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Sneak Peek: The Lefson Analog Devices Resistor Review for Positive Feedback!

04-08-2017 | By Jeff Day |

I'm hard at work this weekend writing up the Lefson resistor review for Positive Feedback.  I hope to get the review all finished up and published in the next week or two.

Here's a little sneak peek until then! Enjoy!

Lefson: French High-End Analog Audio Devices - The Lefson Resistor

By Jeff Day

Lefson resistors!

I have been enjoying quite a lot of audio adventures over the last year or so while doing audio projects where I was experimenting with various wire types, capacitors, inductors, and resistors in audio circuits.

As a result, my knowledge, skills, and confidence related to developing, modifying, and optimizing audio circuits have been progressing to where I feel a bit more adventurous than I used to in getting out my soldering iron, and doing a little audio surgery on a circuit, so I can hear what happens as a result.

Some of you have experienced how much difference just changing out vacuum tubes in audio electronics can make to the overall sonics & musicality of a hi-fi, and my experience has been that you can get an even more dramatic difference when you start changing out components at the ‘DNA’ level of audio circuits.

It never ceases to amaze me how much changing even a single length of wire, a capacitor, a resistor, or an inductor, in an audio circuit can influence the overall ‘voicing’ performance in terms of sonics & musicality, and it is a very powerful tool for optimizing performance just the way you want it to be.

This was a powerful revelation for me as an audio hobbyist and music lover.

No longer do I have to make the very expensive choice of replacing components in an attempt to voice a system the way I want it, which can cost many thousands of dollars, but rather I can just tweak my existing audio equipment’s performance until it matches my definition of musical perfection, for tens to hundreds of dollars, by making a few key substitutions of wire, resistors, capacitors, or inductors, as the case may be.

Lefson: French High-End Analog Audio Devices

While in the midst of all this audio adventure circuitry fun, Dr. David Robinson (Managing Editor of Positive Feedback) asked me if I could write about the three new ranges of carbon/silver audio resistors from Lefson in Wormhout, France, and of course I said, “Heck yeah!”

Doc put me in touch with Lefson owner Xavier Lefebvre so we could talk about some possibilities that would match well with his resistor product lines, and be complementary to one of the audio adventures I had going, the vintage Altec A5 Voice of the Theatre project crossovers.

Before I dive into what we ended up doing with the Lefson resistors, let me give you a little background about Xavier Lefebvre and his company, Lefson.

Xavier Lefebvre was born in 1984, and has been truly passionate about audio since childhood.

Xavier graduated from ISTS in Paris (Institut Supérieur des Techniques du Son) at the age of 22, and after graduation Xavier followed his passion and worked as a sound engineer in a number of different recording studios in Paris, where he was able to meet and work with some of the most experienced French sound engineers.

Xavier’s personal interest in audio led him to expand his studies into the field of audio electronics, as he wanted to understand and find out more about how the electronics work that he used for sound engineering in the studios.

With Xavier’s growing interest in audio electronics, he decided to put his career in the recording studio aside, and he now devotes all of his time to his Lefson audio business.

Lefson officially opened its doors in November 2013 in Boulogne-Sur-Mer in Northern France, and in August 2016 Xavier moved Lefson to Wormhout so he could expand his manufacturing capabilities.

Lefson Ultimate Resistor.

Xavier is very interested developing fundamental circuit components, such as resistors and capacitors, according to the specifications that he believes would best preserve audio signal transmission for high-fidelity sound reproduction, and the Lefson Resistors you see here are the result of Xavier’s research & development.

Xavier also designs & manufactures audio equipment for both personal audio use and for professional recording studio use, including preamplifiers, compressors & limiters, equalizers, microphones, etc., which you can read more about here.

Xavier says his customers have appreciated the performance of his Lefson products, and several of his customers are now using Lefson products during their studio sessions.

Xavier also has a service business, Lefson Repair, where he restores, modifies, and performs maintenance for home audio and studio electronics.

Xavier tells me that Lefson is much more than a business for him, it is a philosophy, a  passion, where all his research and development’s end goal is for the preservation of audio signal transmission for high-fidelity sound reproduction, both in the home and in the studio.

