Tube amp left ch. hum - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 February 2012, 08:44 PM   #1
diyAudio Member
 
Join Date: Aug 2005
Default Tube amp left ch. hum!

I have an Audio Electronics Super Amp MkII power amp made by Cary Audio which has left channel hum. It has been this way since I bought it used 3.5 years ago, though the hum has gotten somewhat louder since then.

Upon inspection, none of the caps (mostly Kimber) look bad, though I haven't tested them because I would have to remove them to do so. I have replaced and rotated tubes around with no change in the hum. I have made sure the point-to-point wiring is isolated as best as possible.

There is a chassis mounted headphone type plug on the rear for biasing, that seems kind of a funny design. I should mention when I plug in the bias cable to hook to a meter the hum stops. I can take a photo of this area if necessary.

What could be the problem and/or what should I test first? Here are photos of the unit.
Attached Images
File Type: jpg angle_1210.jpg (90.1 KB, 209 views)
File Type: jpg entire inside_1396.jpg (445.2 KB, 209 views)
File Type: jpg front half_1397.jpg (422.4 KB, 206 views)
File Type: jpg rear half_1398.jpg (402.6 KB, 199 views)

Last edited by mjatabor; 17th February 2012 at 12:22 AM.
  Reply With Quote
Old 16th February 2012, 08:54 PM   #2
GloBug is offline GloBug  Canada
Banned
 
Join Date: Jun 2011
The usual thing to do is check and or replace electrolytic capacitors. (I'm assuming you know how to do so safely)

How old is the amp? The caps could be failing early due to heat. (85 degree caps)

The layout looks like it would humm, but you say it is getting worse and only in one channel.
  Reply With Quote
Old 16th February 2012, 08:58 PM   #3
diyAudio Member
 
firechief's Avatar
 
Join Date: Sep 2008
Location: Near Seattle Wa
Disconnect the inputs completly. With the power on and speakers connected, do you still hear the hum? We need to eliminate a few things first. Does the hum increase with volume? Or just stay at a low level. Do you have schematic? If so post it.
__________________
"You can keep your insurance baby nothing is guaranteed" -Tom Petty
  Reply With Quote
Old 16th February 2012, 09:02 PM   #4
diyAudio Member
 
dagerman's Avatar
 
Join Date: Feb 2011
Location: Greater Seattle Area
Disclaimer: I am not an expert, still learning this stuff myself.

I may be completely off, but just to see reactions of the real experts out there: The yellow wire coming off of the OPT look like they provide feedback to what could be the driver stage tube. Is it a good idea to route those right past the choke? It looks like the speaker output wires have been routed as far away from any inductors as possible.
__________________
There are 10 types of people: Those who understand binary and those who don't.
  Reply With Quote
Old 16th February 2012, 09:36 PM   #5
diyAudio Member
 
Join Date: Aug 2005
Thanks for a super quick reply!

Quote:
Originally Posted by GloBug View Post
The usual thing to do is check and or replace electrolytic capacitors. (I'm assuming you know how to do so safely)
How old is the amp? The caps could be failing early due to heat. (85 degree caps)
The layout looks like it would humm, but you say it is getting worse and only in one channel.
Amp is 2007. Are the big silver cans the electrolytic caps. What is the safe way to test? Yes, it looks like a hum design to me, but only the left channel hums.

Quote:
Originally Posted by firechief View Post
Disconnect the inputs completly. With the power on and speakers connected, do you still hear the hum? We need to eliminate a few things first. Does the hum increase with volume? Or just stay at a low level. Do you have schematic? If so post it.
Hum is only the left channel. It hums with no input, does not change volume, and is easily heard from 12' or more away with no source playing. Music at reasonable volume drowns out hum, that is why I never addressed it before.

Quote:
Originally Posted by dagerman View Post
The yellow wire coming off of the OPT look like they provide feedback to what could be the driver stage tube. Is it a good idea to route those right past the choke? It looks like the speaker output wires have been routed as far away from any inductors as possible.
Is the choke that little transformer between the output trannys. If so I moved the wire away and still hum, only in left channel.

Last edited by mjatabor; 16th February 2012 at 09:40 PM.
  Reply With Quote
Old 17th February 2012, 01:16 AM   #6
GloBug is offline GloBug  Canada
Banned
 
Join Date: Jun 2011
The choke is that little transformer between the outputs.

The electrolytic capacitors are the ones wrapped in blue plastic. If the amp is from 2007, these "should" be fine.

The big silver caps "appear" to be an oil cap, which usually last a long time.

The fact that the hum does not vary could mean the output transformer is picking up noise from the power lines/transformer.

I do notice the red wires that come from the power transformer are close to the left output transformer. If you have enough slack, use some zip-ties to move the wires away from this area a bit.

Read up on tube safety before you go sticking your fingers in there, safely discharge the capacitors first, ie: the blue electrolytics and the oil caps. It's good practice to drain all the caps until you get to know which ones are the dangerous ones.
  Reply With Quote
Old 17th February 2012, 01:56 AM   #7
diyAudio Member
 
firechief's Avatar
 
Join Date: Sep 2008
Location: Near Seattle Wa
Tube Compliment: 6SN7 x 3, EL34 x 4
Try pulling the 6SN7's one at a time and see if the hum goes away. If it was the power supply caps it would be common to both chanels. There is no problem running the amp with the preamp tube's removed.
6SN7 is a dual triode vacuum tube, on an 8 pin octal base. So proballly one 6SN7 is common to both channels and the other two tubes are unique to a channel. Knowing this is a big help in narrowing it down. Are you with me?
__________________
"You can keep your insurance baby nothing is guaranteed" -Tom Petty

Last edited by firechief; 17th February 2012 at 02:02 AM.
  Reply With Quote
Old 17th February 2012, 02:18 AM   #8
GloBug is offline GloBug  Canada
Banned
 
Join Date: Jun 2011
Good tip.

Also see if you can find a schematic, what does the bias meter look like? You might be onto something with that. A manual would be good too.
  Reply With Quote
Old 17th February 2012, 10:43 AM   #9
diyAudio Member
 
Join Date: Jun 2011
remove the bias jack; as this should be a set of bananna or a jones socket.

1/4 inch should be for signal use only and I recommend only used for input purposes (as speakers should always be speak-on connectors).
  Reply With Quote
Old 17th February 2012, 12:34 PM   #10
speaker is offline speaker  United States
diyAudio Member
 
speaker's Avatar
 
Join Date: Mar 2004
Location: USA
Quote:
Originally Posted by firechief View Post
Tube Compliment: 6SN7 x 3, EL34 x 4
Try pulling the 6SN7's one at a time and see if the hum goes away. If it was the power supply caps it would be common to both chanels. There is no problem running the amp with the preamp tube's removed.
6SN7 is a dual triode vacuum tube, on an 8 pin octal base. So proballly one 6SN7 is common to both channels and the other two tubes are unique to a channel. Knowing this is a big help in narrowing it down. Are you with me?
The hum could go away because the tube is pulled from the circuit if the problem is upstream. Rather than remove the tubes completely, try swapping them one at a time from one channel to the other. If the problem follows the tube, you might have the culprit.

I suspect though that is not going to be the case. Even though it looks like high-quality parts were used, I'd bet you have a bad coupling cap on the hum side. If the tube swap does not yield good results, I'd replace them and see where you are.
  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
Broken amplifier - Hum in left channel. MaxWar Solid State 7 28th April 2011 05:51 PM
Help With Left Channel Hum Monjul Tubes / Valves 4 21st April 2010 10:24 AM
Hum in left channer - rogers cadet 3 cr0wl3y Tubes / Valves 6 7th January 2010 11:44 PM
Tube Amp - Crackling Sound on Left Channel Noak Tubes / Valves 8 28th December 2005 01:46 AM
Left Ch Zenv4 Circuit Board Design Blues Pass Labs 0 20th March 2005 11:54 PM


New To Site? Need Help?

All times are GMT. The time now is 09:15 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