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Modified RF-25 cross overs, Mundorf supremes and North Creek Inductors

Dave C

Dave C

Super Member
To much reading of SET12's thread on his cross overs and then the trips over there (sigh) So I talked with Dan and ordered up some parts. It all started off when I noticed my new Klipsch RF-25s didn't sound quite the same. One was a bit brighter than the other. A call to Klipsch a couple of years ago yielded me a pair of new tweeter horn drivers and cross overs. The said they had changed the design of the drivers as they had some problems with over heating. A close look at the cross overs saw every capacitor was also a different value, WAY different in fact. I got on the phone and talked to SET12 about it. To make a long story short Dan worked out a revised cross over using boutique components. This thing looked really pricey so I went with Mundorf Supreme caps instead of the silvers. (I did my homework on this one though, I think I made a good choice.) This is the layout work I'm doing. I put the inductors on opposite ends in hopes I can mount them both flat, they are about 14" apart. Comments? I need to anchor it all down yet and I'm still working that out, I'll sleep on it for a while. The original cross over is in first picture.
 

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I know these RF25's are going to fly.

As I have already heard them in stock form, they are already good sounding, but like a stock pair of Fortes vs my modified, I expect the RF's will grow in their presentation (like on steroids) and do some amazing things, defying their actual size, with detail and authority. I'm looking forward to hearing these with these mods! :thmbsp:

:lurk:

SET12
 
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I worked on making mounts on the board for the inductors and the big Mundorf Capacitor. The inductors were easy, I used some PVC I had that fit nicely into the inductor cores. The Cap mount was made with a larger size PVC. I cut it in half and then cut a slot in the underside for a zip tie to slide through. I used 2 1/4" pieces of plastic that I cut out to reinforce the PVC halves. I glued this together with Zap GOO, it looks a lot like Shoe Goo.
 

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Tonight I wired up one of the new cross overs. I took some junk speakers and wired them in to verify that it all worked. After a couple minutes of listening I was going to turn off the lights and watch the tube for a while. I then sail S@#%&^t and took it up to the living room. I have to say I looked at the stock speaker standing there in its glory and I had to think about cutting wires off the old cross over, it was something that once cut would take a lot of work to go back to factory condition. I grabbed the wire cutter and went to work. I set the new cross over on a small box and hooked it up to the left speaker, held my breath and turned on the 300B amps. I started off with a couple of good sounding CDs. John Denver's "Whispering Jessie" has a very nice sound stage. HOLY CRAP!!! The violins filled the left side of the room almost sounding like some of them were slightly behind me!! GEEZE!!! I put on "Hell Freezes Over" by the Eagles. The sound on the left sounds so well defined and balanced compared to the sound on the right. I'll be getting up early tomorrow to solder up the second cross over. It will be very easy to cut the wires and hook it up. Then comes the carpentry to finish the cases for them. I'll post pictures later. The guys that spend their time rolling tubes should put them away and try this, the reward is much higher. I'm not saying I'm done yet, I'll know that in a week or two but for now I can hardly wait to finish the other cross over.
 
:lurk::lurk::lurk:

:music:

:) It doesn't surprise me of course, but I'm glad someone else is finding out just how much mods like these can return.

As I have said many times in my own thread, networks are one of the least area's looked at, And often people are well meaning but IMO they don't go far enough to get the results that really make their speakers take off! And I really mean that literally, its as though the sound stage space expressed in my own Fortes defy the Fortes own size. And put me on the wings of an eagle, it darn near a spiritual experience at and by the sound of yours Dave they are going to do the same thing!

And your right, I to believe these mods do a bit more then tube rolling!

In the end everything works together, and when it is all good, good things happen! And I'm sorry to say but IMO, wimpy networks = wimpy sound.

I can't wait to hear more :yes: but no doubt good things sound like they are happening!

