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Heresy Crossover Mod - Less Bright


JohnA

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The attached file is a schematic of a Heresy Type E crossover with modifications (in red) to reduce the output of the squawker and tweeter. the woofer's output rating is a fraction below 95 dB/w/m, but the squawker is run at a nominal 98+ dB/w/m and the tweeter is run at a nominal 99dB/w/m. Moving the taps down one on the autoformer reduces the output 3 dB and adding the resistors preserves the impedance seen by the network so the caps and inductor don't need to change. The resistors can be connected to the screw terminals for the squawker and tweeter. You could unsolder the autoformer connections and use temporary jumpers to see if you like the mod.

I just added a Heresy to my HT for a center channel. The difference in brightness between a Heresy and La Scala is obvious and this is why.

Give it a try and tell me how you like it. After I build the redesigned circuit and listen to it a while. I'll publish it, too.

post-2142-13819246216148_thumb.jpg

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John A.

Gee, that looks real nice. Congratulations on the work.

I'd like to point out that Al K. has addressed a mechanical/electrical issue regarding connecting to the autotransformer. I don't know how I've been such a dunce to think the connections have to be soldered. He uses push on automotive connectors.

I've used them on the autotransformers from Universal Transformer of Texas. The typical 1/4 inch connector is the correct size for them. (Others might be familiar with the Al. K. design and the flexibility of using various taps on the autotransformer to adjust the level.)

I also fool around with RS 70 volt line transformers, using the primary 4-8-16 ohm taps as an autotransformer. These take a smaller push on connector which I found at an automotive "speed shop".

There is some need for caution. Sometimes the fit is too loose or too tight and the push on connector has to be fiddled with. If to loose, there is not a snug connection. If too tight, there is the danger that pulling the connector off will pull out the windings. I haven't ruined anything yet.

They sure are handy. Soldering and resoldering might damage the connections between the "tab" and the windings too. The push on connector is a nice compromise for the experimenter.

Least I forget. The cludgy automotive world has a push on "female" with two "males". These can be used when you have to connect two wires to the same tap. They cost a couple of bucks in a blister pack at the speed shop. No need to order from Parts Express.

Gil

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Sometimes Gil is surprising, but I never pictured him in a speed shop either. :)

The circuit I uploaded this time is the quick and dirty version. With the mods the impedance in the midrange is still over 110 ohms and the tweeter is 32 ohms, while the woofer is 11 ohms. This is WAY too high. The next one will have a swamping resistor like Al's network has. He has provided invaluable assistance analyzing my ideas.

The old "conversation" we had only addressed the tweeter, but the squawker is too loud as well. It stands out a lot compared to my La Scalas. That's what got me looking at the crossover network. After a little study, I noticed both horns are 3 to 4 dB hot.

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John,

After listening to my heresies the past couple of days with the specific intent to pay attention to the treble I came to a sort of a conclusion(to my ears anyway).

At lower volumes the heresy seems well balanced, it is only as I get into the upper 90dBs range that the treble sounds too hot.

My only slightly educated guess is that this is due to the same reason some recievers have a loudness button.

As the volume drops off our ability to hear the treble and bass frequencies diminishes, I believe that this is called the "equal loudness curve" or something similar.

Now that I think about it I'm kind of worried that I would lose some of the detail I am used to at lower volumes, I don't always listen at 100dB usually somewhere in the mid 80's.

I may still try your first mod since it is easily reversible.

Also I realize that you are doing this to match the timbre of your beautiful LaScalas, a "problem" I don't have.

Happy listening.

Peace, Josh

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John,

I see what your are doing with the extra resistors across each driver but I think there is a problem. The 2 uF cap in sereis with the tweeter will not be the right value when terminated by the lower impedance. The tweeter crossover will move in frequency. A better way is a single resistor across the autoformer (0-5) to reduce the load reflected through it after lowering the taps back to where it was. This will maintain the correct impedance seen by the tweeter cap. It will only requere a single resistor rather then two also.

Al K.

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Al is correct. I wasn't thinking clearly. This was intended to be an easy mod and for a test, but the extra resistor should not be installed across the tweeter. I've uploaded a corrected version. We used to be able to delete files on the server. I can't figure out how, now.

post-2142-13819246217198_thumb.jpg

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Its my fault, I'm the one that suggested to John that he put the 8 ohm resistor in parallel with the tweeter.

For the adventuresome I would still try it, but increase the cap to the tweeter to 4µF to keep the crossover point the same.

The idea behind this is to reduce impedance variations at the resonant frequency of the tweeter.

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This is what I found in my '85 Heresy

8556731 Tweeter - K 75

Mid Horn - K 53R

Woofer - K 22K

8556732 Tweeter - K 77

Mid Horn -53

Woofer - K 22K

It look as if xxx31 has had some work done to it while it was a demo befor I purchased them. I have wondered if I sould replace the K-75 with a K-77, but my question now is, caracterisicly how does the K-53 compair to the K-55V.

I am intreguged by this modification mentioned and I can hardly wait to try it out. I glanced quickly at the cross over and if I remember correctly they have the type -E, I'll have to verify that later. I am kind of leaning towards the tweeter mod alone first, any sugesstions.

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I was just thinking about this modification to the crossovers, and maybe I am wrong, or just thinking on a different tack. John is using the heresy as a center, and I am assuming that is is not sitting on the floor as the heresy was intended. But, from what I recall on a article about professional sound, you get a +3db free from a subwoofer placed on floor level versus being elevated. Had something to do with the floor bounce, I don't recall exactly. So, if the woofer is 3db less efficient then the midrange and tweeter, does this mean floor placement will equal a flat frequency response ? Also, would l-pads to attenuate the midrange and tweeter be an easier / simpler / better fix ? Or would this stil change the crossover values due to added resistance ? Maybe Al k could clear this up for me.

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L-pads could be used, but that would be a more complicated mod than the second schematic.

One of my Heresies are not on the floor (it's over the RPTV), but the others are. Placing a speaker on the floor or in a corner gives a boost below 200 Hz (mostly below 100 Hz). If you add 3 below 200 and 3+ above 700 or 800 you have a smile-shaped response curve. That's exactly what my rears sound like. I'm sure you get some HF reverberation in most rooms reinforcing the HF output, so saying in-room boost occurs only in the bass may not be accurate.

The proper circuit will be a complete redesign, but I have to hear it first before I publish it.

The schematic is for experimentation, anyway. You may not like it after all.

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  • 4 weeks later...

John, your revised schematic still shows a 16 ohm resistor across the squawker. (Was at terminals 0-2 you changed to 0-1 -- where the numbers are the autoformer terminals.)

I think Al K. was suggesting a single resistor across the autoformer (0-5).

Al, what would be value of that resistor?

Any help would be appreciated as I intend on trying this out this weekend.

Thanks!

TC

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The second schematic is for experimental purposes, but could be used indefinately. The 16 ohm resistor is in parallel with the squawker so the squawker cap is still correct. Both the tweeter and the squawker are to be moved down one tap (to one labeled one number smaller). One step reduces the output 3 dB and doubles the impedance seen by the amp.

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