Thump on power up, pop on power down - Page 2 - 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 6th October 2012, 09:30 PM   #11
diyAudio Member
 
lanchile's Avatar
 
Join Date: Sep 2008
Location: AREA 51
if it is a big thump...the cap in the switch will not solve this problem. That sounds like caps charging/discharging at turn off/on and in some amps this is common since they do not have output relays to avoid this. also with high SPL speakers you can hear it louder. I had an Adcom amp that had this thump noise at on/off it is not bad for speakers as long as you measure the voltage at the outputs when you turn it on/off and see it is safe for speakers. some amps designs are like this...
  Reply With Quote
Old 6th October 2012, 09:31 PM   #12
diyAudio Member
 
Join Date: Feb 2010
try disconnecting the pilot lamps. they would have a large current draw on switch on, delaying power up times.
otherwise build a dual tracking dc servo for the return legs of the driver transformers
  Reply With Quote
Old 6th October 2012, 09:32 PM   #13
diyAudio Member
 
lanchile's Avatar
 
Join Date: Sep 2008
Location: AREA 51
Quote:
Originally Posted by whizgeek View Post
Unless you are into some serious stuff, the turn on/off thumps are a fact of life for this amp. Its the in design of the signal path.
Every capacitor in the signal path needs time to charge up at power on, and during this time, the dc voltage on the previous stage is carried through to the next stage in the chain.
The 24v supply to the driver transistors will take much longer to charge up than the 17v supplies, so power to the outputs will be up before the driver stage has stabilised.
Bingo!!! I agree 100%
  Reply With Quote
Old 6th October 2012, 09:49 PM   #14
diyAudio Member
 
djmeverett's Avatar
 
Join Date: Dec 2011
Location: Washington
Quote:
Originally Posted by djoffe View Post
Did it have this behavior before you re-capped?
Don't really know...it was essentially dead when I got it.
I found 2 open 270ohm 2W power resistors on the output transistor stage which I replaced and an open e-cap in the audio board (the section before those output transformers).
I have some new .47ohm replacement resistors that I can replace at the output transistors as well as new .01uf film caps, but I haven't replaced those yet.
I did replace all the small e-caps on the audio board. And as it sits right now both channels work now.

I also replaced the PS e-caps to see if that would improve anything but nothing really changed there (that I can tell)....I tested the old PS filter caps and only 1 was bad (open). it was C431 the 50uf 50V between the +17/-17VDC rails.
After replacing that the rails now measure +19/-19VDC. Before they measured +24 and -13VDC.
Also the thump when you switch it on is not too loud, but the pop when you switch it off is really loud even with the volume turned all the way down!

I've been thinking about putting the old filter caps back in. I replaced them with same values and voltage. I used radial Nichicon VZ and and axial VX series. These were much much smaller then the original axial style metal cans that were in there.
All the older caps also measured much higher when I removed them than they're listed values...i.e...both 1000uf read 1650uf.
I do have a couple of 2200uf 25V SM series that I could try in place of the 1000uf....if you think that would help?
Is it possible my replacement filter caps are causing this problem?
Or is it something to do with the output transistors and maybe I should replace those .47ohms and caps?
  Reply With Quote
Old 6th October 2012, 10:13 PM   #15
diyAudio Member
 
djmeverett's Avatar
 
Join Date: Dec 2011
Location: Washington
Quote:
Originally Posted by whizgeek View Post
try disconnecting the pilot lamps. they would have a large current draw on switch on, delaying power up times.
otherwise build a dual tracking dc servo for the return legs of the driver transformers
There is only one pilot lamp installed right now. It's the only good one left.
The others including the stereo indicator lamp were burned out.
I'm sure your correct whizgeek that this may be the way it is per design.

I'm not in a position to spend more money on this unit and was hoping for a cheap easy fix. Hard to believe it has such a nasty pop!
I suppose the cheapest workaround would be to put a switch on the back to the speakers and turn them on after the receiver is powered up and switch them off before it's switched off.
Would using a standard DPDT toggle switch for each channel be suitable for that.
I'm willing to try something simple if it is something I have on hand and won't cause the thing to melt down...
  Reply With Quote
Old 6th October 2012, 10:18 PM   #16
diyAudio Member
 
djmeverett's Avatar
 
Join Date: Dec 2011
Location: Washington
Quote:
Originally Posted by nigelwright7557 View Post
It could be the mains switch.
100nf across it or something similar would help.

