Project files: Little helpers – Alps PCBs III

What is it?
These are “little helper” boards for the Alps RK168xx series of motorised potentiometers. These pots are not quite as good quality as the standard Alps “Blue Velvet” RK27-series, but they are cheaper and smaller. They are also used in many commercial products, so they should work fine for many diy projects. The motor also means that the pots have a nice mechanical feel to them 🙂
There are two board versions, a 2-channel (for stereo with the RK16812) and a 4-channel (for balanced amps with the RK16814). Alps also makes a six-channel version of the pot and adjusting the footprint to fit these should be relatively easy, but I have no need for these now so I couldn’t be bothered 🙂

How big are the boards?
Both boards measure 1.85″ x 2.0″ (app. 47 x 51 mm) and the rear mounting holes are in the same place on both boards.

What is the status of the boards?
Both are version 1.0 since they are exactly as my prototypes.

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, so not really 😀

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. You can also use the grounding pad on the bottom instead.
  • 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.
  • The basic Eagle footprint for the RK168 was one I found in a diyaudio-thread, so I can’t take credit for that. All I have done is modify it to match the Quad-version 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.

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Project files: LED tester

What is it?
The PCB files for my version of Håvard Skrodahls LED-tester as described here.

How big are the boards?
The board measures 2.0” x 1.6” (app. 51 x 41 mm.).

What is the status of the boards?
This is version 1.0 as everything (for once) worked the first time 🙂

Does it use any special/expensive/hard-to-find parts?
None, really. The 16mm pots can be bought from ebay and everything else you should be able to get from multiple different sources. If possible, I would suggest using a stereo 5k-10k pot and the fully-isolated version of the LM317. The former gives the best adjustment range and the latter helps protect against mishaps with flying test leads 😀

Anything else I need to know?

  • For information about how the circuit works, read the hackaday-post linked above.
  • Output current can be calculated as 1.25V/Rtot. For max. current Rtot = R1 and for min. current the value is Rtot = R1 +  the pot value (with the decks in parallel if you are using a stereo pot obviously)
  • There is a difference between Lin/Log pot as described in the build article, so you’ll have to decide up front which adjustment profile fits you best (or keep the pot offboard so you can change – or just build two boards 🙂 ).
  • If you want to use the “high-current” mode, populate R2 as well and short the jumper. Remember that power dissipation in both the resistor and the LM317 regulator increases with higher current. The calculations for min and max current above have to be adjusted to reflect the fact that R1 and R2 are in parallel.
  • The connection for the ammeter is required as it is in series with the LED being tested. If you don’t want the ammeter, bridge If+ and If- connections as shown in the picture. The connection for the voltmeter is optional.  Note that I have tried using a cheap LED meter from ebay for the ammeter and I had some problems with it, whereas if i connect my normal multimeters everything works fine – YMMV.

Downloads:
Download design files here

Related information:
Be sure to read the original post for the exact circuit description, information and tips.

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

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 😀 ). 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 😀 )

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 😀 ).
  • 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.

Downloads:
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 😀

Project files: Little helpers – Ground Loop Breaker

One more little helper for you guys 🙂 Once again, not exactly a major effort with this one, but I hope it is still useful.

What is it?
It’s a Ground Loop Breaker as described in this article by Rod Elliot on grounding/earthing of audio equipment.

How big is the board?
The board measures 2.0″ x 2.0″ (app. 51 x 51 mm.) This is my new semi-official standard for modular circuits like this and will allow stacking of boards 🙂

What is the status of the boards?
The board is version 1.1 as I had to replace the original bridge rectifier with a different footprint.

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

Anything else I need to know?

  • Read the article and follow the recommendations on connections.
  • The rectifier bridge should be in a so-called GBPC-W package with wire leads. The rating should be 25A or higher and both the bridge and the capacitor should be rated for at least the mains voltage where you live (so 250VAC/400VDC in 230V countries)
  • The connections on the “ground” side (input) are either via the screw clamp or a couple of FAST-ON tabs. Connections on the “earth” (output) side are either via FAST-ON tabs to a dedicated ground screw or a plated-through hole that can be used to make the chassis connection. The board mounting holes are isolated. Use cables that are as short and thick as possible for all connections.

Downloads:
Download design files here

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

Be careful with working with any mains wiring and be sure to ask questions if you are not sure about anything, either in an online forum or to a local electrician (preferred).

Project files: Little helpers – Capacitor boards

Another post in my “little helpers” project series consists of a couple of capacitor boards for mounting input/output capacitors that will not otherwise fit on an amplifier board.

What is it?
Universal boards for (input) capacitor mouting, either for testing purposes or for designs where there is no space to mount a decent-sized capacitor on the main PCB. I made the small board to supplement my P3A clone where adding a large input capacitor would have increased the overall board size quite a bit, so using an off board input cap gives more flexibility. The background for the ridiculously large “MegaMKP”-version you can read in my previous post.

How big are the boards?
This big 🙂

  • The “normal” board measures 2.0″ x 2.0″ (app. 51 x 51 mm.)
  • The “MegaMKP” board measures 3.95″ x 0.625″ (app. 100 x 16 mm.)

What is the status of the boards?
Both boards are in v1.0, meaning they have been tested and are working.

Does it use any special/expensive/hard-to-find parts?
Well, there’s really nothing on these boards except the capacitors 😀

Anything else I need to know?

  • The small board has capacitor mounting for small caps on the top and for larger caps. Max dimensions are approximately:
    • Bottom side mounting: 25 x 38mm axial capacitor (with holes for 33mm long caps as well).
    • Top side mounting: 27mm lead spacing x 15mm thick box cap or app. 20 x 28 mm. axial capacitor.
  • If using the bottom side mounting points, either mount the board upside down on standoffs or don’t use the footprint for the terminal block but solder wires to the board instead.
  • The large board has holes for a various combinations of 2/3/4 large caps. There are screw holes that can be used to mount the boards to the chassis via standoffs so you can use caps as big as you like.

Downloads:
Download design files here

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

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) 😀 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 😀

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.

Project files: Little helpers – Connectors

The second part of my “little helpers” project series consists of a few connector boards amplifiers or for testing/lab use.

What is it?
Three boards for various connectors and purposes:

  • An XLR/TRS-board which is a small breakout-board for a Neutrik NC6FI-H XLR/TRS combo connector that means you can then use bare wires or a three-pin connector to wire up the socket.
  • An XLR I/O board which is intended for XLR in and loop out with “standard” PCB-mounted Neutrik D-series XLR connectors.
  • An RCA I/O board which is designed for some board mounted RCA connectors. I don’t actually know who makes these but they are pretty much the only decent-quality style PCB mounted RCAs that I know of. There are a couple of of internet sources for them (ebay, audiophonics, Rapid electronics, ) and I think they are identical (if nothing else then in size/dimensions) to the ones sold by Vampire at a more “audiophile” price 😉 If anyone knows the “true” source of these then I’d like to know?

How big are the boards?
Small… I don’t want to list them all here 🙂

What is the status of the boards?
The boards are in v1.0 which means they have been tested and are working.

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

Anything else I need to know?

  • Note that although the XLR/TRS sockets do fit into a standard Neutrik D-series hole, for reasons I don’t quite understand the board will not sit completely straight if mounted that way. For most uses that will not be a problem, but if you want to use these in a 1U enclosure you need to be a bit careful or mount the board upside down. To avoid this, make your panel holes exactly as it is shown on the drawing.
  • On the XLR-boards there is an onboard jumper to connect pin 1 to ground, so depending on usage (SE or BAL) and grounding scheme of your build, this is an easy way to manage ground loops. There is also a jumper to connect the chassis to ground which should not ever be necessary if everything you connect is made properly. If it isn’t, then that jumper is here to save the day 😀
  • The “XLR loop” boards are included in a “right” and a “left” version which are mirrored. If you only need one version and don’t really care which one, I’d recommend the one marked “left” as it has the nicest routing (unbroken ground plane).

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 datasheets as well and ensure that you verify the connector part numbers before hitting the “buy” button on anything :).

Project files: Little helpers – Alps PCBs

These “little helpers” are small supporting boards I have developed for my various audio projects. I have a few different ones and I don’t think they are really “big” and sophisticated enough to warrant a post for each one so I’ve decided to lump them together in a few groups instead.

What is it?
The first collection is PCBs for mounting Alps (and a few other types, including the Noble I have used in some of the pictures 🙂 ). Included are boards for different types of potentiometers namely stereo without motor and quad with and without motor (i.e. Alps types RK27112 and RK27114/RK27114MC).

For the unmotorised version there are two variants: “Preamp” groups input and output terminals together and “Breakout” groups the individual decks of the pot together. The “preamp” version is used when you want the signal to flow through the pot (such as in a pre-amp), whereas the “breakout” version is used when you want to insert the pot into an existing circuit, i.e. for wiring an off board pot to an amplifier PCB that has onboard space for it. This distinction is mainly to help simplify wiring – unless the circuit has a really strange design with respect to grounding, you can of course use the boards interchangeably.

How big are the boards?
Small… I don’t want to list them all here. The biggest board is the quad motorised which measures 3.5″ x 1.75″ (app. 89 x 45 mm).

What is the status of the boards?
The boards have been tested in v1.0 and for a couple I made some cosmetic changes, including changes to the footprint of the motorised quad pot, to upgrade them to v1.1.

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 😀

Anything else I need to know?

  • The stereo boards have 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 various quad boards have all holes in the same places so the motorised and unmotoriseed boards can use the same chassis footprint (even if of course the unmotorised board is smaller)
  • The “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.
  • On the motorised quad pot the shaft is connected electrically to the solder pins for the motor housing, so if you want to ground one of these you only need to connect a small jumper on the underside of the board from one of the housing pins to the ground pad – no messy wiring needed.
  • The eagle footprints for the quad pots are not “official” but ones I made myself by chopping up the stereo footprint. They work fine, but they probably aren’t the last word in accuracy and the holes for the housing pins could have been done more elegantly…

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.

