Project files: A PGA231x Volume Control

What is it?
A “digital” volume control based on the well-known PGA2310/PGA2311 ICs from TI. These aren’t actually digital, but just digitally-controlled resistor attenuators integrated on an IC – which doesn’t really matter anyway.

As is often the case, there are two board versions: One is a “normal” stereo version with a single PGA chip onboard, the other is a balanced/multichannel version that has two chips onboard (for balanced setups) and the possibility to daisy-chain more boards (for multi-channel systems). The boards are intended to be controlled from an Arduino or a similar microcontroller via an SPI-interface. I haven’t included any software in the download file, but there should be plenty of examples online that shows how to do this integration (especially for the Arduino).

As even the not so keen-eyed observer will notice, this isn’t a new layout. I recently realised I didn’t post these before and as the project they were meant for died somewhere along the way I am not sure I’ll ever pick these up again (at least not within the foreseeable future).

Note: I had some minor noise-issues with the boards. As I never got beyond bench-testing, the noise could be from any number of sources other than the layout (my shoddy test wiring, poor PSU, the poor USB supply that I used for the arduino etc.). This means that although the PCB layout is made according to (what I believe are) the TI recommendations for the PGA231x, I cannot guarantee that the finished board will perform 100% flawlessly without tweaks.

How big are the boards?
The stereo board measures 2.525” x 1.6” (app. 64 x 41 mm.)
The balanced board measures 2.525” x 2.65” (app. 64 x 67 mm.)

What is the status of the boards?
The boards are v1.0, meaning finished and technically working as I expected. Please do note the caveat above around noise though.

Does it use any special/expensive/hard-to-find parts?
None, really.

Anything else I need to know?

  • There are plenty of examples online for interfacing the PGA ICs with Arduino and other microcontrollers – do a search of diyaudio and the Arduino forums for a start.
  • The PGA chip wants to be driven from a low-impedance load and the input buffer sees to that – use whatever dual opamp you prefer here. If you don’t have a favourite already, I’d recommend the LME49720/LM4562 as long as they are available:) The PGA has a buffer of its own on the output and it is spec’ed to drive loads down to 600 ohms which should mean that all common configurations are catered for.

Download design files here

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

Please also refer to the data sheet for the PGA2310 for information about controlling the chip etc.


Been very busy lately, with both life in general and (especially) a job change. So, finally it’s been a (relatively) free weekend and a chance to relax with some solder fumes. Haven’t build anything that’s worth showing off at the moment, but it was nice to have some time to build again :D

Apart from a bit of soldering I also managed to finish some PCB files as well. Most important was the PCB for my version of the Audiokarma CNC RIAA (or, actually the “Muffsy” evolution version of it). I’ve been listening to a lot of vinyl lately and this looks like a very interesting (and simple) RIAA, so I had to give it a try – albeit with a few changes over the original. Boards should be here in a couple of weeks :)

Front panels are here…

I’ve had quite a few projects “stuck” for the last few months. They are more or less only pending final assembly, which I couldn’t/wouldn’t start because I have been missing the front panels. I mostly use Modushop-cases but I send the raw front panels to Schaeffer/FPX for milling and engraving.

It’s a bit costly so I normally try to bulk up on orders to save on shipping. I had been putting off ordering for a while to get as much as possible included, but before I left for Hong Kong I did manage to finally get the order out. Which now means I have got many projects “unstuck” so I can move on with assembly :D


Gone shopping?

Had some holidays left over and so I have just returned from two weeks of vacation in Hong Kong with a small “detour” across the border in to Shenzhen in mainland China.

Shenzhen and the surrounding area is probably the world’s biggest ecosystem for electronics manufacturing of all kinds. Most likely your mobile phone, tablet, laptop and many of the other electronic devices you use every day were made in the gigantic factories here – along with the corresponding accessories and a multitude of other things.

