I am noticing in audiophile magazines and in catalogs, more and more transformerless amps.
Of course for size and cost, this approach is a dream come true.
But I have questions and reservations about such.
There is no isolation from the power mains for the driver!
These amps are being used in powered speakers. Most are class D, or some class G, and real high power. So the rectified line voltage could be about right.
But I still have reservations. You would have to provide isolation for the input signal.
But drivers, as I know, are not made to provide line isolation. I guess the enclosure could be build for isolation, and with a non-removable grill cloth?
Does anyone have feelings about this? Anyone seen what parts are used for the input isolation? Anyone looked real close at how such a enclosure is designed? Anyone know about the saftey legalities?
Anyone have links to any articles about this phenomenon?
Of course for size and cost, this approach is a dream come true.
But I have questions and reservations about such.
There is no isolation from the power mains for the driver!
These amps are being used in powered speakers. Most are class D, or some class G, and real high power. So the rectified line voltage could be about right.
But I still have reservations. You would have to provide isolation for the input signal.
But drivers, as I know, are not made to provide line isolation. I guess the enclosure could be build for isolation, and with a non-removable grill cloth?
Does anyone have feelings about this? Anyone seen what parts are used for the input isolation? Anyone looked real close at how such a enclosure is designed? Anyone know about the saftey legalities?
Anyone have links to any articles about this phenomenon?
Hi zenmasterbrian,
It's very simple. They lied. Otherwise this equipment would never get by UL and CSA.
They use a high frequency switching supply to reduce the weight (and cost) of a normal power transformer. They can improve line regulation this way as well. But there is still a power transformer in there. It's a smaller high frequency model.
This also saves on shipping costs.
The down side is that as your supply voltage goes down, the current draw goes up. That and EMI if it's improperly designed.
-Chris
It's very simple. They lied. Otherwise this equipment would never get by UL and CSA.
They use a high frequency switching supply to reduce the weight (and cost) of a normal power transformer. They can improve line regulation this way as well. But there is still a power transformer in there. It's a smaller high frequency model.
This also saves on shipping costs.
The down side is that as your supply voltage goes down, the current draw goes up. That and EMI if it's improperly designed.
-Chris
That is very interesting. I hope what you say is true.
I've seen a parts express plate amp.
I've also seen a brand of tower speakers that has its own little circuit board in with the subwoofer. The biggest stuff on it is a few capacitors, and two TO-3 devices on small heat sinks. It is about 3" by 5", 500W
I don't see enough there for a switching power supply of the type you describe.
Maybe you are right. If you have any links to articles or product adds or anything, I'd love to see it.
If anyone else has had any contact with such, I'd like to know about it.
I hope it is like you say, that the stuff is isolated.
( By the way, I have always felt that power transformers for isolation could be eliminated if we went to strictly polarized AC plugs, and made the neutral ground. Any thoughts? )
I've seen a parts express plate amp.
I've also seen a brand of tower speakers that has its own little circuit board in with the subwoofer. The biggest stuff on it is a few capacitors, and two TO-3 devices on small heat sinks. It is about 3" by 5", 500W
I don't see enough there for a switching power supply of the type you describe.
Maybe you are right. If you have any links to articles or product adds or anything, I'd love to see it.
If anyone else has had any contact with such, I'd like to know about it.
I hope it is like you say, that the stuff is isolated.
( By the way, I have always felt that power transformers for isolation could be eliminated if we went to strictly polarized AC plugs, and made the neutral ground. Any thoughts? )
anatech is probably right, what you are looking at is an amplifier with switching power supply. As an example, look at the one we manufacture:
http://www.coldamp.com/opencms/opencms/coldamp/en/productos/SPS80
http://www.coldamp.com/opencms/opencms/coldamp/en/productos/SPS80
That looks real neat!
But I can clearly see the high frequency transformer.
The one I saw in a magazine looked about half the board size, no transformer, and 500W.
