Upgrading the Forte II

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mwoods

New Member
Creating this new thread so that you can follow along with my progress, just has SET12 has done with the Fortes. I've decided to simply upgrade the Forte II's crossover components rather than re-evaluate the crossover circuit itself. This is due to reviewing Al K's work on the Fortes. If I may quote his findings regarding the Forte's stock xovers:

"Here are the plots of efficiency, frequency response and impedance of the stock speaker. The frequency response is very impressive. It goes from below 30 Hz to 20Khz with a nominal sensitivity of 95 db SPL at 1 meter for 2.83V input. That would be 1W into 8 Ohms except that it is NOT 8 Ohms! The impedance is all over the place because of the usual cut-every-corner you can "balancing network" Klipsch put in all the heritage speakers! The impedance comes to a peak of 106 Ohms at 2150 Hz. At 950 Hz it looks to the amp like a 7.19 Ohm resistor in series with a 3 mHy inductor. At 5150 Hz it resembles 5.09 Ohms in series with a 1.68 uFd capacitor. Then at 14.5 Khz it's more like 9.28 Ohms in series with 2.59 uFd. This is all the result of the network. The individual drivers provide much more reasonable loads."

The stock freq response is very smooth and actually despite the above sounding kind of dramatic, it seems a very benign impedance plot as well! Later we see that Al K's network is "nearly completely resistive between 4.5 and 6 ohms" That's great, but it would've been nice to see all these plots on the same scale. Ugh! Anyway moving on...

So I dove in and purchased 10pcs of 1uf Ampohm Mylar PIO's and 2pcs of the .47uf, all in matched pairs. I plan to buy the 8ga North Creek woofer choke and figure some lytic for the woofer as well. I'm going to build this as an outboard network with separate sections so that it can be bi- or tri-amped. The tweet diaphragms and auto xformer will be replaced toward the end.
 
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Do the midrange diaphragms too. IMO, it was a more noticeable upgrade than the tweeter diaphragms on my Forte Is.
 
I will be keeping an eye on this thread. I have caps from crites on the way and I am just trying to decide on what to do with the rest. Brian
 
kappa7krazy said:
I will be keeping an eye on this thread. I have caps from crites on the way and I am just trying to decide on what to do with the rest. Brian
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You might as well pull the trigger and go all out. :thmbsp: Itll set you back about $140 for the mids and tweets....very well worth the price of admission.
 
You are correct sir. I will be getting the replacement transformers but I not sure which way to go for the woofer inductor or the resistor. I hope to get all my parts soon and not be too far behind mwoods.
 
I've attached the Forte II schematic that I've found elsewhere on AK. I think there may be an error in it though, as it shows a short between the + and - input phases. See where the wires make a full intersection node? (looks like a "+") Shouldn't the pos phase to the squawker only connect to the pos terminal, and not continue on and tie to the neg as well? That would make a lot more sense to me! :scratch2:
 

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mwoods said:
Creating this new thread so that you can follow along with my progress, just has SET12 has done with the Fortes. I've decided to simply upgrade the Forte II's crossover components rather than re-evaluate the crossover circuit itself. This is due to reviewing Al K's work on the Fortes. If I may quote his findings regarding the Forte's stock xovers:

"Here are the plots of efficiency, frequency response and impedance of the stock speaker. The frequency response is very impressive. It goes from below 30 Hz to 20Khz with a nominal sensitivity of 95 db SPL at 1 meter for 2.83V input. That would be 1W into 8 Ohms except that it is NOT 8 Ohms! The impedance is all over the place because of the usual cut-every-corner you can "balancing network" Klipsch put in all the heritage speakers! The impedance comes to a peak of 106 Ohms at 2150 Hz. At 950 Hz it looks to the amp like a 7.19 Ohm resistor in series with a 3 mHy inductor. At 5150 Hz it resembles 5.09 Ohms in series with a 1.68 uFd capacitor. Then at 14.5 Khz it's more like 9.28 Ohms in series with 2.59 uFd. This is all the result of the network. The individual drivers provide much more reasonable loads."

