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 :D

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 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 ( :D ) 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 :D

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 :D

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 :D

Project files: The Muffsy RIAA clone

What is it?
My version of the “Muffsy” RIAA board. As I observed in the first post my version really looks nothing like the original, so here’s a quick rundown of what I have changed:

  • The board is mono and intended to be stacked two channels on top of each other as shown in the pictures because that was what I needed. Side-by-side placement and/or dual-mono configurations are of course possible as well – if maybe a little less practical…
  • The board uses single opamps instead of the duals on the original. This of course increases the cost a bit, but it also offers more flexibility for those that want to experiment with how different opamps change the sound (because the choice of singles is much bigger – especially after this).
  • Because I’ve found myself using the mute button on my amplifier quite a lot when changing records, I got the idea to include a relay-based mute on the output of the RIAA so that mute is available even if your amplifier doesn’t have a mute option.
  • The input cap position has been kept because my usual cartridge expects a slightly higher load capacitance so I need a capacitor in that position (you can of course still leave it out if you want).
  • The output cap position is bigger to make space for a more “audiophile” sized capacitor :-)
  • The selectable input impedance resistors have been removed. All of the cartridges I am reasonably going to use on my Pro-Ject turntable will be MM-types that need a 47k load impedance so I skipped this option – not that it’s a bad idea though.
  • The selectable gain I have kept, but instead of a DIP-switch I used a header/jumper which doesn’t take up as much space on the board. It’s only marginally less user-friendly than the DIP-switch in my opinion.
  • Otherwise the basic schematic and the component values remain the same as the original Muffsy.

How big are the boards?
The board measures 3.925” x 1.45” (app. 100 x 37 mm.).

What is the status of the boards?
The board file is v1.1 as I’ve fixed some minor niggles with the prototypes. I’ve tested the board and it works but I still don’t have detailed listening impressions, not least because – as the pictures show – I’m missing a couple of fairly important PSU components ;-)

Does it use any special/expensive/hard-to-find parts?
Most of these components are standard sizes and it should be easy to find from the usual sources, however note the following:

  • Capacitors in the signal path should be polypropylene** film types and ideally 2% tolerance or less and in packages with 5mm pin spacing. If you can’t find 2% capacitors, buy a few 5% types of each value and match them using a multimeter to at least keep the variance between channels as low as possible (honestly this is worth checking regardless of what you buy).
  • Resistors should be 1% tolerance (or better – so if you want to “splurge” on 0.1% types go right ahead :D ). Obviously the resistors for the relay and the LED are exempted from this requirement :)
  • The muting relay is a tiny G6K type from Omron and as far as I know there are no substitutes from other manufacturers. Make sure you get the version with even 0.1” pin spacing.
  • I don’t really recommend buying expensive opamps from eBay or aliexpress because it is simply too easy to fake the markings on a standard DIP-package to make a surplus TL071 look like a NOS OPA627 at 10-20 times the price, but only you can decide if you think the risk is worth taking. There are some great offers on eBay, but sometimes you have to go through quite a bit of grief to find them…
  • **No, in actual fact no one is really going to die because you use polyester film caps but you’re an audiophile so you should aim for the best (within reason, if you happen to be both an audiophile and an engineer or just an audiophile that still has a bit of common sense left :D )

Anything else I need to know?

  • The muting relay is powered by the positive supply rail (via a resistor if the voltage is higher than 12V) with the switch in series, so any latching switch will be usable as the mute switch.
  • As standard, the muting relay switches both signal and ground. Not sure if this is always a good idea, but if not then it’s quite easy to bridge the GND-connection on the back of the board so only the signal is switched.
  • If you don’t want the mute option at all just bridge both of the positions marked on the back the board and you can skip the relay, the resistor, the diode across the relay and of course the connector and switch.
  • As is my custom for PCB layouts this is quite tight (ok, make that “cramped”), so a couple of tips: 1) remember the decoupling caps on top and 2) measure the voltage on the opamp sockets to ensure that everything is OK before mounting the opamps becasuse the decoupling electrolytics make it a bit difficult to remove the IC afterwards. If you want to experiment with different opamps, consider stacking two sockets on top of each other. This should lift the actual opamp above the electrolytics making it easier to remove.
  • Again: Note the two SMD decoupling caps on the top of the board. They need to be mounted before you solder the opamp sockets!!. They also mean that you have to use a socket and you can’t mount the opamp directly to the board.
  • I’ve used a basic LM317/LM337 power supply for mine (this one to be specific), but there might be something to gain by using more sophisticated low-noise types. It is also possible to power the circuit from a couple of 12V SLA batteries, but if it is worth the trouble I’m not sure (probably not though – if you want to put that much effort into a RIAA you should maybe consider starting from a more advanced circuit instead :D ).
  • Regarding the opamps, the “default” option is the LME49710, but there are lots of other DIP-options as well that could potentially be used (LT1363, LT1028, AD797, OPA627 etc. are all common choices for RIAA-circuits) as well as of course several others in SO-8 packages that can be used with suitable adapters. Unless you already have a favourite IC, my advice would be to start from the default (which should be among the best “value-for-money” options anyway) and then change once you’ve tried it so you can more easily identify changes.

