Furman SMP is NOT real series mode surge technology!

If you have read erik_squires misinformation, please understand that he does not even know what a MOV looks like.


Erik is merely trying to hawk his affiliate links for profit. If you are interested in the Furman PST-8 that he promotes, this is the only link to use AFTER clearing your internet browser of cookies:


Here is a summary of the relevant information:

Furman does not license series mode surge technology. They were sued by Zero Surge - the originators and license owner of the series mode technology patent - and lost. Furman was forced to call their technology SMP (Series Multi-Stage Protection), which still uses MOVs.


SurgeX, Brick Wall, and Torus Power are the only licensees of series mode technology that I'm aware of. McIntosh - with the MPC1500 - appears to use series mode surge technology as a repackaged Torus. "Torus Power Technology under license from Plitron Manufacturing Inc."


"Zero Surge® was incorporated in March 1989 by J. Rudy Harford." He is the founder, and was the former owner and president. And yes, he’s the license owner.


Look at the SMP circuit linked below. There are clearly MOVs. The same circuit board is used in all Furman products with SMP.


Still don’t believe me? "Furman’s Series Multi-Stage Protection Plus (SMP+) addresses some of the shortcomings of traditional MOV-based protectors by employing a variety of circuits to clamp, absorb, and dissipate transient voltages without having the device sacrifice itself. The company claims that MOVs used in a properly designed circuit will not fail.

Furman’s SMP+ circuitry takes pages from both shunt-and series- mode playbooks and adds its own twist. Along with a high-voltage MOV and a high-amperage thermo-fuse varistor, SMP+ uses a tuned circuit that includes series inductors, a bridge rectifier (which con- verts AC to DC power), and high-voltage capacitors."


"SMP allows Furman products to offer this protection without damaging any of their own internal components—that is, they are virtually non-sacrificial" Virtually, meaning not quite.


"• Zero Surge’s patented filter technology protects sensitive electronics from even worst case surges, repeatedly, without degradation or failure. MOV-free."


" • No sacrificial or wear components (no MOV’s)"


The series mode surge technology patent states, "Provides an inductor system as the first means of protection."

"A branch circuit SPD (Surge Protection Device) using an MOV in front of, in back of or sideways of, a small ferrite core series inductor, labeled as ’series something’, is in my opinion, a marketing persuasion by our competitors intended to ride on our back and confuse you, and the only way to promote a product ’looking like ours’ without violating our patents. Are you a Switch or a Filter?

An MOV is a semiconductor switch. Switches will wear out and can suddenly fail when stressed. The monitoring of these switching devices over time as ’functional’ is tedious and a guessing game at best. A filter properly designed for its application will not wear out and will only fail if misapplied. Think about your passive LC subwoofer crossovers...when will it wear out?...perhaps when you wire it up to 440V just for fun?...or when you listen to too much music?" Michael McCook, SurgeX International

Furman purposely added MOVs to create a hybrid surge protection device that does not violate the patent. Due to the patent, Furman can not call the design series mode technology, and renamed it SMP+ in 2005. The whole point of series mode technology and the reason it was created is to avoid the use of MOVs. It’s fully ironic to use MOVs and call it series mode. It would be akin to saying you’re dying of thirst, and then eating the saltiest food you can, or calling a fat guy slim.

SurgeX does not have the same basic technology as other series mode designs. They have added ASM (Advanced Series Mode) technology. This adds an extra winding to the air-core inductor to further improve the surge protection and lower the let-through voltage.

Yep, you are right. I missed that Furman uses an MOV and thermal fuse AFTER they use the series mode supression. In all other ways the circuitry and behavior are the same. There is literally no way that little MOV and thermal fuse would survive the testing alone.

It’s a belt and suspenders approach.

Despite this, adding an MOV and thermal fuse to a series mode supression circuit would still violate a patent for the series mode suppression.  The idea that you can add two parts to an existing patent and call it something else is just not true.

As I’ve asked you to show before, please show where Furman was sued and lost.

