Need Help with Khorns and F-Mods

[InventiveAudio.com]

Hi,

I'd like to drive my K-horns with a set amp for the highs and use my SS amp for the lows. I was thinking of splitting the signal coming out of my CD player and sending L & R channels to both amps. The set amp would get a full signal while the SS amp would have an F-MOD in line with the RCA cables. This would only allow the lower 100 Hz (100 HZ Low Pass) to the SS amp. I'd run my speaker cables from the set amp top my K-horns. I would also remove the woofer leads from the crossover and then run speaker wire from the SS amp directly to the woofer. I was wondering if this would work. I also have a gain setting on my set amp so I think I could integrate everything together if I have the right crossover point for the woofer.

My other option is to isolate the lows from the crossover and not use the mods. I would send a full signal to the SS amp and then run my speaker cables to the isolated lower range of the K-horn's crossover. I posted a pic of the crossover I had built. I'd like to hear your opinion and could use some advice.

Thanks

[D-MAN]

Direct to woofer will work, of course.

The only draw back to this is getting a good balance between the lows and highs from 2 difference amps and their respective volume controls/preamp.

It is entirely possible that once the "safety" wattage absorbing ability of the woofer is removed from the circuit feeding the mid and tweet, even a relatively low power amp could theoretically toast the far more delicate voice coils without the buffering of the woofer "sucking it up" first. Unless the amp in question is never clipped and is not powerful enough to exceed the ratings of the repective drivers. I would fuse each circuit for a security blanket if I had any doubts. Even an unprotected thump at turn-on could fry an unprotected tweeter.

But there is nothing wrong with your approach that I can see.

DM

[InventiveAudio.com]

So you're saying that I would really have to push my little set amp hard to fry my voice coils. Currently there are no fuses in my crossovers. I opted not to put them in when I had them built. I like to play my music loud sometimes but not where the music distorts. I always like to stay in the sweet spot.

I was wondering if you could explain how the induction coil keeps the top end from getting fried? I guess the crossover diverts frequencies to the woofer and if you removed that circuit from the crossover you would have a problem. But if these circuits were still there and I simply removed the woofer from the crossover how would this put the upper end in jeopardy. My thoughts were that the capacitors would still protect the top end but there would be a reduced load on the set amp (not having to drive the woofer) so it would have more power to run the top end with less distortion. My hope was that I could get better sonic definition overall by splitting the load and also reap the benefits of a simple set amp design. Does any of this make sense or am I having a play date with myself (:?

[JohnA]

Trader,

Your configuration could work with some modifications.

The crossover point for the bass horn to squawker is 380 to 500 Hz depending on the crossover Klipsch put in the speaker. You must use that frequency, typically 400 Hz. A "Y" adapter to a 400 Hz high pass and then to the tube amp and finally to the crossover inputs will cover the highs. From the "Y" to a 400 Hz low pass to the SS amp and finally to the woofer terminals on the woofer doors will cover the lows.

100 Hz F-Mods are too low and would leave a hole in the frequency response from 100 to 400 HZ.

Disconnect the woofer inductors and capacitors so they will not be in the circuit.

D-Man means that even a low power tube amp could fry the tweeter since the woffer in no longer available to absorb excess power.

[D-MAN]

Like I said, I don't see anything wrong with your approach, I was just mentioning some potential issues...

I am a little confused - are you planning to use the ENTIRE crossover (i.e., the woofer band pass coil) in the circuit of the midrange/tweeter) for one amp and the woofer (using a 100Hz bandpass) connected directly to the SS amp? That would work.

If not (that is, you are going to NOT use the full crossover circuit for the mid/tweeter circuit) then there's a problem:

The woofer upper freq band pass is roughly around 375Hz, so ENSURE that you send all of that to the woofer; you will most likely fry the midrange if you send it anything too much below 375Hz. That is, the 100Hz is far too low to be safe.

Typically, the woofer is the first reactive load on the crossover (i.e., it is a series circuit rather than a parallel one), and it eats up the most current, which occurs in the lower frequencies. The "remainder" of the current is then handed off to the upper frequency drivers via the respective band pass being employed. As frequencies go up, the wattage typically goes down as does the ratings of the drivers. The crossover doesn't limit wattage, it limits the frequencies passed.

Very little wattage is required in the top-end. High output transients such as pops, turn-on power spikes, dropping a tone arm, and such will be sent with (potentially) the full output wattage from the amp (worst case) to the high frequency drivers, where before, you had the woofer in the circuit, which effectively "cushioned" them from such harsh treatment. It's the transients that you will have to watch for.

The wattage output of the amp MAY exceed the individual rating in an abnormal transient signal, but probably not in the case of a Klipschorn which will eat up probably (and I am guessing here) about 40 to 75 watts peak or so in the mid/tweeter combination before damage. If your amp is not capable of even approaching half of that, you should be fine. Most likely you will have no problem at all.

