Magnetic Enclosure and Solid State amps

knl · 8th June 2010, 08:00 PM

Hi All

I am busy building a Velleman pre-amp kit and have purchased a steel enclosure and accompanying tranformer at the same time.

I then realized that the enclosure is magnetic.

I know that it is a bad idea with valve amps that have an audio transformer, but does it make a difference on a solid state devices? I have shielded wires for connections.

Thanks in advance!

KNL

nigelwright7557 · 8th June 2010, 08:34 PM

The steel case is a steady state magnetic field and so wont cause AC induction into your wiring system.

knl · 8th June 2010, 08:40 PM

Hi Nigel

Thanks for the response, but just to be sure, should I be worried that the power transformer inside the enclosure (I plan to host both the transformer and preamp circuit in the same box) induce a magnetic field in the enclosure and in turn into the wiring system?

DCPreamp · 13th June 2010, 04:55 AM

As long as nothing shorts to the chassis, which goes for any hardware, there is no problem whatsoever between steel and transformers.

Consider that huge quantities of commercial power amps, preamps, A/V receivers, CD players, etc. all use stamped steel enclosures with internal transformers with zero issues.

If your project fits in the enclosure and you follow safe construction practices, you are good to go!

Enjoy!
Paul

AndrewT · 13th June 2010, 10:44 AM

this is not a recommendation just my (in)experience.

I have never been able to make a steel chassis power amp as quiet as a no chassis power amp.

Gordy · 13th June 2010, 02:23 PM

Knl, steel is absolutely fine, just follow a few basic guidelines…

Ground the case to the mains input ground at one point
Do not use the chassis for audio signal return paths
If using an E-I type transformer, ground the transformer mounting frame
Insulate audio signal input sockets from the case
Space circuit boards away from the chassis a few mm

If you are concerned about radiated field from your transformer consider placing it behind a partition. A sheet of 20 awg steel should be useful in this regard, but it must be well grounded.

8th June 2010, 08:00 PM	#1
knl diyAudio Member Join Date: May 2010	Magnetic Enclosure and Solid State amps Hi All I am busy building a Velleman pre-amp kit and have purchased a steel enclosure and accompanying tranformer at the same time. I then realized that the enclosure is magnetic. I know that it is a bad idea with valve amps that have an audio transformer, but does it make a difference on a solid state devices? I have shielded wires for connections. Thanks in advance! KNL

8th June 2010, 08:34 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	The steel case is a steady state magnetic field and so wont cause AC induction into your wiring system. __________________ http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.

13th June 2010, 04:55 AM	#4
DCPreamp diyAudio Member Join Date: Jun 2005 Location: Sacramento, CA	As long as nothing shorts to the chassis, which goes for any hardware, there is no problem whatsoever between steel and transformers. Consider that huge quantities of commercial power amps, preamps, A/V receivers, CD players, etc. all use stamped steel enclosures with internal transformers with zero issues. If your project fits in the enclosure and you follow safe construction practices, you are good to go! Enjoy! Paul __________________ "Believers cling to the myth despite the evidence, reinterpret the myth to suit the evidence, or lie about the evidence to support the myth." "To err is human; to blame errors on external factors is even more so."

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8th June 2010, 08:40 PM	#3
knl diyAudio Member Join Date: May 2010	Hi Nigel Thanks for the response, but just to be sure, should I be worried that the power transformer inside the enclosure (I plan to host both the transformer and preamp circuit in the same box) induce a magnetic field in the enclosure and in turn into the wiring system?

13th June 2010, 10:44 AM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	this is not a recommendation just my (in)experience. I have never been able to make a steel chassis power amp as quiet as a no chassis power amp.

13th June 2010, 02:23 PM	#6
Gordy diyAudio Member Join Date: Nov 2006	Knl, steel is absolutely fine, just follow a few basic guidelines… Ground the case to the mains input ground at one point Do not use the chassis for audio signal return paths If using an E-I type transformer, ground the transformer mounting frame Insulate audio signal input sockets from the case Space circuit boards away from the chassis a few mm If you are concerned about radiated field from your transformer consider placing it behind a partition. A sheet of 20 awg steel should be useful in this regard, but it must be well grounded.

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