Another Borbely clone – almost…

You may remember this post about a clone of one of Erno Borbely’s design. Now there’s another one! …but unlike the last one, which was green, this one is red! :D

It is actually a combo of amp and PSU from ebay seller jimsaudio. The amp is not really a pure Borbely design, but instead a Borbely JFET frontend mated to a (Walt Jung) diamond buffer output stage – which in itself doesn’t really matter if the sound is OK. Quite like the last one though, it is full of parts that are now pretty much impossible to find. However, 20 years of “collecting” parts can actually be helpful sometimes :D.

The power supply is also a “bastard” design – a tweaked version of Borbely’s take on the Sulzer regulator I think. However, Erno has definitely left his mark here as well – even the regulator uses some very hard to find transistors – and I can’t be the only one that winces a little at putting “unobtanium” devices like 2SK170BL/2SJ74BL JFETs in a power supply? OK, it was only one pair of each and I had an odd number anyway, but still it hurts a bit…. ( :) )

Anyway, if the results are worth it then I can live with it and initial impression is definitely that it is. The sound is smooth and detailed without any noise or hum, even from just a simple bench test. Now all that remains is the usual waiting period before I get around to making the rest of the mechanical stuff for the casing – shouldn’t be more than a year or two :D

PS: While looking around the internet I found another Borbely design for a tube/FET hybrid line stage running at just +/- 24VDC. It comes in two variations, one intended for line stage duty and the other one beefed up a little to drive headphones. The differences are small though, so it should be possible to put both variations on the same PCB. I am thinking that there could be a way to redesign this with transistors that are still available – maybe not 100% the same performance, but it would be worth a go I think :)

Project files: Little helpers – Fuseboards

The third part of my “little helpers” project series consists of a few connector/fuse boards for power supplies or for testing/lab use. Not exactly the world’s most interesting PCBs, but still  – they can be quite useful so I decided to publish them anyway :)

What is it?
These are simple fuse-boards with LEDs to be used on the secondary side of a transformer or DC PSUs (such as switchers). There are two versions:

One version can be used to combine two AC or DC voltages to provide a center-tapped voltage. The circuit works on both AC and DC so can be used for example for wiring up two secondary windings on a transformer to provide a +/- voltage or for combining two DC power supplies to do the same.

The second type of board is more or less identical, except that the ground plane is split so they are “passthrough” for the input voltages. This is useful for instance if you want to put fuses between the transformer secondary and a PSU board that already has an onboard rectifier and does not need (or want) a center-tapped voltage.

The boards also include fuses for both rails as well as LEDs to indicate that power is applied. If connected in the “standard” way then the LEDs are connected to the input through the fuse, so if the fuse breaks the corresponding LED will turn off.

How big are the boards?
There are two sizes of both designs:

  • The “small” one measures 2.0″x1.95″ (app. 51x50mm)
  • The “normal” one measures 2.5″x1.95″ (app. 64x50mm)

The two versions are compatible, meaning the board size and hole spacing are the same for the two versions.

What is the status of the boards?
All boards are in v1.0, meaning they have been tested and are working. (Well, to be honest I haven’t received the prototype versions of the “passthrough” boards yet, but as they are made from the schematics to the other ones I expect no issues) :)

Does it use any special/expensive/hard-to-find parts?
Not really. The fuses are standard 5x20mm types with holders (22.5mm lead spacing). The LEDs, resistors and diodes are all “standard” types and the terminal blocks are 5.0/5.08mm types.

Anything else I need to know?

  • On the large boards it should be possible to use PCB-mounted FAST-ON tabs instead of the terminal blocks (not tested though).
  • Note: These boards are not intended for mains voltage use!

Download design files here

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

Panda Headphone Amp

Another half-arsed half-finished project… :D

This is a HA-1 mk2 headphone amp, also known as the “Panda” amp. I bought the kit a few years ago when this amp was FOtM (“flavour of the month” – or as some would say “fad of the month” :D), but of course I don’t really need any more headamps and so it was just lying in my box of “may need at some point” unassembled kits. However, I few weeks ago I was cleaning looking through said box and found it again, and since I felt like soldering something that day I started working on it.

Unlike most “cheap” kits, this actually comes with decent components. I replaced a few components for cosmetic reasons and bought new main caps because the ones provided did look a bit worn, but other than that everything is what was provided. The amp is an all-discrete design with JFET input stage and a BJT output stage, so I had to do some matching to the input FETs, but other than that it is a straightforward build. Initial impression is that the sound is very good, but one of the reasons for the hype around this amp originally was that it is supposedly very good with AKGs and so I need to dig out my K501s and K701s to try that as well (they’re in another box..) :)

Now, I am still counting on the upcoming x-mas break to give me some time to finish some builds, but it’s unlikely that this will be one of them. When I started putting the board together I just wanted to do some soldering, but I didn’t have a case design in mind then. I still don’t to be honest, and since I’ve used 35mm tall heat sinks and capacitors the board is now too big to fit into a 1U modushop case – grr!