It was built into the subwoofer.
Could they really be unisolated?
But I can clearly see the high frequency transformer.
The one I saw in a magazine looked about half the board size, no transformer, and 500W.
It was built into the subwoofer.
Could they really be unisolated?
And what if anything goes wrong ????? There doesn't habve to occur a very exotic failure and your in- and outputs are carring full AC. Just imagine what happens if the device is switchend on and the ground-line is inrterrupted.
Audio devices without proper mains isolation are and remaind a no-no !!!
There would be one solution that would make a seperate isolation transformer obsolete: If the PSU itself is an (isolated of course !) amplifier, like the "ampliverter".
Regards
Charles
Phase, this is kind of secondary, the idea that everything could eliminate isolation transformers if we used polarized plugs.
But say I have a standard amp with a 200w transformer.
Say sold state stuff shorts. So now the speaker outputs connect to this transformer. How much less serious is that than being connected to the power mains directly?? My power transformer could have a center tap grouned. The chassis could be grounded.
So I could get zapped of my amplifier transformer, just like of the mains transformer.
If what you mean is it is less serious because the appliance transformer is much smaller, so its core would saturate sooner. Then I follow you.
But say I have a standard amp with a 200w transformer.
Say sold state stuff shorts. So now the speaker outputs connect to this transformer. How much less serious is that than being connected to the power mains directly?? My power transformer could have a center tap grouned. The chassis could be grounded.
So I could get zapped of my amplifier transformer, just like of the mains transformer.
If what you mean is it is less serious because the appliance transformer is much smaller, so its core would saturate sooner. Then I follow you.
In the case of rectified 110 Volts AC this would be more than 150 volts DC ! Definitely more than your average Hi-Fi equipment rail voltages !
Now keep in mind that there are countries that don't use wimpy 110 Volt rails but 230 Volts .......
Apart from that, the situation that you described would cause DC voltage on an output. The situation that I described could make the chassis (and whatever is connected to it) carry mains voltage.
The small inconvenince of a transformer in terms of weight, cost and space is nothing compared to suffering, lwsuits and the like IMO.
Transformerless mains-operated audio equipment is a NO-NO !
Regards
Charles
Now keep in mind that there are countries that don't use wimpy 110 Volt rails but 230 Volts .......
Apart from that, the situation that you described would cause DC voltage on an output. The situation that I described could make the chassis (and whatever is connected to it) carry mains voltage.
The small inconvenince of a transformer in terms of weight, cost and space is nothing compared to suffering, lwsuits and the like IMO.
Transformerless mains-operated audio equipment is a NO-NO !
Regards
Charles
I can't think of a reason why a big powered PA subwoofer could not use a class D amplifier fed directly with rectified mains and still get all the required safety approvals, provided that adequate isolation techniques are employed.
We have things such as "linear" optocouplers with feedback, signal transformers and differential amplifiers for level shifting of the input signals. Also, now we can manufacture wooferts with very stiff and inherently isolating plastic spiders. And furthermore, PA systems may be horn loaded, thus physically preventing any user access to the driver (even when the grill is removed, which should be already considered a "service" condition).
BTW: As long as we have proper fuses built into the system, they will blow when 350V DC are applied either to a faulty amplifier or to a 8 ohm voice coil.
Note that my latest project (now working and reliable) is just a full bridge class D amplifier powered directly from rectified 230V mains (350V DC) and capable of +-30A peak output (>8KW peak), alhough it's not intended for audio but for driving mains powered motors and the like.
We have things such as "linear" optocouplers with feedback, signal transformers and differential amplifiers for level shifting of the input signals. Also, now we can manufacture wooferts with very stiff and inherently isolating plastic spiders. And furthermore, PA systems may be horn loaded, thus physically preventing any user access to the driver (even when the grill is removed, which should be already considered a "service" condition).