Within Shenzhen itself, there is a number of wholesale electronics malls where the manufacturers showcase their products – think a multi-storey shopping mall packed with small stalls and shops that only have electronics and components – and then imagine a handful of them side by side in the same street! There are also similar mega-malls with computer parts, mobile phones and accessories and security/CCTV-equipment. If you can’t quite get your head around this, the attached pictures might help a little :-)

These markets are where you go to check out what’s available, buy samples or small quantities and negotiate purchases of larger series or custom products. It’s also where you can go to a small shop and buy 100 ICs if you don’t need a full roll of 1000 or find discontinued ICs and transistors that aren’t otherwise available. This is of course because of the many factories in the area which means there are plenty of opportunities for buying excess inventory, obsolete/liquidated stock and so on.

So, for anyone interested in electronics DIY it should be a goldmine and it sort of is, but unfortunately not all that glitters is gold here – not by a long shot. Counterfeit parts and products are everywhere and so in a couple of places the piles of transistor boxes marked “Toshiba Semiconductor” that sent my heart racing a good bit faster, actually turned out to have been refilled many times since they came from one of Toshiba’s factories – at least that was how the parts inside looked.

An additional complication is that while I do like going to China as such, when it comes to shopping there I have some big disadvantages: 1) I don’t speak the language, 2) I look very obviously foreign and 3) I don’t really like haggling, especially for small amounts. Add the risk of getting counterfeit products into the mix and I spent a lot of time looking but didn’t really buy anything there, instead saving my budget for Hong Kong itself :)

Once back to Hong Kong I did some shopping. As is my norm for these trips, I also bought an audiophile present for myself. The obvious choice would be (yet another) pair of high-end headphones, such as the AKG K812, and I did find a pair of those calling my name as well :D. However, in the end I settled for something a little more useful – an Acoustic Research M2 high-res audio player.

I did try a couple of smaller and cheaper alternatives, but the M2 won me over on sound quality and the ease of use with the touch screen and it means I can semi-retire my iPod classics to home-duty. Testing the M2 right now with my AKG K501 headphones (120 ohm impedance) and the sound is much, much better than the iPod or what I’d normally expect from a portable player :)

Hard times ahead for Audio DIY?

It’s no secret that as mass-market electronics become increasingly compact and integrated, the availability of parts that are DIY’er friendly is shrinking rapidly. Most of Toshiba’s audio transistors (bipolar and JFETs) have disappeared, most of the high-voltage parts used for Stax amps have gone as well (together with the CRT TVs they were intended for), Onsemi killed a load of small-signal transistors not long ago and more and more semiconductors are disappearing in their through-hole versions and moving to SMD-only.

This has been going on for at least a decade, but I think a recent diyaudio thread highlights the issue and deals another crushing blow: A while ago Texas Instruments (TI) acquired National Semiconductor, and now TI has decided to discontinue a large chunk of audio-grade parts. You can see the whole list at Mouser here but among the “highlights” for the audio DIY’er are:

  • The LM3875 – discontinued with no replacement (!!)
  • The LM4780 – discontinued with no replacement (the listed LM4766 isn’t really comparable and will not fit the many LM4780-designs already out there)
  • The LM4562 – DIP-package discontinued, but SMD still available.
  • The LME497x0-series and many other LME49xxx opamps – all DIP-packages discontinued. In some cases the SMD-package stays available but some devices are going completely (like the LME49990)
  • The LME498x0 power amplifier drivers – discontinued with no replacement.
  • The LME496x0 buffers – discontinued with no replacement.
  • etc.

Now, according to the PCN the last order date isn’t until September next year and last delivery is in March 2017, but there is no doubt to me that this isn’t the last notice we’ll see of this type in the coming years. Also, there is a risk that some distributors will drop the parts earlier to avoid building up excess stock making parts difficult to source even before the official deadline, and in any case many designers will be reluctant to use parts that are marked EOL.

Certainly, my next Mouser-order will include a few spares of some of these parts and I can only advise you to do the same :(

An “Autopower” Circuit…

This is another Rod Elliot circuit (from here) but as usual I have done my best to add my own personal touches to it.

Basically this is a signal-activated trigger circuit (such as you would expect to find on just about any active subwoofer). The board turns on the power when a signal is detected and switches it off again when no signal has been detected for a while (usually 10-30 mins). For schematic and details on how the circuit works I’d refer you to Rod’s original page.

