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Old 6th February 2013, 10:30 PM   #1
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Default Capacitor for Fostex T90A

Hi all,
The flat pack Fostex 208E Sigma enclosure will be arriving in the next week or so. I've decided on the T90A tweeter, and need to buy a capacitor to use for a passive crossover.

If you have the same F208E+T90A set up, what level of microfarad have you found suits your taste? And what brand of capacitor do you prefer? I read on one thread that the Fostex capacitors give an excellent sound quality (better than Mundorf). Any other recommendations?

I'm considering buying the Fostex R80B attenuator, it doesn't cost any more than other quality products. If you have any other suggestions or tips, please let me know.

Cheers.

Last edited by adejacko; 6th February 2013 at 11:05 PM. Reason: Info was wrong
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Old 6th February 2013, 10:41 PM   #2
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....And to make things even more confusing, the plans the of 208 enclosure show a diagram of the T900A without attenuator.


http://www.madisound.com/pdf/fostexc...ez_enclrev.pdf


Why?

Last edited by adejacko; 6th February 2013 at 10:43 PM. Reason: to add link
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Old 6th February 2013, 10:49 PM   #3
sippy is offline sippy  United Kingdom
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Buy cheaper caps in values above and below the ones in the Fostex paper, buy resistors and attenuators and play.
Learning is part of DIY and good fun
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Old 6th February 2013, 10:53 PM   #4
sippy is offline sippy  United Kingdom
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Resistors/ attenuator is to bring the tweeter output down to 'desired' level.
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Old 6th February 2013, 11:16 PM   #5
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The SPL is the 106dB for both T90A and T900A.
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Old 6th February 2013, 11:20 PM   #6
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I don't want to damage the tweeter. from what I've seen online, people go for 1uF or 1.5uF. Am I right in believing that the 1.5 will allow lowers frequencies to the tweeter than the 1uF?
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Old 7th February 2013, 12:38 AM   #7
Tea-Bag is offline Tea-Bag  United States
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I use a T90A-EX and use a 1uf cap with .25uh inductor for a 12db 2nd order.
The T90 will be too bright without a attenuator and the Fostex one's are good units.
Madisound sells the GE .33uf caps just for the reason sippy mentions, to parallel a bunch until you get the frequency you want.

You can use a 1st order crossover calculator online to determine what the frequency cut-off range. I would listen put start somewhere above 6k.
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Old 7th February 2013, 12:57 AM   #8
adamt is offline adamt  Australia
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I have these drivers in a similar horn. I like a 0.68uF cap, first order, in phase, but the sound is pretty laid back. You might like some more bite, so anything up to 1.5uF first order would be fine. I have tried the following caps - mundorf supreme, GE, Auricaps, Claritycap, Janzen, Jupiter and Obbligatto (copper and gold). To me, Obbligatto gold is the best as it has the lowest spatial distortion. The mundorf for example has a wide open sound, but does emphasize sibilants which drives me crazy. Many of the others do to a lesser degree, before you get to the Claritycap which is just too warm and rolled off in the top end. The good thing is they are relatively cheap, so you can give a few a go.
I tried second order crossovers, which are fine, but I found that i gravitated back to a first order as my sound preference. Not sure why.
The thing that I was most confused about was the difference each cap value made to the upper mid range (rather than the high frequencies). Higher values give you more HF, but they also round out the mid range somewhat, helpping the 208 driver where it is deficient.
The biggest issue to tackle is the 208 rising response in the 4000 hz range which I have found difficult to tame. It is right in the range that can emphasize female sibilants. This is where using the Obbligatto cap in phase without any other taming of the peak can work.
Have fun!
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Old 7th February 2013, 01:13 AM   #9
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I ran the same setup years ago with a different cabinet. I started out with a .47uF then .33 then 1.0, but stayed with the .47uF. What happened was I kept turning the attenuator down to a point where the tweeter was not even on. Ultimately, I preferred 208e Sigma without the T90a. As a side note, a friend loaned me a pair of T900a, and while better overall (less intrusive) was not that great of a difference, in fact the T90a sounded more dynamic. I eventually, got a pair of the T500a in a trade with the transformer attenuators which sounded the best; less of the I'm hearing a separate super-tweeter effect.
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Old 7th February 2013, 01:20 AM   #10
sippy is offline sippy  United Kingdom
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Quote:
Originally Posted by Tea-Bag View Post
I use a T90A-EX and use a 1uf cap with .25uh inductor for a 12db 2nd order.
The T90 will be too bright without a attenuator and the Fostex one's are good units.
Madisound sells the GE .33uf caps just for the reason sippy mentions, to parallel a bunch until you get the frequency you want.

You can use a 1st order crossover calculator online to determine what the frequency cut-off range. I would listen put start somewhere above 6k.
And once you get the crossing right, Then spend
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