Hello,
I hope this is the right section, as my issues are not focused on the amplifiers itself, but they revolve around Sure class D modules... If there is a better suited section, please tell me!
I am currently planning a bluetooth speaker. The first version will use the drivers salvaged from a Logitech Z523 - I was told they should be quite decent and I only paid 5$ for a Z523 with a dead amplifier. I will replace them later on and build a new case as I can't afford a set of good drivers at the moment. The battery is a 5S3P of NCR18650GA (18650 cells with 3500mAh), resulting in roughly 19V during normal operation.
After looking for affordable modules I ended up buying a set of Sure JAB2 and JAB3 as they are not much more expensive than cheap individual modules would be, while saving me a lot of work (and DC-DC converters).
After they arrived I set the DSP up (for now just forwarding the signal from the inputs to the two outputs of the JAB2-50, while the JAB3-100 is only used as a DSP with no speaker connected) in order to try the amps with my home speakers (Boston Acoustics M25). That's where my issues began - apart from a low bluetooth range (which I will address later on) the volume was incredibly low. With the phone maxed to 100% it was still significantly lower than what I see as a convenient listening volume in a 20m² room.
After adding +10dB gain on the DSP (background hissing intensified) and using my notebook as an audio source, the volume got to an acceptable level, but I expect my speaker to be less efficient than my shelf speakers, so it still is too low. Apart from that it still is too silent with my phone. My phone has no apt-X issues, Logitech UE9000 bluetooth headphones get quite loud at roughly 50-70% output volume set on the phone. So I am still looking for a way to increase the output volume of the BT module. Are there some voltage dividers between the module and the connector to the DSP which I could modify for a stronger signal? I hope I won't have to reverse engineer the PCB - it is awfully complicated and black (no visible traces).
Another thing that annoys me is crosstalk between the BT output and the aplifier channels even with no DSP (or volume potentiometer) connected to the JAB2. I read that there was some resistors causing this which could be removed. I wanted to use the JAB2 for the high frequency drivers, which would then always get low frequencies (even if only at a lower volume) no matter how I set up the DSP - unacceptable. I think I know which resistors are used for this and will measure it later on with the multimeter.
EDIT: I was right, found the resistors. I will remove them later on and see if it fixes the crosstalk issues
Last but not least, low bluetooth range. The module only features about 3m of range before the connections starts to stutter with nothing but air in between the module and my notebook or phone. Both get about 20m of distance without issues with my UE9000. I still have the PCB antenna of an old fritzbox wireless router somewhere in a drawer, so I think I will try to cut the antenna on the module's PCB and solder the shielded cable of the fritzbox antenna to it. That should work better, shouldn't it? Both are intended for 2.4 GHz use.
I have no experience with those modules and can find barely any useful information in any of the languages I speak (german, italian, english) online, so I would be really grateful if someone here could help me a little or point out some links where I can read about similar issues (and ways to fix them).
Kind regards,
Moritz
Big EDIT:
I removed the two marked resistors, what changed quite a few things:
1) crosstalk across the DSP is entirely gone. yay
2) it got way louder (phone at ~80% is now a decent room loudness) - I can't really explain why, but I like it
3) less bass, more treble. Before the mod it was bass-heavy (I fixed that by ear with a parametric EQ), now it lacks lower frequencies. Off to the param eq again, I guess. No real issue as the intended use of this module will be to power the high frequency drivers anyway.
https://mpwr.xyz/gallery/2018_09/jab2_rmod.jpg
I also cut the trace of the original antenna and tried the fritzbox one, with kinda bad results. I now have ~4m of range in one direction and ~2m in the other. So it got directional, but still lacks range.
https://mpwr.xyz/gallery/2018_09/jab2_antmod.jpg
So, I am making progress. Everything but bluetooth seems fine!
I hope this is the right section, as my issues are not focused on the amplifiers itself, but they revolve around Sure class D modules... If there is a better suited section, please tell me!
