Project files: An unloved amp?

Well this is really “unloved” in two ways, but I thought I’d share it anyway 🙂

A while ago I ws cleaning up a little and I found the boards for this amplifier based on the LT1210 IC. Despite being from 2016 I never put the design together originally (don’t remember why) so I decided “better late than never” and tried it now. And you know what – it works!

Apart from being “unloved” because it took me nearly four years to put it together and test it, this amp is also “unloved” because the LT1210 doesn’t seem to be used that much for audio applications. It is a a current feedback power opamp with a massive current capability and so it should – albeit with a few caveats – be possible to use for audio as well with good results. Also, like e.g. the AD815 the original applications for the LT1210 (ADSL line drivers and suchlike) have all but disappeared, so – again with a few caveats – it should be possible to pick these ICs up at very good prices.

Read more of this post

Project files: The ACP+ clone…

Well, both my ACP+ clone boards are now fully populated with relays and working as expected so I guess it is appropriate to share the design files 🙂

Read more of this post

Project files: The Borbely non-hybrid headamp

To supplement the original Borbely tube hybrid headphone amplifier are here the files for the solid-state version as described previously here. Have fun!

Read more of this post

Project files: Hypex UcD400OEM adapters

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

Read more of this post

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 🙂

Read more of this post

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.

Read more of this post

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.

Read more of this post

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.

Read more of this post

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 🙂

Read more of this post

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).

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 🙂