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Old 11th December 2006, 04:00 PM   #1
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Default F2 - driving two tweeters

Can someone advise me how to wire a FirstWatt F2 amp to drive two tweeters;
A Fostex T825 (6.3khz - 18khz) enhanced with a T925 which has a more stable response above 15kHz to 40khz. Nelson Pass has explained how to set up a passive XOver for current sources which show the drivers should be put in series rather than in parallel as for voltage source amps .

I thought to
1. leave the T825 directly connected to F2 without any low pass filter
2. set a high pass filter for the T925 to let only signal above 15kHz or 18kHz with no low pass
3. both tweeters would be driven by the F2

Since my abilities are limited, can somebody draw how I should connect it for most appropriated results with the current amps F2

Thanks & regds
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Old 11th December 2006, 04:36 PM   #2
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Seems an easy task, experiment smaller values for C1 and C3, being a current amp don’t know how it good react but looks that it will also depend on speaker impedance you connect to it.

As with other amps changing to smaller caps you will get a higher 3 dB pass band.

For tweeters I would also change C3 to film caps of suitable size.

Happy tweaking
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Old 12th December 2006, 06:50 AM   #3
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Default F2 XOver

Quote:
Originally posted by apassgear
Seems an easy task, experiment smaller values for C1 and C3, being a current amp don’t know how it good react but looks that it will also depend on speaker impedance you connect to it.
As with other amps changing to smaller caps you will get a higher 3 dB pass band.For tweeters I would also change C3 to film caps of suitable size.
Thanks apassgear, but may I ask which C1, C3 values you are refering to. I used http://www.firstwatt.com/downloads/c...r-networks.pdf article. I attached a file with better reference, maybe that may help.
Attached Files
File Type: zip fwatt&tweeterxover.zip (79.2 KB, 42 views)
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Old 12th December 2006, 04:46 PM   #4
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Thought you had the original schematic published by Nelson for the F2 that you can find in other threads,

http://www.diyaudio.com/forums/attac...amp=1164831839

C1 and C3 reffers to this schematic
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Old 12th December 2006, 05:26 PM   #5
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Question F2 driving two tweeter drivers in parallel

Quote:
Originally posted by apassgear
Thought you had the original schematic published by Nelson for the F2 that you can find in other threads, http://www.diyaudio.com/forums/attac...amp=1164831839
C1 and C3 reffers to this schematic
Thanks a lot for the schematic

Ooops, now it's getting hotter, why would you modify the amps ? I must obviously expressing my problem inadequately - sorry about that.
What I'm trying to do is to connect two drivers (tweeters) to a F2. One of the two would have a high pass filter to remove signal lower that 15kHz. But reading Nelson in http://www.firstwatt.com/downloads/c...r-networks.pdf it seems F2 (like F1) need passive cross over filter designed differently (in series) than classical voltage amps. That is where the struggle starts because I can't figure out how to apply to my issue.

I've redraft the word doc in order - hopefully - to make it clearer.
A lots of thanks
Attached Files
File Type: zip fwatt&tweeterxover.zip (80.2 KB, 24 views)
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Old 12th December 2006, 06:34 PM   #6
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Nicola,

My fault since over this Pass Forum we usually don’t discuss passive xover and mainly speak of amps and active electronics. For passive xover there are those speaker Forums on DIYAUDIO.

Now, you are using an active xover for multiamping your system, but there are other ways to accomplish similar setups, not that I’m trying to speak you away form your intended setup so just forget what I said regarding mods to the amp in order to make it a hi pass in itself.

Maybe Nelson could chip in to help on the xover or go to the speaker forum for some advise.

Sorry not been able to help…
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Old 12th December 2006, 07:40 PM   #7
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putting any sort of xover (except some linearizing filter,if needed) in series with your main full range or xtended range driver isn't too smart,just because you'll loose something of primary virtues of that driver.........and this virtues are there exactly tnx to lack of any phase disturbing device in line with driver.

stay with any sort of filter in line with helper tweet........6db or more,that is your call.
besides,constructing two way series xover for Fp~15KHz is pretty funny........this xover is everything for tweet,and almost nothing for low(er) driver,but just enough to spoil phase coherence 2 and more octaves lower

(that was just my generall thinking regarding extended range driver,even in combo with amp as F2)

now-two tweets...........thinking in line with upper paragraph.........I'll try just with one cap and choke in line with lower tweet and just one cap in line with super tweet


but-finall decision is still your's ....if you wish,I'll try to dig in my files how to calculate series xover for 15KHz............
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Old 12th December 2006, 07:53 PM   #8
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You can refer to my paper on crossovers for current source
amplifiers, available at www.firstwatt.com and also you can
play around with responses of various networks using a
simulator (I used Microcap 7 in the article, which is a free
download for a limited version from Spectrum software)

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Old 15th December 2006, 02:28 PM   #9
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Question F2 and Xover on 2 tweeters

Quote:
Originally posted by Nelson Pass
You can refer to my paper on crossovers for current source
amplifiers, available at www.firstwatt.com and also you can
play around with responses of various networks using a
simulator (I used Microcap 7 in the article, which is a free
download for a limited version from Spectrum software)

Thanks, I did read http://www.firstwatt.com/downloads/c...r-networks.pdf and that was exactly my question where I wished some advise. I thought to use schematic on Fig 3A p 4/10 and consider R2, the woofer as the 'lower tweeter' (T825) and the R1-Tweeter as the higher tweeter (T925). I thought to a) remove L1 which I reckon is a low pass filter which acts on the R2 Woofer since I wanted to leave the 'lower tweeter' un filtered and b) to adjust C1 to make a high pass filter as of 15kHz.

I wanted to know if that makes sense or not with the F2
You comments would be most helpfull
regards
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Old 15th December 2006, 06:11 PM   #10
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I don't know. You'll have to actually try it to find out.

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