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Voltage Ratings for Midrange and Tweeter Caps in Forte I Crossover


MCM_Fan

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Three weeks ago I acquired a lovely pair of Klipsch Forte speakers (date of manufacture = May, 1988).  These are the first generation model with the crossovers on PCBs attached to a rectangular terminal cup.  Both tweeters were fried (open circuit).  So, I ordered, promptly received and installed a pair of the Crites titanium diaphragms.

 

As my next upgrade, I'd like to replace the crossover caps.  For convenience, here is the schematic diagram for the Forte crossovers:

 

post-30216-0-26780000-1390166767.jpg

 

I had planned on using the Russian military surplus K73-16 capacitors in the 100V rating for the 1.0uF midrange and 1.5uF tweeter caps.  I would like to use these caps for the following three reasons:

 

  1. They are inexpensive (all six caps delivered to my door will cost a total of $12.90)
  2. They are small enough to fit on the crossover PCB without difficulty or modification
  3. They are highly regarded

 

The original caps in these positions have a voltage rating of 250V.  Is the 100V rating of the K73-16 caps sufficient for these locations?  I have read conflicting opinions in this, and other forums, with no clear consensus.  For example, the original Heresy crossover, which is very similar, had 100V rated caps in these locations.  Of course the Sonicaps that Crites sells are rated at 200V (and also much larger and more expensive).  Intuitively, it seems like 100V should be more than enough for these caps, given the maximum input power rating of 100W for the speakers.

 

So, will 100V caps be sufficient in these locations, or should I move up to something with a higher voltage rating?  They also come in 160V and 250V versions, but grow considerably in size as the voltage rating increases, making installing them a bit more challenging.  I have used the Sonicaps in several other recaps I've done in the past, but it looks like their prices have doubled since the last time I used them.  Jantzen Standard Z-Caps are another option I considered.  Like the Russian K73-16 caps, they are inexpensive and small enough to fit the crossover PCBs without modification, but aren't quite as highly regarded as the K73-16s.

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Being the impatient sort, I went ahead and recapped one of the Forte Crossovers with the 100V Russian K73-16 military surplus caps (stock on the left, recapped on the right):

 

Forte-Crossovers-Before-and-After.jpg

 

I also moved the Fortes downstairs to my primary listening area.  They will get much more use there and I want to give the caps and titanium diaphragms a chance to settle in for a couple weeks before I do a critical comparison of the stock and recapped speakers.  I'll report back after I've done so.

 

In the meantime, I'm still interested in the original question.  I don't play my stereo at live music levels, and my listening space is on the small side of medium.

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3 minutes ago, Westcoastdrums said:

Crazy.  Hope it sounds as good as it looks for you. 

 

Just doing some casual listening of some familiar albums (currently spinning a US first pressing of Steely Dan - Aja) and sounding pretty good so far.  This is the first time I've heard the Fortes.  I had some KG4s years ago, but have been running JBLs (gasp) and KEFs lately.

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5 minutes ago, Westcoastdrums said:

I have owned A LOT of Klipsch Speakers, new and vintage. I currently own GASP JBL, so I get it.   Different flavors for different days of the week.  Fortes are Def nice, but the Chorus... Next step up. 

 

The Fortes basically fell into my lap.  The price was low due to two fried tweeters and one woofer not working.  I couldn't say no.  I think I'd need a bigger space to do justice to a pair of Chorus.  Even the Fortes are about as big as I want to go in my current space.  I've been running a pair of restored JBL 4301B Control Monitors - these were the babies of the blue front professional series designed by Greg Timbers.  They were intended to be control room monitors in smaller recording studios.  So, a good match for my smallish listening area.

 

I recently picked up a 300WPC Bryston amp and am now lusting after a pair of Magnepans.  I've always wanted a pair, but have never had the right combination of space and power for them.  Oh well, it never ends.  Time to start looking for a new house with a bigger listening area...

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4 minutes ago, Westcoastdrums said:

Deal it is then. Yeah, Maggie's need a lot of room to breath. I heard a great pair ONCE with a vintage Levinson amp and some high end DAC. Nearfield listening in yjr middle of the room. Very impressive.   Wouldn't be for me, but I could definitely appreciate them. Nice JBL monitors also. 

 

I'm an opportunistic buyer (aka: cheapskate).  I may end up selling the Bryston and using the proceeds to get either a tube amp for the Fortes or a Rega Elex-R for the JBLs.  The Bryston is more amp than I currently need.  None of my current speakers need that kind of power, and my listening space isn't big enough to use it to it's full capability.

 

Yes, the 4301B Control Monitors are little gems.  Greg Timbers knew how to voice a speaker.  I like the 4301Bs much better than the slightly older and bigger L36 Decades they replaced.

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On 9/9/2021 at 9:26 PM, MCM_Fan said:

Being the impatient sort, I went ahead and recapped one of the Forte Crossovers with the 100V Russian K73-16 military surplus caps (stock on the left, recapped on the right):

 

Forte-Crossovers-Before-and-After.jpg

 

I also moved the Fortes downstairs to my primary listening area.  They will get much more use there and I want to give the caps and titanium diaphragms a chance to settle in for a couple weeks before I do a critical comparison of the stock and recapped speakers.  I'll report back after I've done so.

 

In the meantime, I'm still interested in the original question.  I don't play my stereo at live music levels, and my listening space is on the small side of medium.

 

Doesnt look like you got any answers to your questions, heres some suggestions based on my experience with recapping fortes, chorus, a few KGs & many other speakers.  

 

Im not familiar with the russian caps so cant comment on them but the original caps voltage rating is there for a reason, these speakers have 100watt RMS but can handle a lot more peak power so the voltage rating of the caps isnt really based on RMS, although if you never give them high power the 100v are probably OK,  i would stick with the factory ratings for values & voltage to be safe. 

 

As for size, many other mid grade polypropylene caps arent as big as sonicaps & 250v will fit on the board with little to no modification required.  i have used the dayton 1% before but recently have used ERSE suggested by Bob Crites as a very good budget cap that he said tests as good or better than the daytons & other mid grade caps.  they also uses ERSE for all other parts of their xovers & for the electrolytics in the woofer section.  if price is a concern they are priced better than any of the mid grade caps, can get all the caps for fortes or chorus etc for about the same price as the ones you have & that is shipped.  im no expert & dont have the expensive test equipment to compare them but i trust what bob stated & i know what i hear with them, they sound excellent in all the speakers ive done & definitely fixed bad caps in my chorus 2 that sounded like a towel was over the front of the speakers due to the caps going bad or falling out of spec after 25+ years. 

 

& just to reiterate on the "time to settle in" thing, Mr Crites & many others say caps & small diaphram tweets dont need any break in time, your ears may adjust (break in) to the new sound of TI tweets but its not the tweeter that changed & definitely not the capacitor that changed. 

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