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I have seen this forum but just now read what OTL means and am curious. Whats the deal? Thanks.
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You could also go with an OTL SET and get the best of both, presumably. A few of them exist, such as Transcendent Sound's which is the 'classic' OTL-type design and David Berning's Seigfried, or even his microzotl which puts out 1 or maybe 2 watts but is not your classic or traditional OTL design (see the big thread below about what the Berning 'really' is.)
I found the post that brian walsh posted that had a great link to a good explanation of the OTL amp but now The question I have is, would you use a OTL amp when you need lots of WPC AND all the sound quality of a SET. So if I have speakers that are 112db and only need 4 watts I would not need an OTL. Is this right? Thanks
The "need" for an OTL amplifier is not related to a need for high power. In fact, OTL amps are in general relatively less efficient than transformer-coupled tube amps in converting the power available from an output tube into power that can drive a speaker. The beauty of an OTL amplifier is in the elimination of the output transformer entirely, which leads to lower distortion, wider bandwidth, greater transparency, etc. For your speakers (112db efficiency!!!) you want a low power amplifier with a very high signal-to-noise ratio. But you have not mentioned the nominal impedance rating of your speakers. If your speakers are rated at 8 ohms impedance or higher, and if the impedance curve is relatively flat with respect to frequency (real world impedance or resistance of a speaker varies with frequency), then you might find bliss with an OTL type. If your speakers are rated less than 8 ohms OR if there is a serious dip in impedance at critical frequencies (ultra-high frequencies don't count), then you might look elsewhere or consider an OTL in conjunction with an impedance matching device, such as a Zero autoformer.
Thanks Lew. I have A7 bottoms with 515G which are driven by a Crown 150A, for the mids I have Altec 1505B horns driven by 24ohm 288C drivers and is what I need a new amp for. For tweets I have Beyma CP25 driven by a small digital amp. I am driving the mid horns with a 300B now and at times find it mirky or cloudy. It is hard to explain but there seems to be a lot of coloration. I have heard a lot about OTLs and am thinking that it might be the way to go. One problem with the 1505B/288C combo is that EVERYTHING comes through. A little garbage in and a lot of garbage out. Cheers.
I have a very similar setup.I can only share my experience and opinion.
I drive my 1505/288k16 horns with Wright WPA 3.5 SET monoblocks. These SETs put out 3.5 watts per monoblock, believe me, more than enough to drive the 288's -- at 109db/watt efficiency, and crossed at 500hz-- to very loud, but very clean and musical levels.
Until recently, I was driving my 515b's (825 cabinets) with Carver M-500t monoblocks (700 watts per monoblock).
Then, I bought a pair of Atma-Sphere M-60 II.2's to replace the Carvers. I simply lack the ability to communicate to you in words the extraordinary transformation that those monoblocks brought to an already very musical system!
As a lover of percussion, one of my greatest frustrations with "hi-fi" systems was the inability to faithfully reproduce the sound of "skin on skin" or "wood on skin" or "wood on metal rim". There is no masking it. Once you hear a drum played live, be it rock, jazz or classical, be it a drum set, or congas, timbales or timpani, the feeling, the passion communicated by the direct strike of the instrument stays with you. Then you go home...and ...well, it is not the same, by, in my personal estimation, too far a margin.
Well, with all due allowances, in a word, the Atmas/Altec 515/288 comes awfully close! As close as I have ever heard a home system come to FAITHFULLY reproduce the real percussive sound, and actually all music. You get to FEEL IT, BROTHER!
That output transformerless technology works. It is fast and accurate, and above all, musical. I listen to all sorts of music, and they work exceedingly well with all. Female voices, for instance sound uncanningly real. Piano and acoustic guitars sound absolutely live. It is simply impossible for me to "multi-task" when I fire up my system. The music simply draws me in and forces me to listen to it, feel it.
I have not heard all OTL's. But I tell you, my personal experience has made me a believer, and I suspect that I will stay with this basic system for a very long time.
I agree with you. With very efficient horns, like the Altecs, garbage in, and a lot of garbage out. There are some very respectable solid state amps out there, such as Krell. But I think nothing comes even close to OTL's and/or other SET's when combined with Altec, IMHO.
Don't worry about the Atma-Sphere OTLs. You'll be grinning. Get yourself a pair, and get ready to rediscover your music collection.
For your information, I use Fane ST-5022 tweeters, crossed at 4k and driven by Antique Sound Labs Wave SET monoblocks.
I use a Conrad-Johnson PV-11 tube pre, and Rane AC-23 electronic crossover.
I will show my ignorance of horn speakers by admitting that I have never heard of ANY of the drivers you mention, but it is enough to know that your midrange driver is rated at 24 ohms impedance. This is OTL heaven! You can use anything you want, but I would try the Atma-sphere S30 and the Berning Siegfried for starters. I think eventually you will want to replace the Crown amplifier driving your woofers with a second OTL, too. OTLs, particularly Atma-sphere ones, deliver superb, deep, and articulate bass into a high-impedance load.
The 515G woofers are also 24 ohm. Now it is my turn to admit my ignorance, I was always told that if an amp rated at 10 wpc, lets say, into an 8 ohm driver, then it was only good for something less than 10 wpc when driving a speaker with 16 or 24 ohms. Is this true or false? If it is true then I would need to rethink the power required when buying an amp. Cheers.
Transistor amps tend to produce power in inverse relationship to speaker impedance. In other words, an ss amp rated at 100W into 8 ohms might make 200W into 4 ohms. This relationship has limits and is dependent upon the power supply design and execution. So for example the same amplifier probably would not develop 800W into a 1 ohm speaker. (It would probably explode first.) Conversely, tube amplifiers tend to develop more power into higher impedance speakers. This is because transistor amps are "current amplifiers" while tube amps are "voltage amplifiers". I hate to repeat that confusing bit of mumbo jumbo, because it does not tell you anything. Think of it this way: Power = current X voltage. SS amps are better at making current and tube amps are better at making voltage. Tube-type OTL amplifiers certainly tend to like high impedance loads better than low impedance loads. This is not only due to the foregoing rationale but also to the fact that OTLs tend to have high-ish output impedances, which makes it doubly difficult for them to drive low impedance speakers. (You want the output impedance of your amplifier to be significantly less than the input impedance of your speaker for best results.)
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