Direct drive ribbon with modified F5T

[dhenryp]

I currently have a line array with an array of 7 DIY ribbon tweeters. The resistance of the ribbons is a total of .2 ohms. I am planning to change out the ribbons with thinner aluminum which should give me a total of .5 ohms. I am currently driving the ribbons through a DIY transformer.

I am thinking of building a variation of the F5T V2 in order to drive the ribbons directly. The changes are:

1. Lower voltage +- 16v
2. High current PS - good for up to 20 amps continuous (one supply for each channel)
3. 6 parallel output pairs biased at about 6 amps total

With .5 ohms, I think this will give me about 35 watts class A. This should be enough since they are pretty efficient at 95 db/watt. I should get much more power A/B before I run out of current.

Thoughts?

 

[Nelson Pass]

I think you should give it a go and see what you get.

😎

 

[a.wayne]

Yes please do , give it ago and 35 watt Class-a at .5 ohm. Dont think so ....🙂

 

[dhenryp]

Yes please do , give it ago and 35 watt Class-a at .5 ohm. Dont think so ....🙂

Please correct me if my math is wrong. I thought

P = I**2 X R / 2 where
I = 2 X bias current
R = .5 ohm
so
P = 12**2 X.5 / 2
P = 144 X.5 / 2
P = 36 watts

 

[AndrewT]

P=I²R
Where you use Ipk the formula becomes
P=Ipk²R/2
Ipk = 12Apk gives the calculation you show in post4.

i.e. for 36W into ½ohm you need 6Vpk and 12Apk

If you want that all to be in ClassA, then the output bias of the push pull F5T must be set to > 6A (continuous).
The supply rails would probably work @ > +-12Vdc
Pq ~ 12+12 * 6 ~ 144W per channel.

Doable ?

1. Lower voltage +- 16v
2. High current PS - good for up to 20 amps continuous (one supply for each channel)
3. 6 parallel output pairs biased at about 6 amps total

your brief exceeds the minimum requirements.

 

[a.wayne]

What about PSU sag , 12v ..?, 16v would be closer to target, how much class -a power at 8 ohm ,,?

 

[AndrewT]

Sag?
PSU is passing 6A continuously when quiescent.
Where is it going to sag to?