BTW: As long as we have proper fuses built into the system, they will blow when 350V DC are applied either to a faulty amplifier or to a 8 ohm voice coil.
Note that my latest project (now working and reliable) is just a full bridge class D amplifier powered directly from rectified 230V mains (350V DC) and capable of +-30A peak output (>8KW peak), alhough it's not intended for audio but for driving mains powered motors and the like.
This one could be tolerated as an exception. But keep in mind that large PA equipment is usually operated by professionals. You'll never know what happens with consumer stuff operated by Joe Average. Keep in mind that it isn't possible to make any design foolproof since most fools are much too inventive.
I am of course aware that there was once consumer equipment that used rectified remains. Old tube radios for instance that used constant current filaments instead of 6.3 Volts (or 4 Volts or ....) that could be connected in series. These radios had the advantage that they could be operated from AC mains and DC mains. The latter was once quite common in earlier days.
Also old TVs used the same PSU principle. Especially the radios were responsible for some lethal accidents though often provoked by misuse.
I seriously doubt whether equipment like that would pass any certification nowadays.
And I think it isn't bad practice to build equipment in a way of which could reasonably be assumed that it would pass certification - even when it is just for personal use.
Regards
Charles
Transformerless radios and TVs were still being produced into the 1970s, with all the tube filaments in series.
One condition is that they had long plastic insulators on all the controls, and no external connections.
For the antenna connections, they had mains isolation in the RF balun.
I am used to vacuum tube stuff as well as solid state. There the appliance voltage is much higher than our 115volt mains.
But it still might not be as dangerous because of the current limits due to the small transormer, and hopefully some fusing.
As far as the hypothetical case of highly polarized power mains connectors, it is not clear to me that you could not make things transformerless then, so long as neutral is ground, and these are never mixed up with hot.
But there may be other saftey issues.
Here in the US, most stoves are 230VAC, with the neutral centertap too. So the stove body ground to neutral
But in the last 10 years its been changed to 4 wire plugs with ground and neutral separate.
I think saftey grounding, and avoiding ground loops in signal handling gear is complex.
As far as transormerless class D amps under our present wiring scheme, I think some maybe on the market, and I have reservations about them.
I would assume you need to have a plastic coned woofer. But woofers are notorious for voice coil rub.
So unless someone makes one specially designed and approved, I don't see how.
I think you could make the grill cloth hard to take off and print warnings.
I've only seen this stuff in advertisements. That is why I asked the question.
One condition is that they had long plastic insulators on all the controls, and no external connections.
For the antenna connections, they had mains isolation in the RF balun.
I am used to vacuum tube stuff as well as solid state. There the appliance voltage is much higher than our 115volt mains.
But it still might not be as dangerous because of the current limits due to the small transormer, and hopefully some fusing.
As far as the hypothetical case of highly polarized power mains connectors, it is not clear to me that you could not make things transformerless then, so long as neutral is ground, and these are never mixed up with hot.
But there may be other saftey issues.
Here in the US, most stoves are 230VAC, with the neutral centertap too. So the stove body ground to neutral
But in the last 10 years its been changed to 4 wire plugs with ground and neutral separate.
I think saftey grounding, and avoiding ground loops in signal handling gear is complex.
As far as transormerless class D amps under our present wiring scheme, I think some maybe on the market, and I have reservations about them.
I would assume you need to have a plastic coned woofer. But woofers are notorious for voice coil rub.
So unless someone makes one specially designed and approved, I don't see how.
I think you could make the grill cloth hard to take off and print warnings.
I've only seen this stuff in advertisements. That is why I asked the question.
I can't remember who made them, but there have been a couple consumer subs without an isolated power supply. Some had (S/PDIF) optical inputs, others used transformer coupled inputs.
To pass safety standards they were all well insulated things, with flame retardant cones and voicecoils, along with unremovable grounded speaker grills.
To pass safety standards they were all well insulated things, with flame retardant cones and voicecoils, along with unremovable grounded speaker grills.