Download design files here

Related information:
As this is effectively a clone of the Muffsy board, you should read the Muffsy website for additional information (and if you really want the background, the original Audiokarma CNC thread as well).

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

Oh, and remember I did this because I wanted to experiment and tailor an existing design to my own requirements and preferences. If you just want to build a board and get sound out of it, don’t bother with this but buy boards/kits of the original Muffsy instead :D

The Great B1-binge…

I’m obviously a fan of the Pass B1 design but the last couple of weeks have seen the arrival of no less than three more B1s which is a bit much, even by my standards… :D

Not sure how this really came about, but it must be something like this: A while ago a saw an ad on a forum for a B1 clone board (the original type which is pretty much the same as the original pasty board). It was quite cheap and so I bought it. Since I now use both analog and digital I thought I could build one with two inputs (because my previous one only has a single input).

Shortly after I received this board and had started populating it, I realised I already had a partially-assembled board of another clone design that was basically only missing the input and output caps in order to be ready (yeah I know, I should keep a list or something… :D ). Because of the size of the onboard electrolytic caps, the board I had would fit nicely in a 40mm high enclosure, whereas the new board would require a bit more internal height, i.e. an 80mm chassis.

More or less the only thing I don’t like about these B1 boards is the fact that you have to “air-wire” the input switch, which means criss-crossing the inside of the chassis with long wires carrying the input signals. The obvious solution is to use a relay, so I went ahead and made a couple of small adapter boards to accomplish this. With a 24V relay all that is needed to switch the relay is the supply voltage to the B1 so it makes for very simple connections.

The last design was prompted by a reader email asking if I knew of a B1 with more than 2 inputs. The answer was “no”, but I then decided to build a source selector to match my own B1-board. The selector is a simple relay-based type with four inputs but it should work just fine. As I had some PCB mounted RCAs I made a board version for those, but also a more universal one without onboard connectors (not shown).

I’ve tried to put all of these in fairly nice cases, but it’ll still be a bit of a challenge to decide which one to keep as my “personal reference” :-)

Happy 2016!

As 2015 closes behind us and 2016 is just beginning, I would of course like to say a big “hello!” and an even bigger “thank you” to all of the people following my blog and reading what I post.

Lately the posts have been a bit further apart, but despite this the reader numbers are quite high – in fact much higher than I expected and I am of course grateful for that. The blog has now been visited by people from more than 120 countries around the world which I think is extremely impressive – I am not entirely sure I could even name 120 countries :D

In terms of what 2016 will bring there’s plenty of potential content in the pipeline I guess, but as usual work is intruding quite severely on my build time ;)

As a small appetiser of what’s coming, one of the long-term projects that I’ve managed to make som progress on lately is my first AMB Beta 22 headphone amplifier. I built the boards several years ago but then didn’t really make any progress for a long time. Finally a few months ago I summoned up the courage to test the boards and as they seemed to work fine I started on the mechanics. All that’s really left to do now is a bit of wiring and some final adjustments, so maybe sometime this summer is a realistic timeline? ;)

Best wishes for the new year to everyone out there reading :D


The Muffsy RIAA clone (teaser…)

It’s been a while and I’ve got no time to do a big writeup right now (it’s Christmas eve!!) but it’s here, it’s working and no, it looks nothing like the original. More in a few days but a very merry Christmas to everyone for now :D

Project files: Amplifier PSUs

Digging in the back catalogue a bit again here.…and found some of my power supply boards that I haven’t published yet :)

What is it?
Power supplies for amplifiers, d’oh! :D Two basic variants, namely a “class AB” type and a “class A” type. The “class A” type is intended to be used in a CxC configuration with resistors onboard for CRC and pads for a choke to make it CLC. The “class AB” one is a standard unregulated design for class AB or D amplifiers that allows using both small 16/18mm radial capacitors and large snap-in types (up to 35mm). Here there are two versions, one for 2 off 35mm caps (or 8 smaller caps) per rail and one for 3/12.

