World-Designs-Forum  

Go Back   World-Designs-Forum > World Designs > Problems
Register FAQ Members List Calendar Gallery Today's Posts Mark Forums Read

Problems For questions and answers re World Designs Projects

Reply
 
Thread Tools Display Modes
  #1  
Old 21st December 2020, 08:39 PM
Rhod Rhod is offline
Junior Member
 
Join Date: Nov 2020
Location: Carmarthen,Wales
Posts: 5
Default HD3S hum problem.

Hello, I'm new to the forum and to DIY audio so please forgive any ignorance or lack of etiquette as regards to both!
I built my HD3S xl and it worked beautifully for about 5 hours then developed a low hum through both channels, independent of the volume control. I've put shorted phono plugs on the inputs, tried it disconnected from everything except power, checked any earthing connections I can find with a multimeter, done a visual check for any loose wires, solder bridges and generally poked around with a chopstick to see if anything makes it better or worse, all to no avail. Could it be a component in the power supply or still an earthing issue? This is my first proper build (previously just a few guitar effects pedals) so I'm pretty much in the dark and any help would be much appreciated as the amp sounded great before this started.
Reply With Quote
  #2  
Old 21st December 2020, 10:13 PM
John Caswell John Caswell is offline
Super Moderator
 
Join Date: Dec 2005
Location: Wokingham, Berkshire
Posts: 1,649
Default Re: HD3S hum problem.

Hi Rhod and welcome to the forum.
First things - are you absolutely sure you have wired it correctly?
Second - are the voltages all correct to within 10%
Third - does the hum occur on both channels? - If not try swapping the valves over.

Try these and report back here please

John
Reply With Quote
  #3  
Old 21st December 2020, 10:16 PM
Greg.'s Avatar
Greg. Greg. is offline
WD Archivist
 
Join Date: Dec 2005
Location: Bristol, UK
Posts: 3,467
Default Re: HD3S hum problem.

Welcome Rhod. Were friendly here so let us know your real first name.

Im sure the likes of John Caswell and Richard will chip in here very soon as they have the knowledge. My uneducated immediate impression is that as it is on both channels, the fault is in the power supply section. It could readily be a dry solder joint or a hum loop, although the later should be in second place because from what you say, it sounded great for five hours. I would revisit all the solder joints in your PSU section, reflow them and see if this is a solution. If not, as said, its more a Richard or John Caswell response you need which surely is on its way
Reply With Quote
  #4  
Old 21st December 2020, 10:58 PM
A Stuart A Stuart is offline
Senior Member
 
Join Date: Jan 2006
Location: Selkirk, Scotland
Posts: 313
Default Re: HD3S hum problem.

Wikipaedia -
Rhodri is a male first name of Welsh origin. It is derived from the elements rhod "wheel" and rhi "king".

It may refer to the following people:

Rhodri Molwynog ap Idwal (690754), Welsh king of Gwynedd (720754) and about 20 others.

We can cope with Rhod, lucky he doesn't sign himself Molwynog.
Reply With Quote
  #5  
Old 22nd December 2020, 07:50 AM
bob orbell bob orbell is offline
Senior Member
 
Join Date: Nov 2009
Location: kettering northants.
Posts: 2,256
Default Re: HD3S hum problem.

Just to add my notes, I have built two of these for friends and both did have a small but irritating hum, I addressed both by twisting the transformer cables very tight and routing these and other cables to lessen the hum, I never did or could remove it completely at that time I had no scope. to see the hum. Bob
Reply With Quote
  #6  
Old 22nd December 2020, 03:51 PM
Rhod Rhod is offline
Junior Member
 
Join Date: Nov 2020
Location: Carmarthen,Wales
Posts: 5
Default Re: HD3S hum problem.

Hi everyone, thanks for replying so quickly.

Thanks John, yes it's on both channels. Matthew checked my voltages as a couple were slightly high but he was happy with everything. As for wiring, I was very careful and it worked well and very quietly for the first 5or6 hours.
Hi Greg, real name Rhoddy which is actually Scottish so no Welsh king I'm afraid A Stuart . When I get a chance I'll reflow the power supply joints to eliminate that possibility.
I've looked at the transformer cables which i twisted pretty tightly, and tried moving them around with no effect.
The thing that gets me is that it's both channels and it was fine for a while, which makes me wonder if
as Greg suggests, it's the power supply. Could a faulty capacitor cause it?
Reply With Quote
  #7  
Old 22nd December 2020, 07:15 PM
A Stuart A Stuart is offline
Senior Member
 
Join Date: Jan 2006
Location: Selkirk, Scotland
Posts: 313
Default Re: HD3S hum problem.

I do apologise for mis-interpreting the name. We live and learn. No doubt you are fed up with explaining the whole time. I take it you moved to Carmarthen to stop Scottish people like me asking ?

Alastair

Last edited by A Stuart; 22nd December 2020 at 07:27 PM.
Reply With Quote
  #8  
Old 22nd December 2020, 10:32 PM
John Caswell John Caswell is offline
Super Moderator
 
Join Date: Dec 2005
Location: Wokingham, Berkshire
Posts: 1,649
Default Re: HD3S hum problem.

Hi Rhod,
Just as a silly, please measure the heater voltage on the valve base pins 4-5 and report back here.

John
Reply With Quote
  #9  
Old 23rd December 2020, 09:44 AM
Richard Richard is offline
Super Moderator
 
Join Date: Dec 2005
Location: Notts
Posts: 5,091
Default Re: HD3S hum problem.

Quote:
Originally Posted by Rhod View Post
Hi everyone, thanks for replying so quickly.

Thanks John, yes it's on both channels. Matthew checked my voltages as a couple were slightly high but he was happy with everything. As for wiring, I was very careful and it worked well and very quietly for the first 5or6 hours.
Hi Greg, real name Rhoddy which is actually Scottish so no Welsh king I'm afraid A Stuart . When I get a chance I'll reflow the power supply joints to eliminate that possibility.
I've looked at the transformer cables which i twisted pretty tightly, and tried moving them around with no effect.
The thing that gets me is that it's both channels and it was fine for a while, which makes me wonder if
as Greg suggests, it's the power supply. Could a faulty capacitor cause it?

Hi Rhod, yes or a faulty diode, they don't like too much heat, have a look around them and if you have spares fit new ones using a small clip on heat shunt and soldering quickly. I only have the old info and don't know if it uses separate diodes or a package. That said dry joints are the favourite so go over them with a magnifying glass.
Reply With Quote
  #10  
Old 24th December 2020, 11:11 AM
Rhod Rhod is offline
Junior Member
 
Join Date: Nov 2020
Location: Carmarthen,Wales
Posts: 5
Default Re: HD3S hum problem.

Quote:
Originally Posted by A Stuart View Post
I do apologise for mis-interpreting the name. We live and learn. No doubt you are fed up with explaining the whole time. I take it you moved to Carmarthen to stop Scottish people like me asking ?

Alastair
It's the H that does it Alastair, that and the fact I live in Wales so no need to apologise. My surname is Farquhar, so I'm a sasanach with a Scottish name living in Wales...plenty of cause for confusion!
Reply With Quote
Reply

Thread Tools
Display Modes

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
Forum Jump


All times are GMT +1. The time now is 05:47 AM.


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Copyright World Designs