Swiss Digital Fuse Box - "What headroom sounds like"

Swiss Digital Fuse Box (SDFB) is non-sacrificial overcurrent protection device that serves as a replacement for fuses in audio equipment.

There are four devices in my sound system that I’ve replaced fuses with the SDFB, and its transformative capacity to upgrade sound quality beyond that of fuses has compelled me to write a review. I’m not associated with Verafi Audio, the company that sells them, nor did I receive anything from them as "review units". There’s another thread on Audiogon about them that an audiophile friend referred me to, which got me interested enough to buy them. I am now enamored with the sound of my system in its current state, so I wanted to share my take on one of the more significant steps in how I arrived here.

Before getting into details about its form and function, I want to share my impression of what the Swiss Digital Fuse Box (SDFB) does for sound quality. It makes my components sound like they are operating without any limitation of power. It sounds open and unrestricted across the audio frequency spectrum. The sound is dynamic, detailed, defined, and there a sense of harmony and completeness about it. It’s like my components can now output their full frequency and harmonic potential.

A few things about me... I’m more of an artist than anything. I’ve been a music lover for 35 years and an electric bass player for 15 of those years playing in two bands, with which I was the bass player on one full LP recording and one EP. I’ve recorded, mixed and mastered my own multi-layered solo bass recordings and their backing tracks from sampled percussion using digital audio workstation software. I’ve also fine-tuned two of my custom car audio systems using DSP software and built, tweaked, and tuned a high end home stereo system (yes I said *tuned*, without using DSP) . Given this experience and the resultant development of a keenly perceptive and informed "ear", yet having no formal electrical theory or engineering background, I feel comfortable suggesting that the results of using SDFB can be likened to how audio sounds when the device producing it is operating with ample headroom. What does headroom sound like? The term headroom has different meanings in its use within pro audio recording/engineering and electrical circuitry operation, but they are related in a way that the end result sounds uncompressed, undistorted, fully dynamic, and expresses the sense of the effortlessness of unrestricted flow.

Does this sound like embellishment? It probably does. And I haven’t even mentioned the typical audiophile terms like "inner detail", "layering", or "rock solid imaging", nor have I even mentioned soundstaging attributes yet -- even though all of these qualities have also gone through upgrades due to the SDFB’s being installed. Am I merely in an irrational, excited state because my whole system now sounds much more expensive than it is? I don’t think so. I’ve been using all four SDFB units for three weeks consistently, and the initial excitement phase I was experiencing settled at least a week ago. I also think that the more components a system has which have replaceable fuses, the greater the potential upgrade from replacing each of those fuses with SDFBs. Like I said, I replaced all fuses in four of my audio components (six fuses in total), and there were notable step-up improvements in sonics as I progressively installed each of them.

Now I’ll describe the physicality of the device and how to use it. Then, I’ll try to describe specifics about why my previous fuse setup, which was a combination of Synergistic Research Purple and Master fuses, was completely replaced by SDFBs. These SR fuses were already a major upgrade in sound relative to the stock, generic fuses, and the SDFBs transcended the SR fuses in every discernible way.

These things have two separate parts that work together: 1) a small box that is inserted as the middle of a chain created between an audio component and the electrical outlet from which it draws power, and 2) a solid, cylindrical metal slug (referred to as a "Sluggo") which is the same size as the typical fuse. To install a SDFB, first, with your component off, plug its power cable into the AC socket on one end of the box, and on the other end of the box there is a male IEC connector (C14) which you connect to an outlet using another power cable or an adapter. I’m using a combination of two short, homemade mini-cables, and two generic adapters with my four SDFBs for the best sound (details shared in my Audiogon virtual system). Once the box is connected to a live electrical line, it will go through a brief setup period, and after maybe 8-10 seconds, you’ll hear a clicking sound and the small green LED will stay lit, indicating that charge is now allowed to flow through the box. The second and final step, with the component still off, is to replace the fuse(s) with a Sluggo. The device comes with both copper and brass Sluggos. You can then turn the component on. Don’t replace a fuse with a Sluggo without the SDFB in place because you’ll have no overcurrent protection and you’ll incur the risk of severely damaging your component and/or having a catastrophic fire in the even of a short circuit or other overcurrent scenario.

These units monitor current magnetically, and are calibrated to whatever fuse rating is needed when you order them. They are also calibrated to operate as either slow blow, or fast blow, like a normal fuse. When the set parameters are exceeded (too much current), a relay is switched to the closed position and charge is halted from flowing. Being non-sacrificial, you don’t need to buy a new one, you just unplug it from the outlet for about 30 seconds and it will reset the state. Then it can be plugged back in and reused. There’s no damage done to the device due to the overcurrent condition, unlike a fuse which melts due to high heat. Currently, devices being produced are to be calibrated at 10 amps max, so if there is some crazy high current event, perhaps then it could be damaged. I don’t know. I believe that’s pretty unlikely though. I think I remember reading that there’s a 15 amp version in the works.

