50ASX BTL conversion (part 2)…

So, I’ve done some more testing on my BTL-converted 50ASX-modules…

As you can see, I’ve used a slightly less improvised test setup compared to last time (it looks worse than it is…). While I wouldn’t call what I have done “extensive testing” by any means, my gut feeling is that this works 🙂 It also ties in well with how the other ASX-modules work and some “insider knowledge” from years ago that I can still recall 🙂

Note and disclaimer: I would very much appreciate if someone else tried this to verify and maybe do more testing, however I will accept no responsibility for damage to property, people or pets (or anything else for that matter) if you find a problem – this is DIY after all 😀

You can of course hack this conversion anyway you like, but I opted for removing the old jumper altogether and soldering in a new one. If you do that, be advised that the ASX-board is four layers and soldered with lead-free solder, so it will take a bit more heat to reflow the joints than I am at least used to. If you use a soldering iron that is too small, you’ll just heat up the board and possibly damage it.

My suggested approach would be to cut the jumper on the top side of the board. Heat the solder joint from the bottom and pull out the jumper wire with small pliers. Then clean the remaining solder off the board with desoldering braid or (better yet) a vacuum desoldering station if you have access to one. Then solder in the new jumper in the BTL position. There isn’t much space to work on and you should be careful not to damage any of the (sometimes annoyingly) small SMD-components on either side of the board. Once the new jumper is in place, follow the wiring diagram for the BTL-version in the 50ASX data sheet/designer’s manual and you should be good to go.

Bear in mind that what you end up with isn’t a “real” balanced (= differential) amplifier, but two SE amps referenced to ground and driven with opposite phase input signals to produced a bridged output. As such, the input ground is still required in order for the amp to produce a correct signal on the output. I’ve found a good sketch here for LM3886 modules that should show the correct input wiring. Output on the ASX is taken from the P104 connector, so ignore what the sketch shows here (and of course the DC wiring is irrelevant as well).

If you do try this, let me know how you get on 😀

PS: Yeah and the picture is still crap – but don’t worry, the light should be better from around April onwards 😉



9 Responses to 50ASX BTL conversion (part 2)…

  1. Did it the other way round. Had a broken donor board where I got the missing spool (can’t remember the word for it now)
    Used 4-5 years now.

    • theslowdiyer says:

      Thanks Claus, that’s a good confirmation. I thought about removing the inductor/coil/choke (that’s the word 😀 ) but after some connectivity testing on the pins I found it shouldn’t be necessary 🙂

  2. Frederik Pedersen says:

    So, all one need to do is to move one jumper? Does the modified amp accept single-ended RCA input or is it necessary to put an unbalanced->balanced board in front of it?

  3. I have a Fender Rumble 150 bass amplifier and this amp works with an Icepower 50asx2 btl module. Unfortunately, the Icepower module failed some time ago and I couldn´t find a btl module, so I bought the stereo version. I supposed that changing the jumper from se position to btl would fix the problem but it was impossible for me to find information about it. So I decided to ask via e-mail to the Icepower Support what would happen if I use the se module in btl and they answered that “Using the SE module in BTL mode will cause Bad audio performance in BTL mode with high distortion (since the two channels are not switching in sync as they should when running in BTL, because they are designed for SE mode) – Also the two common mode chokes will not work (bad EMC performance)”. After that response, I didn´t want to convert the module to btl because I have no information about it. Then I found this post and you said that it worked for you the conversion So, now I want to do it too, my question is, is it necessary just to change the jumper to btl position? or I need also to remove the parts labeled as P101 and L402? and finally, do you think this conversion is suitable for my fender amp?

    Thanks in advance

    • theslowdiyer says:

      Hi Ramon,

      All I can say that the conversion worked for me, but it wasn’t exactly an extensive test I did. To your specific points: I believe that changing the on-board jumper enables the channel sync, so that takes care of that issue. As for removing components I don’t believe it is necessary, but I haven’t tested EMC performance of the converted module so it could be that I’ve missed something. You can probably quite easily cut the choke off the board if you want to (desoldering is a bit harder/riskier), but leaving the connector in place at least isn’t likely to hurt anyone as long as you don’t use it 🙂

      In short: Yes, I believe you can do this to repair your amp, but obviously I’m not really in a position to offer any guarantees.

    • Benny says:

      Hi’ Ramon

      I’d love if you could post when/if you’ve done the conversion, to we if the Fender runs as usual.
      I’ve done a se/btl conversion along side theslowdiyer, but I haven’t measured any increase in dB after the conversion.
      I’m afraid the it only performs 1×50 watt and not 170 watt as the original btl module.

      You of all must be able to hear a big decrease from your Fender, if it only runs 50watt. So please come back with a follow up 😊

  4. Here us my build with the converted btl module and my asc200 modules.


  5. marxfu says:

    Hi I need replace Rumble 150 , power Board. That is a 50asx2 BTL , but i buy SE version…
    Help !!

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