Direct Drive amplifier for DIY ribbon?

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thadman

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#1
I'm interested in building a ribbon loudspeaker in my free time over Christmas break and would like to drive it directly. Following the resolution of some meetings with faculty in the engineering department, I might be able to gain access to the Universities Laser Vibrometer and Anechoic chamber for measurements (and comparison with the RAAL 140-15D)😀

I do not wish to use a transformer, as I believe it may contribute excessive distortion. As a result, I will need a special amplifier to drive the ribbon. The impedance of the ribbon will be almost purely resistive, but very, very, very low. Most of my knowledge in the field of loudspeakers is related to acoustics and the physics of transducers...I haven't yet been able to extend it to amplifier design.

My primary goal for the project is reproducing a Dirac Pulse/Square Wave, so impulse response will be weighted with the highest significance.

Are there any designs available? Can anyone recommend any texts?

How difficult would it be to build a direct drive 10 watt amplifier with negligible distortion (linear and non-linear distortion <20khz)?
 
#2
thadman said:
I'm interested in building a ribbon loudspeaker in my free time over Christmas break and would like to drive it directly. Following the resolution of some meetings with faculty in the engineering department, I might be able to gain access to the Universities Laser Vibrometer and Anechoic chamber for measurements (and comparison with the RAAL 140-15D)😀

I do not wish to use a transformer, as I believe it may contribute excessive distortion. As a result, I will need a special amplifier to drive the ribbon. The impedance of the ribbon will be almost purely resistive, but very, very, very low. Most of my knowledge in the field of loudspeakers is related to acoustics and the physics of transducers...I haven't yet been able to extend it to amplifier design.

My primary goal for the project is reproducing a Dirac Pulse/Square Wave, so impulse response will be weighted with the highest significance.

Are there any designs available? Can anyone recommend any texts?

How difficult would it be to build a direct drive 10 watt amplifier with negligible distortion (linear and non-linear distortion <20khz)?
Click to expand...

Not sure what ribbon you intend to use but I drive my Maggie IIIas 3-way active ... so my ribbon amp is directly attached to the IIIa ribbon.

Maggie ribbons are almost entirely resistive, so that is not a problem - the only issue is ... can the amp handle the (low) resistance of the ribbon?

My Maggie ribbon is 2 ohms ... so what I did was put a 1ohm res in series with it ... and the amp can cope with 3ohms! 😀 I use a ss AKSA amp which is 25w into 8ohms (ie. 60w into 3ohms) ... however, I doubt that it would be able to cope with much less than 2ohms!

So, I would suggest if the ribbon you intend to use is much lower than 2ohms resistance, you have 3 choices:
1. use a different ribbon
2. add a res in series to bring it up to at least 2ohms
3. use a Krell or similar which seem to have no problem driving 1ohm loads.

Regards,

Andy
 
#3
I seem to recall an amplifier design for direct driving ribbons in an Elektor magazine quite a few years ago but I do not have it. You need to be thinking modest power supply voltages, high current capability and parallel bipolar output devices. You may get more suggestions in the Solid State forum.

Keith
 
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