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In Reply to: Re: Greg Boynton articles from Sound Practices posted by Ian L on March 14, 2007 at 22:29:21:
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. !!
Follow Ups:
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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