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In Sound Practices #1 Greg Boynton did an article on horns near the end of which he says he'll be back with another one about crossovers. Does anybody know if it ever appeared in SP?
Thanks
Follow Ups:
LC-type filters at line level are the same as LC-type filters for speakers. As DrLowMu says, you just type in a higher load into a speaker XO calculator. In practice, you are going to have to keep the impedance pretty low to use inductors, probably below 1000R like the 600R suggested. Also, due to the rarity of inductors for use around those levels (unlike speaker inductors), you may have to adjust the load to your desired crossover point, rather than using a fixed load (600R for example) and adjusting inductor values.Actually, designing an LC network for line level is much easier than a speaker XO, because you don't have to deal with the oddities of speaker drivers, and instead typically have an idealized resistor load.
For higher impedances (100K etc) then CR filters are more appropriate. Use TubeCAD's filter designer software for an easy fix.
When designing an active XO, it is likely you'd end up using something like a stepdown transformer (15K:600R as suggested) as otherwise you'd end up with too much gain.
For those interested in active XOs, I would consider a dedicated headphone amplifier used as a preamp. The Gram Slee and HeadRoom models seem appropriate, and they of course come with volume controls as well (and even internal USB DACs). They are typically designed to drive 32 ohm headphones so they can easily drive a line-level passive LC network, maybe even one using aircore speaker inductors.
Hi Ian,No, Greg never wrote the crossover article. I called him up out of the blue a couple of years after SP #1 and he was nice enough to answer my questions. Very nice guy, just really busy with his prosound business.
Hi Steve,
Your questions didn't happen to have anything to do with LC passive crossovers at line level did they? `,;^)
I'm working on that now and was hoping I might learn something from him. There doesn't seem to be much info on LC based passive approaches out there, I'm guessing that not many have tried them, possibly because of the values of inductors that would be needed.
Thanks for your reply !
Are you refering to this:http://www.t-linespeakers.org/tech/filters/passiveHLxo.html
Linkwitz also has Passive line level XO with a lot of correction and a lot of info:
http://www.linkwitzlab.com/crossovers.htm
Hi Saturn,
Thanks for the reply. I looked over on the linked page but couldn't find what you were referring to.
Basically I'm just interested in learning what I can about how others have approached the implementation of pllco's in their systems. My primary focus in this right now is on LC (as opposed to RC) circuits.
Also of interest is something of the theory, but I don't understand math as a language and so most of the more straight ahead technical explanations are just way outside my abilities. I'm looking for pages that can explain with words what it is that the math is saying to the engineers - very hard to find at anything other than introductory levels "a crossover is a device that is used to separate. . ."etc.
Hello,FYI, I contacted Greg back then, and it WAS 600 ohm passive at line level, 12 dB per octave two way crossovers he was going to suggest.
I've built them since then . One of my circuits was shown in SP, and an article on the 600 ohm crossover circuit was published in a different, later SP. Use 600 ohm Daven Bridged T pots, constant impedance pots, as a volume control on the output, and install an absolute phase reversal switch after the step down trannie. Becomes a very useful piece. !!
C'mon Jeff, don't be a tease `,;^D) You mean a 600/~ stepdown after the Daven?
I think I also saw a post of yours somewhere talking about a single gain stage. Did you try it both on the in and the out?
Hi,The Daven T attenuators ( and an absolute phase reversal switch ), all get used after the 15K to 600 ohm step down, when you have a balanced signal to process, all at 600 ohms Z.
It was a single triode gain stage, usually a 5687, cap coupled into a Peerless 1509 as I recall the number. Clearer to you now ??
Regards,
Hi Jeff , thanks for your reply. "Is it clear to me now?" Well, partially, but I can still imagine several variations, so in other words no. If you have the time and inclination can you walk me (us ?`,;^) through the whole sequence of stages from in to out?Thanks !
I don't have my design notes here, so its from memory.1) A 5687 gain stage, as I recall, a 211 ohm grid stopper
2) 2 uF coupling cap
3) Altec 1509 15K to 600 ohm step down trannie
4) Absolute phase switching, DPDT swiches, On- On
5) Daven 600 to 600 ohm bridged T attenuators ( constant impedance )
6) Biamp L/C line level crossovers at 12 dB octave, used either vintage UTC VIC or HVC - series adjustable inductors, and set crossover for about 400 Hz for RCA field coils.
7) Three sets of RCA output jacks, Full Range Out ( off of the 1509 trannie secondary ). Low Out and High Out.
Thats all there was to it . Kimber Kable TCSS wire, multiple paralleled runs on grounds and B + es. Wonder solder. Go for it.
Jeff Medwin
Thanks Jeff, now I see.
One of the things I was wondering about was where you had put the tube, on the in or out-put. I thought of reasons why I might want it on the output but that made four triodes appear out of thin air. A single dual triode at the input looks neat (in my mind anyway`,;^)
Thanks for sharing your stuff. It's helpful !
Ian
Jeff, I once read an excellent article that described the calculation and construction of line level networks. It may have been in Audio magazine sometime in the 1980s. Do you know of this article?
Hi Steve !!,Yes, Audio magazine originally, and it was reprinted by Joe in SP. I can snail mail you a copy. Now a days, there are calculators on the WWW, usually auto sound sites, where you can get the L and C numbers, say, at 600 ohms, etc., for any frequency... darn easy !!
BTW, thats how myself, and now also Greg, run RCA Field Coils. I can share with you my original circuit values, used a 5687, very well adjusted as to ohmic values and voltages.
Steve, I need to speak to you about Cogent diaphragms for earlier FC's. Please send me by email your home and cell numbers, and indicate a good time for me to ring you. Its urgent that I talk to you ASAP !! Thanks. Regards....
Jeff Medwin
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