J-Mo buffer/headphone amp

A couple of months ago I stumbled upon the discussion thread for Richard Murdey’s J-Mo Mk. 2 headphone buffer on diyaudio.com. Richard runs RJM Audio (which you should definitely check out if you haven’t already) and is also the man behind the Szekeres VE design that I built a while ago (see this post).

I am not sure why the J-Mo caught my eye, probably the simplicity of it, but it did. Richard already has a nice PCB for the design, but as I thought I could make it a little smaller, substitute some parts for more commonly available sizes and also improve the versatility a bit I decided to “roll my own” boards instead :)

I downloaded the eagle-files that Richard graciously provide for download, ripped up the original PCB file and got to work. The result is here in dual-mono format with amp and regulator on separate PCBs similar to the original. Apart from the revised layout my changes are relatively minor, mainly different component footprints where I thought it made sense and of course different heat sinks.

The rectifier bridge PCB is from my second Gainclone design and was perfect for making the unregulated DC voltage that the Zener regulator requires. The bottom plate in the pictures was just one that I had left over from another project and was suitable for mounting the boards. There is no wiring in the pictures, but the boards were wired up and it does play wonderful music (although feeding it with wonderful music seems to be required… :D)

As usual I didn’t really listen for a long time while it was sitting on my desk in “prototype mode”, but what I heard was good enough that I have ordered a proper mounting plate (i.e. one that fits in a standard enclosure), a transformer and some chassis part so I can give these great boards a “real” home :D

Project files: The EL2k headamp

What is it?
The PCB files for the EL2k headamp in the previous post (here)

How big are the boards?
The board measures 3.95″ x 3.0″ (app. 100 x 76 mm.) and contains one channel.

What is the status of the boards?
The files are v1.1 of the board. I corrected a few minor issues in the prototype such as the footprint of the input capacitor and the package dimension for the CRD.

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

  • The Elantec buffers (EL2008/EL2009) that for the basis of the EL2k have been out of production for a long time. You can find them in various places online, both as pulls from scrapped equipment and as unused new-old-stock (NOS) ones. I bought a single pair of EL2008s from a long time diyaudio-user and member of the headphone community who was cleaning out parts so I have no doubts that mine are genuine, but if you do try to source from elsewhere always beware of fakes or substandard parts.
    That said, demand for 15-year old analog video buffers in TO-220 packages probably isn’t at an all-time high now, so I would judge the chance of getting genuine ones as quite good. Unlike various power transistors and small signal JFETs that are regularly counterfeited – even in channels where you would never suspect it – there probably isn’t a lot of money to be made from faking these in the first place.
  • The heat sink is not hard to find as such, but it must be a specific one (the SK68/75 from Fischer). It’s quite common in Europe with Reichelt and TME both stocking it, but I am not really aware of any other sources.

Anything else I need to know?

  • When you mount the buffer as shown, the heat sink will be grounded (because the tab-pin is grounded on the PCB). Not a problem in itself, but it does mean you should be careful of flying PSU leads :)
  • Mounting the buffer is a bit of a hassle, firstly because the electrolytics can get in the way unless you wait with mounting those (I didn’t…) and secondly because it doesn’t line up 100% true with the grooves in the heat sink. You can either have the buffer sit flush with the board as I did and use the M2.5 slot, or you can use the M3 slot and have it raised quite a bit above the board. In the first case, there is barely enough room for the screw and in the second it might be necessary to bend the buffer leads a bit to make them reach the holes. It works, but it isn’t as elegant as I would have liked :)
  • The PSU for this board should be +/-12 to +/-15V. 15V is recommended unless you are using an opamp that doesn’t tolerate 15V. In theory, the PSU should be capable of at least 2A output currents, but in any normal audio application 1A should be more than enough.
  • If used, the recommended value for the CRD is app. 2mA. I used a J508 because I had a pair left over, but there are other options out there. You can also use a resistor instead or skip this entirely. See this page about class A bias of opamps.

