10 - 16 ohm project for Atma-Sphere OTL amp - diyAudio
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Old 7th May 2006, 09:07 PM   #1
j.burtt is offline j.burtt  United States
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Default 10 - 16 ohm project for Atma-Sphere OTL amp

I recently acquired a pair of Atma-Sphere M60-MKiii monoblocks. I spoke to Ralph Karsten @ Atma-Sphere and he advised me the amplifiers are optimized to play a 13 ohm load. I have looked at several of the speakers his sight recommends and have liked what I have seen in the Coincident line. The Total Eclipse ii looks like a very nice match for theses amps (14 ohms, 94 db), but they are a tad bit pricey ($8000.). They are a 3 way design using (2) Vifa 10's for bass, (2) Seas 6-1/2's for mids and a SS Revelator for the tweeter. They claim the drivers play a full octave above and below crossover points, which allows them to use a simple 1st order crossover. I am thinking about building my own using similar drivers. I am going to guess the 10's and 6-1/2's are 8 ohm drivers run in series and the tweeter is 8 ohms.

Is anyone aware of a proven design that is 10 - 16 ohms. It doesn't have to be like this design, just something that works.

1. Is there a single program that will allow me to test the drivers and design the crossovers?

2. I am also looking for a good deal on a calibrated test Mic/Preamp to go with that program?

It would be nice if someone offered a turn-key setup that included everything you needed to get started.

Thanks for reading my post, your reply is appreciated.

James
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Old 8th May 2006, 05:33 PM   #2
kevinkr is offline kevinkr  United States
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A lot of vintage JBL, Altec and Jensen drivers are 16 ohms, some are quite good even by today's standards and are available on ePay. Iconic currently makes a version of the Altec 515 (165-16G) which has a 16 ohm VC.

All of these offer relatively high efficiency which keeps the average power low, making those Atmosphere otl output tubes quite happy..

The old expedient of putting a couple of drivers in series is effective at least in the bass and lower midrange, depending on orientation directivity of multiple drivers in an array can be rather interesting (possibly frustrating) in the mids/highs.

I recall there were several autoformers made for use with atmosphere amplifiers to transform lower impedance speakers to something usable with the otl amplifier, in my limited experience these are reasonably good, but seem to suffer some loss of transparency.
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Old 8th May 2006, 06:34 PM   #3
el`Ol is offline el`Ol  Germany
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Here are some concepts for the 16Ohm 97dB PHY-HP.

http://www.auditorium-23.de/Welcome/Contents.html
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