Project files: INA217 Microphone Preamp

What is it?
Board files for my INA217-based microphone preamp and the matching PSU as shown here. The design is meant to be “configurable” with three different gain options and phantom power selectable via jumpers. The amp also has a full complement of protection features. The matching PSU has three rails via two small onboard transformers for a compact “all-in-one” solution.

How big are the boards?
The amp board measures 3.1” x 1.9” (app. 79 x 48 mm.) and the PSU board measures 3.95” x 2.7” (app. 100 x 69 mm).

What is the status of the boards?
The amp board is version 2.1. Version 2.0 was my update of the original design as showcased in the previous blog post (link) and 2.1 adds a few minor tweaks including an LED to indicate directly on the amp board if phantom power is on or off.
The PSU board is version 2.1 as well for much the same reasons (although the v2.1 “tweaks” consisted mostly of fixing a couple of fairly serious mistakes in component labelling 😀 )

Does it use any special/expensive/hard-to-find parts?
Not really hard-to-find as such, but still worthy of some attention 🙂

  • The regulator for the phantom supply regulator must be a LM317HV type which allows for a greater in/out differential. You can use the standard version as well, but a short will then kill the regulator.
  • As for the INA217: I am not sure if there are fakes about, but buy from reputable sources just in case. Anything in an 8-pin DIP is an easy target for fakes really.

Anything else I need to know?

  • This board adds nearly all the bells and whistles described in this paper from THAT corp on instrumentation amp IC-based microphone preamps. These extra components for short-circuit and EMI-protection are optional, but definitely recommended.
  • The board has a Neutrik A-series Combo-jack onboard which is very practical and versatile. Unfortunately it means that if you use the TRS it shorts the phantom voltage to ground if it is plugged/unplugged while the amp is on. Protection features have been added, but this scenario is best avoided so only (dis)connect the TRS while the amp is off.
  • See the INA217 datasheet for gain calculations. While you can add a switch to select between the different gain settings, doing so may add quite a lot of noise so it’s not recommended.
  • Voltages for transformers: The two transformers will have to be 2×12-15V and 2x18V respectively. They are usually single-primary, so choose the ones that you need. Note that with transformers in this form factor you will not be able to deliver more power than is required for a single mic amp. If you need a triple PSU that can supply more than one amp board, this design should work just fine (with external transformers.
  • Replacements for the INA217 are mainly the THAT1510/1512, but there are some differences so I am honestly not sure if they are a drop-in replacement. Refer to the files under “related information” if you want to check for yourself.

Downloads:
Download design files here

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

Before you start I strongly suggest you read through the INA217 datasheet. Please also refer to the aforementioned paper from THAT on this type of microphone preamps, this THAT design note and the datasheet for the THAT1510/THAT1512 ICs.

Project files: The last of its kind…

…for a while at least 😀

What is it?
The last (and smallest) version of my EL2k buffered headphone amp using NOS Elantec 2008/2009 buffer ICs. This is the smallest version designed for 1.5″ heat sink profiles as described here. The two other versions are of course also still available (here and here):

How big are the boards?
The board measures 3.95″ x 1.5″ (app. 100 x 38 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5 as it is a redesign. Apart from the redesign work described in a previous post, the circuit is identical to the other published files.

Does it use any special/expensive/hard-to-find parts?
Yes.

  • The EL2008/EL2009 buffers have been out of production for 10+ years. They can still be found and I don’t think you need to be especially concerned about fakes – there can’t be a lot of demand for these anymore – but of course no guarantees. The main risk is probably that instead of NOS parts that you get used parts that have been pulled from old equipment. This is annoying, but should be OK.
  • The heat sink profile is the same as the original, Fischer SK68, in 37mm length. Easy to get in Europe, but I’m not sure about elsewhere.

Anything else I need to know?

  • I’ve had to mount the buffers on the side of the heat sink that has an M2.5 slot and not an M3-slot. This isn’t a problem as such because there’s no need to isolate the tab, you’ll have to remember to buy M2.5 screws for mounting 😀
  • Otherwise this is a bog-standard buffered opamp circuit and there isn’t much that can go wrong 🙂

Downloads:
Download design files here

Related information:
Be sure to read the original posts for additional information and tips.

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

Project files: The (modified) EL2k headamp

What is it?
The board files for the new “medium-sized” version of the EL2k buffer/pre as shown a few weeks ago. The smaller 37mm board version will follow in a while.

How big are the boards?
The board measures 3.95″ x 2.0″ (app. 100 x 51 mm.) and is obviously a mono amplifier channel.

What is the status of the boards?
I’ve called this board version 1.5. Apart from the redesign work described in the last post, the circuit is identical to the originally published v1.1 files.

Does it use any special/expensive/hard-to-find parts?
Yes.

  • The EL2008/EL2009 buffers have been out of production for 10+ years. They can still be found and I don’t think you need to be especially concerned about fakes – there can’t be a lot of demand for these anymore – but of course no guarantees. The main risk is probably that instead of NOS parts that you get used parts that have been pulled from old equipment. This is annoying, but should be OK.
  • The heat sink profile is the same as the original, Fischer SK68, in 50mm length. Easy to get in Europe, but I’m not sure about elsewhere.

Anything else I need to know?

  • I’ve had to mount the buffers on the side of the heat sink that has an M2.5 slot and not an M3-slot. This isn’t a problem as such because there’s no need to isolate the tab, but some swearing will likely ensue when you sit there on Sunday afternoon and realise you don’t have any M2.5 screws to hand 😀
  • Otherwise this is a bog-standard buffered opamp circuit and there isn’t much that can go wrong 🙂

Downloads:
Download design files here

Related information:
Be sure to read the original posts for additional information and tips. You should be able to reuse the linked BoM as well.

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

Project files: THAT1646 in stereo…

What is it?
A stereo version of my THAT1646 balanced converter/preamp shown here. I wanted to build a small controller/pre for some active monitors and while the stacked mono boards were probably a good idea in princple, I decided to resurrect the stereo layout instead 🙂

How big are the boards?
The board measure 2.7″ x 1.9″ (app. 69 x 48 mm.).

What is the status of the boards?
There are two board versions which differ only slightly. One is 100% through-hole and basically a stereo version of the mono-board shown earlier. The other has the R4 gain resistor replaced with a 1206 SMD type and mounted on the top of the board (under the IC socket). This means the feedback loop area is much smaller and the routing is a bit neater. Both boards are otherwise the same size and electrically identical. If you want to change the gain after building the through-hole version is probably easier to work with, but otherwise the SMD-version should be the best design. Both boards are labelled as version 1.0 although I’ve only prototyped the SMD-version in stereo.

Does it use any special/expensive/hard-to-find parts?
As usual, not much. Maybe the THAT IC itself. Mouser has it though, so that should work for most people I guess.

Anything else I need to know?
A few things:

  • Gain: You can tweak the gain of the circuit as you wish using the resistors for the pampas, but remember that the THAT1646 should add 6dB gain on its own when you go from SE to BAL.
  • Opamp selection: You should be able to use pretty much any single opamp here. if you don’t have a favourite already I’d once again recommend that you start with either the OPA134 or the LME49710 and then experiment from there.
  • SMD resistor: If you are using the board version with the SMD gain resistor, remember to solder R4 on the board before you fit the IC sockets (otherwise some swearing may ensue when you discover it… :D)
  • BW limiting capacitors: There is no space on the board for BW-limiting capacitors for the opamp. Not sure why really, but with the opamp only driving a very short trace with a fixed load at the end (the THAT1646) I felt quite sure most opamps will behave. If not, soldering some small ceramics on the bottom of the board should be easy 🙂

Downloads:
Download design files here

Related information:
As usual, RTFD! (= read the f’ing datasheets :D)

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

Project files: Universal Mini-preamp

A few weeks ago a reader was commenting on simple buffers/preamps and also asked about ebay-kits to use since I haven’t posted anything with a volume control yet. That got me searching to see what was actually out there and very quickly came the realisation – “I can do this better” 😀 Not sure if I did, but I at least tried 🙂

What is it?
A very simple opamp-based buffer/pre with an onboard volume control that can be used as a “buffered volume control” with a power amplifier module, a real preamp with or without gain or even a “CMoy”-style headphone amp. The board has space for a DIP-8 dual opamp, polypropylene input caps and a full-size Alps volume control and still manages to be very compact. I’m showing the board now as I already have a couple of applications for it in the pipeline myself which you will see later 🙂

How big are the boards?
2″x2″ (app. 51×51 mm) – a theslowdiyer standard size (TM) 😉

What is the status of the boards?
The board file is v1.0. I’ve built a prototype and everything seems to be fine.

