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I came across a web-site which was selling some VERY expensive, low value resistors made from (thin) silver wire wound round a 1/2" piece of hardwood dowel.I would have thought a resistor made from many coils of wire would be inductive but these are claimed not to be ... any comments anyone? They are "bifilar wound" - whatever the hell that is!
The reason I ask is that I wish to make up some low value series resistors (like, 0.7 ohm, 1 ohm) which I can use to attenuate some Maggie drivers ... but they need to be able to take 10 or 20 watts.
So DIY using thin magwire seems like a good way to go if I can end up with a low inductance result!
Regards,
Andy
Follow Ups:
A "bifilar" coil, R, etc. is a wirewound device that has the wire coil wound back and forth against itself i.e. one layer wound clockwise and the next layer wound counter-clockwise, which cancels the inductance.Happy Listening !
I've done that out of silver and copper.
See link.
Thanks for the DIYaudio link, Tom. I've made one up out of 6' of 30awg magwire ... I just have to see what inductance it's come out at.I'm also going to try using "resistance wire" ... a 60:40 Cu/Ni alloy (which is not NiChrome). This has a resistance of ~2ohms/ft for 27awg.
Regards,
Andy
Can't say about the sound.However, I have measured the inductance on some low value ( <1 ohm) wirewound resistors in the past. Actually they are inductive but the measurement was ver low - less than 1uH. For many purposes this can be considered non-inductive. Many DMMs with an inductance fuction will report them as zero.
Even a piece of wire has some resistance, capacitance and inductance if you can measure low enough. The question is: when does "low" become functionally equivalent to "no"? It depends on your circumstances.
Nonetheless, I think that for most audio purposes any resistor below 0.47 ohms can be treated as non-inductive.
BTW, don't assume all metal-film resistors are non-inductive. For many series a spiral is cut in the film in order to achieve val;ues lower than approx 300 ohms. Sometimes you can find this in the datasheets, sometimes not. If it is really, really important I suggest that one assume nothing -- measure it yourself.
Never tried it. Bifilar winding is when two lengths of wire are wound side by side (closely coupled) and then connected so the magnetic fields are opposing (currents in opposite directions), thus cancelling most of the inductance. Of course, that increases the winding capacitance a lot but it's OK at low resistances. There are other more costly winding techniques for higher resistance values, but many wirewound power resistors are made this way on a ceramic or fiberglass core as standard, or as an option. The low current precision wirewound resistors are usually wound on a plastic epoxy bobbin core with two sections that are wound in opposite direction. I think it's called reverse pi. Then coated in silicone rubber and encapsulated in epoxy. Great sounding resistors, better than any other IMO. No ceramic core as in most other types.But it would be interesting to find out if that 100 meters of copper or silver really sounds better than the 1 meter of nichrome. I did an experiment with solder one time, and the results were very unexpected. I wanted to investigate the sonic properties (if any) of various solder alloys. After considering many options, I decided to construct interconnects using the different types of solder as the conductor. I 'knew' that the cables would not sound as good as my normal ones but it would allow me to hear the degradation caused by the different solders in a controlled manner. What I was not prepared for was the astonishing improvement these cables were over my previous best which consisted of multiple strands of Teflon insulated solid core oxygen free copper. I subsequently tested them against a number of other cables I and others had on hand and also loaned some to others to listen to on their own. All agreed the solder cables were substantially better than anything they were tested against. YMMV :-)
Hi MB,Very interesting experiment ... your solder-wire ICs.
You mentioned "nichrome" - is that what the wire in "normal" (eg. Mills) ww resistors is made of?
Can you tell me which resistors you were referring to when you said "The low current precision wirewound resistors ... great sounding resistors"?
I was thinking if one of these reses had to withstand, say, 20w continuous of power (when put in series with a Maggie panel), that's probably 1/2 an amp? 2 metres of 30awg mag-wire gives me 0.68 ohms (which is about what I want) so all I have to do is find out whether 30awg will take, say, an amp without glowing!!
Regards,
Andy
I was thinking if one of these reses had to withstand, say, 20w continuous of power (when put in series with a Maggie panel), that's probably 1/2 an amp?
If a 0.68 ohm resistor is dissipating 20 watts, that means you've got about 5.4 amps running through it. Which means if the speaker is a 4 ohm load you've got about 116 watts in the speaker.
So when you say 20 watts, do you mean that the RESISTOR has to dissipate 20 watts or that the SPEAKER is dissipating 20 watts? If you mean the speaker, and the speaker is 4 ohms, then that comes to about 2.2 amps which means the 0.68 ohm resistor will only have to dissipate about 3.4 watts.