There is some inconvenience involved with transitioning to SDFB due to the extra weight of the box (not that heavy, really) and extra length added to the power chain, as well as potentially requiring additional investment in more power cables. I feel that I achieved an optimal result for only about $200 of additional investment by using some DYI cable materials I had available, some high quality plugs to terminate the cable with, and some cheapo adapters from Amazon. For me, dealing with the extra weight and length to the cabling and putting in the work to create the best solution for connecting the SDFBs to my power conditioners has not been a big deal compared to the profound jump in sound quality. Totally worth it.

Before I went all SDFBs, the best configuration I found with SR fuses in my system was one small Master fuse in the LPS that powers the modem and router (I have an all-digital streaming system), two small Master fuses in the DAC, one small Purple fuse in the preamplifier, and two large Purple fuses in the amplifier. It’s worth mentioning that total retail cost of this setup is about 33% more expensive than the retail cost of my final SDFB setup. However, if you choose to buy a bunch of new, expensive power cables to connect your SDFBs, that would quickly become more the more expensive option.

I thought the SR setup sounded great at the time. I was impressed with the top end detail that a few of the Master fuses added to the fuller midrange and mid-bass sound of the Purple fuses which I already had. I’ve seen comments from others on this site in agreement about this. This combination is getting some praise. However, when comparing that sound to the SDFB sound, it was like the SR fuses are stuck at a level of trying to boost certain frequency ranges to make up for how restrictive a fuse really essentially sounds.

How do you improve on a small, low resolution, blurry, drab looking photo? Well, you manipulate it in Photoshop, of course! You try to crank up values of various visual (light-based) metrics to make it more attractive. However, that process will never produce something as close to the original subject as when you start with an ultra-high resolution, high-dynamic range photograph. You can’t "add resolution" to something that is intrinsically underpinned to a state of reduced resolution. To me, this is analogous to the task of starting with the tiny, resistive piece of wire in a fuse and trying to add crystals and various substances of specific resonant frequencies inside and around it to end up with something representative of the innate completeness of the source material.

Comparatively speaking, I was surprised to switch back to the SR setup and find that the soundstage was compressed towards the center. It was like there was a somewhat spherical haziness in center stage from which the sound was straining to emanate from, even with the Master fuses in play. I attribute this sense of "haziness" to a combination of reduced dynamic range, and a distortion of the frequency response coming from the system’s components. If the hypothetical ideal response for a natural sound (assuming the important aspects of room acoustics and one’s hearing quality are held constant) is essentially a linear response from top to bottom in both amplitude and purity, then the sound of the SR setup was now perceived as distorted and a deviation from linearity.

The sound of the SDFB setup is far more natural, far more detailed, and imparts a sense of ease while listening. I’m using all copper Sluggos, as their tonality is more natural to me than the brass versions. The soundstage has opened up with more dimensionality and all of that perceived haziness and limitation of full expression is (seemingly) completely gone. Images became more defined and image positioning is on a more advanced level. I can now perceive the two singers positioned near center and side-by-side in the mix, with a gap of about about a head’s-width between their mouths. This wasn’t perceivable with the SR fuses. The positioning of cymbals on a well recorded drumset are precisely locateable in space. Listening to Russion choral music, I can now hear individual tenor and bass voices and their unique tonal qualities. On one excellent recording of a solo harp, there’s beautiful overtones resonating that I’ve never been able to hear before. The sound is descriptively harmonious.

Over the course of a couple weeks, the sound of these units opened up. To begin, there was some minor coloration of the sound, but I’m not sure I can hear it any more. I think most of it has gone away as the units have burned in. Even with the minor coloration in the beginning, the immediate leap above the SR fuses in sound quality was obvious and highly desirable.

One last thing, I did a rough test of the overcurrent protection functionality, as this is obviously a major thing to get right and have working properly. I’ve been told that most refrigerators pull about 1 amp of current, so I used that as a basis for testing since I don’t have any more sophisticated method (I could use my desktop computer PSU which has a wattage display to achieve more accurate testing, but I’d rather not have its power suddenly cut and risk problems). I have two SDFBs calibrated to trip at levels below 1 amp, and two units calibrated at significantly above 1 amp. With each of the two sub-1A units inline with the fridge’s power cable (doing two test rounds for each unit), they immediately tripped and the fridge’s power was disconnected when I plugged in the power chain into the outlet. For the above-1A units (also did two test rounds each), the units did not cut power, and the fridge turned on and operated normally. I feel like this testing demonstrates enough for me to have a boost in confidence in the overcurrent protection operational integrity.