What I have done to make my mark is partly to keep the relay offboard and make a matching relay board instead, and then of course to actually lay out a PCB for the design. Both the relay board and the main PCB are in my own industry-standard of 2” x 2” :D

The main connectors on the control board and the relay board line up so the boards stack perfectly on top of each other. The relay board also includes a separate regulator (mostly because there was a bit of space left :D), so the board can be powered from any DC voltage above app. 15V. If you have no suitable standby voltage available in the device, I have also made a small unregulated PSU that can provide power to the circuit using a small (app. 1.5-2.5VA) mains transformer.

I’ve done some basic testing on the prototypes and it seems to work fine as such. However, one potential issue needs further exploration: The time is set by an electrolytic discharging through a very large resistor (10M). This makes the delay time a bit unpredictable. Also because the “must-release” voltage of most relays is around 10% of the nominal coil voltage the relay doesn’t actually release until very late and the indicator LED is therefore slightly pointless.

Project files: LM1875 Gainclone

What is it?
The project files for my mini gain clone with the LM1875 IC as described here. The download file includes both the amplifier board and the matching PSU-board.

How big are the boards?
The amplifier boards measures 1.8” x 1.3” (app. 33 x 46 mm.)  and the PSU board measures 3.9” x 1.8” (app. 99 x 46 mm.)

What is the status of the boards?
Both boards are v1.0. I have built a working prototype, but detailed testing is on hold until I have build another set that I want to turn into a finished amplifier. All I know is that the design plays music just fine on the test bench :)

Does it use any special/expensive/hard-to-find parts?
Not really, unless you choose to go overboard with expensive boutique parts, such as premium capacitors and fast rectifiers. You can, but you don’t have to… :D

Anything else I need to know?

  • The boards are intended to be used in dual-mono configuration with one supply board per amplifier. Take the speaker output from the amplifier board and the speaker ground connection from the spare ground terminal on the PSU output connector. It is of course also possible for two amps to share a PSU, but you may struggle with wiring everything with reasonably thick cables.
  • If you want to mount the amplifier in a 1U/40mm heatsink you need to keep the capacitors on the PSU board below app. 30mm in height and the amplifier board mounted perpendicular to the heatsink. If you have more space it is possible to mount the boards directly to a 50mm heat sink (parallel to the heat sink with the IC mounted from the underside). This would however mean you have to bend the pins of the LM1875 to fit yourself, because there is no standard pin configuration that supports this way of mounting.
  • You can mount R4 either on the top or the bottom of the board. I’d recommend that you use the opposite side of where the amplifier IC is mounted for easiest access.
  • There are more versions of the LM1875 IC depending on how the leads are shaped (straight and two different bend patterns in both 90deg and 180deg versions). From the datasheet I honestly can’t determine the correct order code for this board, so you’re on your own here… ;)

Download design files here

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

Read the LM1875 datasheet for more information. I’d also recommended the kit manual as a good source of information.


Past projects: Old ICEpower Amps…

I’ve built quite a few ICEpower amplifiers over the years, but many of them were built and sold before I started this blog. Recently I actually saw an amp for sale that I am pretty sure I built and so I started looking to see if I had any pictures of these amplifiers. Mostly I don’t, but I did manage to find a few:

The first amp is a small amp based on a 200ASC-module with a 200AC hanger. Unlike the ASP and A-series, the amplifier sections on the AC/ASC are the same so it is possible to build a (deceptively compact) stereo amplifier this way. I used this amplifier in my office system before I eventually replaced it with the B1/125ASX combo.

The second amp is a full-size amp based on 2 pcs. 1000ASP-modules. At the time, this was intended to be my own reference amp, but firstly I preferred the sound of the 500ASPs I were using before and secondly I got a very good offer on it so I decided to sell it soon afterwards.