The Lefson Resistor

Xavier offers the PremiumSupra, and Ultra lines of Lefson resistors, and describes his resistors thusly:

“The Lefson Resistor is a very high performance pure silver/carbon audio resistor. It contains a pure graphite resistive element and two pure silver leads. Suitable for speaker crossover or Emitter/Source resistor of transistors in preamplifier/amplifier, the Lefson Resistor is pushing up the limits of sound reproduction.”

The Lefson Premium Resistor.

The Premium resistor from Lefson is made with a carbon resistive element and silver leads, and is available in values from 0R68 (0.68 Ohms) to 200R (200 Ohms), with power ratings of 4-10 watts.

The Lefson Supra Resistor.

The Supra resistor from Lefson is made also made with a carbon resistive element, but with double-wound silver leads, and is also available in values from 0R68 (0.68 Ohms) to 200R (200 Ohms), with power ratings of 4-10 watts.

The Lefson Ultra Resistor.

The Ultra resistor from Lefson is made with dual carbon resistive elements, with double-wound silver leads that are gold-coated, and available in values from 0R33 (0.33 Ohms) to 100R (100 Ohms), with power ratings of 6-15 watts.

The Lefson Resistors in the Vintage Altec A5 Voice of the Theatre Project Crossovers

I had suggested to Xavier that we try his custom, hand-crafted, resistors in my Altec A5 Voice of the Theatre loudspeaker project crossovers.

Vintage Altec A5 Voice Of The Theatre loudspeakers.

First let me briefly describe the vintage Altec A5 Voice of the Theatre loudspeaker project for you, and then I’ll go into how we incorporated the Lefson Premium, Supra, and Ultra resistors into the project’s crossovers for this review.

The Vintage Altec A5 Voice of the Theatre Project

I’m a vintage loudspeaker enthusiast, and for ages I’ve wanted a pair of the legendary Altec A5 Voice of the Theatre loudspeakers. The A5’s were first produced in 1945 for sound reinforcement in movie theaters, then made famous among hi-fi enthusiasts by Jean Hiraga through his L´Audiophile demonstrations in Paris, and who proved that the big unruly A5 movie loudspeakers could be tamed for high-fidelity home audio use.

I really wanted my Altec A5’s to be as original & pristine as possible, and I chose two 825B cabinets, two 515B Alnico low-frequency drivers, two 1005B horns, and two 288C Alnico high-frequency compression drivers as the foundation for my project, which also happens to be a classic Altec-Lansing A5 Voice of the Theatre combination of components.

Gary Fischer Altec A5 Voice Of The Theatre restoration.

Back in October 2015 I commissioned vintage Altec specialist Gary Fischer (Gary Fischer Speakers) to restore a pair of vintage Altec A5 Voice of the Theatre loudspeakers for me, and Gary did a beautiful job of providing me a restored pair of A5’s with all-original components.

Gary got the big A5’s all done, crated, and shipped, and after braving winter storms that made roads almost impassable, somehow Old Dominion Freight Line was able to push through the winter storms to deliver the A5’s on Christmas Eve 2015 - Merry Christmas, Jeff!

Altec 825B cabinet with the back off to reveal 515B Alnico driver.

Above you can see the Altec 825B cabinet with the back off to reveal the vintage Altec 15-inch 515B Alnico low-frequency driver inside.

Altec 1005B horns with 288C compression drivers.

Above you can see the Altec ten-cell 1005B horns with the Altec 288C Alnico compression drivers.

Close-up of Altec 288C compression drivers.

In the photo above you can see a close-up of the Altec 288C Alnico compression drivers.

Modified Hiraga-style crossover.

With a little help from my friends Yazaki-san (SPEC Corporation) and Pete Riggle (Pete Riggle Audio Engineering) we came up with a modified version of the Jean Hiraga designed Altec A5 crossover that we thought would make the A5’s adjustable enough to be optimizable for a couple of the smaller living spaces in my home, where they would ultimately live out their retirement from movie theater life.

Pete’s A5 crossover bases.

First I bread-boarded the crossovers, which I’ve been working on optimizing for home use for over a year, and when I was satisfied with the result, then Pete Riggle (Thanks, Pete!) made up some more compact chassis for the crossovers so that I could sit them on the 825B cabinets to get easy access to them for component trials (above).

