Both hum and radio interference in an audio circuit - diyAudio
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 4th July 2003, 04:45 PM   #1
mnw21 is offline mnw21  United Kingdom
diyAudio Member
 
Join Date: Jul 2003
Location: Cambridge
Question Both hum and radio interference in an audio circuit

I have an audio circuit that I built a while ago (ten years), and I have been recently trying to upgrade it, and seem to have got into all sorts of problems.

My audio system is split into two separate boxes - a stereo amplifier, with satellite speakers, and a bass amplifier. The bass amplifier has a transformer to provide +-70V DC to a 50W power amplifier attached to a 300W bass speaker in the same case, and another transformer to provide +-12V regulated DC to the preamplifier. The stereo box has a transformer to provide single rail 14V DC to a couple of 8W amplifiers to power the speakers. Until recently, the input to these two 8W amplifiers was completely passive, but since then I have incorporated an input stage, which uses the +-12V power from the bass amplifier, supplied over an umbilical cord between the two.

The intention of the new circuitry is to allow more than one input to the system, and to provide those inputs as balanced receivers, to eliminate an earth loop problem I had whenever I plugged the system into my computer or video machine (interestingly the CD player was fine).

Once I had put this circuitry in, the system was fine, but it hummed a little - I assumed this would be due to an earth loop between the stereo and the bass boxes. Therefore, I made another balanced receiver circuit and placed it between the two systems, disconnecting the earth connection on the umbilical cord. Both systems have their own earth connection. Now the hum is much reduced (but still bad), but I get a large amount of radio interference from all three speakers. The interference is never intelligible, but consists of whistling, squeaking, and other similar sounds.

I currently have two ideas, but I'm not entirely confident of them:
1. Connect a low resistance across the inputs of everything - at the moment, all the inputs are relatively high impedance. This might reduce the interference a little by shorting it out as such.
2. Power the new circuitry from batteries temporarily, to see if the power umbilical is to blame.

Any help or advice would be much appreciated,

Matthew Wakeling
  Reply With Quote
Old 4th July 2003, 10:15 PM   #2
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
See if you can borrow a copy of the Radio Amateur's Handbook. It includes good advice on RF suppression.
I just bought some transformers because I intend to wire my PC audio to the rest of my audio system. Your findings have verified I haven't wasted my money...
  Reply With Quote
Old 5th July 2003, 09:08 PM   #3
mnw21 is offline mnw21  United Kingdom
diyAudio Member
 
Join Date: Jul 2003
Location: Cambridge
Default Hmm. Possible misinterpretation.

The system produces this noise when there is nothing plugged into the stereo box except the bass box. Plugging other things in doesn't seem to make any difference - I assume this is my balanced line receivers working.

Matthew
  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
Radio Shack analogue SPL meter circuit diagram EC8010 Multi-Way 14 13th February 2011 12:41 AM
Audio [Radio] Amplifier Ideas Needed audiohobby Solid State 0 27th February 2009 01:21 PM
Looking for analog audio circuit designers and audio researchers cnotley Everything Else 1 29th September 2008 09:04 PM
Odd Amplifier/Radio Interference Problem normalicy Car Audio 5 5th July 2008 05:59 AM


New To Site? Need Help?

All times are GMT. The time now is 04:18 AM.


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