 

EDIT July 28th 2014: Added pictures (which I stupidly forgot when I posted this…)

Project files: Audio meters

What is it?
Two designs for audio level (VU) meters. One is a driver for analogue VU meters based on this design.
The other is a small VU meter based on the National/TI LM3916 VU-meter IC. This design comes from here and incorporates a peak-detector with (adjustable) hold.

How big are the boards?

  • Analogue driver: 1.95″x1.625″ (app. 50×41 mm.)
  • LM3916 meter: 2.175″x1.275″ (app. 55×32 mm.)

What is the status of the boards?
The analogue driver board is in version 1.1. It has been built and tested and looks to be working (only a quick functional test, nothing extensive). I have made some cosmetic fixes (silkscreen etc.) for v1.1.
The LM3916 layout is in version 2.1. It is a revision of an old design of mine, so was upgraded to v2.x. I built and tested v2.0 and then fixed a couple of mistakes (including an unconnected power rail – doh!) to get to v2.1.

Does it use any special/expensive/hard-to-find parts?
Not really. The 10-segment LED matrix for the LM3916 circuit is available in both bicolor (red/green) and tricolor (red/yellow/green) versions that match the audio indication levels of the LM3916, but they can be a bit hard to find. I believe they are made by Kingbright and they typically show up on ebay – i honestly can’t remember where I bought mine, but it was probably there 😀

Anything else I need to know?

  • Due to the peak detection circuit, the LM3916 circuit isn’t likely to work with the LM3914 (linear scale) or LM3915 (“standard” log scale) ICs. If this is what you want, have a look at the respective data sheets and google – plenty of other designs out there then 🙂
  • The LED matrix should be mounted on the back of the PCB, but then the board should be reversed for mounting on a panel. The gives the correct orientation for a multicolor matrix as well.
  • You should note that the analogue driver is designed with a balanced input.

Downloads:
Download design files here

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

Please refer to the respective design articles and to the data sheet for the LM3916 IC for additional information.

univumeter-1

DIY project files: General Information

This part of the blog is devoted to sharing design files for some of my various audio DIY projects. Please take a moment to read the following general information before downloading and using any files.

Each project post will contain a short description of the project(s) and some key information that you may need to know as well as a download link to the project files. The downloadable file for each project will normally contain:

  • The circuit schematic and board files in Eagle 6.x format
  • A set of Gerber files generated in Eagle with the Itead cam job (see below)
  • A set of renderings of the Gerber files (made with www.circuitpeople.com which I highly recommend)
  • Other files (BoMs, circuit diagrams, code samples etc.) as needed

In principle, I try to design my boards as compact  (some would say “cramped”) as possible using two layers where one is normally a ground plane. There is some dispute as to whether this is the right way of doing it for all boards, but it normally makes layout easier and the routing cleaner so it can’t be all bad 🙂 I normally follow the original schematics as closely as possible, but sometimes I make decisions on parts, configuration and placement because I had a specific application in mind when doing the layout. I try to select parts as a compromise between compactness and flexibility and I try to use footprints that does not leave you tied to a specific manufacturer’s parts.

My prototype boards are normally manufactured by Itead and the Gerber files included in the downloads are therefore made with Itead’s own customized cam job for Eagle. I have no affiliation with Itead at all, but I have used them extensively and the prices are good, the quality is more than decent enough for normal DIY use, and I have (so far) received good service for all my orders so all in all I have no hesitation in recommending them to others. If you prefer, you can of course use the Eagle files to generate Gerbers for your own preferred board house (Seeedstudio, OSHpark, batchPCB etc.), many of which also offer cam-jobs for Eagle to make this process easier.

Happy building!

 

Important! Since these are DIY projects, the usual DIY project disclaimers apply here:

  1. These files are intended for use by individuals in and for non-commercial DIY projects. Use in group buys through forums as well as any and all forms of commercial usage are only allowed with my prior written consent (that means send me a message to ask permission before you do anything…)
  2. These are DIY projects for people with at least some basic experience in building DIY electronics including soldering, measuring, troubleshooting etc. I will do my best to provide support via email but there are no promises of help expressed or implied if you can’t get a design to work properly, regardless of whether that is my fault or yours. 
  3. Some designs may involve hazardous voltages, mains wiring and/or modifications to existing equipment. Before undertaking any of these projects, be sure to verify that you have the required knowledge to do so and that you are not violating any laws or voiding any insurance polices or manufacturer’s warranties. 
  4. The project files are shared in good faith and and will normally have been tested to provide working designs that are safe for use. However, I have no access to any special labs or measuring equipment beyond what a normal hobbyist would have, so I cannot always verify everything  before posting a design. If you find any issues, please help me (and others) by sending me a mail.
  5. Lastly: I will accept absolutely no responsibility or liability for any errors/omissions in the files and/or for any loss of or damage to anything including (but definitely not limited to) persons, pets or property that may arise from the use of these files and the building and use of the circuits they represent.