Epic CF-4 Bi-amp Crossover Project

[Maxwell_E]

I recently purchased some V1 CF-4's from another forum member and I've been having the best time so far. These are the best speakers I've owned, but like most of you, the urge to modify has fallen upon me. I'm specifically interested in bi-amping these with a 3-8 watt SE tube amp on the compression drivers, and a 100-200 watt SS amp for the woofers. In that vein I started investigating the possibility of building an active crossover in a separate chassis.

 

Looking at schematics online I found (linked below), as well as my existing crossovers, I noticed there's a little more going on here than I'd expect. The LF section looks like a pretty standard 4th order, while the HF has an extra LCR leg running across the speaker terminals when compared to a standard 4th order. Also there is an autotransformer, T4A, in series between the first cap and LR leg on the HF side. On the Crites website he has these listed as padding the signal by 4db. I have to assume that these "extra" components are there from real-world speaker tuning, time alignment, and driver matching, or some combination of those three.

 

I'm not interested in re-engineering the entire speaker, so my first instinct is to just replicate these exact networks with my own components. Ideally, I would like to omit the T4A autotransformer to get the most out of whatever low-power amp I have driving the HF side. Do you think this would alter the behavior of the crossover besides just making the HF louder? The HF amp would have a level control (if needed) for matching the CD's and the woofers.

 

Am I crazy for wanting to mess with an already great speaker? I think building some nice crossovers in a custom box would be a fun project, and I've always wanted to try active crossovers and true bi-amping.

Klipsch CF-4 Schematic.pdf

[wvu80]

Nice first post.  Welcome to the Klipsch Forums, from a fellow CF-4 fan. 

+++

 

First of all:  If you haven't listened to your speakers yet I suggest you do that.  Just spend some time with them, play different music, see what you like and don't like.

 

AND THEN...if you find something with the sound you don't like, that would be the time to try some mods.  I've modded mine but I don't want to discuss mine right now because I don't want to influence your expectations.  I do think electronics make a difference in speaker sound and the CF-4's love power.  I run an Emotiva XPA-5 external amp with about 250 wpc and I think the power helps the woofers, with my Onkyo TX NR717 110 wpc being a bit anemic. 

 

There is absolutely nothing wrong with modding and playing with your speakers, IMO.   Just know that to some other Klipschites, once speakers have been modified they are no longer Klipsch.

 

I just saw your CF-4 XO schematic.  It refers to red/black wires which would make it the XO for the Version 3, the least liked of the CF-4 v1, v2 and v3.  The XO's ARE different.  The v1 gets the most rave reviews with its 5.5 inch long port tubes.  The first two versions use Monster wire with a clear plastic sheath.

 

Welcome to the Klipsch Epic Owners club.  Here is some interesting reading.

 

 

[glens]

7 hours ago, Maxwell_E said:

Looking at schematics online I found (linked below), as well as my existing crossovers, I noticed there's a little more going on here than I'd expect. The LF section looks like a pretty standard 4th order, while the HF has an extra LCR leg running across the speaker terminals when compared to a standard 4th order.

 

I'd call the low pass a third order, as well the high pass.

 

The LCR bits in parallel with the drivers are for frequency response shaping.  If you go the low-level crossover / bi-amp route, making your own circuits, then I'd suggest leaving all those parallel LCR parts in place.  If using a digital crossover with which you can frequency-shape, then remove all the components and just drive the bare drivers.  If you go that route...

[Marvel]

8 hours ago, Maxwell_E said:

Also there is an autotransformer, T4A, in series between the first cap and LR leg on the HF side.

 

Welcome to the forums. I would love to hear some of the Epic series speakers some time. Concerning the autoformer, I wouldn't worry about power to the HP side of things. I have used my SET 2A3 amps alone to drive my LaScalas and Heresy II speakers, and they have worked quite well. In any case, enjoy your speakers!

 

Bruce

[Maxwell_E]

These are great responses.

 

I have owned them for about 4 months now, so I'm pretty familiar with the sound. I've read a lot of the forum posts and other thoughts on these speakers, and I'm thinking I'd also be willing to start small with some damping on the horns and woofer baskets.

 

I realized that the pdf I posted was the V3, but it was the closest approximation I had to the network. I plan on taking the crossovers out of my speakers and fully documenting them sometime in the near future. One thing that I've found is that my old 30wpc Sansui has a hard time driving the woofers to match the horns. I started going off on a tangent of "fixing" that by having separate amps to tune the speakers to my room. the first step will be to try some larger amps, specifically a 50wpc NAD that I've got out for repair right now.

 

Generally speaking, is it kosher to create a low-level/active crossover as a clone of the speaker level design, albeit with the ability to use lower power rated components?

[avguytx]

It's been said that the efficiency stated for the Epic CF series is really not as high as shown on the paperwork; something to the tune of 7 to 8db difference maybe.  The best sound I had out of the CF-3's I owned was with a highly modified Carver M-1.0t amplifier, upgraded to what's called an MkII Opt 002, that takes it from 200wpc to over 400wpc.  Those speakers love power but will also work reasonably well with lower power.  I also ran them some with a Tubes4HiFi Dynaco VTA ST-70 with 6550 tubes which sounded quite good and also a Mcintosh MC250 that also did a great job.  The Carver did the best by far.  I'd thought about bi-amping with the Mac on low end and the ST-70 on high side but sold the speakers before it got to that point.  (Built a pair of Belle clones)

[BEC]

21 hours ago, Maxwell_E said:

On the Crites website he has these listed as padding the signal by 4db

Normally autotransformers are used to attenuate or reduce the output of a driver.  In the case of the CF-4 the autotransformer is installed backward and it effectively boosts the output by 4db.

Bob Crites