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A 13 ohm, nearly flat impedance curve that will mate best with my OTLs. Great speakers and equally great amps don't always get along well...
Maybe Rick can elaborate a bit more on the array design, but I see it as a close sibling of the "Boston arrays", contrasted in these ways:- high, flat impedance (a must for 60 watt/ch OTL amps). Higher sensitivity and the 3dB/meter spl drop off of the an array also make for a much better OTL match than the Firebirds, wonderful as they were.- same ScanSpeak 8531 midbasses (also used in the "SSR"), but with Fountek NeoPro 5i ribbons. I've had DIY speakers with the huge Raven R3.1, and running ribbons into the upper midrange does something special. The NeoPro 5i ribbons won't play quite as low as the Raven R3.1, but better the smaller Fountek in this regard.- less subwoofer impact (I'll have "only" a pair of the same ScanSpeak 10 inch aluminum sub drivers per channel, also in sealed boxes for lower Qtc than ported);Given Rick's satisfaction with the "Boston arrays", mine should also be quite nice.
I do appreciate reading gme109's experience. A few points are worth making, though:- Pulling output tubes from Atma OTLs requires lowering the bias correspondingly. For my M-60s, pulling two of the eight 6AS7s requires bias change from 550mA to 435mA. If not done, sound degrades.- Even with the correct bias adjustment, an Atma OTL amp without its full complement of output tubes will not perform as well as with a full complement of its output tubes.Over the past few years I've had several conversations with the folks at Atma-Sphere about these issues and the above are their comments, not mine. Eliminating one of the 6SN7 voltage gain tubes with a bypass socket plug to decrease gain (NOT power output) is less deleterious to sound quality, but still alters the voltage gain stage from its optimum cascode design.I'm not saying that these factors explain the degraded sound gme109 heard when dropping his MA-1s' power output, but they might. OTLs, even Ralphs, are fragile creatures. Just getting a design that doesn't spontaneously combust like Michael Jackson's hair is, apparently, a monumental achievement...
Did you find the "60 watt" MA-1s a bit lean-sounding? Besides the relatively modest power, it's the only other significant shortcoming of the M60s to my ears.Just "in case", I'm having Rick put my line array crossovers outboard to allow the option to actively biamp down the road. I used an early version of the DEQX with my Raven R3.1 speakers and have much familiarity with it. Should I want to flesh out the upper bass a bit more I have a means to do so while keeping my OTLs on top.
Quote from: jgb0194 on 12 Jul 2007, 03:31 pmA 13 ohm, nearly flat impedance curve that will mate best with my OTLs. Great speakers and equally great amps don't always get along well...I have a pair of custom Line Arrays made by Rick, the Excelarray's. I believe they are 16 ohm, and about 91 db efficient. I tried a pair of Atma-Sphere MA-1's, and they had no problem powering the Excelarray's. I then pulled out half the tubes to simulate the M60's, as the MA-1's were too expensive, and way too hot. Things became a little confused, with less focus and impact. A lot of the magic that I was hearing with the MA-1's, was not there when dropping the power to 60 watts. From everything that I've read, 60 watts of OTL should've been fine with a 16 ohm load, but it just didn't seem to cut it. My guess is, even though the impedance and efficiency is high, there is still six drivers and a 45' ribbon tweeter per channel, in the Excelarra's, for the amp to have to muscle around, and they seem to like current. Even my present amp, a pair of Channel Island D-200's, which are 200 watts per channel, don't have the impact or bass that my previous amp, a 500 watt Spectron had. The Spectron also had about twice the current of the D200's as well. Sorry to be throwing this out there, but that was my experience. Maybe there's something I'm missing, that makes your line array an easier load to drive, don't know.
Quote from: gme109 on 13 Jul 2007, 02:49 amQuote from: jgb0194 on 12 Jul 2007, 03:31 pmA 13 ohm, nearly flat impedance curve that will mate best with my OTLs. Great speakers and equally great amps don't always get along well...I have a pair of custom Line Arrays made by Rick, the Excelarray's. I believe they are 16 ohm, and about 91 db efficient. I tried a pair of Atma-Sphere MA-1's, and they had no problem powering the Excelarray's. I then pulled out half the tubes to simulate the M60's, as the MA-1's were too expensive, and way too hot. Things became a little confused, with less focus and impact. A lot of the magic that I was hearing with the MA-1's, was not there when dropping the power to 60 watts. From everything that I've read, 60 watts of OTL should've been fine with a 16 ohm load, but it just didn't seem to cut it. My guess is, even though the impedance and efficiency is high, there is still six drivers and a 45' ribbon tweeter per channel, in the Excelarra's, for the amp to have to muscle around, and they seem to like current. Even my present amp, a pair of Channel Island D-200's, which are 200 watts per channel, don't have the impact or bass that my previous amp, a 500 watt Spectron had. The Spectron also had about twice the current of the D200's as well. Sorry to be throwing this out there, but that was my experience. Maybe there's something I'm missing, that makes your line array an easier load to drive, don't know.Two points worth noting....First, when you raise the impedance to 16ohms, you likely half the wattage available from your OTL amp, so 60 watts becomes 30watts.Second, although the impedance becomes benign and the sensitivity high, Rick will probably not like me for saying this, but reactance is probably high due to the number of drivers...therefore, low output Z is very important with such a speaker. I'll let you fill in the blanks. Rick designs killer sounding speakers from what I have heard. However, if you want to use an OTL amp you are seriously limited with the speakers you use. I really don't think the elimination of output transformer is worth the design choices it forces. To each their own.Josh
The inductive reactance is increased a little from the series wiring of the woofers; however, the Revelator woofers are very low in inductance. With a conjugate filter the reactive part of the crossover can be countered so that the impedance is very benign.
