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Old 9th February 2012, 07:25 AM   #1
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Default No output transformer tube amp

Hi

Is it possibel to make a tube amp without output transformers.

I am thinking of a sort of line array with lots of seriesconnectet fullrange loudspeakers.

If you have 20 or more 4" speakers with 8 ohm impedance in series you get a load of at least 160 ohm is that enough?

best regards

Uwe
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Old 9th February 2012, 08:39 AM   #2
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Yes it is possible, search for OTL amplifiers.

Here is an article on tubecad about the subject: OTL Amplifier Design
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Old 9th February 2012, 08:40 AM   #3
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Old 9th February 2012, 09:32 AM   #4
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Quote:
Originally Posted by heinz1964 View Post
Hi

Is it possibel to make a tube amp without output transformers.

I am thinking of a sort of line array with lots of seriesconnectet fullrange loudspeakers.

If you have 20 or more 4" speakers with 8 ohm impedance in series you get a load of at least 160 ohm is that enough?

best regards

Uwe
An old OTL amp, seems the first one, used one(1) special made to order fullrange driver with 600 Ohms impedance.

About the line array, I sorry inform you that various series connected FR will delivery a slow sound, how many drivers, how many slow?? +Just a real test may say.

I remember a great book(missing the name) from Eng.Bessel, where he test various series LA, with 1 out of phase driver in the center.
If you can read this book, it will help a lot.
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Old 9th February 2012, 09:40 AM   #5
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This is the best LA I see today, no tweeters as the PipeDreams, it use 25 small fullranges.
But it use a EQ discrete box to boost the bass.
WWW.IDS25.COM
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Old 9th February 2012, 08:40 PM   #6
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As a compromise I built a pair of speakers with a single fullrange x-over'd at 300Hz, and have two series connected woofers below the x-over. Gives a system with 8ohms where less power is needed and 16ohms where more is. Most OTLs deliver about twice as much power into 16ohms than 8, so it works out pretty ok. I use a Fostex 6" (can't remember nomenclature, it's the one with mag-shield) and two SEAS 8" woofers. Turned out to have pretty close sensitivity so didnt need to pad either drivers. Not the best speakers perhaps, but a nice easy load for my OTLs.
There are some 16ohm drivers out there, but very little information about them. I wish there was more attention into higher impedance drivers, not only for OTLs, but also tube amps could use less turns ratios in the output trannies, which is very beneficial.
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Old 9th February 2012, 09:23 PM   #7
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Quote:
Originally Posted by FullRangeMan View Post
This is the best LA I see today, no tweeters as the PipeDreams, it use 25 small fullranges.
But it use a EQ discrete box to boost the bass.
WWW.IDS25.COM
I did that once in restaurant: using 31 - band EQ I made 12 dB/Oct bust below 80 Hz of my line arrays. Sound quality was magnificent, though loudness was very low.
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