The Lefson Resistors in the Vintage Altec A5 Voice of the Theatre Project Crossovers

I sent the crossover schematic to Xavier to look over, and Xavier sent me two each of his 100R (4/6W) Supra Resistor to try in the R4 positions, the 10R (6/10W) Premium Resistor to try in R3-1, R3-2, or R5 positions, and the 10R (10/15W) Ultra Resistor to also try in R3-1, R3-2, or R5 positions.

Xavier said:

“So you could make many tests between Premium and Ultra Lefson Resistor, replacing R3-1, R3-2, or R5. The power rating is expressed with two values (example 6/10W). The first one is the maximum allowed power without any heatsink. The second one concerns the maximum allowed power when the Lefson Resistor is fixed on a heatsink or to a reliable case. All these power values were measured with direct current. When AC operating (audio), the maximum allowed power is significantly higher. During our post-manufacturing tests period, the Lefson Resistor is stressed with current peaks, up to 25/30W.”

When the Lefson resistors arrived, I was impressed with the level of their fit & finish, which are impeccable, giving me a good first impression of their level of quality.

My photos really don’t do the Lefson resistors justice, they are just stunning to look at!

Lefson Resistors with LP for scale!

The Lefson resistors are also huge, as you can see in the photo above, where they are sitting on top of my Acoustic Revive RL-30 LP Demagnetizer, with an LP for scale.

They also remind me somewhat of the Duelund CAST capacitors in the way they’re potted, which also impressed me.

The Review System

I live in a rather small & modest nuevo bungalow home, with my living room area serving as my primary music listening room (it is 27’6’’ long by 20’4’’ wide, and with variable ceiling height from 9 to 20 feet).

A5’s in my main music system.

After I was satisfied with the A5’s crossovers’ performance in my living room (above), I then moved them into my smaller TV room.

A5’s in my TV room.

The Altec A5’s are impressive loudspeakers that are surprisingly flexible and room friendly, and somewhat to my surprise they adapted remarkably well to their new home, which happens to be a spare bedroom in my home that I use as a TV room, with the rather small dimensions of 11-feet x 12-feet x 9-feet (ceiling), with a 6′ x 3’5″ x 9′ foyer on one end.

My TV room has an aging Philips television hung up on the wall so I can watch movies or TV shows, which is kept company by the new OPPO UDP-203 Blu-ray player for spinning DVD or Blu-Ray movies, or CD’s for music. I also stream Netflix and Sling via my MacBook Pro when the mood strikes me.

Sablon Audio Quantum Gran Corona.

I use one of Mark Coles’ Sablon Audio Quantum Gran Corona power cords on the OPPO UDP-203, and it was completely transformed with a level of musicality & sonics that I never would have thought it was capable of!

For amplification I’m using my Leben RS100U line stage, with an Acoustic Revive RAS-14-TripleC NCF Power Conditioner and Sablon Audio Gran Corona power cord, along with my vintage McIntosh MC225 stereo amplifier, for a very happy amplification match with the Altec A5’s.

Acoustic Revive RAS-14-TripleC NCF Power Conditioner.

Interconnects from the Philips TV to the Leben RS100U preamplifier, and to my vintage McIntosh MC225 stereo amplifier, are Belden 8402 microphone cable interconnects with the shield connected to ground at both ends, Yazaki-san style.

Belden 8402 microphone cable interconnects.

Interconnects from the OPPO UDP-203 Blu-ray player to the Leben RS100U are Duelund DCA16GA tinned-copper conductors terminated with Duelund gold RCA’s.

Duelund DCA16GA tinned-copper conductors terminated with Duelund gold RCA’s.

Listening Impressions

Ok, that's it for now! As soon as the full article is published and up at Positive Feedback I'll let you know!


I want to thank all of you who have donated to help me recover Jeff's Place from the recent hacking event. Thank you so much!

I appreciate all your encouragement, advice, and donations, it really helps!

I've placed a PayPal donation button above the comments section, and if you feel like you would like to donate to keep Jeff's Place secure and up & running, I'd really appreciate it!

I am fortunate that I was able to get Jeff's Place back up quickly, and it looks like most or all the content has been recovered, thankfully. If you see anything that looks amiss let me know!

I'm working through adding in security software and plugins, backup strategies, and other security techniques that have been recommended to me in order minimize the risk of a similar hack happening again.


As always, thanks for stopping by, and may the tone be with you!

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