Further, weren’t you all mad about inductance?
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I red it on a Pro AV news site, but for the life of me I can't currently find the article. At the very least, Furman used to call their technology series mode, then switched to naming it SMP+, and ultimately SMP.
I can't and don't want to try to speak for Erik here, but thank you for that run down on some relevant info. This part of the hobby has long been operating in the dark, ever since its inception by the likes of Tice and Richard Grey, and makers are known to...uh.."borrow" tech from each other more often than they come up with it on their own. Thank you for at least shining a spotlight on the licensing aspect enough for us to see what that looks like.
Hey Sadano,

It would be really useful, because I think you may in fact be talking about a trademark issue, which is different from a patent dispute.

Do you think it is possible that Furman lifted the SurgeX label, but also licensed the patent?

I know this can be complicated, but from what you’ve described, this is what I expect.

Like, I could license from Brickwall, and call it ErikBlock! If another company licenses the same tech from Brickwall, they can't use the name ErikBlock! because the trademark is mine, not Brickwall's.

Furman and SurgeX/Zero Surge are competitors. Furman did not license the series mode technology, so when they used the name, Furman was forced to rename their technology. No license equals more profit and a bigger piece of the pie.


You're welcome!

Wow! You edited the heck out of that first post!

You are incorrect, again! There are MOVs BEFORE the inductor. Look at the input off the power from the IEC inlet to the power switch, to the SMP circuit board.


And while it is shady behavior, parts can be added to a design if it is in a way the original designer didn’t think of, and it makes a "better" product, and not infringe on a patent. The main addition being EVS. SurgeX has this beat with their COUVS technology.
Thank you Erik for your honesty. 

No need for aspersions here- we all want to learn and get better educated. I confess I am starting from ground zero :-)

That said, I wonder if AQ Niagara (Furman designer went to AQ) or Audience Adepts use any MOV or have patented from zero surge in current products?

Also Sadono- you raised issue of Inductance- any relevance to newer products and designs?


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How has Erik been honest? He has dragged his feet every inch of the way, while learning the truth. You can bet he will continue to - now knowingly - spread misinformation, in his attempt to make a profit off his affiliate links. This is immoral and unethical behavior. He is slowly digging his hole towards h*ll.

Audioquest uses MOVs. Audience does not.

Audioquest, Audience, Furman products with SMP, some IsoTek products, and Richard Gray’s all use inductors in some shape or form. Real series mode products are of course based around inductors. There are probably other companies that escape me at the moment.
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Placing inductors and capacitors in front of surge elements to reduce the surge voltages that hit the surge element predates ZeroSurge's existence, let alone their 2004 patent"

You are so confused, disoriented, and misinformed it is absurd check in to when this patent was issued it was 1988!! You will want to assemble accurate , verifiable facts before trying to convince us that your an expert on anything hear!
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sadano…" You can bet he will continue to - now knowingly - spread misinformation, in his attempt to make a profit off his affiliate links."...

For those of us not that tech savvy, how does affiliate links work and how does one make a profit from them?
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How many electronic products that you have designed have been sold clearthink? How many surge suppressors that you have designed have been sold clearthink?"

How many electronic products that you have designed have been sold, "robertcan"?  How many surge suppressors that you have designed have been sold "robertcan"?
Do you think you could add to the conversation instead of harassing me and complaining to the moderators even though you just joined yesterday????
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For those of us not that tech savvy, how does affiliate links work and how does one make a profit from them?

Here is everything you might want to know:


The semi-summary is an affiliate link - either through a link, shortcut link, or picture/ad containing a link - is placed on a website linking to another website. These linked sites pay their affiliates based on either pay-per-views or a certain percentage of the purchases made by the customer.

Many of the links are to merchants, and specific products. If you see a merchant link that is shortened, it is probably hiding the affiliate referral link.