I am currently planning a bluetooth speaker. The first version will use the drivers salvaged from a Logitech Z523 - I was told they should be quite decent and I only paid 5$ for a Z523 with a dead amplifier. I will replace them later on and build a new case as I can't afford a set of good drivers at the moment. The battery is a 5S3P of NCR18650GA (18650 cells with 3500mAh), resulting in roughly 19V during normal operation.
After looking for affordable modules I ended up buying a set of Sure JAB2 and JAB3 as they are not much more expensive than cheap individual modules would be, while saving me a lot of work (and DC-DC converters).
After they arrived I set the DSP up (for now just forwarding the signal from the inputs to the two outputs of the JAB2-50, while the JAB3-100 is only used as a DSP with no speaker connected) in order to try the amps with my home speakers (Boston Acoustics M25). That's where my issues began - apart from a low bluetooth range (which I will address later on) the volume was incredibly low. With the phone maxed to 100% it was still significantly lower than what I see as a convenient listening volume in a 20m² room.
After adding +10dB gain on the DSP (background hissing intensified) and using my notebook as an audio source, the volume got to an acceptable level, but I expect my speaker to be less efficient than my shelf speakers, so it still is too low. Apart from that it still is too silent with my phone. My phone has no apt-X issues, Logitech UE9000 bluetooth headphones get quite loud at roughly 50-70% output volume set on the phone. So I am still looking for a way to increase the output volume of the BT module. Are there some voltage dividers between the module and the connector to the DSP which I could modify for a stronger signal? I hope I won't have to reverse engineer the PCB - it is awfully complicated and black (no visible traces).
Another thing that annoys me is crosstalk between the BT output and the aplifier channels even with no DSP (or volume potentiometer) connected to the JAB2. I read that there was some resistors causing this which could be removed. I wanted to use the JAB2 for the high frequency drivers, which would then always get low frequencies (even if only at a lower volume) no matter how I set up the DSP - unacceptable. I think I know which resistors are used for this and will measure it later on with the multimeter.
EDIT: I was right, found the resistors. I will remove them later on and see if it fixes the crosstalk issues
Last but not least, low bluetooth range. The module only features about 3m of range before the connections starts to stutter with nothing but air in between the module and my notebook or phone. Both get about 20m of distance without issues with my UE9000. I still have the PCB antenna of an old fritzbox wireless router somewhere in a drawer, so I think I will try to cut the antenna on the module's PCB and solder the shielded cable of the fritzbox antenna to it. That should work better, shouldn't it? Both are intended for 2.4 GHz use.
I have no experience with those modules and can find barely any useful information in any of the languages I speak (german, italian, english) online, so I would be really grateful if someone here could help me a little or point out some links where I can read about similar issues (and ways to fix them).
Kind regards,
Moritz
Big EDIT:
I removed the two marked resistors, what changed quite a few things:
1) crosstalk across the DSP is entirely gone. yay
2) it got way louder (phone at ~80% is now a decent room loudness) - I can't really explain why, but I like it
3) less bass, more treble. Before the mod it was bass-heavy (I fixed that by ear with a parametric EQ), now it lacks lower frequencies. Off to the param eq again, I guess. No real issue as the intended use of this module will be to power the high frequency drivers anyway.
https://mpwr.xyz/gallery/2018_09/jab2_rmod.jpg
I also cut the trace of the original antenna and tried the fritzbox one, with kinda bad results. I now have ~4m of range in one direction and ~2m in the other. So it got directional, but still lacks range.
https://mpwr.xyz/gallery/2018_09/jab2_antmod.jpg
So, I am making progress. Everything but bluetooth seems fine!
Last edited:
Hi,
you could ask from their technical support, Sure Electronics website footer gives technical support contact info Skype:zhangcheng0519
I was amazed he replied rather fast to my messages and even tried to call me but I didn't dare to answer during my office hours
anyway, got help.
I built jab2 + jab3 combo recently. Plenty of volume with Bluetooth, altough I think the standard DSP program has some gain since it got somewhat lower after I put my own program in.
Bluetooth range is bad. I got aluminum/steel chassis and the range is only 2 meters. With lid open, maybe 5 meters.
