How do they get away with this?

Cassiel · 04:26 PM

I'd like building compact amps and preamps but it always worries me the distance between the power transformer and the signal circuit (SMPS may be an option, haven't tried that yet). So when I see something like this I wonder. Is it enough a metal screen around the tube? I really don't understand how they can get away with that PT so close to the inputs. But it seems it can be done. Is it because that is a buffer stage? I have a small torodial PT and my guitar preamp circuit has quite some gain. Would it be a waste of time to try something similar? Any tricks? I have also seen people using metallic mesh screens (2nd pic). What works best?

http://www.hdmag.dk/valvulator.jpg

Cassiel · 20th September 2011, 03:23 PM

Oh well, I have read the manual.

Quote:

The custom
power transformer is ruggedly built to withstand years of road
abuse. It features a low noise design that allows for installation
in tight quarters and close proximity to other devices with
minimum hum and noise.

So there's hum and noise. No big surprise after all. So I'm narrowing down my questions. No mu-metal here so what's best to isolate the trafo? Copper, aluminium or steel? Solid or mesh? Maybe I should use the search bottom...probably this has been asked before.

Merlinb · 20th September 2011, 03:35 PM

Quote:

Originally Posted by Cassiel

No mu-metal here so what's best to isolate the trafo? Copper, aluminium or steel? Solid or mesh?

A screen like that can only shield against electric fields, not magnetic ones, so the type of metal is immaterial (geddit?!).
Solid or mesh, it doesn't really matter since we're working at low frequencies.

TheGimp · 20th September 2011, 03:42 PM

Mu metal will help, however bending it changes it's characteristics. Proper shields are made to shape and then heat treated by taking them above the critical temperature (currie point?) and cooling them at a rate to optimize their shelding properties.

Joschl · 20th September 2011, 03:45 PM

I guess the metal screen around the tube in the first picture is only against heat radiation to the electrolytics.

Cassiel · 20th September 2011, 04:10 PM

Quote:

Originally Posted by Merlinb

(geddit?!).

Affirmative, over and out.

Pano · 20th September 2011, 04:24 PM

Please be kind to your fellow forum readers of limited bandwidth. Don't include inline photos of 1.4 Meg

Please see this thread: Pictures -- Why Not attach Them ??

kevinkr · 20th September 2011, 04:28 PM

Quote:

Originally Posted by Pano

Please be kind to your fellow forum readers of limited bandwidth. Don't include inline photos of 1.4 Meg

Please see this thread: Pictures -- Why Not attach Them ??

And not so limited bandwidth, even here at work it took 30 seconds to load and I had to resize it in firefox so that the thread displayed properly..

Cassiel · 20th September 2011, 04:29 PM

Sorry for that. That photo grows all by itself....it wasn't that big. You can delete it if you want to.

Fryette Vavulator (Tube Buffer/Special Sauce))

markusA · 20th September 2011, 05:26 PM

Interesting dilemma that I've wondered about myself.

20th September 2011, 01:41 PM	#1
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	How do they get away with this? I'd like building compact amps and preamps but it always worries me the distance between the power transformer and the signal circuit (SMPS may be an option, haven't tried that yet). So when I see something like this I wonder. Is it enough a metal screen around the tube? I really don't understand how they can get away with that PT so close to the inputs. But it seems it can be done. Is it because that is a buffer stage? I have a small torodial PT and my guitar preamp circuit has quite some gain. Would it be a waste of time to try something similar? Any tricks? I have also seen people using metallic mesh screens (2nd pic). What works best? http://www.hdmag.dk/valvulator.jpg Last edited by Pano; 20th September 2011 at 04:26 PM. Reason: photo linked

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20th September 2011, 03:42 PM	#4
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Mu metal will help, however bending it changes it's characteristics. Proper shields are made to shape and then heat treated by taking them above the critical temperature (currie point?) and cooling them at a rate to optimize their shelding properties.

20th September 2011, 03:45 PM	#5
Joschl diyAudio Member Join Date: Dec 2005 Location: Ruhrgebiet	I guess the metal screen around the tube in the first picture is only against heat radiation to the electrolytics.

20th September 2011, 04:24 PM	#7
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Please be kind to your fellow forum readers of limited bandwidth. Don't include inline photos of 1.4 Meg Please see this thread: Pictures -- Why Not attach Them ??

20th September 2011, 04:29 PM	#9
Cassiel diyAudio Member Join Date: Sep 2004 Location: Madrid	Sorry for that. That photo grows all by itself....it wasn't that big. You can delete it if you want to. Fryette Vavulator (Tube Buffer/Special Sauce))

20th September 2011, 05:26 PM	#10
markusA diyAudio Member Join Date: Dec 2009 Blog Entries: 8	Interesting dilemma that I've wondered about myself.

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