Does it use any special/expensive/hard-to-find parts?
None, really. You can get what you need from Mouser/Reichelt and similar places and most of the component values aren’t that critical anyway.

Anything else I need to know?

  • The opamp should be a dual-type with standard pinout. My recommendations would be either the LME49720 (sadly discontinued in DIP) or the OPA2107 (still available but fairly expensive), but there are loads of other options. The board layout should be suitable for using adapters as well (for DIP/SO-8 singles or SO-8 duals) and if you want to go all-out there’s even a discrete option from Burson that should fit as well.
  • The only surface mount components are the optional (but recommended) 1206 bandwidth-limiting caps on the bottom – otherwise it’s through-hole all the way.
  • The PCB should be happy with just about any (regulated) dual power source – linear PSU, switching PSU or even a pair of 9V batteries.

Downloads:
Download design files here

Related information:
Even though this is a basic opamp circuit and I can just about draw the schematic and recite the parts values from memory, I went back to look at it once more to try and read up on the theory behind. If you aren’t very familiar with the basic schematic already I can absolutely recommend the old but still excellent articles from Headwize/Head-fi member Tangent here and here. Tangent’s pages also have a ton of other useful information and although the site isn’t updated any more (and it’s quite old) there’s still plenty of good stuff even for inexperienced diy’ers.

If you are more technically inclined then probably the best resource is the “Opamp Applications Handbook” from Analog Devices and edited by Walt Jung.

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

Project files: A bal. driver with the THAT1646

Still busy at work, but being home for (most of) the weekend and I have time to dig in the back catalogue a bit – hope this is useful for someone 🙂

What is it?
A simple SE/BAL line driver board using the THAT1646 line driver IC. This should make it compatible with the DRV134 from TI and the – now obsolete – SSM2142 from AD as well. The board can be used as a pure line driver to feed a balanced input or of course also to bridge two suitable power amps.
The THAT-chip is combined with an on-board opamp, partly to ensure that it is driven by a low-impedance source as per the datasheet recommendation, partly to increase the versatility as the opamp can provide more gain if required.

How big are the boards?
The board measures just 1.6” x 1.9” (app. 41 x 48 mm.) The boards can be placed side-by-side or stacked. I originally had this as a stereo board with two channels on the same board, but decided that the mono-version was probably more versatile overall. If you disagree feel free to let me know 😀

What is the status of the boards?
The board is v1.0. I’ve built a single prototype and tested it (I needed one channel for a test setup) and it sounds fine as far as I can tell. No further sound impressions yet I am afraid.

Does it use any special/expensive/hard-to-find parts?
None. I am not actually aware of a source for the THAT-chip in Europe, but Mouser has them and that should work for most people I guess 🙂

Anything else I need to know?
A few things:

  • Protection circuitry: I’ve omitted the protection circuitry described in the data sheet for the THAT1646, mainly because I only expect to use it in home applications where there is no risk of a phantom power supply being present. If you are using it with PA gear that (potentially) has a phantom power supply on the inputs then you might need to look into this.
  • Grounding: I have connected the ground pin of the output connector on the PCB to GND on the board, which is actually a no-no. Connecting all three pins to the XLR would (potentially) give you “pin 1-problem”.
    As I understand it, the proper way of wiring an XLR is therefore to only connect “hot” and “cold” from the PCB connector to the XLR out connector and then connect  PIN 1 on the XLR connector to the chassis ground via as short a wire as possible.
  • Preamp-mode: Given that the THAT1646 already has an opamp onboard to drive it, if you use 100k-220k input impedance (R1) it should be possible to put a 10k-20k log pot in front of the input capacitor and convert the board (well, two of them…) to a stand-alone preamp with SE in and Balanced out. I haven’t tested this, but I see a couple of potential applications here 🙂
  • Chip substitution: The DRV134 has the same pin connections as the THAT1646. The only thing I can see that makes them different is that the DRV134 data sheet specifies 1uF decoupling caps on the supply pins rather than the 100nF for the THAT1646.
    Note that the DRV134 also has a reputation (at least in some DIY-circles) for sounding pretty unspectacular. I have no personal experience to offer here, so try for yourself if you want 😀

