Printable View
I started collecting parts for Jeff's XO. He specifies a 3.7uF cap. I can't find any. I can find a 3.9, or I can get a 2.2 and a 1.5. Which is best? I hate adding extra parts. The 3.9 is a 5% difference. The Chicago caps I replaced from my Heathkits were +/- 10%. So how critical is hitting that number? I'm thinking of using Dayton 1%ers.
I'm like you and prefer to stick with less clutter. either way will probably be pretty unnoticeable.
Regarding the first question..... the standard values for the resistors and capacitors were chosen intentionally in a particular manner so that one can reach any value with the right combination. As 3.7uF is not a standard value, you will have to go for the "combination" route. Here you should go for the 2.2uF & 1.5uF combo.Quote:
Originally Posted by alancohen
Now regarding how critical one should be about these values....... well for all practical purposes, a shift of +/- 5% will normally not be audible in most cases. But again it all depends on the driver parameters and the type of xover design, and the placement of the xover "frequency". Also here we are talking about Altec-duplexes and Jeff's work (the critically-computed-types). So we should respect the overall picture and go for the actual values. But I also must add it here that the end result may vary, but even if it does, at least you will have a starting point to tweak your way through.:)
Thanks aditya...good info. I noticed that Jantzen, Dayton, Solen etc all seem to offer the same values. I thought it might just be the result of expediency of manufacture rather than by design.
I emailed Jeff and he was kind enough to assist me. He said to go ahead and use the 3.9. I was glad. In my mind, more parts equate to more potential for failure. He said the same thing CD and you did. It is not likely I will be able to hear any difference. Especially given the fact that most reasonably priced caps are +/- 5% tolerance anyway. I'm using 1% Daytons.
And like you say, that should get me started. I'm not prone to tweak unless something really jumps out at me. I'd rather spend my time listening, than measuring.
Thanks Alan for the 'thanks'. You are welcome.
Nice to hear about the go-ahead signal from Jeff. So expectations are that you will post the developments here, which will be great. Actually I have not yet tried this design myself, but CD probably did it, but I am not sure. What I know from his posts is that he is with the GPA ones. He himself only can conform this, as his present avatar of the 'mad-scientist-image' throws me completely out of my resources.:) (hi CD !) But I am sure Jeff's design will definitely work nicely. Have a great Altec-Duplex-journey.
Aditya
I certainly will. I'll post the whole build, including pics. Right now I'm wrestling with the layout and hook up hardware. I can never seem to find everything I need from one place.Quote:
Originally Posted by aditya
I'm using the inductor calculator here...Inductor Designer / Calculator
Using a value of 4.7mH with 15 AWG wire, a core of .75" and length of 1" I get a DCR of .5 Ohms. 19 levels with 17.5 turns will make a pretty symetrical coil. Good?
Inductance 4.7 mH
DC Resistance 0.5 Ohms
Wire Gauge 15 AWG
Wire Diameter 57.1 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 0.75 in
Coil Outer Diameter 2.92 in
Average Turn Diameter 1.77 in
Wire Length 152.58 feet
Copper Weight 1.5 pounds
Turns 330
Levels 18.84
Turns/Level 17.51
Hi Guys, :) The parts express catalog shows all inductors and their DCR's and impedance's, It comes in handy for hunting inductors. You can always use your DATS to measure the caps...and everything else for that matter just to see where they're at. I have never built one of Jeffs Crossovers and right now my GPA crossovers are collecting dust.
HI guys
COIL winding: Try to pick the coil form so cross section is square and the finished hole radius is the same dim.
This will minimumise the length of wire, DCR , and turns for a given mH
CAP values: Give the designer a break.
If the design calls for 3.7 do not sub a 3.9. Use a 2.7 plus a 1.0 or some other combo. And do not tell me
it looks ugly with all those caps. We want the best performance. i have built a number of pretty XOs that did not work as expected. Some did not work worth a dam. OK I will get off the soap box . I apologize if I stepped on any toes.
Don
Now I'm confused. I'll build the XOs to plan and then re-examine the hook up after.
As far as the inductors, using the calculator above I get a pretty symentrical 4.7mH by using 1" length and 1" core:
Inductance 4.71 mH
DC Resistance 0.51 Ohms
Wire Gauge 15 AWG
Wire Diameter 57.1 mils (1 mil = .001 in)
Coil Length 1 in
Coil Inner Diameter 1 in
Coil Outer Diameter 3.06 in
Average Turn Diameter 1.94 in
Wire Length 156.03 feet
Copper Weight 1.54 pounds
Turns 307
Levels 17.53
Turns/Level 17.51
But if I go .4" core with .4" length, the overall diameter jumps from 3.06" to 4.17, but the DCR drops to .44 and wire required is reduced as well. That makes for a flat looking inductor, and probably harder to wind, but the values are better.
Inductance 4.72 mH
DC Resistance 0.44 Ohms
Wire Gauge 15 AWG
Wire Diameter 57.1 mils (1 mil = .001 in)
Coil Length 0.4 in
Coil Inner Diameter 0.4 in
Coil Outer Diameter 4.17 in
Average Turn Diameter 2.23 in
Wire Length 135.19 feet
Copper Weight 1.33 pounds
Turns 232
Levels 33.12
Turns/Level 7.01
I see why you want to roll your own. The only one I see in the book close to what you want is 4.7 DCR .60 ohm and 96 bucks a piece!!! PN# 255-698