Many of these merchants use a technique called "cookie stuffing", that places a cookie on your computer/device, to tell the merchant to refer all sales made by the customer to the affiliate. This tells the merchant how much to pay the affiliate in commissions. These cookies usually last 30 days, or until the customer has clicked on someone else’s affiliate link.

The important takeaway, ALWAYS clear your internet browser of cookies before going to a website to make a purchase. ALWAYS go to the merchant and directly search for the product you want to buy, as to avoid affiliate links, unless you learn what a safe affiliate-free link looks like.

Here is an example of one for Amazon:


merchant=Amazon/product name/product ID

Anything beyond that including "&", "ref", etc. can be removed and saved for future reference to the product.
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I politely in another thread tried to inform you that what you were stating is not really true, or at least not all true. You did not take that information to heart ... and called my search "half-hearted, incomplete, and mistaken".    In fact, you are mistaken.
- SurgeX sued for trademark infringement and false advertising, not patent infringement- A core piece of what Furman uses is almost exactly like the original SurgeX Series Mode technology

I am in no way trying to discredit the ZeroSurge products, just pointing out what you are saying about Furman is not really true.


There are current patents that protect new variations of a series surge protection circuit (as you noted above). The original patents, from the 80s, have long expired. You cannot create new patents to protect old material. Half the circuitry in the Furman is essentially what is in the 80s patent. Anyone can use that technology at this point which was the SurgeX Series Mode protection (you can't use the trademark nomenclature though).

SurgeX's series mode protection (original) is non sacrificial, but it is not perfect. It relies on an inductor as a filter element to block the high speed surge waveform before dumping what is left into a capacitor. As you know, in audiophile circles, adding inductance in front of a power-amp is often frowned upon. It of course also has a limit to how big a surge it can take before the inductor saturates, the diodes blow, or the capacitor is degraded.   Adding MOVs in front of this type of surge protector, especially big ones, can significantly increase how big a surge the combined device can handle. Using both, as Furman does, is a feature, not a design fault especially at a given cost point, and the Furman units are competitively priced.

SurgeX Suit Triggers Furman Response

By AVNetwork Staff (Systems Contractor News) January 28, 2005 Business 

  • Furman Sound has responded to a complaint filed by New Frontier Electronics d/b/a SurgeX, rejecting its claims in U.S. Federal Court and filing a counter claim against New Frontier. New Frontier's complaint is in part for promoting MOV-based power conditioning products as Series Mode products.
  • SurgeX, citing the false advertising and promotion prong of Section 43(a) of the Lanham Act, is claiming that the Furman Series II line of products use MOVs (Metal Oxide Varistors) as the main surge suppression technology and that the promotion and marketing of these products as Series Mode is false, deceptive and/or misleading.
  • Furman purports that the words in question, "series mode," refer to a common electrical configuration and are not owned by any individual or organization. Furman's Series II line of products does employ this technology, said the company, however the technology in Series II units goes above and beyond typical series mode protection with a total package called SMP Plus.
  • All SurgeX power conditioning products incorporate advanced technology, referred to as Series Mode, to mitigate surge and transient energy without the use of any diversionary or sacrificial components such as MOVs.
  • Furman Sound...www.furmansound.com
  • SurgeX...www.surgex.com


I think an apology is in order.  Everything that atDavid said is true.  Furman and ZeroSurge indeed use the same technology.  ZeroSurge's patents expired long ago.  Furman uses the same series mode technology and then subsequently uses MOV's for any remaining excess voltage.

Wirecutter did a test, comparing the Furman PST-8 vs high-priced series mode products and the Furman product actually performed BETTER than the high-priced series mode products.

And, atDavid's explanation of the lawsuit is correct.  It wasn't for patent infringement.  It was for FALSE ADVERTISING, filed by ZeroSurge.  ZeroSurge claimed that since Furman added the MOV, they can't call it series mode protection.  Isn't that petty?  Furman adds additional protection to the technology and ZeroSurge says you can't say it's series mode protection.  What a BS lawsuit.  If you go to ZeroSurge's website, it's full of misleading and deceptive information and articles.