Can you explain a bit more about the crosstalk issue? I don't understand
you could ask from their technical support, Sure Electronics website footer gives technical support contact info Skype:zhangcheng0519
I was amazed he replied rather fast to my messages and even tried to call me but I didn't dare to answer during my office hours
anyway, got help.I built jab2 + jab3 combo recently. Plenty of volume with Bluetooth, altough I think the standard DSP program has some gain since it got somewhat lower after I put my own program in.
Bluetooth range is bad. I got aluminum/steel chassis and the range is only 2 meters. With lid open, maybe 5 meters.
Can you explain a bit more about the crosstalk issue? I don't understand
Hello, I drew a little very simplified schematic to illustrate my issue:
https://mpwr.xyz/gallery/2018_09/jab2_rmod2.jpg
The issue was not "crosstalk" between channels (not the best choice of words from my side) but between DSP input and output. Even if the DSP output was set to mute, the amplifier would still receive a (more silent, but still prominent) audio signal.Very annoying if you want to use the DSP as an active crossover like me and half of the low frequencies still "leak" by.
I read about a german guy who did this mod, but he did not explain which resistors he removed. It was not too hard to figure out by looking at my board which ones might be the culprits and a quick check with the multimeter confirmed my expectations.
Klein aber Oho, DSP, Lithium und Bluetooth inklusive - Projekt AMG, Sonstiges - HIFI-FORUM
So it seems like the bad BT range is an inherent issue of this board, not only mine? I will keep trying to modify the antenna and see where it will lead me. If I should find any new clues I will update this thread.
I think the standard DSP program set gain to one of the potentiometers on the DSP board, mine got more silent with my custom program as well. I then added 10dB of gain what resulted in a good volume with acceptable background hissing noises.
https://mpwr.xyz/gallery/2018_09/jab2_rmod2.jpg
The issue was not "crosstalk" between channels (not the best choice of words from my side) but between DSP input and output. Even if the DSP output was set to mute, the amplifier would still receive a (more silent, but still prominent) audio signal.Very annoying if you want to use the DSP as an active crossover like me and half of the low frequencies still "leak" by.
I read about a german guy who did this mod, but he did not explain which resistors he removed. It was not too hard to figure out by looking at my board which ones might be the culprits and a quick check with the multimeter confirmed my expectations.
Klein aber Oho, DSP, Lithium und Bluetooth inklusive - Projekt AMG, Sonstiges - HIFI-FORUM
So it seems like the bad BT range is an inherent issue of this board, not only mine? I will keep trying to modify the antenna and see where it will lead me. If I should find any new clues I will update this thread.
I think the standard DSP program set gain to one of the potentiometers on the DSP board, mine got more silent with my custom program as well. I then added 10dB of gain what resulted in a good volume with acceptable background hissing noises.
Okay, I linked the wrong picture and for some weird reason can not edit my post :/ Apologies for the double post...
https://mpwr.xyz/gallery/2018_09/jab2_rmod2.jpg
This would be the correct image.
https://mpwr.xyz/gallery/2018_09/jab2_rmod2.jpg
This would be the correct image.
Ah, damn it. Apologies, I changed the folder structure on my page a little and killed the links. Forum won't let me edit.
This is a quick sketch of where the resistors are in a simplified schematic: https://mpwr.xyz/gallery/2018/09/jab2_rmod2.jpg
This is the resistors marked on the PCB: https://mpwr.xyz/gallery/2018/09/jab2_rmod.jpg
Yes, I am quite annoyed at this... I bought what I thought was the hassle-free premium product from china, only to reverse engineer and fix their failed circuit design...
This is a quick sketch of where the resistors are in a simplified schematic: https://mpwr.xyz/gallery/2018/09/jab2_rmod2.jpg
This is the resistors marked on the PCB: https://mpwr.xyz/gallery/2018/09/jab2_rmod.jpg
Yes, I am quite annoyed at this... I bought what I thought was the hassle-free premium product from china, only to reverse engineer and fix their failed circuit design...
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