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

Edit May 5th 2016: Download a BoM from 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.

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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 😀

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 😀

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 😀

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: 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.

 

Project files: OPA+BUF preamp/headphone amp

What is it?
This is a small universal preamp/headphone amp based on a single opamp of your choosing and the BUF634 buffer. This circuit has fallen out of favour with DIY’ers over the last few years but with the right opamp it does sound very good – in fact I think that for many people this would be all they really need 🙂

How big are the boards?
The board measures app. 3.3″x2.3″ or 84x59mm.

What is the status of the boards?
This board is in version 2.0 because it is based on one of my earlier layouts that has been recently updated. It has been built and tested and seems to be working fine.

Does it use any special/expensive/hard-to-find parts?
No, not really. My recommended opamp for this would be the LME49710 as the best value for money, but you can easily go overboard with something more esoteric (= expensive) if you want. For all-out quality I’d probably prefer the OPA627, but that’s a personal preference and there are many other options as well (AD797, AD843, AD8610/OPA827/LME49990 on SMD-adapters etc.).

Anything else I need to know?

  • The BUF634P used to be very hard to get, but should now be manageable to find again with Mouser, Digikey etc.
  • The bandwidth limiting cap (C3) is intended to be mounted inside the socket for the op-amp. If you are not using a socket, you can mount it on the back of the board. The footprint is for a 2.5mm leaded type but a 0805 SMD cap should fit between the holes as well without issues.
  • Note that in my picture I have used Wima MKS-02 decoupling capacitors (the small red ones). This was just because I had them available and they look nice – in reality 100nF X7R multilayer ceramics will be just as fine if not better.

Downloads:
Download design files here

Edit May 5th 2016: Download a BoM from here.

Related information:
Note: Always read the “intro post” for additional important information about my designs.
Read the BUF634 datasheet for more information about this design as well.

Project files: Szekeres VE headphone buffer

What is it?
This is a board for my version of Richard Murdey’s Szekeres VE (for “virtual engine”) buffer. This design is based on the original buffer concept by Greg Szekeres published at headwize a long time ago (c. 2002). The Szekeres buffer was one of the original headwize designs that I was very interested in when I started building amps due to its simplicity, but I never really got round to it. When I stumbled upon Richard’s revised version I had to try it – just to see if it was as good as I had imagined all those years ago (well, almost 🙂 ) Oh, and be sure to check out Richard’s site for some other very interesting DIY designs as well.

How big is the board?
The board measures 3.925″x1.95″ (just under 10×5 cm.), so just small enough for a 5×10 cm board service at itead.

What is the status of the board?
The board is in version 1.1. I have tested v1.0 and made a couple of alterations to the board as there were some minor space-issues here and there, but nothing serious.

Does it use any special/expensive/hard-to-find parts?
Yes. The power resistors are TO-220 types, Caddock MP-915 or MP-930 or equivalent and they are quite expensive. The FETs are cheap but need to be matched, so buy 10 pcs. or so. The heat sinks are Fischer SK129 types (or any one of many equivalents)

Anything else I need to know?

  • The layout is pretty tight so the mounting sequence is quite important, especially if using heat sinks taller than 25mm. Start with mounting the small resistors on the board. Then loosely assemble FETs, power resistors and heatsinks before mounting them one by one on the PCB. The mounting sequence should be to first to solder the heat sink pins and then the FET/resistor pins in place before tightening the FET mounting screws. Then move on to the next heat sink.
  • There is only room for small capacitors on the board so a regulated PSU is recommended (several options available from this site 😉 )
  • The FETs are the IRF510 types recommended in the article. The FETs need to be matched as described in the article as there is no way to null DC offset.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.
Refer to the RJM audio site for BoM and information of component selection.

szekeresve-1

Project files: BUF-03 stereo buffer

What is it?
This is the board for the BUF-03 based stereo buffer described here. The board is a stereo buffer that can be used as a preamp or headphone amp. The board requires a dual, regulated 12-15VDC power supply capable of supplying at least 150mA.

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

What is the status of the boards?
This board is in version 1.0. It has been prototyped and tested without any errors found.

Does it use any special/expensive/hard-to-find parts?
Yes. The BUF-03 IC was discontinued several years ago and is not easy to get. 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).

Downloads:
Download design files here

Related information:
See the links referenced in the original blogpost for build articles etc.
Note: Always read the “intro post” for additional important information about my designs.

buf03

Project files: Mono op-amp buffer/driver

What is it?
This is a board for a generic mono buffer/gain stage based on a single op-amp. Depending on the chosen op-amp, the board can be used as a preamp or headphone amp on its own or be combined with a suitable output stage for even more oomph. The board requires a dual, regulated DC power supply (for details on voltage/current ratings, refer to the spec sheet of your chosen op-amp).
This board has the same hole dimensions as the discrete Alpha20 buffer from AMB and while the connections are not 100% identically located, the boards should be interchangeable in most applications.

How big are the boards?
Boards measure 1.8×1.4″ (app. 46x36mm) which means they are just small enough to be made very cheaply by Itead or several other companies.

What is the status of the boards?
This board is in version 1.2. Version 1.1 added an LED to indicate power (on the positive rail only though). Version 1.2 incorporates minor changes to the silkscreen and a change of signal spacing from 6 to 8mil. Both versions 1.0 and 1.1 have been prototyped and seem to work fine.

Does it use any special/expensive/hard-to-find parts?
No, not really. You can use a really expensive op-amp such as the AD797 or the OPA627 if you want though 🙂

Anything else I need to know?

  • The output socket has two GND terminals because the board was originally intended to work with ICEpower ASP-series amp modules. These have differential inputs, so when connected to an SE buffer the In- terminal needs to be grounded.
  • The bandwidth limiting cap (C3) is intended to be mounted inside the socket for the op-amp. If you are not using a socket, you can mount it on the back of the board. The footprint is for a 2.5mm leaded type but a 0805 SMD cap should fit between the holes as well without issues.
  • Note that the spacing around certain parts (mainly R4 and R6) is quite tight, so be careful when populating and soldering the boards.

Downloads:
Download design files here

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

unibuf-1

Project files: Opamp buffer for ICEpower ASX-modules

What is it?
This is the PCB design for the dual opamp-based input buffer for the ICEpower ASX-modules as described in a previous post. This can be used before ICEpower ASX-modules in SE-mode if you need to raise the gain and/or the input impedance of the modules. You can also tune the sound quality and sound signature by using different opamps (yes, it does make a difference).

How big are the boards?
Boards measure 1.975″x1.75″ (app. 50x45mm) which means they are just small enough to be made very cheaply by Itead or several other companies.

What is the status of the boards?
This board is in version 1.1. I have previously prototyped version 1.0 which had a slightly different layout and only one input capacitor footprint, otherwise they are electrically identical. At the time of posting this I have ordered prototypes of v1.1 for myself but they haven’t arrived yet.

Does it use any special/expensive/hard-to-find parts?
No. At least not unless you go completely overboard with your choice of opamps 🙂

Anything else I need to know?

  • You can omit the input caps (bridge them) if you are using a source that does not have DC offset.
  • This board is not compatible with the ASX-modules when running in bridge mode because both opamps operate in phase.
  • You can’t power the board directly from the AUX supply on the ASX-module because the voltage is too high and the supply is unregulated. Use an external regulated supply or read the ICEpower docs for instructions on how to use the AUX supply.

Downloads:
Download design files here

Related information:
See the links referenced in the original blogpost.
Note: Always read the “intro post” for additional important information about my designs.

EDIT 07-09-2013 – added picture of the board.

asxbuffer-1