Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 12th March 2006, 10:49 PM   #1
diyAudio Member
 
Join Date: Dec 2003
Location: Houston
Default Simple OP amp preamp hum only with both channels connected

I built a very simple preamp with input jacks, channel switches, a volume pot, an OPA2134, and output jacks. It is pretty simple, non-inverted, and built on a perf board. The power supply is very cleanly regulated.

The input jacks are connected the chasis ground. PSU ground is also conneted to the chasis ground. Volume pot body is connected to the input ground.

However, when I connect the preamp with my gainclone amplifier, it is absolutely quiet when one channel is connected. The moment the other channel is connected, the left channel started to hum. When I connect the output jacks also to the chasis ground, both channels hum when both channels connected. Again, remove one channel, no hum at all. Absolutely quiet with nice music.

Can someone give me a hint what might be the problem? Why does it hum only when both channels connected?

By the way, my gainclone does not have any hum when connected with my HK preamp.
__________________
Bing Yang
  Reply With Quote
Old 13th March 2006, 12:27 AM   #2
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
ground loop problem
  Reply With Quote
Old 13th March 2006, 12:41 AM   #3
diyAudio Member
 
myhrrhleine's Avatar
 
Join Date: Jan 2006
Location: Avalon Island
Ground loop.
  Reply With Quote
Old 13th March 2006, 02:27 AM   #4
diyAudio Member
 
acenovelty's Avatar
 
Join Date: Aug 2004
Location: SF Bay Area
Star ground everything to one central point at the power supply.
__________________
Two people can keep a secret if one of them is dead.
  Reply With Quote
Old 13th March 2006, 02:42 AM   #5
rabbitz is offline rabbitz  Australia
diyAudio Member
 
rabbitz's Avatar
 
Join Date: Jul 2003
Location: Newcastle, Australia
Don't connect signal grounds to the chassis.

Check the grounding scheme on your pre amp board so the power ground is separate to the signal ground and only come together at power ground input to the board. Sometimes a 10R resistor can help by placing it between the power ground and signal ground connection. I also make sure the grounding doesn't go all the way around the board and has a break in it.

Here's a pic of a little pre using a OPA2134 in a plastic case (powered by a 16VAC wall wart). You'll notice the power ground is at the opposite end to the signal grounds and those grounds all come back to the power ground input. There is a break in the signal ground track between the red signal input and output at the top of the board.

If all fails, add a 10R resistor between ground and chassis which tends to shut it up.
Attached Images
File Type: jpg p44 inside.jpg (67.6 KB, 264 views)
__________________
No longer DIY active
  Reply With Quote
Old 17th March 2006, 02:01 AM   #6
diyAudio Member
 
Join Date: Dec 2003
Location: Houston
After spending a lot of time trying all kinds of combinations, hum persisted. When combined with other equipment, neither the Gainclone nor the preamp caused any hum.

This prompted me to search all Gainclone related articles. I finally came to the conclusion that it is the connection between the signal ground and power ground on BrianGT's board that causes the hum.

After I unsoldered the resistor right on top of the connection and cut the trace, the amp is now nice and quiet. There is still a very low trace of hum on the left channel. Since I understand how ground works now, I think I know the reason. The left channel has a longer wire from the board ground to Power Ground on the chassis. I am sure it will be reduced once I change that into a shorter and thicker wire.

It is nice to finally find out why!
__________________
Bing Yang
  Reply With Quote
Old 17th March 2006, 06:23 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
your solution to the hum elimination of cutting the signal to power ground interconnection resistor indicates that you have a second signal to power ground interconnection.

It is the second you should find and cut and then re-establish the resistor connection that Brian has designed in.

Quote:
Power Ground on the chassis
that sounds suspicious.
__________________
regards Andrew T.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Mixing two channels in the preamp or at the phase splitter? flysig Tubes / Valves 7 29th April 2009 07:59 AM
Ground loop only when both channels connected Nuuk Solid State 16 1st April 2007 04:28 PM
Why is GND of scope channels connected to case? luka The Lounge 7 18th February 2007 07:35 AM
5.1 channels preamp? roibm Solid State 7 13th October 2004 11:53 AM
Increasing output channels of preamp. hugobross Solid State 19 6th February 2002 04:13 PM


New To Site? Need Help?

All times are GMT. The time now is 06:27 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2