Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

New amp project has some hum
New amp project has some hum
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 5th December 2018, 04:16 PM   #11
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
5Hz could be motorboating. Try a smaller value for the 0.22uF coupling capacitor.
  Reply With Quote
Old 6th December 2018, 05:21 AM   #12
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
You have lots of magnetics in a small space. The Lundahls are less sensitive to fields than most, but you also have some other chokes.

This could cause hum because of power transformer, and because of filter choke getting into the other magnetics.

It could also cause magnetic coupling of the tube stages, and maybe even oscillation, like the 5 Hz.
If you look at B+ you may also be seeing line bounce, with the power line voltage jumping as loads in your house and neighbors turn on and off.

You have lots to look for.
  Reply With Quote
Old 7th December 2018, 02:53 AM   #13
nigelwright7557 is offline nigelwright7557  United Kingdom
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
1/ Keep heater wires away from audio.
2/ Don't mount transformers next to valves.
3/ Keep input circuit as short as possible.
4/ Decouple each valve stage separately.
5/ Don't run HVAC near audio signals.
6/ Use star grounding where possible.
7/ Elevate heater centre tap to 45 VDC.
8/ Use grid stoppers close to grids..
Some of problems I found causing noise in my early designs.
Definitely not exhaustive.
__________________
PCBCAD51 download or CDROM 2019 version out now http://www.murtonpikesystems.co.uk

Last edited by nigelwright7557; 7th December 2018 at 03:04 AM.
  Reply With Quote
Old 7th December 2018, 06:37 AM   #14
Tjj226 is offline Tjj226
diyAudio Member
 
Join Date: Dec 2012
Quote:
Originally Posted by 6A3sUMMER View Post
You have lots of magnetics in a small space. The Lundahls are less sensitive to fields than most, but you also have some other chokes.

This could cause hum because of power transformer, and because of filter choke getting into the other magnetics.

It could also cause magnetic coupling of the tube stages, and maybe even oscillation, like the 5 Hz.
If you look at B+ you may also be seeing line bounce, with the power line voltage jumping as loads in your house and neighbors turn on and off.

You have lots to look for.

Well what gets me is that I have a nice perfect 300mv 60hz sine wave on the plates of the 45s on both channels.

No modulation that I can see, and it is exactly 300mv on the dot. All of the AC wires are shielded to the hilt and are grounded at only one end of the shield. The AC wires are going right past the chokes for the 45, but if I move the wires away, the hum doesn't change.

If it were something like DHT hum or imbalance, I would expect to see slight variances between each channel. But nope. Same nice clean 60hz sine wave on both channels.

Im semi suspicious of the way I have the filament transformers mounted. I have one transformer on top of the other with the steel plate in between them. I tried moving them a while back and it didn't seem to make a difference, but I will move them again and see if I don't discover something.

I have a feeling that when I figure out that issue, a lot of the other issues (5hz noise) will solve themselves.
  Reply With Quote
Old 7th December 2018, 04:50 PM   #15
kodabmx is online now kodabmx  Canada
diyAudio Member
 
Join Date: Oct 2011
Location: Toronto
You could try running the 45 filaments from a bridge (no cap) and see if it changes to 120Hz...
  Reply With Quote

Reply


New amp project has some humHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
The BiAmp (aka My LM4766 + 6p15p project, and LM1875 project.) valtra103 Chip Amps 21 4th December 2015 09:32 PM
Newby project idea for HND main project help and advice needed please WIGANWEZ Chip Amps 1 17th September 2011 05:59 PM
Newby project idea for HND main project help and advice needed please WIGANWEZ Chip Amps 0 17th September 2011 02:39 PM
CDPRO2 Group Project (open source project) BrianGT Digital Source 147 8th August 2008 12:37 PM


New To Site? Need Help?

All times are GMT. The time now is 10:58 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki