toroidal mechanical noise - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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
Thread Tools Search this Thread
Old 13th December 2014, 09:41 PM   #1
diyAudio Member
Join Date: Feb 2013
Default toroidal mechanical noise

I am building a tube microphone preamp, schematic here:

The PSU has two toroids (80VA Nuvotem encapsulated). Both work and measure fine when hooked to the mains power, but in the PSU configuration the 12 V makes a continuous buzzing sound. It is not from the PSU as same happens when nothing is hooked to the trafos except mains power. It is not that loud but one can hear it when its quiet and the noise doesn't sit well with the purpose of the gear.

I also tried each secondary besides the parallel, and same. Also from the other secondary of the 15V, all combos make the buzz.

Is it something wrong with the 12V trafo, or will it go away once the amp is completed with the tubes drawing (maybe adding some positive effect from the closed chassis?) I only tested them "in the air". Moving them around doesn't help.

  Reply With Quote
Old 14th December 2014, 12:02 AM   #2
roclite is offline roclite  United Kingdom
diyAudio Member
Join Date: Dec 2011
Location: Middlesex
Send a message via Skype™ to roclite

I have had a similar problem and my post may help you:

Keces DA-131 toroid (torid?) noise tamed!

You need to be clear exactly where the noise is coming from. If it is the toroid, then it could be caused by mechanical vibration of the core at your mains frequency. This is a quality issue and an encapsulated toroid will be very difficult to quieten using the method I used on my DAC. Make sure both transformers are not interacting together (keep well apart). Sorry I cant offer any more direct help. Good luck
  Reply With Quote
Old 14th December 2014, 12:10 AM   #3
diyAudio Member
Join Date: Feb 2013
Thanks. It is coming from the toroid, and only when fed from the 15V. If I feed it from the mains it is quiet. It does it even if placed about 1 foot from the other. It is free-in the hand, trying to squeeze it doesn't help. When mounted it is going to be bolted on the top of the other with several leather gaskets in between but I have the feeling that won't help. Maybe a proper electrical load will help, or simply replacing it?
  Reply With Quote
Old 14th December 2014, 12:55 AM   #4
diyAudio Member
Join Date: Nov 2006
Location: Adelaide, South Australia
Blog Entries: 28
Some toroids do this. In fact I might suggest that in general purpose power toroids, this is not at all uncommon. In most applications it is not an issue. For hifi gear it is.

You will find a number of people in the forums who have tried using DC blocks on the mains. This might work for you but adds complexity and is something I have not got into.

In my experience the only (other) solution is to buy an alternative transformer. Which I have done more than once.
  Reply With Quote
Old 14th December 2014, 08:28 AM   #5
JMFahey is offline JMFahey  Argentina
diyAudio Member
JMFahey's Avatar
Join Date: Mar 2009
Location: Buenos Aires - Argentina
I'd get another one.

Not a fan of the "line DC " theory, or to be more precise: if a transformer can't be connected to Real World mains voltage without trouble, then something's wrong, either design or construction (or both) but anyway: the buzzing one here is not directly connected to mains but to floating 15VAC supplied by another transformer, which should act as a natural high pass filter.

Just looping the loop and to leave no stone unturned: that transformer ***might*** be too tightly specified, it can stand 220V on the 220V winding but not 15V on the 12V one.

Just for kicks connect it to any 12V transformer you have available and check whether it still buzzes or not.
  Reply With Quote
Old 14th December 2014, 08:36 AM   #6
diyAudio Member
Join Date: Mar 2002
Location: Glasgow
I think this is correct, putting 15V into the 12V winding is probably saturating it.
"Sadly, audio is like that. It is about the only branch of electronic engineering where lack of knowledge is regarded as a more advanced form of wisdom."
  Reply With Quote
Old 14th December 2014, 09:52 AM   #7
diyAudio Member
Join Date: Feb 2013
The first version of the schematic had 15V on both trafos but in many cases there wasn't enough HT voltage so the designer changed the second trafo. I might try with a 15V instead of 12 as currently I seem to have plenty of juice, without load it goes to a whopping 400V !

But first will finish the build as is and see if the noise gets in the signal path. That would be a bummer. The mechanical part can be less of a problem if I place the preamp far enough from the recording spot.
  Reply With Quote
Old 14th December 2014, 10:19 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Buy the correct B+ transformer.
One that goes from mains 220/240Vac to your required Vac without using a stepping up back to front contraption.
regards Andrew T.
  Reply With Quote
Old 14th December 2014, 10:40 AM   #9
diyAudio Member
Join Date: Feb 2013
Thanks, good idea. This one for example. 200mA seems to be enough, and has the exact voltage I am getting from 15 to 12V: 275

Amp Maker: Guitar amp kits and parts :: Power transformers :: 0-190-275V/6.3V toroid power transformer
  Reply With Quote


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
Logitech Z-5500 Subwoofer Toroidal Transformer Hum Noise nathanson666 Parts 3 27th March 2015 10:23 PM
Mechanical noise in amplifier circuit hpt Solid State 15 15th October 2011 06:12 AM
NAD 6240 Cassette Deck Mechanical Noise Uncertain Analogue Source 0 8th November 2010 05:43 PM
Best Transformers (Encapsulated Toroidal or Open Frame Toroidal) Rixsta Pass Labs 10 23rd April 2004 03:41 AM
How can I reduce mechanical turn on and turn off noise? soundNERD Chip Amps 8 28th October 2003 01:43 AM

New To Site? Need Help?

All times are GMT. The time now is 08:27 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2