50ASX BTL conversion (part 2)…
December 12, 2016 23 Comments
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 😉
theslowdiyer 
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.
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 🙂
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?
Yes, that’s correct. You need the SE/BAL converter though (unless of course you have a balanced source).
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
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.
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 😊
Here us my build with the converted btl module and my asc200 modules.
https://www.facebook.com/Icepowerdiy/
Hi I need replace Rumble 150 , power Board. That is a 50asx2 BTL , but i buy SE version…
Help !!
hello… i bought a BTL instead of a stereo version… do you think I can just change the jumper position to go from BTL to two channel amp? Thank you very much for your help
No, unfortunately it doesn’t work like that. There are components missing on the BTL board which are required for SE operation.
thanks for the prompt answer. Ebay seller had the wrong version in product description, and I didn’t notice the second channel output connector missing on the board.
That’s really annoying. I have regularly seen people looking for the BTL version, so it is possible that you can post an ad on diyaudio or a local forum and find someone willing to trade you for an SE-module. There is also a comment on this blogpost from someone who has sucessfully converted from BTL to SE (I’d forgotten about that) so it is possible if you can get the right part from a dead module or similar.
Great advice. thank you
Alejandro, Do you have one or two of the modules? I have some spare stereo modules and may be interested in a swap.
Nisbeth,
This is great but what do you say about B&O’s reply about this (is the two halves not switching on sync) as outlined in this post on DIYA:
https://www.diyaudio.com/forums/class-d/190311-icepower-50asx2-modules-11.html#post5299847
Cheers,
Niklas
As far as I am aware, what they mean is that if you just hook up the two halves of a stereo 50ASX as a BTL amplifier, then there is no sync. If however you move the jumper to the BTL position, then there should be. This is how I remember the module being designed at last, but I have not verified it with measurements.
I know, it’s just that the guy who emailed them to ask, Philip, explicitly stated that he would be converting them by moving the jumper from W401 to W400. Of course, B&O is incentivised to not see this becoming widespread and replying like they did. However, why did they also say that “the two common mode chokes will not work (bad EMC performance)”?
I have a few of these modules that I’d like to convert for more power and I may go ahead doing one of them and see if I can figure out how to measure its distortion with REW or similar.
I am not sure a distortion measurement is enough, I was actually thinking that you would have to measure the switching frequency both at idle and under load to see if they track and that’s at least not something I am personally going to attempt.
Originally the 50ASX was supposed to be a universal module that was switchable between SE and BTL. However, it turned out that it was possible to save quite a bit of BoM-cost on the BTL-version if it was a dedicated board because the components you can leave off (mainly the choke, connector and jumper) were a surprisingly large part of the cost. That cost-reduction was important to make the amp interesting for use in small subwoofers etc. and therefore it was decided to do two “hard-wired” versions.
Whether any other engineering changes were done in the process I don’t know, and to find out I guess you’ll have to compare the mounted versions and see if you can spot any differences in the components that are fitted. The fact the there is still a jumper position on the board tells me that the two versions are built on the same PCB, so the difference would be if any of the small SMD-components are not mounted and whether that would lead to any performance difference as described in the reply.
Hello Nisbeth,
Just a couple of FYIs: I just replaced a BTL version with a converted SE (just changed the W40x jumper) in my Galien Kruger MB115 bass amp and it seems to work. Double the voltage across P104 vs. each side to Ground, but I haven’t listened to it yet or made any measurements. The W40x jumper is what reconfigures the outputs so that they both appear on P104. I don’t think it has anything to do with the sync.The only other difference I could see between the two types is that the BTL has a 560 ohm sm resistor in the middle of the group of sm components between IC400 and IC401-402 whereas the SE has a resistor which is marked with what seems like a 0 (it’s a tiny square). It also looks like the 560 ohm was hand soldered, as was the jumper .Maybe a clue about the difference.
Hope this is useful to someone.
Cheers, David
Thanks David, very helpful observations.
A couple of further things: I measured the two resistors in question and they are, in fact, 0 and 560 Ohms. Also, I looked at the magnified photos of both types on eBay,etc. and they all correspond to what I saw with my two amps. At least on the top side. I couldn’t find any clear enough photos to check the back side and I already installed the converted SE amp in my bass amp and don’t feel like taking it out again (right now anyway). 🙂
Annoyingly, for me anyway, the BTL version is now widely and cheaply available (eBay, PartsExpress, etc.). I bought the SE a while ago and procrastinated installing it.
Cheers and Happy Holidays, David
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