Maybe it is time to head to ebay for some “inspiration” instead then? :)

Amp Camp Amp

Here is another one of Nelson Pass’ brilliant designs, the “Amp Camp Amp” or ACA for short, that I managed to put together (halfway at least – as usual…).

First launched a couple of years ago, the ACA was developed by Nelson for an “amp camp”, an audio maker event and the schematic since posted as a project article on his website The ACA is a very simple and easy to build class A amplifier that produces around 5W (which goes surprisingly far in most “at-home” applications). To make the ACA more “beginner friendly” it is designed to work off a 19V switching adapter from a laptop computer. This makes it cheap to build and ensures that an inexperienced builder does not have to worry about mains wiring etc.

For this build, I have used the “official” boards from the diyaudio store. There is also a very sexy looking custom chassis for the ACA in the diyaudio store, but since they would be shipped from the US and I would be hit with well over 30% extra in VAT, import duty and brokerage fees I elected not to go that route.

Instead I found some special heat sinks from ebay to brighten up an otherwise black chassis :D The main argument for choosing these was otherwise that they are 80mm long as opposed to the more commonly available 75mm ones which would be just a tad small for the ACAs recommended mounting. The quality is decent although the colour washed off a bit while I was threading them (using lots of spirit for lubrication). The aluminium alloy is also a bit softer compared to the Fischer or Alutronic heat sinks I normally use, but that isn’t necessarily a problem.

As usual with the Pass designs, the components for the ACA are completely standard “off the shelf” types and the only part that could be difficult to obtain is the 2SK170 input JFET. There are a few alternatives though (the 2SK246, 2SK369 and LSK170 should all work if you just respect the pinout) so even that should not deter prospective builders.

The original ACA design used external switching supplies but I prefer to keep the PSU internally in the chassis, because the laptop supplies are a bit impractical. Instead, I have got a standard “industrial grade” 20V/100W SMPS from Mouser in a 3″x5″ open-frame format.

Looking forward to the Xmas holiday where I should be able to make some more progress on this one :)

WCF amp completed

It’s been quite a while since I really finished a build. Sure, lots of small steps forward on lots of other projects, but nothing really finished to that fantastic moment where you can actually hear music for the first time :) (or the slight less fantatic moments where you see smoke, a broken fuse or simply nothing at all… :D )

This is the just the WCF headphone amp I build a while ago (see this post) which has now been cased up. Instead of putting in a lot of effort on DIY mechanics I took a shortcut and bought the bespoke ebay-chassis for the design. It’s not bad, obviously fit and finished has been seen better, but given how I normally struggle to do the mechanical stuff it was still worth it. And anyway, this was a bit of a “sideline” project anyway. The transformer is from Audiophonics because they had an “off-the-shelf” model with the right specs which also was about half the price of a custom one from Toroidy.

Listening at the moment with a newly-purchased (but second-hand) Arcam rDac as the frontend and this amp is still not bad at all for the modest outlay I think :)

Click-click! A relay-based attenuator…

Yes, when you are not lucky enough to score a good deal on expensive pots (see my last post) then getting suitable attenuators for your project can be a bit of a pain :D If you are looking for a balanced attenuator there isn’t really much “middle ground” out there between an Alps RK27 costing app. €30 and a real stepped attenuator such as a DACT (which retails for more than €300).

The typical answer to this is simple – use relays. I was never really a fan of relay attenuators though, having always found the loud clicking noises whenever you even looked at the volume knob really annoying and not something I’d want to have to live with on a daily basis. However, relay attenuators do have a couple of advantages, among which that they can be built for a reasonable cost. A stepped attenuator also has very good channel matching, but whereas even the expensive DACT only gets you 24 steps, typically with 2dB between them, 128 or even 256 steps of 0.5dB each are quite easily achieved with relays. So, having thus abandoned my principles, I wanted to try one as well :)

Even a cursory look at the schematics would reveal this as a clone of TPAs “Joshua Tree” attenuator, however it is by way of another design. I actually started from the eagle files shared by diyaudio user MaxW in this thread. I have kept the circuit more or less intact, but removed the input selector that Max had and converted it to a (nearly) complete through-hole design.

I have decided to keep the I2C-controller and the attenuator itself onto a single PCB. A couple of reasons for this, mainly that it makes for easier wiring when the PCB is “self-contained” apart from the controller and PSU, but also that when the attenuator is used in a balanced or multichannel configuration each channel gets its own I2C-address, meaning you can easily control levels separately. The added parts cost is negligible to me. The attenuator stage itself uses Omron G6K 5V miniature relays and Vishay RN55 resistors. As far as I know there are no substitutes from other manufacturers for the relays (because of the uniform 2.5mm pin spacing), but Reichelt has them for a decent price so even that is manageable. The unit is intended to be controlled by an Arduino (or similar microcontroller) with I2C-capability and I have used MaxW’s sample code from the diyaudio thread as my starting point which seems to work very well.

Now, I have put together the first sample PCB and I am honestly a bit impressed. Obviously the clicking is still there, but it isn’t too loud with the tiny Omrons. The volume ramps very smoothly when you turn the encoder and I heard absolutely no audible clicking or noise in the headphones I used for testing. My next step is to build a pair of additional boards for a balanced setup and modify the Arduino code to support a balanced configuration as well :)


PS: If you need a different value for the relay attenuator, there are a few good pages out there with information and online calculators:

- AMB’s “Delta 1″ project. (also the AMB discussion forum is a good source of information)

- Jos van Eijndhoven’s “Relaixed” preamp.

