Question about Forte crossover mod

[RobBeam]

Bought a second pair of Fortes from someone here a year or two ago and they

had modified the crossover by changing three caps ... I think. Can't remember

the name of the person I bought from so if anyone (including him) can tell me what

the intended affect of changing these is supposed to be I'd appreciate it. Attached

is a pic of the mod'ed crossover.

Thanks for any help.

[Deang]

Need a shot of the whole board.

[RobBeam]

Here's the whole pic ... think I might have already decided that I like the stock x-over

better but still curious.

[RobBeam]

And what's up with this board?

Knew that these weren't a matched pair but this is big different than

the other three that I have.

[leok]

I've reworked the crossover for the Forte-II and it is similar. The 3 crossovers appear to be an older vintage. The components on the different one appear closer to what I've seen on Forte-II (and Chorus-II for that matter). The cap changes are the Solen metalized polypropylene film to replace what were probably mylar. For the trouble, I would have (and have) used even better substitutions: Hovland polyprop. film/foil. On my Chorus-II I went so far as using Jensen foil/paper-in-oil for the mid.

I don't know why stock mylars would sound better. Dean doesn't like the Solens much (that might be understatement), but I like them ok. I would expect them to be better than mylar .. smoother, more natural sound and slightly better detail.

leok

[Deang]

I need some clarification here on what's going on.

You have two sets of Fortes.

One set came with modded boards, and what I'm picking up here is that this particular "pair" weren't really a pair at all, but two singles from different years being used as a "pair"?

If this is true, have you determined the other differences between the two? If the crossovers are different, are the drivers different as well? What about the lenses, are one set of lenses polymer resin and the other metal?

If you are in fact using two "different" speakers in a pair, and are doing direct comparison to the other unmodified, matching pair -- your preference of the unmodded pair might not have anything to do with the crossovers.

If this is what you have, then you should be able to see the problem. These are two very different speakers. Shower us with details, maybe I'm not clear on what's going on here.

http://www.klipsch.com/product/product.aspx?cid=113

http://www.klipsch.com/product/product.aspx?cid=117

[RobBeam]

Is lense another term for the actual horn part of the driver? Regardless, all the bits

and pieces are the same except for the crossovers. This is not something that I'm particularly

worked up about ... just curious. I've upgraded the various parts of my system to the point

that I'm hearing some of the differences they talk about in the magazines so curious about

the potential tweaks available.

Here are the particulars though:

I have one set of Fortes that I posted pics of a few weeks back ... last pair of Ebony produced,

signed by PKW ... that I've owned since I sold klipsch part time back in college. These are stock.

I have a pair that I bought a couple of years ago that are very obviously not the same grain pattern

and do not sequential serials so they are mismatched although all the components except for the crossovers

are the same. He told me before I bought them they weren't matched so this wasn't a surprise ... he also

told me he'd modded the crossovers which is why I opened them up to see how much different they were than

stock since I'd already had my ebony's open while refinishing them.

I posted three pics but they were only of the two crossovers from the mismatched pairs. The first two were

of the same crossover .. the second being a picture of the whole crossover in response to DeanG's post.

I haven't spent a lot of time a-b'ing the two sets but spent some time with one of my stock speaks on one

channel and one of the modded ones on the other (not ideal but I don't really have the time to get too complicated

right now). In my very limited, very unscientific testing the stock speaker seemed to have a little more detail.

I realize there could be number of other factors in the different histories of these speakers that could impact

their sound and I might try putting one of the modded crossovers in the ebony klipsch to see what that sounds like

in the next week or two but I just didn't have time to take everything apart and put them back together again right now.

Before I start dedicating some time to spend swapping out caps and doing whatever mods might be available wanted

an idea the intended results of some of these mods are and also get educated about the science behind it. Getting

additional detail is always a good thing but if a certain mod only provides more warmth or smoothness I wouldn't really

be interested because my current combination of source/pre/cables/amp is already incredibly warm and smooth. Can someone

explain the science behind why a different cap creates a specific result or is it more a subjective thing because the science is a little to subtle to pin down the exact explanation? Do you really just need to get in and experiment and see what sounds better to your particular ear?