Downloads:
Download design files here

Edit 14th april 2016: Link has been updated to point to the correct file 🙂

Related information:
As usual, RTFD! (= read the f’ing datasheets :D)

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

Project files: The Zen Headphone Amplifier

What is it?
The board files for my Zen Headphone Amplifier “remake” shown here.

How big are the boards?
The board measures 3.575” x 3.75” (app. 91 x 95 mm). This is obviously for a mono-channel.

What is the status of the boards?
The boards are version 1.0. The prototypes seem to work well and there wasn’t really anything that needed changing in my view.

Does it use any special/expensive/hard-to-find parts?
Not really.

Anything else I need to know?
A few things:

  • Heatsinks: The basic type for me here in Europe is the Fischer SK129, but there are many manufacturers of this profile. The board is designed for the heatsinks to be soldered in place with pins, but screw-mounted versions might work as well. You can use 1″/25mm heat sinks, but in that case I recommend to tune the bias a little lower. My prototype measured app. 240 mA of bias and the heat sinks seemed to stabilise at around 55C in free air, which probably is a bit too much when the board is cased. So, either turn the bias down a bit and/or use taller heat sinks if your case allows for it.
  • Adjustments: Space around R10 and R12 is quite tight, especially with heat sinks/output caps taller than 25mm. In order to easily be able to adjust bias and balance of the amp, my suggestion would be that you don’t trim the leads of the two resistors completely flush but leave enough of the resistor legs that you can connect crocodile clips to them on the underside.
  • Output capacitors: The recommended value is 2 x 470uF from the original schematic, but if you’re using low-impedance headphones I think you should consider 2 x 1000uF instead. This is one place where I think “audiophile” capacitors can’t hurt, so look for Nichicon Muse (KZ/KW, FG/FW, ES etc.), Elna Cerafine/Silmic capacitors or similar. Bypassing the electrolytics with small film capacitors is easily done on the underside of the board if you want to.
  • Transistors: The Q3 footprint on the board is for a BC550C, but the original ZTX450 from the schematic can be used as well if it’s turned 180 degrees. Remember also to match at least the two Q2 FETs between channels as described in the build article. If you buy 8-10 of the IRF610 FETs you should be able to get a couple of very tight matches and the leftovers can be used for the current source (Q1).

Downloads:
Download design files here

Related information:
See the original post for some more information and links to the build article for this design. After posting I actually also managed to find the original headwize article cached here – amazingly it seems that most of the headwize library has been kept intact there! 🙂

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

zenhppcb-1

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.

Downloads:
Download design files here

EDIT 23/4-2017: In response to the reader comments below, here is a basic BoM for the single board. As the dual-board is basically two sections of the same circuit, you should be able to work out the BoM for that yourself 🙂

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.

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… 😀

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… 😉

Downloads:
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 chipamp.com kit manual as a good source of information.

 

Project files: The J-Mo Headphone Buffer

What is it?
The project files for my version of Richard Murdey’s  J-Mo mk. 2 buffer with gain.

How big are the boards?

  • Amp: 2.45” x 1.975” (app. 62 x 50 mm.)
  • PSU: 2.35” x 1.975” (app. 60 x 50 mm.)

What is the status of the boards?
Both boards are version 1.0, meaning I have prototyped them and they work. However, I am still waiting for some mechanical parts for my own build so this isn’t final yet which means I have only done very basic tests.

Does it use any special/expensive/hard-to-find parts?
Well, the J-FETs are getting harder and harder to find but it isn’t impossible yet.

Anything else I need to know?

  • Can’t really think of anything. Be sure to read through the article on Richards website though, that contains most of what you need to know.

Downloads:
Download design files here

Related information:
See the original post for some more information and links. There is also a big discussion thread on diyaudio that may be of help.

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