Project files: Hypex UcD400OEM adapters

Well, since I shared these on diyaudio already I supposed they should be here as well 🙂

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Project files: The BBA3FE

Haven’t really had time to fully complete my BBA3FE project yet, but as I am otherwise happy with the design I might as well release it in case anyone wants to have a play with it 🙂

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Project files: The BalBUF and PSU

I’ve made a little bit of progress on my balanced mono block 700ASC-amplifiers lately, so now is probably a good time to release the project files for the balanced buffer input board and the accompanying PSU that I used in that design. It’s a pretty obvious clone of AMBs Alpha24, but since I did my own board and ditched some of the configurability I figured it’d be OK. Big thanks to Ti Kan though for actually showing how to build this circuit which I previously attempted a couple of times without getting it right.

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Project files: The “MoFo” power follower

I did this version of the “MoFo”-design a while ago and also mentioned it briefly (here) but didn’t manage to complete it or even test the boards. In the mean time the “official” boards have become available from the diyaudio store, but since I now finally got round to testing my boards I still thought I’d share my version as well.

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Project files: The RJM Emerald RIAA

Last week I showed my version of the “Emerald” RIAA design by Richard J. Murdey. The Emerald is a neat little design: It has switchable gain and load for MM/MC, if you use good components it’s got a very accurate RIAA-curve, and of course with just two opamps per channel as the active devices, it’s very easy to build.

Richard has graciously shared the Eagle-files for his version and so it seems only right that I do the same here. Richard is also selling boards from his website, so if you want something that is proven to be working and comes with support then I suggest you buy your boards from him instead.

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Project files: The Kuartlotron Buffer

Sometimes projects that have been on hold for a long time can restart with just a tiny nudge. A while ago I built (and showed) a clone of the Kuartlotron buffers. My original prototypes had one obvious mistake (an incorrectly connected Q3) which I fixed, but I still couldn’t properly zero the offset as described. I left the project, did nothing about it and then a few days ago by accident went back into the discussion thread on diyaudio. Here there was a single post discussing exactly that issue and a very short response from Keantoken (the “inventor”) that offset had to be zeroed with the input open. This is not what you normally do so I didn’t think about it after building my boards, but that small clue was enough for me to go back to the prototype boards and confirm they were OK. With the problem fixed I can finally share the project files here 🙂

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Project files: PA100 parallel gainclone

What is it?
Board files for my “PA100” parallel chip amp with the LM3886 first presented here.

I’ve used the app. note version of the circuit which is non-inverting and uses low-tolerance components to minimise offset between the two ICs. There is also the Jeff Rowland-derived inverting circuit that is normally employed as a PA150/BPA300 configuration with three ICs per board.

I’ve mosty stuck to the datasheet circuit, but in some areas I have drawn inspiration from Tom Christensens article on the LM3886 IC. I’ve used SMT-components where I believe it makes sense to get a tight layout, but mostly its nice and diy-friendly leaded parts 🙂

How big are the boards?
The board measures 3.9” x 2.4” (app. 99 x 61 mm).

What is the status of the boards?
The files are for board version 1.1. I’ve made the following changes compared to the v1.0 prototype.

  • Mute capacitor footprint enlarged.
  • Mute resistor moved to the center of the board to make space for the larger capacitor.
  • Footprint for the LM3886 changed as the holes were very too small.
  • Made a small space between the large reservoir capacitors so they don’t touch each other.

Note that I haven’t tested the v1.1 (yet – will include them with my next PCB order) but I don’t expect any adverse effects of these changes.

Does it use any special/expensive/hard-to-find parts?
Not really, but the recommended resistors are lower tolerance than what is common (the 0805 resistors are 0.1% and the 0R1/3W output resistors are 1%). Mouser has them all and there should be plenty of other sources. The amp will work with standard tolerances (1% for the SMTs, 5% for the outputs) but if you’re unlucky with the tolerances then performance will suffer a bit (higher DC-offset on the output and higher idle dissipation in the ICs). The recommended parts are not much more expensive so I definitely recommend you stick to them.

Anything else I need to know?

  • The gain setting resistors (the SMD-ones) should be 0.1% tolerance for best performance (see above).
  • Similarly, the load-sharing resistors on the output should be 1% tolerance for best performance (see above).
  • The power LED on the board is only between the negative supply and ground, so it is not a 100% indication that everything is OK.
  • The board obviously works with both versions of the LM3886, but I recommend the isolated (TF) version because it’s easier to mount.
  • Decoupling: My decoupling scheme is somewhere between the datasheet recommendation and TomChrs decoupling scheme. The topside parts are intended to be 100nF MKT or X7R MLCCs which is more or less what the data sheet specifies, but on the bottom there are pads for 1206/1210 SMD caps which you can fill with 4u7-10uF X7R MLCCs. You can also use the SMD pads for 100nF MLCCs and then mount electrolytic on top, but there isn’t much space so be a bit careful.
  • The board should be fed from a DC power supply, linear or switching. The large reservoir caps can be as big as you like, but as my prototype boards are intended to be powered by an SMPS (which is sensitive to capacitive loading) I’ve used fairly small capacitors. If you use a linear supply by all means use bigger capacitors.
  • Bridging: You can bridge two boards to create a BPA200 amplifier, but remember a) to lower the supply voltage to around +/-28VDC and b) that you need either a fully-balanced source/preamp or you need to invert the phase using a balanced line driver such as a DRV134/THAT1646 or or fully-differential amplifier of some sort.
  • Mechanics: The C-to-C spacing between the ICs is 1.5” (38 mm).

Downloads:
Download design files here

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

You can find additional information about the LM3886 amplifiers in the data sheet, the AN-1192 appnote linked above and several other resources – check them all out 🙂

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

EDIT 20th July 2019: Not sure why the BoM for this project did not make it into the download file, but here it is 🙂

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.