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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.
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