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

Solid State Talk all about solid state amplification.

Preamplifier Power Supply Problems
Preamplifier Power Supply Problems
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 24th November 2010, 05:48 PM   #1
FlyAndy is offline FlyAndy  Australia
diyAudio Member
Join Date: Apr 2009
Default Preamplifier Power Supply Problems


I built a NAP-140 amplifier which I run from a 25-0-25 transformer. It works fine.

I want to include a preamplifier in the case, so I incorporated a separate 12-0-12 toroidal transformer.

Im having trouble wiring the preamp and the amplifier together. Whenever I do so, the 12V toroid starts humming and gets very hot. I measured the voltage between the two 0V connections and found 7V difference. Obviously the smaller transformer is being forced to deliver current.

Both of the transformers are floating (i.e. the 0V is not connected to the chassis ground).

Should I connect the 0V to the chassis ground?

Any other suggestions on what the problem might be?

Many thanks for your help!!
  Reply With Quote
Old 24th November 2010, 06:53 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
the 12-0-12Vac transformer needs it's own PSU and this PSU powers the preamplifier only.

The existing 25-0-25Vac transformer already has it's PSU and this powers the power amplifier only.

The chassis, if any is metal must be connected to Protective Earth (PE).
The point/bolt/welded connection for making this contact is being called the Safety Earth, to differentiate it from the various other grounds that get used and abused in electronics gear.

All exposed conductive parts must be (electrically) connected to the Safety Earth.
That usually means that the centre tap of your main transformer must be connected to somewhere on the chassis using a connection that can pass Mains Fault Current to PE. This allows the fuse to blow and isolate the damaged gear and thus to be safer to touch (not to probe about inside).

If any part of the pre-amp has any exposed conductive parts then it too must be connected to chassis to blow your mains fuse in event of a mains fault.

If you are unsure about this Safety stuff, then seek expert local help or keep asking questions until it becomes absolutely clear, before you start building mains powered gear.
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 24th November 2010, 06:54 PM   #3
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
You can't couple two amplifiers which are floating except via a transformer. This means that the two secondaries will, at least indirectly, be connected somehow. The trick is to connect them in the right way.

Why not show us a diagram of what you did? Then maybe we can tell you what you should do. We are good, but we can't read minds.
  Reply With Quote


Preamplifier Power Supply ProblemsHide 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
Power Supply for Preamplifier skogs Solid State 15 15th June 2007 01:16 PM
Which is the better power supply for a preamplifier? fotios Solid State 16 2nd March 2007 07:35 PM
Power supply problems Devius Power Supplies 8 2nd July 2006 02:17 AM
problems with my power supply Pablo Solid State 10 4th June 2004 12:02 PM
Power Supply problems sirtiff Solid State 3 3rd May 2003 04:53 AM

New To Site? Need Help?

All times are GMT. The time now is 09:36 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio