So I've built the PCBs, and tested the thing with some cheap ratshack fullrange drivers, and everything is working perfectly.
Now it's time to build the enclosure.
How big of a deal is a metal case v.s. one built out of wood when it comes to EMI and grounding issues? Is it better to have an alu bottom to place the boards on, and just ground to the chassis, or does it matter?
What about on the back panel, where the RCA inputs are panel mounted? Will the lack of a 'groundable' material cause interference or other problems?
Since I'm using an LM3875 based design, and simple non-switching PSU, EMI should be _less_ than say.. oh a class D, right? I mean.. I shouldn't have to worry too much about placing the amp too close to say, a AM radio tuner (not that I listen to AM radio all that much...)
Now it's time to build the enclosure.
How big of a deal is a metal case v.s. one built out of wood when it comes to EMI and grounding issues? Is it better to have an alu bottom to place the boards on, and just ground to the chassis, or does it matter?
What about on the back panel, where the RCA inputs are panel mounted? Will the lack of a 'groundable' material cause interference or other problems?
Since I'm using an LM3875 based design, and simple non-switching PSU, EMI should be _less_ than say.. oh a class D, right? I mean.. I shouldn't have to worry too much about placing the amp too close to say, a AM radio tuner (not that I listen to AM radio all that much...)
A well designed PCB should operate fine in a wooden enclosure, it's you who should place ground leads 'near' the signal leads and you'll still be fine with a wooden enclosure....
I prefer aluminium becase it's easy to manufacture for me, and brings a larger ground plane (I DO like to use class D).
Some audiophiles place wood in their book of favorables.... for many 'reasons'....
I'd say if you like the looks or find it nicer to handle... go for wood...
I prefer aluminium becase it's easy to manufacture for me, and brings a larger ground plane (I DO like to use class D).
Some audiophiles place wood in their book of favorables.... for many 'reasons'....
I'd say if you like the looks or find it nicer to handle... go for wood...
Google is your friend.
Now is time for my flame bath...
Take the very same amp build it into a metal box, give it a good listen, then build it into a wooden box. Do the same.
I am willing to bet you almost anything (its realy a shame I'm a poor man) the wood enclosed amp, will knock the socks off your metal case.
I have been reading about this phenomena for a while now, and have been doing some tests of my own. (doesn't anyone want to die and leave me a scope in their will?) I am pretty sure the changes shoud show on a scope.. thats how diffirent the sound is.
The very materials you use will affect the sound. Get rid of plastics and steel, when you need standoffs, stay with brass, aluminium or wood.
http://www.soundstage.com/maxdb/maxdb111998.htm
I linked a nice article by Doug Blackburn, and will try to find some of those I read in the past as this is a topic I was getting the guts together to start.
Now is time for my flame bath...
Take the very same amp build it into a metal box, give it a good listen, then build it into a wooden box. Do the same.
I am willing to bet you almost anything (its realy a shame I'm a poor man) the wood enclosed amp, will knock the socks off your metal case.
I have been reading about this phenomena for a while now, and have been doing some tests of my own. (doesn't anyone want to die and leave me a scope in their will?) I am pretty sure the changes shoud show on a scope.. thats how diffirent the sound is.
The very materials you use will affect the sound. Get rid of plastics and steel, when you need standoffs, stay with brass, aluminium or wood.
http://www.soundstage.com/maxdb/maxdb111998.htm
I linked a nice article by Doug Blackburn, and will try to find some of those I read in the past as this is a topic I was getting the guts together to start.
I have just scanned over that link to the sound stage article, expecting to find a suggestion that electronics are subject to micrphonics. Some are, ie the good old EF86.
I have never seen a reference to solid state micrphonics, except in the case of dry joints, or a faulty part. Now I accept that could be due to my ignorance, or lack of knowledge.
That article refers to mechanical or acustical resonance as if it were electronic.
I'll stick by my time old method of sturdily mounting PCBs on aluminium, and to keep out stay fields, shield the case in some manner. If you choose timber, line it with foil.
That article, is to me, proof you can not believe everything you read. It's your choice to go along with it, or dissagree with it, but please think about it.
Geoff.
PS I-forgot, you said in your footer, by Charles Darwin.
I have never seen a reference to solid state micrphonics, except in the case of dry joints, or a faulty part. Now I accept that could be due to my ignorance, or lack of knowledge.
That article refers to mechanical or acustical resonance as if it were electronic.
I'll stick by my time old method of sturdily mounting PCBs on aluminium, and to keep out stay fields, shield the case in some manner. If you choose timber, line it with foil.
That article, is to me, proof you can not believe everything you read. It's your choice to go along with it, or dissagree with it, but please think about it.
Geoff.
PS I-forgot, you said in your footer, by Charles Darwin.
Its amazing how when people are faced with doing simple experiments some would choose to burn you a the stake.
I could understand if I said use only branches from a willow tree watered with virgin urine of which I have samples at $10000, but a simple request to try the same amp in a wooden case compared to a metal case.