The last amp is a three-channel model with a single 500ASP and a pair of 200AC hangers. The amplifier I used for a couple of years to power the center and rear channels. As the front amplifier I had two stereo amplifiers with dual 500ASPs wired in bi-amp mode, which made for a very compact surround system with plenty of power – around 3kW into 4Ohms – on tap :D. I eventually sold all these amps and started using the 6-channel 50ASX instead.

Project files: ICEpower Linear PSU

What is it?
The project files for the linear ICEpower PSU board I showed here. The first version of this board concept was made around 10 years ago, but as I didn’t have any boards left over I updated the design and cleaned it up a bit in the process.
The basis of this is once again the GP-PSUs shown here and the same file that I also used in a triple-configuration here. I have simply added a single high-power rail with a rectifier, two main caps and the usual decoupling + discharge LED – absolutely nothing fancy :)

How big are the boards?
This is the “XL”-version for 35mm main caps and the board measures 4.4” x 3.45” (app. 112 x 88 mm.).

What is the status of the boards?
The design is called v2.0 as it is based on a previous idea. It’s been prototyped and I see no mechanical or electrical issues.

Does it use any special/expensive/hard-to-find parts?
Not really, unless you choose to go overboard with expensive boutique parts, such as premium capacitors and fast rectifiers for the low-voltage supply (which I kinda did…).

Anything else I need to know?

  • The board should work with the ICEpower 200AC/300AC and the 250A modules which require around a 50VDC Vp voltage. For the 500A and 1000A modules you might need to check and modify the board files to get enough high-voltage clearance for the higher supply voltages used (nominal 80VDC/120VDC respectively)
  • The high-power supply uses a pair of snap-in capacitors up to 35mm in diameter and a GBU-type rectifier (available up to 25A). The low-voltage supply uses 22mm snap-in or 18/16mm standard radial caps with 1N540x or similar rectifiers.
  • Due to the rectifier setup on the low voltage supply, it is possible to use it with both single (voltage-doubled) and dual AC connections. In that case you should connect the transformer to one side of the AC-connector and you need only fit the required pair of diodes (either DA/DB or DX/DY), although of course there is no harm in mounting both pairs.
  • If you have space, I would recommend that you run “dual-mono” with separate power supplies for each channel, mainly to ensure that there is a good amount of capacitance on the high-power rail. If, like me, you still want one box and avoid a true mono-block design, then the high-power rail can use separate windings on the same transformer and the low-voltage transformers can be separate or shared between the channels. The sharing can of course be done either as parallel-connected dual rectifiers or as separate voltage-doubled circuits with each board using one transformer winding (honestly not sure what would be better here :) ).

Download design files here

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

Read the ICEpower module datasheets carefully as well (and, if you can get your hands on them, the Designer’s Manuals as well).

Note: For once, I do actually have some spare boards left as I only needed the pair and I had to order 10 pcs. As you can see, they are green, HASL-plated and made with 2 oz. copper. If you are interested in boards, drop me a line.

Back from Canjam…

Yes, I have returned from the CanJam meet in London! (see previous post). Overall a very good experience – although it was my first show/meet of this type. I met quite a few interesting people and had some good discussions with fellow hifi-nuts. As always, the enthusiasm clearly shines through (as is the case with any hobby I guess?). I also thought (and that might just be me) that it looked like a more diverse crowd than what I typically see at audio shows – not surprising as such, but just enough to be noticeable :)

I brought the camera, but there were so many other people with cameras that I only managed a few shots before putting it away. If you want to see what went on, check out the official head-fi “meet-thread” for pictures etc. instead.

As expected there were quite a lot of interesting new products to see, touch and try, but I managed to get out with my credit cards (relatively) unharmed – at least for now :D Best sound of the show for me was definitely the combination of the Stax SR-009 electrostatic headphones and the Headamp “Blue Hawaii SE” tube amplifier as pictured below. This is a killer setup – unfortunately with an equally killer price tag.

The most annoying thing was probably that I’ve never listened to the SR-009s before and I was a bit surprised at how big a step up from the SR-007s that I own they represent. That does not bode well for whenever I decide to go to Japan again :D

Looking forward to next year’s CanJam because if my schedule allows I will definitely be there! :)


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