Oct 082018

I really want to thank Frederik Carøe for being so generous as to indulge a resistor idea of mine, and then going way beyond what I imagined to handcraft a truly amazing resistor, which Frederik has humorously dubbed the “Jeffistor”.

The Duelund CAST graphite / Sn-Cu “Jeffistor”.

The idea behind this resistor was a result of my listening impressions while doing trials with various resistors, where I observed some desirable aural traits.

My first aural observation was that I found the musicality and sound of carbon composition resistors more enjoyable than the other types I’ve listened to, like metal film resistors and wirewound resistors, for example.

While those other types of resistors can be nice in the right applications, overall they don’t display the natural “organic” sounding musicality of carbon composition resistors in the applications I have compared them in (preamplifier & amplifier electronics, and crossovers).

My second aural observation was that resistors with smaller gauge number leads (larger wires) tended to have more natural overall tone than those with larger gauge number leads (smaller wires).

This was similar to the result I noted when I wrote the article for Positive Feedback about the Duelund DCA series of tinned-copper wires (HERE), where I observed that: “The smaller-gauge number tinned-copper cables (like the DCA12GA) go from sounding warmer and richer, to sounding brighter and clearer with the larger-gauge number tinned-copper cables (like the DCA26GA).”

Prototype Duelund CAST resistors with tinned-copper leads.

My third aural observation was that the composition of the lead wire makes a difference to overall voicing of the resistor. When I tried identical Duelund CAST carbon composition resisters in my Westminsters’ crossovers, one with pure silver leads, and one a prototype with tinned-copper leads (above), they sounded and performed a little bit differently.

The silver leads had more “sheen” in the upper frequencies, and the tinned-copper leads sounded subtly more relaxed tonally, which I liked. The Duelund CAST carbon composition resistors with the Sn-Cu leads also displayed greater ease dealing with dynamic peaks, which I also liked.

My fourth aural observation was that when I compared two resistors in parallel versus a single resistor of the same value, the tone improved and the sound was more natural when there were 2 resistive elements in parallel.

So when you put all those observations together, my preferences were for carbon composition resistors with dual parallel elements, and with tinned-copper leads with larger a gauge number.

When Frederik and I were talking about the Duelund-Altec Project in early 2018, I shared the above perceptions with him, and asked him if he would be interested in making some resistors with those traits for the project.

Frederik said “yes” and the “Jeffistor” is the resultant resistor.

Duelund CAST “Jeffistors” with three parallel conductive elements and DCA12GA leads.

The “Jeffistor” is a Duelund CAST carbon / Sn-Cu resistor that contains three individual carbon resistive elements in parallel (thus the jumbo sized body), DCA12GA leads (!), and is treated with CAST material for damping in the same way as the Duelund CAST inductors and capacitors.

I must confess I was rather stunned by the sheer size of the “Jeffistor” and with its DCA12GA leads. Frederik never does anything that isn’t impressive in the extreme, and the “Jeffistor” is a case in point.

There are 4 resistor values used in the Altec crossover circuit, as shown above (not counting the L-pad).

R2 Duelund CAST Carbon / Sn-Cu 140 Ohm 10W Resistor

Duelund CAST carbon / Sn-Cu 140 Ohm 10W “Jeffistor” for R2.

We’ll be using the Duelund CAST carbon / Sn-Cu 140 Ohm 10W “Jeffistor” in R2, and they are about six inches long, about as big around as a cigar, and weigh in at a hefty 69 grams, as do the other values of “Jeffistors”.

R3 Duelund CAST Carbon / Sn-Cu 24 Ohm 10W Resistor

Two Duelund CAST carbon / Sn-Cu 48 Ohm 10W resistors.

For R3, two Duelund CAST carbon / Sn-Cu 48 Ohm 10W “Jeffistors” will be connected in parallel to create the 24 Ohm value for R3.

R4 Duelund CAST Carbon / Sn-Cu 100 Ohm 10W Resistor

The Duelund CAST carbon / Sn-Cu 100 Ohm 10W resistor.

For R4 we’ll be using the Duelund CAST carbon / Sn-Cu 100 Ohm 10W resistor.

R5 Duelund CAST Carbon / Sn-Cu 10 Ohm 10W Resistor

R5 Duelund CAST Carbon / Sn-Cu 5 Ohm 10W resistors.

For R5 we’ll be using two Duelund CAST Carbon / Sn-Cu 5 Ohm 10W “Jeffistors” in series to get the requisite 10 Ohms needed.

I should point out that these”Jeffistors” are prototypes, or perhaps I should call them one-off experiments to test an idea about resistors. Whatever you want to call them they are rather amazing to behold!

All I can say, Frederik, is “Wow!”

Frederik has told me that were these to be made available for sale they would be expensive due to the huge amount of hand labor involved in making them, probably in the realm of €150 or thereabouts.

If you really want to get some “Jeffistors” of your own to try you’ll need to contact Frederik directly as they aren’t a production item.

Ok, that’s it for now.

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

 Posted by at 3:45 pm

  4 Responses to “The Duelund CAST Carbon/Sn-Cu Resistor: The “Jeffistor” makes its debut!”

  1. Jeff, tell me how you chose values, how did you know when resistors were to be connected in parallel and when in series? Regards, Chris

    • Hi Chris,

      I’m not completely sure what you are asking me, but let me try to answer and cover the various bases.

      The overall resistor values were chosen based on the recommend values for the Hiraga-style crossover values.

      Inside the “Jeffistor” are three paralleled resistor elements, which were chosen by Frederik based on my listening trials that two parallel resistive elements sounded more natural and spacious than one.

      In the case where the two 48 Ohm resistors were paralleled to give 24 Ohms the choice was simply because Frederik sent me four 48 Ohm resistors instead of two 24 Ohm resistors. Ditto for the series 5 Ohm resistors to give 10 Ohms. While I don’t know for sure – we’d have to ask Frederik to clarify – I suspect that it Frederik’s choice of paralleling or series for particular values was just related to the Ohm value of the individual resistive elements that Frederik has to work with when building the resistors, so a matter of practicality when building the resistors is what I imagine dictated the choice.

      I think that covered all the resistor choice bases, and I hope that answered your question.

      Kind regards,


  2. Jeff, you just told me that it was Frederik who made the decision whether in a given place the value of resistors would be calculated in a row or in parallel. Thank you so much. Regards, Chris

    • Hi Chris,

      That’s an over simplification of and a not quite correct version of what I said in my response to your question.

      Let me try to explain again and see if that is of some help: The internal resistive elements of all the individual “Jeffistor” resistors (R2-R5) were paralleled based on my listening trials where paralleled resistor elements sounded better to me than a single resistive element for the same resistor value.

      I had reported these listening impressions to Frederik and asked if he would be interested in making some experimental resistors with internal paralleled elements for the Duelund-Altec Project, and Frederik was so kind as to indulge my idea for the project as an experiment in the form of the “Jeffistor” resistors.

      To further elaborate, my listening trials involved dual paralleled resistive elements, but Frederik’s inspiration was to add a third paralleled resistive element in the “Jeffistors”, as well as the very robust DCA12GA leads, and building up the “Jeffistors” in an extra-large size CAST enclosure fashion.

      The “Jeffistors” that Frederik built are amazing to behold and exude that classic Duelund quality!

      Now for all of the experimental “Jeffistor” resistors Frederik sent, each was paralleled internally as mentioned earlier, but in the R3 and R5 positions these internally paralleled “Jeffistors” were then themselves paralleled, and placed in series, respectively, for R3 and R5.

      I hope that makes what was done with the resistors a little clearer for you.

      Kind regards,


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