As with anything one needs to use the right thing for the right job. None of my audio components pick up any RF yet all are in wood now. You realy think you can listen to radio indoors which makes it all the way through your house yet shield your case with 2mm aluminium?
Anyhow, I'm alover not a fighter. I can smile and dissagree without ever holding a grudge... benefit of a short memory.... anyhow I had my flamesuit on as I was expecting this response, so all is ok...
People are going to have opposing thoughts, thats part of life. Heck some folks even voted for Bush.
I could understand if I said use only branches from a willow tree watered with virgin urine of which I have samples at $10000, but a simple request to try the same amp in a wooden case compared to a metal case.
As with anything one needs to use the right thing for the right job. None of my audio components pick up any RF yet all are in wood now. You realy think you can listen to radio indoors which makes it all the way through your house yet shield your case with 2mm aluminium?
Anyhow, I'm alover not a fighter. I can smile and dissagree without ever holding a grudge... benefit of a short memory.... anyhow I had my flamesuit on as I was expecting this response, so all is ok...
People are going to have opposing thoughts, thats part of life. Heck some folks even voted for Bush.
I have the opportunity to put the tranny inside of the speaker cabinet (wood and about a good foot+ away from the amp pcb).
Are the any drawbacks? Do toroids need airflow to cool? Do they generate that much heat?
Would one be tempted to put the rectifying board down there as well?
Would one rather traverse from the tranny to the amp box in AC or DC?
My other concern is the distance of the DC or AC wires going from the tranny sitting at the bottom of the speaker cabinet going up to the amp aluminum box sitting atop (think of a guitar combo amp for an idea of the general layout).
Are there any special considerations traveling about a foot+ with AC or DC at 35V?
One other benefit from doing this is that the tranny would in effect be "double insulated" and I could opt out of having a ground safety.
Are the any drawbacks? Do toroids need airflow to cool? Do they generate that much heat?
Would one be tempted to put the rectifying board down there as well?
Would one rather traverse from the tranny to the amp box in AC or DC?
My other concern is the distance of the DC or AC wires going from the tranny sitting at the bottom of the speaker cabinet going up to the amp aluminum box sitting atop (think of a guitar combo amp for an idea of the general layout).
Are there any special considerations traveling about a foot+ with AC or DC at 35V?
One other benefit from doing this is that the tranny would in effect be "double insulated" and I could opt out of having a ground safety.
I'm in the prototype stage of an LM4780 parallel amp. I got two of those beautiful gold anodized heat sinks from Apex Jr. and some cherry wood from my Bro-Inlaw. The power supply is in a separate case but there is NO shielding used what so ever.
I've set it next to a monitor and on top of a CD player with no hum at all. Nor have I experienced any EMI. I think good grounding techniques are more important than shielding. At least within the chassis.
Hey Nordic! Could you come down a bit on those sample prices?
I've set it next to a monitor and on top of a CD player with no hum at all. Nor have I experienced any EMI. I think good grounding techniques are more important than shielding. At least within the chassis.
Hey Nordic! Could you come down a bit on those sample prices?
Nordic, it's not a matter of flame throwing. I am just suggesting that people read carefully, and research.
I have had my share of electo-magnetically induced hum and feedback.
My AM-FM tuner picks up plenty of stations on it's indoor antennae.
Have you not heard of RF break-through?
Facts: Timber will not stop magnetic fields, RF radiation, Static discharge or X-rays. It will reduce airborn sound, but not mechanically coupled vibration. It does however block light, including UV, so your EPROMs are safe.
The above is well documented, and whitnessed over 35 years exp in Electronics, Electro-medical, Telecommunications, Magnetics, and process control. And that's just the stuff used for an income. I won't bore you with all my other interests.
And to every one else, just don't take my word, do the research.
Make attractive cases by all means, but don't overlook shielding.
FWIW, RF break-through CAN destroy speakers. CB radio on the highway a KM away can push the noise floor of my Realistic SPL meter to -70 dB, due to it's plastic case. In the days of AM radio, inc CB, caused a few red faces in churches as the Hamond organ became the receiver and PA.
Geoff.
I have had my share of electo-magnetically induced hum and feedback.
My AM-FM tuner picks up plenty of stations on it's indoor antennae.
Have you not heard of RF break-through?
Facts: Timber will not stop magnetic fields, RF radiation, Static discharge or X-rays. It will reduce airborn sound, but not mechanically coupled vibration. It does however block light, including UV, so your EPROMs are safe.
The above is well documented, and whitnessed over 35 years exp in Electronics, Electro-medical, Telecommunications, Magnetics, and process control. And that's just the stuff used for an income. I won't bore you with all my other interests.
And to every one else, just don't take my word, do the research.
Make attractive cases by all means, but don't overlook shielding.
FWIW, RF break-through CAN destroy speakers. CB radio on the highway a KM away can push the noise floor of my Realistic SPL meter to -70 dB, due to it's plastic case. In the days of AM radio, inc CB, caused a few red faces in churches as the Hamond organ became the receiver and PA.
Geoff.
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