The picture below is of the large class AB board. It’s actually the board from the previous post that has had some caps mounted in the mean time :-)

How big are the boards?
The AB board measures 3.55” x 3.9” (app. 90 x 99 mm.) for the standard version and 3.05” x 6.1” (app. 77 x 155 mm.) for the XL version. The CRC board measures 3.15” x 3.95” (app. 80 x 100 mm).

What is the status of the boards?
Both of the “class AB” boards are in v1.0. The “class A” board is in v1.1 as I made a couple of tweaks (including the pads for off board R/L) to my original version. The original v1.0 is the board that I use in my “Green Monstre” amps.

Does it use any special/expensive/hard-to-find parts?
Nothing, really. You can go overboard with expensive capacitors if you want, but even if you have the money to put NOS Black Gates in your power supplies I’d still suggest you spend them elsewhere in the circuit :D

Anything else I need to know?

  • Unless you are building very small amplifiers I’d recommend that the CRC and the small AB boards are used in dual-mono configurations with one PSU per amplifier channel. The large AB board can be shared across channels for a medium power class AB or D amplifier (meaning anything with a rail voltage up to around 55V and 63V caps).
  • The boards all include LEDs that indicate power and bleed the capacitors when no load is connected (albeit very slowly). The corresponding resistor footprints should be large enough to allow fairly high LED currents but remember to calculate the power dissipation.
  • The CRC board has space for two resistors in parallel per rail, either axial types (up to around 3-5W will fit) or MPC7x radial types up to 5W.
  • The rectifiers are GBU-types which are available from Mouser up to a 25A rating.
  • Input connections for the Class AB “XL” board are via FAST-ON tabs. All other input/output connections are via 5mm spacing screw terminals.
  • The capacitors on the class A-board can be up to 30mm in diameter. Since class A amps tend to get hot, I’d recommend 105 degree types here. As mentioned above, the class AB boards use either snap-in caps up to 35mm diameter or 16/18mm  radial caps with 7.5mm pin spacing.
  • Needless to say, all capacitors should be rated appropriately for your amplifier’s rail voltage.


Download design files here

Related information:
These are very simple circuits, but there’s some god background on PSU design for amplifiers over on Rod Elliot’s pages (under “power”)

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

An unusual clone…

Well, it isn’t actually that unusual when you look at it, but to most audiophiles these days cloning a Harman/Kardon amplifier doesn’t make a lot of sense – they’re nothing special. That used to be different though**. Before Harman became a big conglomerate, took over many other brands and positioned the Harman/Kardon brand as a middle-of-the-road consumer brand, they were actually quite a decent hifi-company. Especially their top-of-the-range “Citation” series became home to a few popular classics.

Small wonder then, than even Nelson Pass had a go at improving of one of these – go and have a look (or download pdf here). Admittedly it was a while ago (1981), but if Nelson’s had a hand in it I think it might be worth trying and so what you see in the pictures is actually a “Pass Citation 12” clone.

As for my contribution here it’s honestly quite limited – I bought the amplifier PCBs som time ago from user Tazzz who always makes nice stuff :) The power supply is mine though, but it’s just a bigger version of a previous design I did (as I recently upgraded to a different version of Eagle which can do bigger boards than the standard 80×100 mm.), so honestly that’s not much of a contribution either :D

As the picture shows, I am stilling missing the main PSU caps but otherwise I already have most of the parts I need to finish this. I need an enclosure that fits as well though, so interesting project or not, it’s going on to my (already very long) list of half-finished projects :D

**Fun fact: My first “real” amplifier and CD-player back in 1994 were the entry-level models from H/K. That set kept me in music for over 10 years and then did another few years of service with my brother when her moved into his own apartment for the first time. Unfortunately I don’t think the entry-level models from H/K of today are the same quality…


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