Go Back   Home > Forums > >

Chip Amps Amplifiers based on integrated circuits

LM3886/LM3876 Hum and motorboat sound come Ground line
LM3886/LM3876 Hum and motorboat sound come Ground line
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools
Old 8th March 2021, 04:34 PM   #11
tomchr is offline tomchr  Canada
diyAudio Member
tomchr's Avatar
Join Date: Feb 2009
Location: Calgary
Originally Posted by Nadeesh View Post
Without preamp lm3886 input connect 100 ohm with ground hum start, see image
As others have said: You have an issue with the amp, not with the preamp+amp. Fix that first.

The LM3886 circuit is copied directly from the data sheet. It'll work fine. Its HF stability can be improved, but you're dealing with LF stability. Fix that first.

Size Rmute such that you have at least 0.5 mA flowing in it. For the best THD, design for closer to 1.0 mA. There's no reason to go beyond 1 mA. I find 33 kΩ works well for power supply voltages above 20 V. Cmute should be at least 100 uF. A 6.3 V cap is fine here as it only sees about 3 V in operation.

Make sure you have proper decoupling. You need a minimum of 10 uF (tantalum or electrolytic) right next to the chip in parallel with a minimum of 100 nF ceramic (X5R, X7R, X8R dielectric types or better). In addition, you need 470-1000 uF where the power enters the LM3886 board. You can improve further on that if you'd like. If you haven't already, I recommend reading this: Taming the LM3886 Chip Amplifier: Power Supply Decoupling – Neurochrome

Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
  Reply With Quote
Old 14th March 2021, 09:17 PM   #12
nigelwright7557 is offline nigelwright7557  United Kingdom
diyAudio Member
nigelwright7557's Avatar
Join Date: Apr 2008
Location: Carlisle, England
If star grounding doesnt fix it then its possibly an earthing fault.
The system should have one earth connected to input.
No earth or multiple earths is not recommended.
  Reply to this post


LM3886/LM3876 Hum and motorboat sound come Ground lineHide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ground isolation loop problem ? Motorboat ticking sound rajkumar88 Chip Amps 13 26th April 2017 08:46 PM
LM3875, LM3876 or LM3886? Which one produces better sound? cumesoftware Chip Amps 11 2nd February 2015 03:30 PM
Buzz/Hum from Audiosector LM3876 board itself - no buzz in speakers dakku Chip Amps 4 12th April 2014 02:51 PM
ISO a motorboat stajo Tubes / Valves 133 2nd June 2013 10:22 PM
Southeast Conference (SEC) DIY 2011 - October 22! Come one, come all!! Tieftoener Clubs & Events 9 26th October 2011 04:03 AM

New To Site? Need Help?

All times are GMT. The time now is 11:31 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio