Switch with internal arcs - Help! - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

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 22nd November 2001, 10:42 PM   #1
lwi is offline lwi
diyAudio Member
 
Join Date: Nov 2001
I have a DIY guitar amp (a mesa/boogie 2:90 copy), and it has a problem.

One of the switches produces a rather large popping noise when turned off.
I believe it's because of internal arcs inside the switch.
I have read here and a few other places that a contact suppressor and a vdr might help.

Can anyone provide me with more detailed info on this?

thanks in advance,

Lwi
  Reply With Quote
Old 22nd November 2001, 11:00 PM   #2
diyAudio Member
 
Join Date: Nov 2000
If the switch is the main power switch, I would suggest replacing it. After 10 years or more of service the contacts inside the switch a probably damaged (burned to a more or lesser degree).

You can place a ceramic disc capacitor over the contacts of the switch 10nF/630VAC to supress arcing and this will increase the life of your switch and amp.

Be extremly carefull when you replace the switch. 120Vac or 240 Vac is extremly lethal. If you are not sure how to replace the switch or put in the capacitor, please do not attempt this your self, but have a qualified technician carry out this small repair. Maybe you can take your amp over to a local repair shop. I am sure they will be happy to take care of this for a reasonable price.
  Reply With Quote
Old 22nd November 2001, 11:37 PM   #3
lwi is offline lwi
diyAudio Member
 
Join Date: Nov 2001
Thank you very very much

the switch is brand new so it's age is not an issue.
I built the amp myself, I just finished it recently, adding a cap shouldn't be a problem

cheers

lwi
  Reply With Quote
Old 23rd November 2001, 12:01 AM   #4
walker is offline walker  Australia
diyAudio Member
 
Join Date: Nov 2001
Location: Perth West Australia
Send a message via ICQ to walker
Iwi, I have done many such repairs and agree with Rtirion. Just thought I would mention RC snubbers, they include a series resistor with the capacitor for even longer switch life, (less stress). I use Evox-Rifa units, 0.1uF + 47ohm 1000V, (these seem to suit our 240v system and equipment upto 500VA). If you want the best supression you can calculate the correct values of R and C with the following rule of thumb;
R=E/Iload
C(uF)=Iload(Amps)

I also agree that though the job appears simple, it should be done by some one with the apropriate training.

Regards WALKER
  Reply With Quote
Old 23rd November 2001, 04:45 AM   #5
lwi is offline lwi
diyAudio Member
 
Join Date: Nov 2001
sorry guys, it did not work. It is still popping.

here is the part of the schematics concerning my problem:

Click the image to open in full size.
("output" = to the power tubes)

the switch (this switch!) is used for decreasing (when turned off) the cathode voltage. The end result is a drop in volume, but the tubes still saturate as if playing at loud volumes.
Putting a 10nF cap on the contacts of the switch resolved nothing.

any thoughts?

  Reply With Quote
Old 23rd November 2001, 05:39 AM   #6
walker is offline walker  Australia
diyAudio Member
 
Join Date: Nov 2001
Location: Perth West Australia
Send a message via ICQ to walker
Iwi does the pop sound come from the switch or through the speaker?

Regards WALKER

PS As usual I was off on a tangent thinking about the mains power switch.
  Reply With Quote
Old 23rd November 2001, 05:49 AM   #7
lwi is offline lwi
diyAudio Member
 
Join Date: Nov 2001
through the speaker.... its quite loud when I turn it off... but less so when turned on.
  Reply With Quote
Old 23rd November 2001, 06:03 AM   #8
walker is offline walker  Australia
diyAudio Member
 
Join Date: Nov 2001
Location: Perth West Australia
Send a message via ICQ to walker
I suspect that 10nF was too small but seeing the circuit I'm now concerned that a cap shouldn't be used at all. Could you scan a larger section of the circuit please.

Regards WALKER
  Reply With Quote
Old 23rd November 2001, 07:36 AM   #9
lwi is offline lwi
diyAudio Member
 
Join Date: Nov 2001
here you go:

Click the image to open in full size.

Just to clarify: the feedback is fed into a small eq section (two switches and a presence pot) wich is the added to the normal signal.

if anything else seems nebulous, just say so.

thanx
  Reply With Quote
Old 23rd November 2001, 08:55 AM   #10
walker is offline walker  Australia
diyAudio Member
 
Join Date: Nov 2001
Location: Perth West Australia
Send a message via ICQ to walker
Iwi, a cap across the switch will effect the sound I believe, though by how much Iíve no idea, (depending on the value of course). You could try 1uF but listen out for loss of top end, before and after it is in the circuit, (switch open of course). Snubbers would not be any better. The solution maybe to replace the switch with a pot, (power dissipation permitting). I don't really like that solution though either.
The Messa circuit must be different or maybe the manual suggested the selection be made before turning on.
I have repaired a Messa before, (love the wicker speaker cloth) I donít believe I have any schematics. If I remember correctly, they had Groove Tubes, donít you love marketing?

Try posting this in the valve forum, some of these guys would, I suspect, be quicker than I on thermionics questions.
Regards WALKER

PS I know this is redundant, but, there is lethal voltages on this circuit, be werry careful!
  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
Protecting a power switch from arcs antomas Power Supplies 12 19th June 2007 09:56 AM
switch-on, switch-off sequence for preamp/amp cbutterworth Tubes / Valves 1 2nd March 2007 01:41 PM
Never try to switch 450V DC at 3A with a conventional mains switch... Eva Power Supplies 28 1st November 2006 10:24 AM
Main on/off switch for amp using a piezo switch using_e Solid State 13 20th June 2006 06:55 PM
Using a momentary switch for main power switch? FullThrottleRic Parts 9 25th June 2002 09:23 PM


New To Site? Need Help?

All times are GMT. The time now is 12:04 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