Downloads:
Download design files here

Related information:
See the two original posts for some more information and links.
Note: Always read the “intro post” for additional important information about my designs.

More old silicon – the EL2k headamp…

After my adventures with the obsolete BUF03 buffer comes a design with another discontinued buffer-chip – the Elantec EL2008 :D

The EL2008 is definitely an overkill-device for audio duty. It’s got high bandwidth, high slew-rate and a 1A current capability with a built-in limiter. Like the BUF03 it was originally intended for video applications and like the BUF03, it has also been discontinued for a decade or so. There is also an EL2009 with even more impressive specs for bandwidth and slew-rate if you want and since both ICs should work in this design coming up with the name was pretty simple – the EL2k.

The design itself is a fairly straightforward “buffered op-amp” circuit, the only “tricks” being a resistor between the opamp and the buffer (because the buffer needs a controlled source impedance) and a current-regulation diode (CRD) to bias the opamp into class A (something else that was very popular in diy headphone amplifiers 10 years ago – my age is starting to show here I guess…).

I’ve possibly gone a bit overboard with the heatsinking, but this was the type of layout I had in mind and it seems to work well (electrically at least, there are some mechanical niggles). The input caps are ClarityCaps ESA which probably also qualifies as overkill, but I am sure they do no harm :D

The opamps used are LME49710s because I had a pair to hand when I did the test. However, in my opinion the obvious choice for this build would be another one of “yesterday’s heroes” – the OPA627. Back in the day when the EL2k buffers were around, the OPA627 was pretty much the king of the audio-grade opamps so I think that match is sort of meant to be. The OPA627 also has a warmer, less clinical sound signature that might offset a bit of brightness here.

I have only listened briefly to this design so far, but the immediate impression is “detail, loads of detail” Whether this turns into listening fatigue in longer sessions I don’t know yet but we’ll see when I get some more time. In any case: the guy that sold me the Elantec buffers told me “to build something awesome with them” – not sure I succeeded, but I definitely tried :D

Project files: Little helpers – Alps PCBs II

What is it?
Not exactly the most complex designs ever made ;) A couple of PCBs for mounting Alps (or pin-compatible) potentiometers. Unlike the previous boards these ones have screw clamps for input and output, making them better suited to testing use and people with fat fingers (like yours truly) :D There are two versions, a 2-channel (for stereo) and a 4-channel (for balanced) amps.

How big are the boards?
The SE board measures 1.15″ x 1.975″ (app. 29 x 50 mm) and the balanced board measures 1.975″ x 1.975″ (app. 50 x 50 mm.)

What is the status of the boards?
I’ve called these version 1.5 since they are based on the previous boards of the same type, just modified with screw clamps for the input/output connections.

Does it use any special/expensive/hard-to-find parts?
Mostly there’s only one real part on the board and that is the pot itself which can be a bit expensive, so yes, I guess so :D

Anything else I need to know?

  • These are “preamp” style boards have a ground plane and a ground pad that can be used if you grounding scheme requires the shaft of the pot to be grounded. Use a piece of wire connected from the ground pad to either one of the screws on the back of the pot or soldered to a ring terminal wedged between the pot and the chassis.
  • The stereo board has a four-hole footprint to fit various pots that use that configuration, but the last set of pads isn’t connected to anything so will not work directly with a loudness tap.
  • The boards can also be used to make separate, passive preamps. In this case, a 10k potentiometer should be used.
  • The screw clamps are standard 5mm pin spacing types, but of course it is possible to solder bare wires to the boards as well.

Downloads:
Download design files here

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

As usual, please remember to consult the manufacturer’s datasheet as well if you use a different pot than the recommended type.

Going “retro”….