DM

[D-MAN]

John, I wonder if a 4 ohm resistor should be placed across the low freq coil to keep the crossover in somewhat of a balance?

Probably would be my guess, but I don't know.

DM

[InventiveAudio.com]

Hi,

Lots of food for thought. All good stuff. I guess I should have checked the crossover point on my midrange driver before posting. 100Hz is subwoofer territory. Anyway, all my research seems to disparish FMODS for high-end audio. They seem to be a quick and cheap solution for car audio. I guess they would work well for a sub too since a sub is often reproducing a lot of distortion anyway.

I have to say that I was scratching my head on how an FMOD could replace my hand wound induction coil. If it's true about FMODS then my only reasonable soution would be to modify my current crossover so I could bi-amp my K-horns. In my first post I posted a pic of the crossover I had built. I would appreciate it if anyone could hold my hand and let me know how to re-wire for biamping.

Thanks again. If I ever get this too work I will report back my findings. I have 80 feet of speaker wire in the wings (:

[Al Klappenberger]

Trader,

You must NOT allow full range to the small SET amps running the highs. The lows will overload it. You need an active crossover at 400 Hz BEFORE the two amps. 400 and down goes the the SS amp. 400 and up goes to the small amp.

If that is one of my crossovers desings you can run the high frequency amp directly in the junction of the 39 uF, 2.2 us and .3 mH inductor. Leave the woofer port OPEN (no load). Search for a post I made some time ago describing in deatil how to bi-amp my network.

BTW: the picture shows the .2 mHy coil jamed under the horn. If that's a wooden horn it's OK, but if it's metal, you need to move it away from the horn!

Al K.

[InventiveAudio.com]

Thanks Al. I'll look for the post you mentioned. I wish the Klipsch search engine worked like it was suppose to. There have been tons of posts on biamping and very little is being returned via the search engine. Yes the crossover was based on your design and also the horn you see in the pic is fiberglass.

Thanks

[Al Klappenberger]

Trader,

The picture shows where to connect the high frequency amp.

Note the woofer connections are not used.

Al K.

[JohnA]

I have used F-MODS in my system and I disagree that they are a cheap, car only solution. Since they are passive, they cannot inject any noise and precious little distortion into the signal. I believe you will be satisfied with the F-MODS, if not with the sound of Bi-amped K-horns. The flaw of F-MODS would be the actual crossover frequency will change a little with each power amp's input impedance. Harrison Labs told me it would be close enough if the input impedance was over 10k.

K-horns are difficult to bi-amp successfully. Most on the Forums that have tried it gave up.

[InventiveAudio.com]

Al Thanks for taking the time to post the pic. I'm still a little confused. Are you suggesting that I use an FMOD or some active crossover between source and each amp. ie. SS amp would be only see the part of the audio signal that is 400 and below while my set amp would only see frequencies that are 400 and above. Ok. But if this is the case and I use crossover for each amp and run my SS amp directly to my Woofer why would I need to modify my crossover or wire it differently. If I'm taking out the load that can hurt my set amp then why fusss with the crossover?

Originally I was thinking of seperating your crossover design so that the sub 400 Hz frequencies are seperate from the tweeter and midrange wiring. However, I'm not an electronics person so that would be a little troublesome. I do have a pair of stock Forte II's that I bought like this. I've never opened them up to see how it was done or bimaped this speaker. Then again I've only had it for a few weeks. It makes a great center channel. Replacing a Heresy speaker.

John: Thanks for the first hand experience on FMODS. I have a pair sitting in my drawer but I've nver played with them because they are for a sub I was building but then decided to do things differently.

Thanks All

[Al Klappenberger]

Trader,

The main thing is to keep the low frequencys off the SET amp. If you don't, there's no point in bi-amping. Most of the energy is in the low frequencys. That's why the big SS amp is used for the lows. You can run the Khorn woofer full range since it dies above about 450 Hz and the SS amp doesn't care. Using a true crossover ahead of the two amps simply makes a "proper" and more gracefull cross. The overlap between the drivers is controlled. Remember to try both polarity connections to the woofer. One way my generate a glitch at the 400 Hz crossover. There is really no way to know which polarity is correct ahead of time.

Connecting the high amp to my netwook as the picture show totally removes the 400 Hz crossover from the circuit without cutting any wires or modifying anything. It will become a true constant impedance "multiplexer" at 6000 Hz and present a very good 8 Ohm load to the SET amp.

Al K.

[Ho_Leung]

Khorns should be xover at apr 400 htz .. Fmods have a 500 low pass filter. I am using a Sonic Impact T-amp 10 watts SS amp - $39.00 with the 500 htz Harrison Fmod active filter with very good results, using my Korneff 1.8 watt amp. The bass is much inhansed. Actually with full battery charge, I have to turn down the bass. The T-amp has a gain switch. The reviews are impressive.