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Befaco Output, Phones Noise
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Befaco Output, Phones Noise
allears62
Hi all,

I've built a befaco output from thonk and it seems to be mostly working but the phones output has a horrible noise floor (sounds like power bleed but I'm no expert).

I've tested it with a few different PSUs and it's less with my doepfer case but still noticeable, I've also tested with a pair of dt150s instead of my HD25s that I normally use but it's still there then as well.

Is this an unavoidable quirk of my power situation? or have I likely got an error?



Here's a picture of it. The ferrite beads could maybe do with a bit longer legs for separation as they're pretty squeezed in with the diodes but apart from that I can't spot anything massively wrong... anyone had experience with this issue?
float32
I had the same issue with this module, it's very annoying. I had a look at the schematic and found that it uses the NJM2073 as a headphone amplifier. The 2073 requires a very small signal input to minimize distortion, then internally boosts it up by ~160x. You can see there is heavy attenuation at the 120ohm/10k voltage dividers:



This has the side effect of also boosting the noise floor to very noticeable levels. So, being a professional tinkerer, I decided to fix it! I designed a board using the LME49723 that would replace the 2073 and drive headphones with much lower noise.



OSH Park renderings:



It also requires removal of the attenuation on the Befaco board by removing R105, R106 and jumping R108, R109.

I've just finished with this and it gives a much cleaner headphone signal. Here it is plugged into the module.



Shared project on OSH Park: https://www.oshpark.com/shared_projects/lNyhQNLK
soporus
float32 wrote:
Shared project on OSH Park: https://www.oshpark.com/shared_projects/lNyhQNLK

Thank you for breaking down the issue and for sharing your PCB. Got a few of those PCBs to split with friends, sounds much better.
drmarble
Was considering getting one of these modules. Looks like they may have fixed the issue in the current (version3) offering. It uses paralleled 5532s (instead of the NJM2073) for the headphone amp.

Can anyone with a v3 confirm?

https://www.befaco.org/en/output-module-iii/
artieTwelve
I have one and have no problems with it. No headphone problems that I have noticed.
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