[leok]

In an AC application (such as a speaker crossover) polarity of the voltage on a capacitor switches as often as the signal crosses 0 Volts. In audio this is happening from a few tens of times per second to over 40,000 times per second.

every time the capacitor switches polarity, a small amount of energy is lost to re-polarizing the dielectric material (insulator) that is between the changed "plates" (foil or metalization in a modern cap). It is expensive to make a cap that minimizes this repolarization energy, and most applications don't care. But with audio, repolarization energy results in a kind of crossover distortion. That's why the big deal over caps and the materials used in them.

leok

[Deang]

I didn't know this. At least now I now why I emptied my bank account on all those parts.

[RobBeam]

Thanks from me as well leok.

That's exactly the kind of information I was looking for. As I try to progress

further along the audiophile curve maybe you can keep an eye out for me in my

quest for knowledge.

[cn1790]

Leok,

I'm curious as to what caps you used and the effect it had. I have the Forte'speakers which have different crossover points (HF is 6000Hz vs 7000Hz and MF is 700Hz vs 650Hz). Did your changing out the caps make much difference? If so, how might I figure out what caps to use?

Thanks,

----------------

On 9/7/2003 11:18:00 AM leok wrote:

I've reworked the crossover for the Forte-II and it is similar. The 3 crossovers appear to be an older vintage. The components on the different one appear closer to what I've seen on Forte-II (and Chorus-II for that matter). The cap changes are the Solen metalized polypropylene film to replace what were probably mylar. For the trouble, I would have (and have) used even better substitutions: Hovland polyprop. film/foil. On my Chorus-II I went so far as using Jensen foil/paper-in-oil for the mid.

I don't know why stock mylars would sound better. Dean doesn't like the Solens much (that might be understatement), but I like them ok. I would expect them to be better than mylar .. smoother, more natural sound and slightly better detail.

leok

----------------

[Strabo]

Bump.

cn1790, you might want to e-mail Leo directly in case he misses this thread.

[Deang]

This is one of the modded Forte II's I did not all that long ago for a customer.

When working with PCBs, your parts choice will at times be limited by the amount of room you have on the board to work with. This board has the very high quality (and very expensive) AudioCap PPT Thetas. They as sound as clean/ good or better than the Hovlands, yet sized fatter instead of longer -- which makes them workable on the Forte and Chorus PCBs. Even still, I had to drill two holes and scrape down to the foil to create two new contact points to accomodate the larger capacitors. I suppose if I hadn't of changed out the inductor -- I might have been able to get the caps in without having to jumper, but don't know for sure.

Generally speaking, the higher the quality the capacitors are, the larger they become as compared to the Mylars (polyester) for any given value. Naturally, the bigger the caps get -- the more challenging it is to negotiate them onto the boards.

Cost also becomes a determining factor. Good parts are expensive, and the more you need to get the job done -- the more it costs. Some choices are just cost prohibitive -- unless you are willing to pay of course.

For example: To do Forte II's with some good film and foils like the PPT theta would cost a little over $100. There are four 2uF, and two 1.5uF caps total. There is no 1.5uF Theta, so you have buy two 1uF and two .47uF caps and parallel them to get the 1.5uF value. If you don't change the inductor, there might be room without too much trouble. If you change the iron core out and replace it with an air core, you have to move/replace the resistor, and jumper.

Based on what I saw ealier in this thread, it looks like the Forte uses two 1.5uF and one 2uF caps each. So you would need two 2uF, four 1uF, and four .47 uF caps. Like the Forte II, you would have to parallel the 1uF and .47uF values to get the 1.5uF values. Basically, you would make a capacitor bank -- stacking and gluing them on top of each other, and then banding them together with a tie strap.

A good compromise is simply to replace the three Mylars with some high quality metallized polypropylene types like the Auricap or the Kimbers. The film isn't as thick, so the caps are smaller. They don't spec out as well as something like the Theta -- but they sound very good. They also both come in the 1.5uF values, and so these caps would basically just "drop in". I receive OEM pricing on the Auricap, and if this interests you let me know. Looks like this option would run you $55, and save you a lot of work too.

[Deang]

Found the picture with the three stock caps in the foreground.