Hi All,
I don't think a wise safety agency will allow non isolated equipment. There are many documented cases of polarized outlets miswired. This negates the positive aspects of polarized plugs. That and you are using a terribly noisy return as a system ground!
Then there are those untrained individuals called upon to repair this, ah, well made (?
) equipment. 
And don't forget the home DIYer who gets a great idea.
In short, for consumer use there must be galvanic isolation. Heck, they even have trouble with that some times!
-Chris
I don't think a wise safety agency will allow non isolated equipment. There are many documented cases of polarized outlets miswired. This negates the positive aspects of polarized plugs. That and you are using a terribly noisy return as a system ground!
Then there are those untrained individuals called upon to repair this, ah, well made (?
) equipment. And don't forget the home DIYer who gets a great idea.In short, for consumer use there must be galvanic isolation. Heck, they even have trouble with that some times!
-Chris
This issue... operating DIY stuff from mains is as I know so far, forbidden in this forum.
I am electrical engineer, I know the risk for "joe average". Even a possibility of electric shock by accident for us are called a big mistake. That's why the world's electric system build with extra safety.
Eva, you talk about motor drive as industrial standard with fix installation and safety when your 'amp' utilized.
Not for sound amplifier! I am also as proffessional sound operator as part time. You can imagine hundreds cable cores on stage. Very dangerous if you hold wrong cables, that most of them are black! As I know, no equipment operated directly from mains even for PRO!!!
Operating in sealed box is not guarantee? Voice coil speaker melted is usual on stage. Amps damage also usual, loosing connection speaker is usual. Rain, wet box, also usual. You can imagine what happen to your non isolated systems.
There are protections such as current leakage to prevent electrick shock that limit to 35mA current line to ground. You can safe with that, but it is not funny when the artist on their job, and your system trip again and again.
So, the conclusion NON ISOLATED is NO-NO!!
I am electrical engineer, I know the risk for "joe average". Even a possibility of electric shock by accident for us are called a big mistake. That's why the world's electric system build with extra safety.
Eva, you talk about motor drive as industrial standard with fix installation and safety when your 'amp' utilized.
Not for sound amplifier! I am also as proffessional sound operator as part time. You can imagine hundreds cable cores on stage. Very dangerous if you hold wrong cables, that most of them are black! As I know, no equipment operated directly from mains even for PRO!!!
Operating in sealed box is not guarantee? Voice coil speaker melted is usual on stage. Amps damage also usual, loosing connection speaker is usual. Rain, wet box, also usual. You can imagine what happen to your non isolated systems.
There are protections such as current leakage to prevent electrick shock that limit to 35mA current line to ground. You can safe with that, but it is not funny when the artist on their job, and your system trip again and again.
So, the conclusion NON ISOLATED is NO-NO!!
anatech, I see that you are a moderator here.
http://www.diyaudio.com/forums/showthread.php?postid=991415#post991415
I am having a pack of trouble on another thread that has degenerated to pure biligerance. I'm telling mzzj, classd4sure, poobah, and djQuan that I don't want them to post there.
It was a thread about an unorthodox aproach to a switching amp. But it has degenerated to uselessness.
Could you take a look at it? I think the class d and digital areas are more problematic.
I am still fairly new here, but this diyaudio is an excellent, truly outstanding forum.
http://www.diyaudio.com/forums/showthread.php?postid=991415#post991415
I am having a pack of trouble on another thread that has degenerated to pure biligerance. I'm telling mzzj, classd4sure, poobah, and djQuan that I don't want them to post there.
It was a thread about an unorthodox aproach to a switching amp. But it has degenerated to uselessness.
Could you take a look at it? I think the class d and digital areas are more problematic.
I am still fairly new here, but this diyaudio is an excellent, truly outstanding forum.
Mains operated appliances were common in the vacuum tube era, right up till the end.