As for the wire, see if you can round up some resistance wire under the name Advance, or Cupron, or Copel, or Alloy 45 or Cuprothol 294. These are trade names for a 55% copper/45% nickel alloy resistance wire. Although it has nickel in it it's non-magnetic and in my opinion sounds fantastic (I had Mills make some custom resistors for me out of this alloy which I used in a headphone amp).
Resistance per foot for this alloy is 2.94 ohms for 30 gauge so you'd only need what, about 3 inches to get your 0.68 ohms? Just use two 1.5" lenghts, one in each leg.
se
from a local mfgr of heating elements. They gave me a 2m length of ~27awg (actually 26B&S) fer free! Res is 3.91 ohm/m = 1.19 ohm/ft and it will take a couple of amps.Thanks for your help with this.
Regards,
Andy
from a local mfgr of heating elements. They gave me a 2m length of ~27awg (actually 26B&S) fer free! Res is 3.91 ohm/m = 1.19 ohm/ft and it will take a couple of amps.
Great! Yeah, since you need so little a "sample" quantity is all you need.
Thanks for your help with this.
You're welcome. Good luck! Lemme know how it works out for you.
se
I will go search for copper/nickel alloy resistance wire.If resistance per foot for this alloy is 2.94 ohms for 30 gauge, I could probably go up to 24 guage to give me some more current carrying capacity.
Although, as you suggested, if the driver (Maggie ribbon) is dissipating 20 watts then the current is ~2.5 amps (3 ohm driver) ... so the 0.68 ohm resistor is dissipating ~4 watts.
So you're positive this copper/nickel alloy resistance wire actually "sounds" good? Would it sound better than just using a standard Mills ww resistor as an attenuation resistor (I've never heard any comments about the sound of Mills reses)??
Regards,
Andy
If resistance per foot for this alloy is 2.94 ohms for 30 gauge, I could probably go up to 24 guage to give me some more current carrying capacity.
Yeah. Here's a chart showing the resistance per foot for a number of resistance wire alloys. The one I mentioned is the same as the MSW-294.
Although, as you suggested, if the driver (Maggie ribbon) is dissipating 20 watts then the current is ~2.5 amps (3 ohm driver) ... so the 0.68 ohm resistor is dissipating ~4 watts.
Yeah, though I don't think you're actually going to be constantly slamming that ribbon with 20 watts. I'd guess the resistor may on average only be dissipating about a watt.
So you're positive this copper/nickel alloy resistance wire actually "sounds" good?
With the all important qualifier "to me," absolutley.
Would it sound better than just using a standard Mills ww resistor as an attenuation resistor (I've never heard any comments about the sound of Mills reses)??
I think it sounds much better than the typical nichrome that's used.
se
Thanks Steve,I have located the Oz office of Kanthal who market Cuprothal 294. I'll give them a call today.
Regards,
Andy
Very interesting experiment ... your solder-wire ICs.
Yeah, I went on to use it for speaker wires too. The geometry is nearly ideal, a hollow center filled with organic flux for damping and good high frequency current transmission, and a relatively inert high mass making it much less responsive to either internal or external forces. And super easy and cheap to make. I just get a roll of high lead content .062" solder and push it down some Teflon tubing and terminate each end with solder terminals and stress relief and put it to use. Works for me :)You mentioned "nichrome" - is that what the wire in "normal" (eg. Mills) ww resistors is made of?
That or some type like it. Nichrome is an alloy of about 80/20 nickel/chromium. There are other resistor wires but they're similar.Can you tell me which resistors you were referring to when you said "The low current precision wirewound resistors ... great sounding resistors"?
It's the RB series of mil-spec type resistors. Many companies make them including Mills, although I don't believe they offer as many types as some of the other companies. I've bought many on the surplus market, and bought many new from a few companies, but they are mostly like the ones shown here .I was thinking if one of these reses had to withstand, say, 20w continuous of power (when put in series with a Maggie panel), that's probably 1/2 an amp? 2 metres of 30awg mag-wire gives me 0.68 ohms (which is about what I want) so all I have to do is find out whether 30awg will take, say, an amp without glowing!!
Well, if you want to make it a 20 watt resitor then it will have to be able to handle a lot more than 1/2 amp! More like 5 amps at 1 ohm. 30 AWG could probably handle 1/2 to 1 amp if wrapped around a thermally conductive core, but not air or wood. And definitely not 5 A continuous. Are you just talking about high frequency panels? Wire charts usually include a column showing a conservative rating for current capacity in air.
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