The stock freq response is very smooth and actually despite the above sounding kind of dramatic, it seems a very benign impedance plot as well! Later we see that Al K's network is "nearly completely resistive between 4.5 and 6 ohms" That's great, but it would've been nice to see all these plots on the same scale. Ugh! Anyway moving on...

So I dove in and purchased 10pcs of 1uf Ampohm Mylar PIO's and 2pcs of the .47uf, all in matched pairs. I plan to buy the 8ga North Creek woofer choke and figure some lytic for the woofer as well. I'm going to build this as an outboard network with separate sections so that it can be bi- or tri-amped. The tweet diaphragms and auto xformer will be replaced toward the end.
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mwoods,

First off, congratulations on the start of your :music: journey :thmbsp:

I think your going to find it will be very interesting and enlightening at the control you will have over your system with just a change of a cap,resistor or an inductor.

I would like to also point out that just about all Klipsch networks especially the Heritage line are pretty far off as far as being a constant impedance according to ALK's measurements. Yet many of the networks continue to sound ok with all the variations in the stock networks.

So essentially we are in the same boat with the Forte and Forte II stock networks.

I'm a big fan of ALK's work, yet musically I suspect the stock networks with some of the highest component subjective qualities may very well hold its own subjectively to the more electrically correct ALK networks that use very high quality parts but are subjectively not quite as good sounding. And would be very costly with the parts count and higher values used in them.

I essentially liked the sound of the Forte with my tube monoblocks. So I thought I would pursue better performance with better passive parts choices. And everything has been quite audible in the networks right down to the 40 ohm resistor used. And includes the replacement electrolytic's with good quality Polypropylene which helps with a greater sense of size and sense of space not to mention laterally placed bass notes which in the end can yield virtually a wall or wave of bass virtually floor to ceiling. Of course the North Creek inductors are a large part of this to. But it just means no stone should be left unturned.

What I didn't realize is just how much of a transformation it would be, Which has been as much as any other component swapped into my system.

Its like soaring on eagles wings.

Cheers

SET12
 
Ampohm caps are in - These things are HUGE! I think the xover is going to have to be at least 2ft by 2ft in size unless some parts are stacked. I have also ordered the following -

2x of 100uf Mundorf MLytic Bipolars
2x of 10uf Mundorf MKP
2x of 39R Duelund standard resistors
20ft of 10ga Belden 5T00UP
20ft of 14ga Canare 4S11 (star quad)

Don't be surprised Set12, if my xovers end up looking a lot like yours. I'm going to order the same distribution blocks and use velcro as well.

I am finishing the 211 amp before digging into the xovers, but it's already 99% complete. Just need some finishing details. I will post the schematic once it's up and running!
 
mwoods said:
Ampohm caps are in - These things are HUGE! I think the xover is going to have to be at least 2ft by 2ft in size unless some parts are stacked. I have also ordered the following -

Don't be surprised Set12, if my xovers end up looking a lot like yours. I'm going to order the same distribution blocks and use velcro as well.
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Yeah, I have been considering some Ampohms myself, I want to hear them in my amps first and I have to a lot of rearranging to get them to fit there, I know I'll have order quick if I decide to give them a try in my networks. The Fortes right now are just awesome as they are and I have people from my local club coming to hear them April 17th so I hate to mess with what I have right now.

But Thats the nice ting about the outboard networks with the terminal blocks in that you can swap parts in just minutes.

And yeah those caps are big, I think I can just fit them on my network platforms if I stack them, So I'd recommend a crossover platform as large as the top of the Forte, mine are just slightly smaller.

I look forward to your 211 schematic.

SET12
 
That extra section bridging + and - is extraneous. The series capacitor on the squawker should only connect to + on one end and the inductor on the other
 
I wouldnt reccomend using canare star quad, or any quad cable for that matter on your speakers unless you do some long listening and decide you want that sound. that cable has a very distinct sound...
 
badman said:
That extra section bridging + and - is extraneous. The series capacitor on the squawker should only connect to + on one end and the inductor on the other
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I think you are maybe a little confused here, So I pulled the schematic and it looks as though I think your thinking the squawker is connected to an Inductor which it is not.

Its an Auto-transformer which is a transformer with a single winding. Autotransformers are capable of stepping up voltages as well as stepping down voltages. In this case it is step down.

The advantage of an Auto-transformer is that it maintains an amplifiers control of the driver better by not having any loss of damping factor,something that L-Pads do have a loss of.

SET12
 
soundguy said:
I wouldnt reccomend using canare star quad, or any quad cable for that matter on your speakers unless you do some long listening and decide you want that sound. that cable has a very distinct sound...
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Thanks for the tip. I am however, planning to take this cable apart and use the individual cables in the mid and high sections of the crossover. I am using the 10ga cable to wire up the bass portion.
 
Just need to make some notes on my listening impressions of my current setup before delving into xover changes. Also FYI, so that everyone knows what the evaluation is based on:

Sources: Slimdevices Transporter, Audio Note CDT Two
DAC: Audial AYA 2.0c (TDA1541a-based DAC from Serbia designer Pedja Rodgic)
Preamp (volume control): Bent Audio TVC with silver-wound S&B TX102
Amp: NOSValves modded Dynaco ST-70 running KT-77 output tubes
Cables: Audio Art IC-1 interconnect and SC-5 speaker, Blue Jeans BNC-BNC digital and stereo XLR cables.

I moved my listening position forward about 3ft and found that this improved things; mostly bass, but also soundstage, imaging and tonal balance seem better. This may have been partly due to swapping in a new BNC-BNC for RCA-BNC from the Transporter to DAC.

All-in-all it's a very enjoyable system. I can't believe how well these things image. During the day I will be listening at a level of 75db to low 80's. The loudest that I go is about 95 for awhile. I'm getting great dynamics and it's fun to listen to. It does tend to get strained after about 85db though and I believe that may be due to the amp. When I had the 211 prototype running, I could crank it up to that level without hearing any problems, just a huge powerful room filling sound.

The main thing that I am expecting from the xover upgrades is more detail and finesse, able to see into the recording more.
 
The 211 amp is finished!

No excuses now! I'll have to get to work on those crossovers! :banana:

SET12 I have also been posting about this amp to the boatanchors Yahoo group, not sure if you are a member. I'll attach a schematic of the amp here anyway. It could probably use another LC on the 1210V supply, but I'm fresh out of 3000V caps!

Here's a link to the project images as well: http://www.flickr.com/photos/8792924@N06/sets/72157621552320226/

On a less happy note; alas, this is not my own amp as I was commissioned to build it. Hopefully I am able to keep it for a few months while upgrading the Forte's however.

*Note that the RC coupling is at about 30hz. This was intentional.
 

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mwoods said:
No excuses now! I'll have to get to work on those crossovers! :banana:

SET12 I have also been posting about this amp to the boatanchors Yahoo group, not sure if you are a member. I'll attach a schematic of the amp here anyway. It could probably use another LC on the 1210V supply, but I'm fresh out of 3000V caps!

Here's a link to the project images as well: http://www.flickr.com/photos/8792924@N06/sets/72157621552320226/

On a less happy note; alas, this is not my own amp as I was commissioned to build it. Hopefully I am able to keep it for a few months while upgrading the Forte's however.

*Note that the RC coupling is at about 30hz. This was intentional.
Click to expand...

Thanks for the schematics!

I tried getting on that site once before but they seem to want me to sign up and get a password.

I did see your photo's and your construction is First Class!

Ideally I learned in Electronics school you would like a cap that is rated a 1/3 more than your actual working voltage as this extends cap life by 50% running a cap at half its rated voltage decreases life by 50%.

I noticed your supply DCR's are fairly high by my standards, but don't mind me I'm not much on the Classical Radiotron Design Manual for doing things. You should hear an amplifier where they are low! As mine are just 3.5 ohms. When they are low, dynamics improve, width, depth height and the overall presentation becomes even more involving. Its about moving energy instead of restricting it. I do use a method of isolation that allows for great speed and transparency as well though.

Very,very nice construction on your amps :thmbsp:

BTW the 211 is one of my favorite all time tubes I have ever experienced listening to!

SET12
 
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