Project files: The last of its kind…

…for a while at least 😀

What is it?
The last (and smallest) version of my EL2k buffered headphone amp using NOS Elantec 2008/2009 buffer ICs. This is the smallest version designed for 1.5″ heat sink profiles as described here. The two other versions are of course also still available (here and here):

How big are the boards?
The board measures 3.95″ x 1.5″ (app. 100 x 38 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5 as it is a redesign. Apart from the redesign work described in a previous post, the circuit is identical to the other published files.

Does it use any special/expensive/hard-to-find parts?
Yes.

  • The EL2008/EL2009 buffers have been out of production for 10+ years. They can still be found and I don’t think you need to be especially concerned about fakes – there can’t be a lot of demand for these anymore – but of course no guarantees. The main risk is probably that instead of NOS parts that you get used parts that have been pulled from old equipment. This is annoying, but should be OK.
  • The heat sink profile is the same as the original, Fischer SK68, in 37mm length. Easy to get in Europe, but I’m not sure about elsewhere.

Anything else I need to know?

  • I’ve had to mount the buffers on the side of the heat sink that has an M2.5 slot and not an M3-slot. This isn’t a problem as such because there’s no need to isolate the tab, you’ll have to remember to buy M2.5 screws for mounting 😀
  • Otherwise this is a bog-standard buffered opamp circuit and there isn’t much that can go wrong 🙂

Downloads:
Download design files here

Related information:
Be sure to read the original posts for additional information and tips.

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

Project files: The (modified) EL2k headamp

What is it?
The board files for the new “medium-sized” version of the EL2k buffer/pre as shown a few weeks ago. The smaller 37mm board version will follow in a while.

How big are the boards?
The board measures 3.95″ x 2.0″ (app. 100 x 51 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5. Apart from the redesign work described in the last post, the circuit is identical to the originally published v1.1 files.

Does it use any special/expensive/hard-to-find parts?
Yes.

  • The EL2008/EL2009 buffers have been out of production for 10+ years. They can still be found and I don’t think you need to be especially concerned about fakes – there can’t be a lot of demand for these anymore – but of course no guarantees. The main risk is probably that instead of NOS parts that you get used parts that have been pulled from old equipment. This is annoying, but should be OK.
  • The heat sink profile is the same as the original, Fischer SK68, in 50mm length. Easy to get in Europe, but I’m not sure about elsewhere.

Anything else I need to know?

  • I’ve had to mount the buffers on the side of the heat sink that has an M2.5 slot and not an M3-slot. This isn’t a problem as such because there’s no need to isolate the tab, but some swearing will likely ensue when you sit there on Sunday afternoon and realise you don’t have any M2.5 screws to hand 😀
  • Otherwise this is a bog-standard buffered opamp circuit and there isn’t much that can go wrong 🙂

Downloads:
Download design files here

Related information:
Be sure to read the original posts for additional information and tips. You should be able to reuse the linked BoM as well.

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

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.

Downloads:
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.

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.

aprilfools

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 😀

staxboards

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).

Downloads:
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.

zenhppcb-1

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.

Project files: GP-PSUs v2

What is it?
Two boards for general-purpose LM317/LM337 power supplies with two rails, useable for many low-power applications (preamps, buffers, filters etc.). There are two versions, one where the +/- voltage is derived from a single AC-voltage via a voltage-doubler and one where it comes from a traditional dual-AC, two-bridge rectifier circuit.
These boards are effectively an update on the old GP-PSUs and they are based on the triple-PSUs I posted a while ago. In fact they are just the three-rail designs with the third rail removed 😀

How big are the boards?
Both board versions measure 3.925″ x 1.8″ (app. 100 x 46 mm.) and they are mechanically interchangeable.

What is the status of the boards?
Both boards are in v1.0. I haven’t actually prototyped these in this format yet, but since they are the same as the three-rail version (which I have tested) I don’t mind publishing them.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires a higher performance PSU than this, you are probably better off looking at entirely different circuits and regulators anyway.

Anything else I need to know?
Yes, pretty much a repeat of what was mentioned for the three-rail circuits:

  • The diameter of the main filter capacitors is 18mm, but the dual footprint means that anything between 10mm and 18mm should be fine.
  • The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
  • Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
    • 1) Loosely assemble the regulator, the isolation components and the heatsink.
    • 2) Mount the combination on the PCB and solder the heatsink in place.
    • 3) Tighten the screw holding the regulator to the heatsink.
    • 4) Solder the regulator in place.

Downloads:
Download design files here

Related information:
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.

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

Project files: The J-Mo Headphone Buffer

What is it?
The project files for my version of Richard Murdey’s  J-Mo mk. 2 buffer with gain.

How big are the boards?

  • Amp: 2.45” x 1.975” (app. 62 x 50 mm.)
  • PSU: 2.35” x 1.975” (app. 60 x 50 mm.)

What is the status of the boards?
Both boards are version 1.0, meaning I have prototyped them and they work. However, I am still waiting for some mechanical parts for my own build so this isn’t final yet which means I have only done very basic tests.

Does it use any special/expensive/hard-to-find parts?
Well, the J-FETs are getting harder and harder to find but it isn’t impossible yet.

Anything else I need to know?

  • Can’t really think of anything. Be sure to read through the article on Richards website though, that contains most of what you need to know.

Downloads:
Download design files here

Related information:
See the original post for some more information and links. There is also a big discussion thread on diyaudio that may be of help.

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

Project files: Universal Triple-PSUs

What is it?
Two boards for general-purpose LM317/LM337 power supplies with three rails, useable for many low-power applications where both a +/- supply and an auxiliary voltage are needed. Examples include analog amplifier + digital/logic circuitry, microphone preamplifier + phantom voltage etc.
There are two versions, one where the +/- voltage is derived from a single AC-voltage via a doubler and one where it comes from a traditional two-bridge rectifier circuit. This design is virtually a copy of my GP-PSUs. I made some minor enhancements and added the extra rail, but it is the same basic design.

How big are the boards?
Both board versions measure 3.925″ x 2.6″ (app. 100 x 66 mm.) and they are mechanically interchangeable.

What is the status of the boards?
The “standard” board is in v1.0 and works fine. The voltage-doubled board is in v1.1 and also works fine. The two versions are completely identical except for the diode/bridge arrangement on the +/- supply. The difference in version numbers came because I originally prototyped a different (smaller) layout for the voltage-doubled version. After making the “standard” version that requires a bit more space for the rectifier bridges, I decided it was smarter if they were both the same size and then changed the layout of the voltage-doubled board to match.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires higher performance than this, you are probably better off looking at entirely different circuits and regulators.

Anything else I need to know?

  • There is a jumper on the boards that links the ground on the AUX-voltage to the midpoint (0V) of the +/- supply. This is optional and probably not required for most applications but can be used for e.g. linking analog and digital ground in mixed-signal circuits.
  • The diameter of the main filter capacitors is 16mm on the AUX supply and 18mm on the main supply.
  • The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
  • Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
    1) Loosely assemble the regulator, the isolation components and the heatsink.
    2) Mount the combination on the PCB and solder the heatsink in place.
    3) Tighten the screw holding the regulator to the heatsink.
    4) Solder the regulator in place.

Downloads:
Download design files here

Related information:
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.

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