SET12
 
Thursday morning.
After a cup of coffee and SSS it was back to the workbench. I finished up the second cross over. These pictures show new and old side by side. After work tonight I hope to do a temp install and listen to the new found sound!
 

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Finished and wired in the second cross over this evening. I now have a wall of sound! My first impressions are as follows after about an hour of listening. The sound stage is huge, it wasn't bad before but this is the cake with icing. The bass, sounds like it picked up an octave and is tighter. Mid range, very smooth and defined. Highs, cymbal crashes sound very nice. Pianos and acoustic instruments have more transparency. However if any part of this isn't totally perfect it would be the high frequencies. For my 50 year old ears I may have to change the value of the 5 ohm resistor back to 2 or 3 ohms. I need to let the capacitors settle in a lot more yet. I also want to upgrade a coupling capacitor in the amplifiers before any further changes are made to the cross overs. I plan on mounting these things on the back of the speakers. I'm building the boxes out of 1/4" PVC sheet. More posts to follow as that project progresses.
 
Dave,

Yes, your RF25's did seem a bit polite in the treble, You might think about unsoldering those two ohm resistors and giving them a try, and if you like what you hear, order the Duelunds.

Glad to hear the RF's sound like they are on steroids :D

Great work Dave :thmbsp:

SET12
 
Thanks xtreme4099, SET12 figured it all out and I did the layout and build. I'll be listening for a while tonight after the work is all done. Sound is very natural.
 
SET12 said:
Dave, how's the sound? Prying ears want to know :music:
Click to expand...
The sound is improved a lot from stock. I need more time with it though. First impressions are it is warmer and better balanced. I'm just not sure the highs are a perfect fit for my ears yet. (real close though!) Looking back, the highs were a bit harsh with the factory cross overs. I'd come to like that I guess. On a side note these speakers are rated at 8 ohms. Just for kicks I put an ohm meter across them today and the meter reads 3.8 ohms. I didn't check them before they went under the knife. Does that sound reasonable?
 
After a few days of intense listening I went down to the work bench and got a pair of clip wires. In an earlier post I mentioned if there was a weakness in these cross overs it was that the highs were a little soft for my ears. I jumped across the 5 ohm Duelund resistors and played through some of the CD's I use for reference. 5 ohms is to much, I need a little more edge in my music. I think I could live without resistors in there at all, I am going to use a couple of 2 ohm resistors from some old cross overs to see how that works out when I have time. I'm thinking though that 1 ohm would work just fine.
 
Today, I removed the Duelund 5 ohm resistors and installed the 2 ohm resistors from the original Klipsch cross overs. (see first post for details) To my ears the 5 ohm Duelunds put out to silky and laid back of a sound. I need to have the highs a little brighter. The 2 ohm OEM resistors provide a little more edge on the highs with out being to bright. Using Mundorf capacitors behind these seems to be the perfect ticket. I listened to several CD's tonight and everything sounded better. Bass is very firm and the mids are silky like mids should be. With the resistor change I feel the highs fit the overall sound very well. Still working on the boxes for the cross overs, one is done and the other is well along. I hope to mount them later this week and will post pictures.
 
Dave,

Its probably a loudness change that gives a sharper picture. You could try paralleling the Duelunds which would be 2.5 ohms and then compare both, but if you do, make sure they are side by side when doing this and not left vs right as I know your listening room is not symmetrically laid out as it has one full corner and one open which can have an influence.

The biggest point I like about the Duelund's is the negative temperature coefficient which enhances dynamics as the resistor heats up it actually has less resistance vs more resistance for the Klipsch sand cast resistors.

So with that in mind I would likely be more in favor of the Duelund's for sheer dynamic response.

SET12
 
Thanks for the input SET, I think that for now I'm going to leave the Klipsch resistors in place. Next parts order will probably include a pair of Duelunds and some Mundorf coupling caps for the amps.
 
The finished install. I have to finish the second box yet. Enjoying the music right now though.
 

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