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In Reply to: Re: No doubling measured posted by Jon Risch on July 18, 2000 at 19:09:10:
I have no interest in using C-M chokes in surge protectors. I agree with you on standard rod wound inductors for that use. I don't like to hear that C-M chokes cause double the output voltage when hit with a diff. spike, because they don't. I agree that current flowing in one winding will induce a voltage in the other winding, thats the whole idea of the C-M choke, but it will not cause a double of voltage.Think of it this way, the top coil receives the spike, the spike is above ground in voltage, (or below if you want to think of a negative going spike), and it wants to flow to ground. So it is an un-balanced voltage and it is ground referenced. Well the voltage that was induced in the other coil is BALANCED voltage it only wants to flow back to the other side of its own coil, not to ground. Trying to flow to the other side of its own coil it will have to go thru the top coil and will be choked out because it is a common-mode signal, (remember it IS balanced) and that is what a C-M choke does.
The other point on why it will not double is the caps on the output shunting the spike to ground and providing a ground ref. point at the output of the winding.
This was not an attack of you or your surge supressor, it was just to defend common-mode chokes. They are VERY important in low RFI power supply design and I don't want people to be afraid to use them because they think they are going to double the voltage.
ED
Ed,Please remember that I measured this effect, it is not something I dreamed up. It is possible that with ordinary RFI or noises, that this is not a factor. I measured this on spikes and surges in the context of a surge protector circuit. A lot of what might occur is going to be due to use of inexpensive CM chokes, not those that can actually handle decent amounts of differential current (the spec to look for), and may be a moot point if MOV's or other limiting devices are not a part of the circuit.
As I related, I had enough surge capability to pop 40 W light bulbs, and had to use heroic steps to isolate my experiments from neighboring AC lines, or I would reset or shutdown other peoples computers.
In order to complete and finish the design work they had to install a dedicated line for me.At the time, my primary concern was to design and build the best surge/spike protector available, at a reasonable cost. AC line filtering was a secondary goal, but one which I wanted to acheive without compromise for audio components. The results are embodied in the circuit I make available as the DIY AC Power Line FIlter and Surge Protector.
All I can suggest, is build one, try it, and see if it doesn't help out the sound of your system, as so many others have reported.
Jon Risch
Jon,I applaud you for all the help you give the readers of this board,and your surge protector is a nice contribution. I feel that everyone should use surge protection on their equipment, along with EMI/RFI filtering.
I know exactly what you are talking about with blowing up light bulbs during testing. Twenty years ago I built a surge generator that charged a 50uf cap to 4kv then discharged it into the device under test. 100w bulbs and MOV's went all over the room during the first tests.
I hope that readers will use common-mode chokes after your surge protector, because they do make a big improvement in sound. On the input of the power transformer and after the doide bridge are the best places to put them. I have used them in pre-amps, power amps, CD players, and FM tuners and there is not one case where they did not make a large improvement in sound quality. After hearing this kind of improvment I wanted everyone to use them.
This whole string started when a reader posted that he heard an improvement when using a very low inductance one in your supressor design. I can believe that. We are all looking to improve things thats why we are in the "tweeks" section of this board.
I felt that your responce to him would stop him or others from trying C-M chokes in their audio systems, so I had to reply. I want people to find out about the big improvement C-M chokes can make in their systems and not be afraid to use them.
Bottom line, use your protector AND common mode chokes and have the best of both worlds, surge suppression and EMI/RFI filtering.
Ed
G'day Ed, could you post some circuit examples of how you've used C-M chokes in your mods? (Aussies don't read too well, so we just love pictures).
Pete,
I do not have the ability to post drawings for you. I suggest you get a back issue of the U.S. magazine "The Audio Amateur" issue 4/95. On page 36 there is a drawing of a raw supply using common mode chokes. The drawing is part of an article titled " Regulators for high- performance audio". It also explains why split bobbin transformers sound better than toroidal transformers.Common mode chokes are very easy to use, try to find some and play around with them, I think you will like what you hear!
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