Being able to safely use solid metal slugs in place of fuses is wholly a paradigm shift in a high end audio system’s sound quality potential. These things deserve attention and I’m grateful to have been pointed to them.


I thought I would weigh in.  I originally ordered the SDFB for a Puritan PM136 power conditioner.  Unbeknownst to Mark and I the new ones do not appear to have a fuse.  He had done some SDFB for the Puritan in the past, but those must have been older models.   So we couldn't use it there.   I decided to try in on my McIntosh MA 8950 integrated amp.  I had my reservations about trying it there because I had an expensive power cord (Hijiri Takumi) and didn't want to put anything in the chain to mess with that.  I had to wait a few days for a newly programed SDFB and Sluggo for the MAC.  Came in and set up was easy.  I started playing some tracks and I was thrilled with what I was hearing.  I really liked the sound of my system before the SDFB, but with it in, the sound from my Polk R700s expanded, got bigger, or better sense of space and everything sounded so much more relaxed, but not in a boring way.  I texted Mark, that I didn't know the Polks could sound like that.   

Copying emails I sent to Mark regarding my experiences with the SDFB:



I’ve had the speaker amps powered on for 10 days straight now. The best description I can give would be the SDFB’s modify the sound akin to a sampling rate upgrade from 44.1 to say 96kHz. Everything is cleaner and more detailed. Soundstage is wider, deeper and taller. Cymbals sound more like cymbals. Imaging is sharper and sounds project forward into the soundstage like never before. If the soundstage is not flat in the recording, it comes through now. Decay is more apparent due to the lower noise floor. The sound is now finally coherent. When I first listened with the SDFB’s plugged in it did not have the coherency top to bottom as after 10 days of burn-in. I’m pretty sure the Paradigm Active 40v2 speakers are maxed out performance-wise with these. With my Job 225 amp & Ascend Sierra Towers w/ RAAL tweeters I can probably discern more of an in improvement in bass frequencies, but I suspect the 40v2’s have reached their potential. If anything, they now sound closer to what I would expect from good quality mid/near-field studio monitors (e.g. ATC, PMC, K&H) in regards to detail retrieval. The 40v2’s are never going to compete with the transient response of RAAL tweeters or my Rythmik F12 subwoofer which has servo technology to reduce distortion.



I recently decided to have a listen to one of my favorite acoustic playlists and in all honesty, the Active 40v2’s sound better than I can ever recall the Ascend Sierra Tower w/ RAAL + Job 225 combo. I’m definitely looking forward to pairing the Job 225 with a SDFB to compare. Based on the results that I’ve heard so far with the Paradigm’s, my money is on the SDFB taking things to the next level. As you are well aware, the SDFB’s are the real deal. I’m sold, literally.


All in all I’d say the SDFB’s are the single best purchase that I’ve ever made. Previous experience with changing interconnects and power cords led me to believe that replacing the fuses in my gear would result in a noticeable upgrade in sound, but I didn’t want to take the chance that a fuse would randomly blow and my investment would be all for naught. The fact the SDFB’s aren’t at risk of going bad led me to take the plunge and I am thrilled with the result. The power cords I’m using with the Paradigm Active 40v2’s are Iron Lung Jellyfish, which can be had on Amazon for $17/ea.

If you’re on the fence about ordering these, you really have nothing to lose since there is a 30 day no questions asked money back guarantee. However, as I told a friend of mine, if you order the SDFB you’re not going to want to send it back.


Many thanks for your feedback and support of the Swiss Digital Fuse Box. 

Your e-mails really make me very happy and inspire my next steps with this Tech.

Super review just published today from Bruce Kinch at Positive Feedback. An incredible read on many levels


Feeling very proud and happy. 

I've not been spending much time here on AGon - but really do wish to thank all of you that stepped up to try our products. The new web site is up and running - but still a few things to sort. 

Thanks again - Mark 



Always want to share my sincere thanks and appreciation


Thanks for your patience and going on this ride with me 

Best to all - Mark 

Nice to see the review in Positive Feedback. However, I’d have some choice words for Bruce.

Let’s just cut to the point of what a review regarding the SDFB should make very clear. By removing the thin gauge fuse from the power signal path, it’s basically removed the resistance caused by a traditional fuse. Plain and simple. If a system sounds worse with the SDFB installed (e.g. brighter), it’s because THAT’S HOW THE COMPONENT ACTUALLY SOUNDS. It’s not the fault of the SDFB. The SDFB merely allowed the component to sound as it would if there were no restrictions in the power path.

There should be no apologies for that. The veil was lifted from the component. You can only polish a turd so much, as they say. If you find out a component sounds like a turd after installing the SDFB, it sounds like a turd because it’s a turd. Don't blame the SDFB for disrupting the synergy between components. Sheesh.