Amplifier pwr down "thump" issue - Page 5 - 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 29th March 2012, 02:42 AM   #41
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
You can replace the existing switch with a double pole single throw switch and use the extra contact to disconnect the +24 volts. Be careful because you have to timing it right.
  Reply With Quote
Old 29th March 2012, 03:24 AM   #42
puppet is online now puppet  United States
diyAudio Member
 
Join Date: Dec 2011
Location: The Dells, WI
I'll check that out tauro0221 ... sounds like that might work great too.

I don't think a toggle is the way to go Mike. I've got family here and just see a scenario where the toggle is left OFF ... the wife cranking the gain wondering why no sound ... then sees the switch.
This has to be bullet proof.

Tapping the +24V off R52's legs would be easy enough. Will that screw up that resistors value? If so, I'll look for the thermal switch and bypass that. ... just don't see it on the PWR module plan view.

You guys have been great working with me on this. Many thanks!!
Phil
  Reply With Quote
Old 29th March 2012, 03:54 AM   #43
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
If you want to go in that direction you can cut one of the wire in the front thermal light indicator and connect one of the wire from the light to the switch and from the other side of the switch to the other wire from the light. The thermal light it is coming from R52 through D21 thermal light to the relay.
  Reply With Quote
Old 29th March 2012, 04:32 AM   #44
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
Can you make another check if you do not mind. Can you check the resistance with the amplifier off between the + side of the speaker and ground. Disconnect the speaker before do the test. This is to check the contact resistance of the relay. It should be zero.
  Reply With Quote
Old 29th March 2012, 07:02 AM   #45
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by puppet View Post
Mooly ... in case it wasn't clear in the first couple posts the "thump" happens the instant the switch is pushed OFF.
Thanks for clarifying.

That's a strange issue as you have tried powering the amp down via other means to eliminate the switch.

The main rails to the amp ! It might be worth connecting a meter (analogue meter is often best but a DVM will do for this or a scope) to each rail in turn and seeing how quickly they collapse.

It's all very "empirical" but might give a clue. The relay should be dropping out quickly but the rails should remain "high" until the relay drops out due to all that capacitance on them.

Check both the rails to the opamps the same way as well as the main rails.

An amp shouldn't be affected by a fall in supply voltage until it reaches a "critical" level and that could be as low as just a few volts so it's something worth checking. If the quiescent current in one amp were very high for some reason then that could discharge the rails quickly. Similarly a DC offset would draw current via the speaker and do the same (so check that too).

A fault like this is a case of gathering as much info as possible to try and reach some conclusions.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 29th March 2012, 03:11 PM   #46
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
I think we already proved what your are taking when we added the resistor to the +60 volts supply. The thump was dampening. That means it is possible that -60 it is discharging faster than the +60 volts. It is possible that capacitors are weakening in the -60volts ?
  Reply With Quote
Old 29th March 2012, 04:36 PM   #47
puppet is online now puppet  United States
diyAudio Member
 
Join Date: Dec 2011
Location: The Dells, WI
tauro0221 ... checked resistance ... got like .001ohm on the meter.

Mooly .. I understand what you're saying just that I'm not able to judge what's "fast" in this context. The experience required to make that type of determination is not something I own right now.

For instance .. I did leave the DMM leads connected out of curiosity and PWR'ed OFF. Meter went to zero ... was it too fast, slow (shrug) .. got me. Certainly fast enough not to be able to apply an everyday clock to the duration.

I know it's not the best way but I'm going to fall back on the more primitive workaround ... switching the +24V circuit, to see if that works here. I know this won't damage anything .. least I wouldn't think so. There's a small hole 3/16" or so in the side panel .. enough to fish a couple wires through to a momentary NC switch. I'll use a rack ear to mount it "temp. like" to see if this is a go.

Only thing I'm not quite sure about is if after measuring the wiring (to and from + the switch) for resistance .. should I change R52 to reflect that additional resistance ... or not worry about it?
  Reply With Quote
Old 29th March 2012, 06:34 PM   #48
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by puppet View Post
Mooly .. I understand what you're saying just that I'm not able to judge what's "fast" in this context. The experience required to make that type of determination is not something I own right now.

For instance .. I did leave the DMM leads connected out of curiosity and PWR'ed OFF. Meter went to zero ... was it too fast, slow (shrug) .. got me. Certainly fast enough not to be able to apply an everyday clock to the duration.
No problem, good luck with whatever you try

(If you do come back to this I would have guessed at the speaker relay dropping out within a second or so of powering off.
As to the amps. With all that rail capacitance and a normal sort of quiescent current draw for a Class AB amp then I would guess it [the amp modules] should work for perhaps 3,4 or maybe much more seconds before the amp complained. I would expect the meter to go something like 60 and 50 and 40 and 30 etc at the speed you can say that )
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 29th March 2012, 06:45 PM   #49
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
Puppet I took the liberty to write this recount just in case people want to joint us in fixing your problem. Please accept my apologies.

This is a recount of test done to the amplifier to correct the "thump" when the amplifier is powered off.
1- Amplifier produce a loud "thump" when powered off.- using the power switch
2- test by disconnected the amplifier from the plug - same result
3-test the amplifier using an outlet switch - same result
4- -60 volts does have 4.7K bleeder resistor and +60 volts does not have one. Added one 4.7K resistor - "thump" loudness when down 20%
5- Power supplies read as follow:
Relay 24V = 22.87V
+15V = 13.75V
-15V = 14.25V
60V(+ -) = 63.2V
After these tests were done one possible conclusion is that the relay is not dropping fast enough to prevent the "thump".

Puppet Please add/correct if something is missing.

Puppet A team
  Reply With Quote
Old 29th March 2012, 07:16 PM   #50
diyAudio Member
 
Join Date: Nov 2008
Location: Victoria,TX
Blog Entries: 1
Mooly you do not think that another possible solution to this problem it is add more capacitors to the +/- 60 volts. By doing so the +/- 60 volts will hold longer than the other power supplies. This is another possible solution.
  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
"Power On" Led using bleeding resistor. An Issue ? coolnose Power Supplies 9 9th April 2010 10:45 AM
What makes an amplifier "bright", "warm", or "neutral"? JohnS Solid State 51 13th December 2009 06:42 PM
Aleph 2 "thump" Bakmeel Pass Labs 8 8th November 2008 09:33 PM
Turn on/off thump with "others" D amps...how it is managed? pat allen Class D 11 16th March 2005 07:58 AM
Is it normal "not" to have any turn on thump? Duo Solid State 23 7th September 2002 05:45 PM


New To Site? Need Help?

All times are GMT. The time now is 03:56 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