I think they are out on the market now, these class-d powered speakers. They are subwoofers, or the subwoofer section of a tower.
I have real reservations about it all myself.
If someone has info about the optical isloation unit I'd like to see it.
As far as changing homes to strict polarization, and making neutral and ground the same, I agree what miswiring would become leathal. I never trust polarized outlets now days.
But as far as it being able to work, I know that saftey grounding and signal grounding are more complex than they seem.
http://www.amazon.com/gp/product/02...=pd_bbs_1/102-8499813-0256115?ie=UTF8&s=books
Deals with these in great depth. Excellent work.
I think they are out on the market now, these class-d powered speakers. They are subwoofers, or the subwoofer section of a tower.
I have real reservations about it all myself.
If someone has info about the optical isloation unit I'd like to see it.
As far as changing homes to strict polarization, and making neutral and ground the same, I agree what miswiring would become leathal. I never trust polarized outlets now days.
But as far as it being able to work, I know that saftey grounding and signal grounding are more complex than they seem.
http://www.amazon.com/gp/product/02...=pd_bbs_1/102-8499813-0256115?ie=UTF8&s=books
Deals with these in great depth. Excellent work.
Reminds me of an employer a couple decades back that recalled a lot of lab equipment. It met code, but DIY wiring by faculty and grad students resulted in a couple of near fatal incedents. The fix was to replace the on-off swith in the instruments with DPST switches because you couldn't count on "neutral" being neutral. I gues just because you have tenure doesn't mean you know how to replace a wall receptacle!
General practice was to plug any transformerless equipment into isolation transformers, before servicing it.
But such are expensive, and not always handy.
In highschool we would sometimes measure to make sure that a TV set had its chassis connected to neutral, and then go ahead and connect the oscilloscope ground and start probing.
Transformerless audio will be the same issue.
Of course things like light dimmers, and motorized clocks all work that way.
There are new intergrated circuits made to go directly on the power mains.
But about these audio amps, I think they might be out there. I'm not sure.
Do they use specially designed drivers that will give good isolation?
I'm not comfortable with the idea myself.
But such are expensive, and not always handy.
In highschool we would sometimes measure to make sure that a TV set had its chassis connected to neutral, and then go ahead and connect the oscilloscope ground and start probing.
Transformerless audio will be the same issue.
Of course things like light dimmers, and motorized clocks all work that way.
There are new intergrated circuits made to go directly on the power mains.
But about these audio amps, I think they might be out there. I'm not sure.
Do they use specially designed drivers that will give good isolation?
I'm not comfortable with the idea myself.
We talk about life danger. You know that this is open forum. Not every people know about electrical by experience nor knowledge.
If you talk about mains circuit, then people follow your instruction, then they get fatal accident of electric shock by your wrong instruction, you may prosecuted, and go to jail.
There is area that law already regulate. Please don't play with that. I believe that you have no knowledge about electrical safety. Electrical safety has its own area, ask IEC, IEEE, NEMA, and every local country standard. So not you who decide this is safe or not!
Hi, Moderator, please review this as usual!
If you talk about mains circuit, then people follow your instruction, then they get fatal accident of electric shock by your wrong instruction, you may prosecuted, and go to jail.
There is area that law already regulate. Please don't play with that. I believe that you have no knowledge about electrical safety. Electrical safety has its own area, ask IEC, IEEE, NEMA, and every local country standard. So not you who decide this is safe or not!
Hi, Moderator, please review this as usual!
I'm not advocating that anyone build or work on anything that is transformerless.
I appreciate your concern.
I'm just questioning whether this stuff is already on the market. Maybe we should be warning people about it if it is.
Personally, I would like to have a medical grade isolation transformer in everything I deal with.
I appreciate your concern.
I'm just questioning whether this stuff is already on the market. Maybe we should be warning people about it if it is.
Personally, I would like to have a medical grade isolation transformer in everything I deal with.
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