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Citation 12 non-complimentary to drive ribbon tweeter
Citation 12 non-complimentary to drive ribbon tweeter
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Old 27th December 2017, 04:57 PM   #1
woofertester is offline woofertester  United States
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Default Citation 12 non-complimentary to drive ribbon tweeter

I am interested in building a non-complimentary version of the MOSFET Citation 12 that Nelson wrote about in AA in 1981. The intended use is ultra-high current devices such as a DIY ribbon that is very sub 1-ohm.

The twist I am interested in is to use a new low RDSon FET. This one

IXTN660N04T4 IXYS | Discrete Semiconductor Products | DigiKey

The RDSon is claimed to be 0.85 milli-ohms. With +/- 10V on the output stage and no current limiting, The amp could deliver hundreds of watts into a very low impedance load.

I have a DIY ribbon design in the works and I am loathe to use an audio transformer. A low-voltage high-current amp would be ideal.

I have no amp design skills and no board layout skills. If someone (or multiple somenones) wants to participate in a collaborative effort, I would buy boards and parts in exchange for a well layed out board and a working design.

I think that the power supply caps will need some consideration for ESR and placement close to the FETs and be connected with copper bus bars.

If this is not the correct forum for such a thread, I can ask to have it moved to the Solid State forum.

...looking for inputs....
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Old 27th December 2017, 05:39 PM   #2
Nelson Pass is offline Nelson Pass  United States
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Citation 12 non-complimentary to drive ribbon tweeter
We would want to ask the question - what is the current you plan to send
through the ribbon / what is the resistance of the ribbon?

It might easily be that you don't need such a large part.
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Old 27th December 2017, 07:01 PM   #3
woofertester is offline woofertester  United States
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Thank you for replying. Its a pleasure to correspond with you. I own two Adcom GFA555 amplifiers and I enjoy them immensely.

Fat ribbon material is 30 milli-ohms for a short tweeter. Skinny ribbon material is 400 milli-ohms. I just measured the material with a Keithley 2750 on the 1-ohm range using 4-wire and offset compensation.

I would also be using this high-current topology for driving sub 1-ohm car subwoofers.

The intent is to be able to create 300A (or more) transients. Weak magnets may require high current.
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Old 27th December 2017, 08:30 PM   #4
Nelson Pass is offline Nelson Pass  United States
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Citation 12 non-complimentary to drive ribbon tweeter
You want to put 2700 watt transients into the tweeter?

300 * 300 * .03 = 2700
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Old 27th December 2017, 09:11 PM   #5
woofertester is offline woofertester  United States
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Yes peak. Maybe just think of it as headroom. The FET power supply would be + / - 10V DC. The power would only be that large if the load impedance was low enough and the program material asked for it.

Average power should be very low with large current transients.
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Old 27th December 2017, 09:32 PM   #6
Nelson Pass is offline Nelson Pass  United States
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Citation 12 non-complimentary to drive ribbon tweeter
One more question, what is the efficiency figure of the tweeter?
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Old 27th December 2017, 09:33 PM   #7
Zen Mod is online now Zen Mod  Serbia
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Citation 12 non-complimentary to drive ribbon tweeter
-22db/KW/ft

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Old 27th December 2017, 11:38 PM   #8
woofertester is offline woofertester  United States
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Quote:
Originally Posted by Nelson Pass View Post
One more question, what is the efficiency figure of the tweeter?
Good question. I have no way to directly measure it at the moment. What I did is to use a WT2 which puts out about 3 1/2 mA at any freq between 1Hz and 20 kHz. I chose 3 kHz. I compared the tweeter to an Audax DH13B 5 1/2" midrange, a favorite from the 1980s.

The midrange is lots louder than the tweeter. The midrange is 85dB @1W@1m or so. My guess is that the tweeter is no better than 75 dB @1W@1m.

I will dig out the SPL meter and also measure the T/S parameters of the midrange. Then a better guestimate of the tweeter sensitivity will follow.

The tweeter may be less than 70 dB@1W@1m. It is not surprising. There is a large air gap and the magnets are inexpensive ceramic units. That said, the tweeter sound is very good. A picture of the tweeter is attached....
Attached Images
File Type: jpg Ribbon.jpg (190.3 KB, 205 views)
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Old 28th December 2017, 12:23 AM   #9
woofertester is offline woofertester  United States
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The midrange T/S parameters include sensitivity of 87 dB@1W@1m.

I found the SPL meter. The ribbon is more than 26 dB less output at 3mA at 3kHz than the Audax midrange.

The midrange yields about 86dB near field at 3mA at 3kHz. The ribbon does not deflect the SPL meter on the 70 dB range which has a -10dB mark at the far left.

So, the ribbon is no better than 60 dB @1w @1m.
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Old 28th December 2017, 01:40 AM   #10
2 picoDumbs is offline 2 picoDumbs  Australia
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Extremely impressive.
Why not work on reducing the air gap first.
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