turn on noise - 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 16th October 2002, 01:12 PM   #1
diyAudio Member
 
Join Date: Oct 2001
Location: Brisbane, Queensland
Send a message via ICQ to junglejuice
Default turn on noise

Hi guys i have a pheonix gold m50 amplifier that has a loud turn on thump. I have measured the output of the amp at
turn on and it gets an ac wave form of 43hz for about 120ms with a peak voltage of 6v which
tapers back to zero. The wave forms are the same for each channel but 180 degrees out of phase.
This spike occurs at the exact time that the voltage starts to rise on the high voltage rails.
My question is does anybody have any thoughts as to how i can fix this or better still does anybody
have the circuit for this amplifier.
Any help will be greatly appreciated.....
  Reply With Quote
Old 25th October 2002, 10:38 AM   #2
diyAudio Member
 
Join Date: Oct 2001
Location: Brisbane, Queensland
Send a message via ICQ to junglejuice
Is there no one on this forum that has any ideas on how to fix this problem????
  Reply With Quote
Old 25th October 2002, 11:20 AM   #3
vbd is offline vbd
diyAudio Member
 
Join Date: Jan 2002
Location: Grenoble, France
The simplest thing to do, without any circuit diagram of the amp : add a delayed turn-on relay circuit... See for instance another aussie's project :
http://sound.westhost.com/project33.htm
__________________
Denis
  Reply With Quote
Old 26th October 2002, 06:49 PM   #4
BrianL is offline BrianL  United States
diyAudio Member
 
Join Date: Mar 2002
Location: USA
The slow turn-on should help, but not always. One could
also put a relay in series with the the output that delays
connection of the speaker until the amp settles.

But why not just let it thump? A number of amps I've
had over the years thump on turn-off (sometimes turn-on)
and it's never damaged anything, including when I was
triamping and tweeters were directly connected to the amp's
output.

So, why worry about it?
__________________
bel
  Reply With Quote
Old 26th October 2002, 10:01 PM   #5
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Junglejuice,

Turn on/off thump is very difficult to eliminate.

It is USUALLY (there are always exceptions!) caused by the power supply to the diff pair, which controls voltage offset at the output.

Most diff pairs are fed from current sources (CCS), and these will come to life within a couple of volts of switch on. However, the rest of the amp takes more volts that this to properly bias up, and strange things happen.

I have found that replacement of the CCS with a simple resistor allows the diff pair to come to life at the same rate as the rest of the amp, and this helps considerably. Many designers don't like resistive feed, however, since it is just too simple! However, at switch off there is then an infrasonic pulse which takes the speaker cone to full excursion for a second - you can't have it both ways.

The good news is, as Brian says, these pulses contain very little energy, well below the rated dissipation of all real world voice coils, and no damage is ever done.

If you like eggs, you must break shells.......

Cheers,

Hugh

www.aksaonline.com
  Reply With Quote
Old 27th October 2002, 06:49 AM   #6
diyAudio Member
 
traderbam's Avatar
 
Join Date: Jan 2002
Location: Earth
"Many designers don't like resistive feed, however, since it is just too simple!"

I don't like resistive current biasing because it compromises the CMRR and the PSRR of the amp!
  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
i get hiss noise when the treble is turn up on high?? prorms Solid State 1 7th April 2008 11:00 PM
Full-turn/partial-turn pots slowpogo Parts 1 12th January 2007 07:40 AM
SAE 2400 turn on/turn off pop Glen B Solid State 16 31st July 2006 01:32 AM
Noise when people turn off lights whee Solid State 13 6th December 2004 04:18 AM
How can I reduce mechanical turn on and turn off noise? soundNERD Chip Amps 8 28th October 2003 01:43 AM


New To Site? Need Help?

All times are GMT. The time now is 10:26 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