For the past few months I have noticed something: Most of my everyday listening is with a portable rig, either at my desk at work or during the daily commute. When I am at home, while I have my entire 800+ CD-collection ripped to lossless files and a whole dedicated setup for listening to it (dedicated Mac Mini with Audiolab M-DAC etc.) I was actually not using it a lot. It’s not that I don’t like the sound, but it is a bit of a faff having to turn everything on, wait for the computer to start up and then having to either turn on the TV to navigate or get out an iPad/iPod/iPhone to use the remote app etc.

After this (slow) realisation, I started thinking back to when I started playing music on my own. My first “real” system was a simple Harman/Kardon CD-player and integrated amp and I lived happily with that for nearly ten years. There was nothing to wait for, just two on-switches and a play-button and then there was music, and there was a bit more “tactility” to the process overall (if not much). I don’t think I’ll ever really go back to the CDs, but I have actually – slowly but surely – started playing a lot more vinyl at home.

Some would say that I have just succumbed to the first “wave” of accumulated nostalgia when you reach your mid-thirties, but it’s not as if I have a long history of actually using vinyl records. Of course I am old enough to know how they work ( ;) ) and I can remember playing records when I was younger on my parents’ stereo. But when I started buying my own music in the early nineties, CD was already the format of choice (and cassettes were still common as well, mainly for exchanging music with friends). The only friends that bought vinyl were a couple with older siblings that had turntables and even they switched to CDs very quickly. As a result, I’ve never really had that much affection for the vinyl format so I do challenge the notion that this is just misty-eyed nostalgia at work :)

To add to that, the turntable obviously has its share of downsides – I had for instance mostly forgotten just how short the side of a record seems when you are working on something and just playing music in the background. I had also forgotten just how much dust a record is capable of attracting and how annoying scratches can be. My turntable is nothing special (a simple Project Debut Carbon albeit with an upgraded cartridge and an aftermarket plexiglass platter), but even so – it sounds very good and it is definitely more of an “experience” or “occasion” to put on a record, lower the stylus and wait for music to come out of the speakers.

So, there we go – I said it: For me this hobby isn’t really about sound quality (at least not only) but also about the experience. Blasphemy to some audiophiles, but a revelation to others maybe? If nothing else, I guess it provides an explanation (or excuse…) for why I continue to design, build and buy a lot of gear that I may never really get to use :D

vinylaction

Project files: B1 buffer/preamp

What is it?
Project files for my miniature version of Nelson Pass’ B1 buffer/preamp (shown here). I was looking through the “back catalogue” my of designs and decided that this has been sitting around for long enough to release :)

How big are the boards?
The board measures 3.55″ x 2.825″ (app. 90 x 72 mm.)

What is the status of the boards?
This board is in version 1.1 – tested, working and with a few minor touch-ups afterwards :)

Does it use any special/expensive/hard-to-find parts?
Well…

  •  The 2SK170 JFETS are obsolete and can be difficult to get (the real ones at least – getting something that is marked “SK170” isn’t hard at all…). There are a few “close enough” substitutes (such as 2SK369, 2SK117, 2SK246 and possibly a few more) which aren’t completely unobtanium yet. Do a google search if you are not sure, make sure to get BL-grades and beware that not all of these have the same pin connections.
  • The input and output caps should be MKP-types (polypropylene). The “square” footprints correspond to normal types from Wima, Evox/Rifa and many others.
  • The 1 ohm resistor in the power supply is meant to be a 5W MPC-71 type. These can be a bit hard to find – ebay and Aliexpress seem to be the best options (some risk of fakes as usual) – but it is also possible to fit a normal 3-5W type instead.

Anything else I need to know?

  • The JFETs should be matched for Idss for best performance. Plenty of guides available for that if you are unable to buy pre-matched pairs, and my JFETmatcher can be used as well.
  • I have used smaller PSU capacitors on the board than Nelson did in the original article, but you should still be able to get away with both regulated and unregulated power supplies. Plenty of advice out there for that as well – as long as you stay between 18 and 24V more or less everything should work.

Downloads:
Download design files here

Related information:
Tons on information out there on the B1 and derivates, but the most obvious place to start is (obviously…) Nelson’s original article.

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

Project files: Little helpers – Powerhelpers

What is it?
A few auxiliary boards to match the mainscontroller boards or for use one their own. More specifically, there are a couple of relay boards for use with the relay-less version of the Mainscontroller. The large relay board is intended for a “T90″-type relay which is typically rated 20/30A. The smaller board is using a Omron G5LE relay which is rated 6/10A.

There is also a simple softstart-board that can be used when powering transformers over app. 250-300VA. This is based on a very old (and frequently copied) circuit from Elektor that seems to work well, at least for medium-sized PSUs.

How big are the boards?
The Softstart board and the large relay board are both 2″ x 2″ (app. 51×51 mm.). The smaller relay board measures 1.5″ x 2″ (app. 38 x 51 mm.) As the pictures show, mounting holes and connectors line up so the boards can be stacked and cables routed neatly between them.

What is the status of the boards?
The softstart board is now in v1.5 as it is an improved version of one I did earlier. The large relay board is v1.1 as I have prototyped it and corrected the relay footprint which wasn’t perfect (my own design, obviously…). The small relay PCB is in v1.0. I haven’t actually received and tested the prototype boards yet, but as it is the exact same circuit as the large board and the footprint for the relay is an eagle standard one I am OK with releasing this design as well.

Does it use any special/expensive/hard-to-find parts?
Not really, but:

  • The T90 relays can commonly be found on ebay. There are name-brand equivalents as well from Omron, Finder and other manufacturers of relays.
  • The Omron G5LE can be puchased cheaply from Mouser or Reichelt. Alternatively there are equivalents available on ebay, usually marked with SRD-xxx designations.
  • The relay on the softstart is an Omron G2R-24V type which is also available from Mouser or Reichelt.
  • Note that the large 330nF capacitor on the soft start board must be an X2-rated type.

Anything else I need to know?

  • When in use, these boards may feature exposed mains parts (the softstart certainly will). One especially “problematic” thing is that the legs of the axial resistors are partly exposed so make sure that the board is protected from accidental touches. If you are stacking boards, I suggest putting the relay PCB on top as it has fewer exposed parts, but even so a cover** of some sort could be a good idea.
  • Whether used with the Mainscontroller board or on it’s own, be sure that you are aware of the current consumption of the mechanical relays. The T90 relay typically consumes app. 1W (1200 mW worst case) and the G5LE relay consumes app. 400mW, which for instance means they cannot be controlled directly by a micro controller.
  • I have never tested the softstart board on transformers larger than 500VA. I imagine it should be good up to around 800-1000VA, but anything more and I would be cautious and probably look for something with bigger relays and resistors. The same applies if you are using exceptionally large capacitor banks.
  • **The cover is based on an idea I had a while ago but didn’t test until now: I wanted to have an easy way to make covers to shield sensitive and hot/live parts from touches. I could use Front panel express to have 2mm acrylic sheets made but that is comparatively expensive, so I came up with another way: The Gerber files give me the board outline for each design and so by rendering the Gerbers e.g. with Circuitpeople I can get a true-size outline. Once that is scaled I can then import into a graphics program to add warning symbols, text or anything else. To get the cover I simply laminate the printout using a home laminating machine with the thickets foil type and then use a hole punch to cut out the mounting holes which are clearly marked. It’s obviously not a safety-approved material in any way, but it fits perfectly and it will protect against accidental touches which is bound to be better than nothing.

Downloads:
Download design files here

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

Project files: Mains controller with offboard relay

What is it?
A version of my Standby-PSU & controller for applications that need to switch very high (or very low) currents, switch multiple relays or simply prefers to use an offboard relay, be it mechanical or SSR. A couple of matching PCBs for relays and a soft start will follow very shortly, I just need to process the pictures and finish the write-up. This is basically the same circuit as the “v1.5″ of the standbyPSU (found here) without the onboard SSR.

How big are the boards?
This version measures 3.2″ x 1.875″ (app. 81 x 48mm) – so just a little smaller than the v1.5.

What is the status of the boards?
This board is v1.0 and it works as expected – not entirely surprising given that it is mostly identical to the v1.5 circuit which also worked well.

Does it use any special/expensive/hard-to-find parts?
No.

Anything else I need to know?
Note that big mechanical relays tend to draw a lot of power, so there might not be that much power left over to power anything else. As an example, the relay board that I will post later draws app. 1.2W. Throw in a couple of LEDs and the losses in the transformer, and there isn’t actually that much left over from the 2.5-3VA transformers that are the maximum that will fit on the board. You can of course use the controller to control a separate standby-PSU as well.
If you want to use an SSR, then be aware that they can be a bit tricky to work with and some attention must be paid to minimum load etc. I can recommend reading this document from Omron that explains a lot.

Downloads:
Download design files here

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

You can also read the other posts on this controller design for information.

Project files: BUF-03 revisited

What is it?
As I mentioned in my post on my still work-in-progress “Ring” amplifier, I am planning to use (at least initially) a version of my BUF03-buffer as the input stage. Since I have now build and tested the revised boards and they seem to work well, I thought I’d publish the files as an update to the original. Key changes are:

  • In/Out connections are now grouped together as single 3-pin headers instead of the previous 2 x 2 configuration.
  • PSU connector has been uprated to a screw clamp type which is easier to work with. Also, there is now only one PSU entry instead of two.
  • The diameter of the decoupling electrolytics has been reduced to 8mm which should still be plenty for low-ESR types (Panasonic FC/FM are what I normally use). The smaller caps make the board look a little less cramped.
  • There is now a provision for a resistor at the input. This sets the input impedance and may be useful in applications where no volume pot is used. It is optional if you either want to use a volume pot immediately before the buffer or just want the previous stage to see the natural input impedance of the BUF03 (which is quite high).

How big are the boards?
The board measures 2.55×1.45″ (app. 65x37mm) – same as the original.

What is the status of the boards?
The board is now in rev. 1.5 as I’ve only made minor changes (described above). Both the original version and this one have been tested and work fine.

Does it use any special/expensive/hard-to-find parts?
Yes. The BUF-03 IC was discontinued several years ago. They are often available as used or NOS on ebay, but as always be wary of the risk of counterfeit/substandard parts in ebay listings.

Anything else I need to know?

  • DO NOT attempt to use this board with the BUF634 or any other buffer IC as that will not work.
  • The BUF-03 ICs are internally biased to class A and will get (quite) hot during normal operation. Small TO-5 heatsinks are recommended if you can find them.
  • The board can be used with the (equally hard to find) BUF-04 from Analog Devices, as long as you note the different pinouts (different location of the DC offset adjust pins).
  • Remember to measure and adjust the DC-offset with the inputs shorted, preferably like this: Apply the power, measure offset and adjust to zero with the trimmer. Once done, disconnect power and let the buffers cool down. Once they are cold, reapply power and check that the offset does not “drift” too much when they heat up (leave them on for 5-10 mins. at least).

Downloads:
Download design files here

Related information:
See the two original posts for some more information and links.
Note: Always read the “intro post” for additional important information about my designs.

 

Use and misuse…

EDIT: The seller has responded and I received a perfectly reasonable explanation (getting rid of surplus boards) so I am happy :)

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I was browsing ebay for some power supply boards this morning, and much to my surprise (intially at least) I found one that looked extremely familiar: ebay-clone It’s actually a rip-off of my “ManyCaps” PSU layout and from what I can see the only change from the version I posted here is that my copyright-notice has been removed… Now, I know that noone is going to get rich selling PCBs at $4.50 each, but I still would have appreciated a note asking for permission and maybe a note of thanks on the boards – especially as this isn’t some Chinese hole-in-the-wall shop, but a longtime DIYaudio member who really should know better :( Oh well, I guess this was bound to happen at some point – I’ll send him a note and we’ll see what happens…

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