) improve the thermal performance and get a bit more output power.

Another slight negative is that the input capacitor is an X7R ceramic type which really isn’t the best choice for audio. Because it’s a 0603 SMD it’s also tiny and very difficult to replace/exchange with something better. The boards seem to be set to the highest gain (36 dB) which is good if the source is a smartphone or similar, but on the high side if it’s a typical hifi source like a DAC. Again, adjustment of the gain would require replacing 0603 resistors which is not that fun a pain in the … but overall it’s a minor downside.

The boards in stock form don’t have any connectors for inputs and outputs, but I’ve added some to my pair to make testing a bit easier. I need to do a bit more listening with these “prototypes”, but if the sound quality is any good I do have a specific project in mind for them for later:-)

The Zen of Headphones…

Oh no, sorry – it’s the Zen for headphones😀

This is another project from the early days of my DIY-career that I have “resurrected” by remaking the PCB. It’s an adapted version of the Zen amplifier by Nelson Pass and optimised for driving (primarily low-impedance) headphones.

The design was developed by an Italian diy’er called Marcello Pellerano back in 2002 and you can still find the original diyaudio.com discussion thread here. In addition to the diyaudio-thread, the project was also later published as a project article on Headwize, the precursor to Head-Fi. Sadly the Headwize project repository is no longer available, but it seems the full text of that article is available here as well.

Fun fact I: Marcello’s project was the first time I ever saw the enclosures from Hifi2000/Modushop and therefore what originally led me to start using these cases.

Fun fact II: Although I haven’t copied the EQ PCB that is described in the build article, I actually own a pair of the original Grado SR-325 headphones that the amp and EQ were originally designed for. Even without the EQ, I can’t really think of a better excuse for getting the Grados out of storage and listening to them once again:)

My main changes compared to the original design is to use onboard heatsinks and some different footprints for the various capacitors. Especially on the output side I’ve scaled up a bit, because 32 ohm Grados aren’t as low-impedance as they were 13 years ago. Many modern headphones are lower impedance than that and so making space for bigger output capacitors seemed worthwhile.

I haven’t copied the PSU either, partly because I already have a few designs that can be used instead and partly because there are just so many other options out there now – more on that later!

Sound quality: We’ll get to that later on as well since I’ve only done bench testing so far, but it definitely works and first impressions are quite positive.

One-button listening…

I know I’m not supposed to admit this, but over the last months I’ve become more and more aware that sound quality isn’t the only factor in deciding how much I listen to my system.

I’ve mentioned this in a previous post, but my first “real” audio system was a Harman-Kardon CD and integrated amp. One of the things I still remember – more than 20 years on – is that I could get music just by turning on the two components and there was next to no waiting time. By contrast I am now using a MacMini as my primary music source, which means having to wait 30-40 secs. for the computer to start up and then controlling the sound either from an iPad app or by having to turn on the TV, selecting the right input etc. It’s a much more complicated process, not to mention that I still need a separate remote to control the integrated amplifier and so on.

Part of my response to this incredible hardship obvious first-world problem (😀 ) was to start listening more to vinyl, but something still wasn’t perfect. Vinyl is great for “serious” listening – I enjoy the involvement in the process – but for background music while I’m doing something else I find vinyl is less than ideal.

All this changed a bit when I recently sold the Musical Fidelity integrated amplifier that I was using in my main system. Instead I went back to using some of my DIY-stuff together with a newly-acquired Arcam IRdac (the “old” version as Arcam has just announced the IRdac II). The original IRdac has an input for an Apple-device to which I’ve connected a 160GB iPod Classic filled with lossless files (officially the Classic isn’t supported by the IRdac but I can report it works fine:) ).

This is excellent for background music even if the MacMini with iTunes/Amarra does mean a step up in sound quality. The remote for the IRdac can control play/pause and forward/backwards skipping on both the iPod and in iTunes which means my whole system can be operated with a single remote. When using the iPod the whole thing is ready to play in the time it takes to switch on the three components as the iPod turns on immediately.

Soundwise the new setup is is a bit better than the Musical Fidelity integrated, but from a usability perspective it’s honestly miles ahead – I can use a “simple” source (the iPod) when I just listen to background music, and I can use a more “complicated” source (computer or vinyl) if I want to. The only thing I need now is that the IRdac remote can control volume as well. Sadly this isn’t possible with a stepped attenuator (for obvious reasons) but this could be the starting point for another project😀

So, you might ask – what’s the point of this post? Well, I don’t know if there is one, only that this part of the “customer experience” with a product should not be forgotten and might play a bigger role (even subconsciously) in how a product is perceived than most people might think.

Evolution of a concept…

I’ve been playing with the (somewhat) unusual combination of a class A amp and a switching PSU before (here). The previous version worked quite well, but even as I was building it I though that there might be scope for optimisation and for making it smaller – which to be honest was my goal all along.

The amplifier section is now my own version of the JLH 1969 with MJL21196 output transistors (because I had them available). The heat sinks are the same surplus items I’ve used before – because they are cheap and exactly the right size for what I wanted to do:)

As I observed in the previous post, the chosen PSU was more than a little overspec’ed for the job, but as luck would have it a much better choice came up recently – the Mean Well EPP-150-27. These are “next generation” supplies (i.e. more compact at 2” x 4”), there’s a convenient 12V aux supply for a fan etc. and the 27V output voltage is spot on for the JLH. There’s a smaller 100W version that could be used as well, but since I could get these as surplus items off ebay there was no incentive to do that😀

I’ve also been looking at getting some more quiet fans, but I’ve now realised that the most annoying noise from fan-cooling doesn’t really come from the fan itself but from the sound of air rushing through the various holes in the enclosure. Once I’ve done the final design I’ll have to test what can be done to keep the amps as quiet as possible. The noise level on the first iteration was OK, but definitely with room for improvement.

To marry the parts together I came up with a “central core” design where the amp and the PSU are bolted to the heat sink tunnel and that’s about what I have done so far. The rest of the mechanics are in the works and there are a few (as yet undisclosed) additions that I will add as well in due time😀


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