Go Back   Home > Forums > > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chipamp IC amp kits & PC boards from ChipAmp

Reply
 
Thread Tools Search this Thread
Old 25th February 2018, 10:34 PM   #81
Hogwild is offline Hogwild  Canada
diyAudio Member
 
Join Date: Oct 2010
Bill_P

Thanks. Actually this was one of the wrong boards for the amp I wanted to build. Same board, but resistors result in higher gain. For the boards that I already finished with the lower gain, I need to test those. That leads to my next question, which I'll post elsewhere.

BTW, I don't understand something-why is it that the connection I made on the POT got rid of the hum. I mean, I didn't actually connect anything to ground, did I?

Thanks
  Reply With Quote
Old 25th February 2018, 10:48 PM   #82
scottjoplin is offline scottjoplin  Wales
diyAudio Member
 
scottjoplin's Avatar
 
Join Date: Dec 2015
Location: Penrhyndeudraeth
Often hum is the result of a connection to earth/ground causing a loop with other wires/equipment also connected to ground. It isn't the ground itself that causes the hum, rather it is this loop that makes a very good aerial that picks up electromagnetic interference. This may help you understand and is very useful info for making your amplifier hum free. http://hifisonix.com/wordpress/wp-co...tober-2017.pdf
__________________
Woofer Assisted Wideband is the New Testament renounce the anachronistic acronym FAST
  Reply With Quote
Old 2nd May 2018, 11:19 PM   #83
OffGridKindaGuy is offline OffGridKindaGuy  United States
diyAudio Member
 
OffGridKindaGuy's Avatar
 
Join Date: Apr 2013
Location: Tuscarawas County, Ohio
Quote:
Originally Posted by Hogwild View Post
Bill_P

Thanks. Actually this was one of the wrong boards for the amp I wanted to build. Same board, but resistors result in higher gain. For the boards that I already finished with the lower gain, I need to test those. That leads to my next question, which I'll post elsewhere.

BTW, I don't understand something-why is it that the connection I made on the POT got rid of the hum. I mean, I didn't actually connect anything to ground, did I?

Thanks

The pot put a load across the input to the amp via the wiper and the resistance of the pot to ground. The resistance varies by turning the pot and never goes higher than the properties of the pot. (10k/20k/50k Ect.) The amp will always have an input load to ground through the resistance of the pot. Without a path to ground, the input of the amp is unbalanced and will pick up any electrical generated noise around it, as from your fluorescent lamp as you stated earlier. When things are open, the wiring between the amp and the pot is basically an antenna..


The grounds of the input of the amp and the source should always be connected together UNLESS both units are being powered with the same power supply. A "Ground Loop" issue could happen but that's another subject..


The positive signal input of the amp is connected to the wiper. The positive from the source is connected to the opposite end of the resistor in the pot. The resistance is fixed to the source by the properties of the pot. (10k/20k/ect..) The wiper is collecting signal from the fixed resistance load connected to the input source. The resistance varies and is seen by the amp. When the wiper gets closer to the source input of the pot, more signal gets to the amp. As the wiper goes farther away along the resistor load of the input, less signal gets to the amp. When the wiper gets to the grounded end of the resistor, the signal is gone.. (But the input of the amp still has a load on it)


Bottom line.. The input to your amp was unbalanced.

Last edited by OffGridKindaGuy; 2nd May 2018 at 11:21 PM. Reason: Hillbilly Grammer Fix..
  Reply With Quote
Old 31st May 2018, 12:52 PM   #84
turk 182 is offline turk 182  Canada
diyAudio Member
 
Join Date: Oct 2012
it would be better to say unterminated rather than unbalanced.
  Reply With Quote
Old 31st May 2018, 11:02 PM   #85
OffGridKindaGuy is offline OffGridKindaGuy  United States
diyAudio Member
 
OffGridKindaGuy's Avatar
 
Join Date: Apr 2013
Location: Tuscarawas County, Ohio
Quote:
Originally Posted by turk 182 View Post
it would be better to say unterminated rather than unbalanced.

I guess so.. Another Hillbilly Grammar Ooops..
  Reply With Quote
Old 1st June 2018, 08:44 AM   #86
turk 182 is offline turk 182  Canada
diyAudio Member
 
Join Date: Oct 2012
not really a grammar thing, more a technical oops.
  Reply With Quote

Reply


LM3886 - Noisy signal unless inputs shortedHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
noisy pre amp, audio transformer noisy? Salomon102 Analog Line Level 5 12th August 2015 07:53 PM
Noise Figures for MC Preamp (Inputs Shorted) thermionic Solid State 21 15th September 2013 07:11 AM
LM3886 Pin 7 to Power or Signal Ground? GregH2 Chip Amps 4 12th March 2010 11:15 AM
What should be the optimim level of Input Signal to a LM3886 based amplifier kuldeepsingh Chip Amps 9 14th May 2008 10:17 PM
noisy noisy noisy noisy noisy tube dsavitsk Tubes / Valves 50 20th February 2006 04:07 PM


New To Site? Need Help?

All times are GMT. The time now is 06:08 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki