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Mystery Capacitor and the Tangent RS4 Crossover

 I have a pair of Tangent RS4s whose crossovers I am currently in the midst of trying to rebuild (Early 80s British 2 way speaker). I used to power them in the 80s with an Adcom GFA1 amp (200 watts/channel which I understand both Bob Carver and Nelson Pass had a hand in designing back when Adcom was based in New Brunswick, NJ, my old home town). Apparently, either time or I did a fair amount of damage to those caps (probably both) and some are hard to id, particularly one that looks like a piece of pink sugar coated candy with green, white and violet stripes? I'm working on a schematic for this crossover so I can get some expert opinion on the project and maybe id the capacitor value by process of elimination. But I am new to this and am learning as I go. If there is anyone out there interested or who could lend some assistance I would be happy to share/learn.
I set out to simply replace the caps but am beginning to question the design and wonder if it could not be improved upon. For starters it seems to have a lot of caps for a two way crossover (8 in five styles), plus 2 resistors and 3 coils. Modern designs I have looked at typically have two or three caps for 2 two way crossover.The drivers and cabinets are in good shape and I have always liked this speaker which sports a 200mm Audax bextrene cone woofer and a 19mm KEF t27 dome tweeter, housed in a nicely crafted 42.5 liter walnut veneered mdf cabinet, all of which has held up amazingly well over the yearsI'll try to figure out how to post pictures to this site if anyone is kind enough to offer assistence.
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timlub
2,041 posts
 
@imhififan   ..... Quick question for you.  I don't know this tweeter, so I have to ask. Have you seen the impedance curves of this tweeter?  Are you considering the inductor to ground? Are you considering the 3 ohm resistor in series?  
Not being  familiar with the impedance curves of this tweeter, these questions need to be asked. 
imhififan's avatar
imhififan
2,210 posts
 
@timlub
The OP ask why so many caps, isn’t those four caps equal to 3uf in value?
I mean the four caps on the left of 0.35mH inductor in his schematic!
timlub
2,041 posts
 
@imhififan            Your basic advice is sound... It would put you in the league.... 2.7, but if the original caps are electrolytic and they change to a quality film, the ESR of 3 capacitors alone can be a difference of up to another ohm or more. ESR is measured at different frequencies, so you would need to take that into consideration also. If the op was willing to do some experimenting, its worth a try, but to just replace all of that with a 3 mic cap would not be recommended.
op @bruce19 The 2.25 mfd, 1 mfd and .47mfd add to each other to combine values, the 10 mfd after those then decreases that value.
imhififan's avatar
imhififan
2,210 posts
 
Correct me if I’m wrong,
2.25mfd, 1mfd parallel = 3.25mfd
3.25mdf, 10mfd in series = 2.453mfd
2.453mfd, 0.47mfd parallel = 2.923mfd
3mfd should be close enough, and I guess the 0.47mfd is not an electrolytic and has low ESR.

timlub
2,041 posts
 
3.72, 10mfd parallel = 2.711

But beyond that,  I have to believe that they would not have gone to that expense to do it that way, a small film cap would be cost effective vs all of that mish mash.  My head says that overall you are correct, but I'd want to run real measurements and see why they ran the .47 the way they did vs just putting it straight in parallel with the other parts. When building I tend to verify everything in measurements.  
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