- Twisted Pear Audio’s “Joshua Tree” and the matching controller.


I don’t normally post about all the audio-related stuff I buy (then this would not be a blog but a twitter-feed :) ), but here’s an exception:

In a post coming very shortly I am going to complain about how expensive it can be to get decent quality volume control attenuators for DIY audio projects. I still think that I am right in saying that, but nevertheless – sometimes you have to be a little lucky ;)

A few days ago I was fortunate enough to find a sales listing on a local audio forum for three Penny & Giles RF15 stereo log pots. I saw the listing only minutes after it was posted and so managed to beat about a handful of others that wanted them.

I know that P&G pots are very highly regarded (and very expensive) but having never handled one before I didn’t really know why. Now that I’ve collected mine from the post office I can however see why. They are heavy, they seem very solidly built and the feel of the action is silky smooth. These are used and probably quite old, but I expect that they will work fine still. I already have a project lined up for one of them and the other two are going into storage until I find something else worthy of these beauties :)

And the price? Oh, about the same as you’d pay for a standard blue Alps pot when purchased from a reputable supplier… (I did say I was lucky to find these, right? :) )


Project files: Mains controller v1.5

What is it?
As promised in the original post, an update of the Mainscontroller design to v1.5.

This is the transformer-based version 1.1 which I have tweaked a bit. There aren’t really any functional changes but I cleaned up the layout a little and included some things from the rev. 2.0 such as a “”proper” terminal block for the switched DC output. Also, two versions are included, one with an onboard fuse and a single output connector, the other without the fuse and with two parallel outputs instead. The holes are compatible between the versions and all parts except the output connectors and fuse holder are identical between the two versions.

There are some minor tweaks to the included BoM as well, mainly the addition of values for a 9V option but also tweaks to some resistor values for more consistent operating points between the versions.

How big are the boards?
Both board versions measure 3.7″ x 1.875″ (app. 94 x 48mm) – the same as the older v1.1.

What is the status of the boards?
As mentioned, this is v1.5 of an already tested design. I have built one copy of the single-output version and it works as expected.

Does it use any special/expensive/hard-to-find parts?
Compared to the original v1.1, no.

Anything else I need to know?
If you’ve read the comments in the original post, then no :)

Download design files here

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

50k and counting…

Regular readers here may remember that I posted when the blog reached 15k page views just before New Year’s and 30k views in mid-May. Now the next milestone is up – 50000 page views since I started writing!

I am still a little baffled (and humbled) by this, not to mention the fact that the blog has been visited by readers from more than 100 countries all over the world – 103 to be exact (!). Also, the project files I have posted have been downloaded a total of more than 1000 times, which hopefully means that at least a few people out there have built some great stuff based on my designs :-D

However, as good as all of this might be, the best part about running this blog is actually that I get a chance to come in contact with so many people from around the world that share my hobby. A big thank you to everyone and I hope you’ll keep checking in – I’ll do my best to keep posting new stuff :-)

Project files: The ManyCaps PSUs…

What is it?
A little sideline project one might say :). For one of my other (upcoming) projects I needed to buy quite a few Panasonic FM series capacitors in one specific value. As is sometimes the case, buying 100 wasn’t much more expensive than just buying the 35 I needed and so I ended up with a question: What can you do with the rest?

In theory, paralleling multiple small capacitors gives you lower ESR/ESL and higher ripple current than a single big cap. However, due to the physical distance required between the many small caps some of the benefit is negated and overall I am not sure I dare say that one approach is inherently better than the other – that depends on what you are trying to achieve I think.

However, as I already had the capacitors I might as well try it. Obviously, something as groundbreaking as this needs to have a suitably audiophile-sounding name, so without further ado allow me to introduce the “ManyCaps”(™) audiophile PSU boards :D

There are two versions, single and dual, with space for either 2×12 or 1×15 13mm radial capacitors. The most obvious application for these is probably gainclones and smaller class D amplifiers but they can be used anywhere where an unregulated supply is OK. The boards can of course also be used with a DC input, either with the rectifier in place or with the rectifier bypassed.

How big are the boards?
The single board measures 3.8″ x 2.0″ (app. 97 x 51 mm) and the dual board measures 3.925″ x 3.2″ (app. 100 x 81 mm).

What is the status of the boards?
Both boards are in v. 1.0. They are simple designs, so I didn’t need to make any changes and they worked the first time round :)

Does it use any special/expensive/hard-to-find parts?
Nothing really stands out:
  • The main capacitors are 13mm max diameter and voltage obviously depends on the application.
  • Rectifier is GBU-type and should probably be rated at least 6-8A.
  • The decoupling capacitor should be around 1.0 uF MKP or MKT. The lead spacing is 22.5mm on the dual board and 15mm on the single board.

Anything else I need to know?
Can’t think of anything :)

Download design files here

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


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