Hello,
At reading some papers about EMI/EMC, wonder if there were some good practice for boxing the sensibles circuitries of the topic question ?
A pcb has several plane plans, top and bottom of the cabinet are thick plans and hearted. Is that layout making bad behaviors as antennas for instance that can harm more than it shields (most of the time boxing is made of ferous material that acts as magnetic shield trap at some frequencies. But what about the next plane that is the pcb ? Antenna effect (stray capacitance that could arm ?
Is metal boxing automaticly better there than wood for instance ? Are there good practices but the expensive material for shielding. Ferous, Copper, Nickel sheets ? Are the EMC not a lost cause because anyway we have wires in and out from that cabinets ?
A little too much open questions, but you got the idea, I am looking for general directions to follow and to understand how important or good enough it is for such sensibles devices and when it becomes a no-subject for audio.
thanks
At reading some papers about EMI/EMC, wonder if there were some good practice for boxing the sensibles circuitries of the topic question ?
A pcb has several plane plans, top and bottom of the cabinet are thick plans and hearted. Is that layout making bad behaviors as antennas for instance that can harm more than it shields (most of the time boxing is made of ferous material that acts as magnetic shield trap at some frequencies. But what about the next plane that is the pcb ? Antenna effect (stray capacitance that could arm ?
Is metal boxing automaticly better there than wood for instance ? Are there good practices but the expensive material for shielding. Ferous, Copper, Nickel sheets ? Are the EMC not a lost cause because anyway we have wires in and out from that cabinets ?
A little too much open questions, but you got the idea, I am looking for general directions to follow and to understand how important or good enough it is for such sensibles devices and when it becomes a no-subject for audio.
thanks
Theoretically external E fields and much EMI cannot penetrate inside a conductive enclosure,
even if it is perforated material, aka Faraday cage. But a multi-layer pcb also helps a lot.
even if it is perforated material, aka Faraday cage. But a multi-layer pcb also helps a lot.
Hi Rayma, nice to see you there.
Yup I understood I think ininterrupted gnd plane as dedicated power planes help a lot, but is there an audio reason to box from metal in spite of wook or acrylic (hummm esd ?) for enthusiasts whom are not exposed to obligations when commercialising a device in a box ?
For instance does metal boxing protect in the audio band ? Or how is important for audio to shield from RF in sensible devices (low currents, digital, high speed so HF, ...) ?
Just needs some guidance to escape the snake oil and false expensive efforts (boxing price really increased, maybe due to the popularity of our hobby and DIY in a general way)
Yup I understood I think ininterrupted gnd plane as dedicated power planes help a lot, but is there an audio reason to box from metal in spite of wook or acrylic (hummm esd ?) for enthusiasts whom are not exposed to obligations when commercialising a device in a box ?
For instance does metal boxing protect in the audio band ? Or how is important for audio to shield from RF in sensible devices (low currents, digital, high speed so HF, ...) ?
Just needs some guidance to escape the snake oil and false expensive efforts (boxing price really increased, maybe due to the popularity of our hobby and DIY in a general way)
There's so much EMI around these days, I would avoid unshielded pcbs if at all possible.
The Faraday cage does not block some low frequency noise, but it does a lot.
You might be lucky and be able to run it out in the open one day, but have noise the next.
Depends on you area and on what noise generating equipment is in your home.
Noise can also enter the enclosure via connecting cables, etc.
The Faraday cage does not block some low frequency noise, but it does a lot.
You might be lucky and be able to run it out in the open one day, but have noise the next.
Depends on you area and on what noise generating equipment is in your home.
Noise can also enter the enclosure via connecting cables, etc.
Thanks.
Do you think a wood box inside doubled with a thin layer of copper would suffice, or does it is "always" advised to put outside the Power traffos whatever they radiate more or less from EI to torroids ? As far I believe to understand the secondaries should not be too far as well from the loads ?
Do you think a wood box inside doubled with a thin layer of copper would suffice, or does it is "always" advised to put outside the Power traffos whatever they radiate more or less from EI to torroids ? As far I believe to understand the secondaries should not be too far as well from the loads ?
When I've mounted the power transformer in a separate enclosure, or on the outside of the main enclosure,
this has worked well for me. If you have EMI concerns and want to have an internal power transformer,
you can use a modular shielded AC line filter at the power input to prevent EMI from entering the main enclosure.
If the transformer is in a separate enclosure, there also should be rectification and filtering there locally,
as well more filtering in the main enclosure. This can reduce a lot of the 120Hz rectification noise.
Thin copper foil applied to the walls of the enclosure should work reasonably well if carefully done.
Copper foil is not really all that cheap these days though.
this has worked well for me. If you have EMI concerns and want to have an internal power transformer,
you can use a modular shielded AC line filter at the power input to prevent EMI from entering the main enclosure.
If the transformer is in a separate enclosure, there also should be rectification and filtering there locally,
as well more filtering in the main enclosure. This can reduce a lot of the 120Hz rectification noise.
Thin copper foil applied to the walls of the enclosure should work reasonably well if carefully done.
Copper foil is not really all that cheap these days though.
yeah, I have some cheap flat copper foil inductances purchased before metals prices raised and that were cheap... and I do not use. But it is no more than 4 cm width so must be overlayed to create some proofness I surmise.... I was just worried about antennas effect in case (no pun inntented) it was a problem !
High power electronics isn't best placed in a wooden or plastic enclosure for fire-safety reasons, let alone EMI/EMC. Low power stuff will usually benefit from good shielding, and every cable joining a PCB should have thought put into filtering out RF interference, ideally. A simple test with audio equipment you can do is hold a mobile phone near the box and its input cables and see if you can hear break-through from the mobile network packets stream. Good shielding will eliminate/minimize breakthrough.
Aliexpress sells adhesive copper tape that takes well solder for next to nothing.
My preference based only on sound is for minimal, light enclosures for the electronics and a separate, sturdy one for the transformers. I also prefer acrylic to wood as it is a lot more neutral.
Yes, the separation means another set of painfully audible DC carrying cables but is still, imo worth it.
Perhaps there are situations where carved out of solid metal block enclosures are beneficial to the sound, I just never encountered such
.
Curiously, a conservative company like ARC eventually figured things out and began offering thin, perforated acrylic top covers for their preamps.
When I read thing like this I'm reminded of my Racal-Dana 9082 signal generator. A molded alu design with pockets for each pcb, separated with 6mm massive molded alu between them. All connections through feedthrough capacitors and fitted with a 4mm thick alu plate fixed on with loads of bolts.
Might be sensible for a radio signal generator. Doubt if audio circuitry should need it.
Might be sensible for a radio signal generator. Doubt if audio circuitry should need it.