Marshall Amp Forum

Go Back   Marshall Amp Forum > The Amps > The Workbench
JTM45 RI noise/hum when power up JTM45 RI noise/hum when power up
Register FAQ Members List Social Groups Calendar Search Today's Posts Mark Forums Read

  

Reply
 
LinkBack Thread Tools Display Modes
Old 09-04-2009, 04:14 AM   #1 (permalink)
Member
 
Join Date: Mar 2009
Location: Norway
Posts: 51
JTM45 RI noise/hum when power up
Hi
Just got a '89 JTM45 RI. It makes loud hum/noise when I turn it on, much more than my other tube amps. What could be wrong? Or is it suppose to be like this?
Most of the hum goes away when I turn off standby.
__________________
Cheers!

Øystein
Birk is offline   Reply With Quote
Alt Today
Marshall Amps

Beitrag Sponsored Links
__________________
This advertising will not be shown in this way to registered members.
Register your free account today and become a member on Marshall Amp Forum
   
Old 01-08-2010, 11:01 PM   #2 (permalink)
Junior Member
 
Join Date: Jan 2010
Posts: 4
Re: JTM45 RI noise/hum when power up
Mine has the same problem, also an 89 model. I joined here to see if I could find an answer.

Mine had it when it was completely orignal and still has it after I replaced everything except the power transformer. I installed PTP board, Marstran OT, new pots, choke and filtering.

The problem must have something to do with the power transformer or wiring from it - I've emailed Marshall to see what the current PT they are using is in the reissues.

I'll let you know what I find out, but something must have changed because the new ones don't hum in standby.
Hank Moody is offline   Reply With Quote
Old 01-09-2010, 12:26 AM   #3 (permalink)
Senior Member
 
Wilder Amplification's Avatar
 
Join Date: Oct 2009
Location: Rohnert Park, CA
Posts: 2,480
Send a message via AIM to Wilder Amplification Send a message via MSN to Wilder Amplification Send a message via Yahoo to Wilder Amplification
Re: JTM45 RI noise/hum when power up
Quote:
Originally Posted by Birk View Post
Hi
Just got a '89 JTM45 RI. It makes loud hum/noise when I turn it on, much more than my other tube amps. What could be wrong? Or is it suppose to be like this?
Most of the hum goes away when I turn off standby.
It's more than likely just a characteristic of that particular power transformer. If the amp is working fine other than the PT hum, I wouldn't worry about it.

How bad/noticeable is the hum?
__________________
Jon Wilder
Wilder Amplification

sales@wilderamplification.com

tech@wilderamplification.com

Quote:
Originally Posted by skeezix View Post
I mean..... if you really believe that turning your amp off a certain way will allow the filter caps to drain off back towards the substation, or whatever... I really don't think a sticky is gonna help you.
Quote:
Originally Posted by MartyStrat54
If Groove Tubes wants to keep putting it to us, we will smile and say, "Please wear a condom."
Wilder Amplification is offline   Reply With Quote
Old 01-09-2010, 03:27 AM   #4 (permalink)
Junior Member
 
Join Date: Jan 2010
Posts: 4
Re: JTM45 RI noise/hum when power up
Quote:
Originally Posted by Wilder Amplification View Post
It's more than likely just a characteristic of that particular power transformer. If the amp is working fine other than the PT hum, I wouldn't worry about it.

How bad/noticeable is the hum?
If his is anything like mine it really gets on your nerves after a while.
Hank Moody is offline   Reply With Quote
Old 01-09-2010, 09:01 AM   #5 (permalink)
Senior Member
 
jcmjmp's Avatar
 
Join Date: Nov 2008
Posts: 2,719
Re: JTM45 RI noise/hum when power up
Quote:
Originally Posted by Birk View Post
Hi
Just got a '89 JTM45 RI. It makes loud hum/noise when I turn it on, much more than my other tube amps. What could be wrong? Or is it suppose to be like this?
Most of the hum goes away when I turn off standby.
That can be normal. When the PT is not under load, it emits more EMF and that is coupled into the OT.
__________________
Marshalls: 1983 JCM 800 2204, 1987 2550 Silver Jubilee, 1993 JMP-1, 1997 JCM2000 DSL50
Marshall Cabs: JCM800 1960a G12-65s, JCM800 1960a G12T-75/Century, JCM900 1960a G12M-25/G12H-30 70th, JCM900 1960a Cab with Marshall G12-Vintage speakers
Other: 2008 2550x Marshall Silver Jubilee SDM Layout, 2009 Union Jack JTM45, 2008 Vox AC30CC 2x12 combo, ADA MP-1, 2x12 2550x Cab with Vintage 30s
jcmjmp is offline   Reply With Quote
Old 01-09-2010, 10:37 AM   #6 (permalink)
Member
 
Join Date: Mar 2009
Location: Norway
Posts: 51
Re: JTM45 RI noise/hum when power up
Yeah, hum/noise goes away when I turn off standby (play mode), and works great.
Well, not great, have some problems with the sound fade away when I run both channels and a boost in front. I made another topic for that. Havn't had time to re-check bias yet.
__________________
Cheers!

Øystein
Birk is offline   Reply With Quote
Old 01-10-2010, 03:03 AM   #7 (permalink)
Junior Member
 
Join Date: Jan 2010
Posts: 4
Re: JTM45 RI noise/hum when power up
Quote:
Originally Posted by jcmjmp View Post
That can be normal. When the PT is not under load, it emits more EMF and that is coupled into the OT.
That makes sense. It doesn't explain why other reissues I've used don't do it though. Might be using a different PT
Hank Moody is offline   Reply With Quote
Reply



« Previous Thread | Next Thread »
Thread Tools
Display Modes
Linear Mode Linear Mode

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 On
Pingbacks are On
Refbacks are On


All times are GMT -5. The time now is 01:42 AM.

Contact Us - Marshall Forum - Archive - Privacy - Top

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2010, Jelsoft Enterprises Ltd.

Our Network: Les Paul Forum | Music Gear Forum | 7 String Guitar Forum