Class AB amps are usually not too bad on thumps at power on/off.

I have seen serious problems with class D amps, i had to resort to a microcontroller holding the class d chip in reset on power up and down !
Quote:
Originally Posted by jaycee View Post
i'd say its likely to be sparking across the switch contacts, so yeah an X rated capacitor across it's contacts should help.
I have these here...would there be any harm or damage caused in trying one across the power switch contacts?

http://www.digikey.com/product-searc...49FAcs8pp2mfAi
  Reply With Quote
Old 7th October 2012, 12:17 AM   #17
jaycee is online now jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Those parts should be safe to use across the switch contacts. There wont be any risk of harm at all.
  Reply With Quote
Old 7th October 2012, 12:54 AM   #18
diyAudio Member
 
djmeverett's Avatar
 
Join Date: Dec 2011
Location: Washington
Quote:
Originally Posted by jaycee View Post
Those parts should be safe to use across the switch contacts. There wont be any risk of harm at all.
Thanks jaycee,
needed that little boost of confidence..appreciate it!
  Reply With Quote
Old 7th October 2012, 03:18 AM   #19
balerit is offline balerit  South Africa
diyAudio Member
 
balerit's Avatar
 
Join Date: Apr 2011
Location: South Africa
You need a 100n 250v X-class in series with a 100 ohm resister across the live wires after the switch to take care of the switch off click. A speaker protector with turn on delay is the only solution for your turn on thump.
Mac

The Book Worm - DIY Audio Ebooks and Manuals - Speakers, Moscode Amplifiers, Electronics, Map Reading, Free Capacitor Intro.
  Reply With Quote
Old 7th October 2012, 03:49 AM   #20
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, on the east coast
Quote:
Originally Posted by lanchile View Post
if it is a big thump...the cap in the switch will not solve this problem. That sounds like caps charging/discharging at turn off/on and in some amps this is common since they do not have output relays to avoid this. some amps designs are like this.....)
This is the basic problem with any mass produced solid state amp. in the silicon era before the the general use of relays around 1980. Even capacitor coupled output designs could deliver a strong thump.

Some high quality units seemed to have had care taken to reduce DC offsets and the imbalance in the charging currents to the preamp and ancillary circuits (this usually causes most of the noise) but all amplifiers had some degree of "thump/crack" and it was once part of everyone's audio experience. I notice that a lot of people who weren't around then, fret about damage to their speakers or just the surprise of it as they aren't accustomed to this in modern audio systems which have muting/protection circuits.

There is an important issue with re-capping that DIYs often ignore by fitting low ESR caps everywhere. Be careful buying caps on a popularity basis - you don't want low ESR cap grades for filtering DC (the big reservoir caps) and they will probably make the noise pulses shorter and louder. You'll have to replace caps anyway, but just use regular types, a little larger in capacitance (<= 100%) may actually be helpful.

As in previous posts, this muting is in the form of a speaker protection relay disconnecting the speakers until a few seconds have elapsed from turn-on and dropping out immediately the power is turned off. You can purchase pre-built universal modules of these (a PCB with ready built circuit) on E-pay for peanuts or you could DIY completely from schematics shown regularly on the forum, if you wish.

Unfortunately, short of just reducing the sharpness or "crack" of the sound , you can't make the effect disappear with a simple tweak or part replacement. I think though, that unnerving as the effect may be, any speaker that can't handle the typically brief burst of energy at moderate level is sure not going to handle music too well either. The rest is down to you doing the proper mod. or simply getting used to retro audio.
__________________
regards

Last edited by Ian Finch; 7th October 2012 at 03:59 AM.
  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
Sure amp in car, thump/noise on power up majorahole Chip Amps 6 14th July 2011 02:03 PM
Fixing the dreaded power up/down thump! paulspencer Everything Else 0 29th March 2010 12:52 AM
Problem with PPI amps - POP on power on and power off Onkel Alex Car Audio 8 19th October 2008 07:48 PM
Pop On Power down guycom Power Supplies 0 26th November 2006 06:20 PM
Power off thump (Korsun) 3Dgeek Solid State 0 13th November 2005 09:25 PM


New To Site? Need Help?

All times are GMT. The time now is 08:03 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