May 2007 - Follow up on Joe's Dream Loudspeaker System  Improvements since January 2006 After more than a year, Norbert "persuaded" (like those Italian guys offering protection against any mishaps) me to update the dream speaker page. In the past year, the whole setup went through a number of changes which are quite substantial. Overall tonality, integration, impact and details improved a lot. What was changed:   1. Arrangement of the drivers 2. (Super)Tweeter 3. Crossover 4. Amplification I start with the most visible - the midrange horn is now exactly centred and surrounded by a kind of ruff. This makes time and phase alignment a lot easier, smoothes the frequency response and lowers the LF cut off. An additional bonus is the improved rigidity of the whole construction, rewarding the listener with increased dynamics and detail.     The next change concerned the super tweeter. I kicked out the JBL 2405 Alnico and installed the Pioneer PT-R9. If one has the possibility to sacrifice a little bit of efficiency, then there is simply no discussion. The PT-R9 (a Beryllium ribbon with Alnico magnets) supersedes the JBL in every way except efficiency. It sounds cleaner, smoother, more extended and lower distorted. The only drawback is the lower efficiency, but 98dB/W/m are not really bad. At first, I was considering GOTOs or the famous Onken T5000S, but the price of these gems is even higher than for the PT-R9 plus the additional power amps. Yes, yes, times are demanding and force the audiophile to make some serious compromises. Pioneer PT-R9 super tweeter Photo courtesy of Joe Aigner   The demand for some extra power made it necessary to take the next step. Originally, the speaker was planned with a passive crossover for the super tweeter, but I did not want to dampen the TD4002z down. So I built a simple small power amp: Input transformer and a triode strapped EL84. To be honest, it will be soon replaced by a differential 6C45 amp using Jack Elliano's 80% nickel core transformers. Last but not least, there is the new crossover. Although not realised at first glance, this is essentially a two-way speaker (ok, on steroids). The concept's core is a pair of Altec 515Bs and a TD4002z separated by 1st order filters at 650Hz. Altec 416As add slam below 50Hz and the super tweeter air above 12kHz.   The new crossover network Photo courtesy of Joe Aigner   I used constant impedance filters similar to the famous Tango RIAA network (recommended reading "Attenuators, Equalizers and Filters" by Howard M. Tremaine and George K. Teffeau). Keep in mind that this filter type presents a constant impedance across the whole audio spectrum. Using four of these filters with 600 Ohm each forces the line amp to drive a 150 Ohm load. Be prepared to rebuild your line amp.   "Tschau" Joe   At the moment Joe's system consists of:   Differential phono stage (EC8020, EC8010) Differential cd amp (PC88)  Differential line stage (5687)   Subbass: differential 6HS5 amp - Altec 416A Midbass: Parafeed VT-4C (Sakuma style) Altec 515B Midrange-tweeter: Differential 7N7, Ultrapath 801 - TAD 4002z Super tweeter: Ultrapath EL84, soon differential 6C45 - PT-R9     All in common are three phase power supplies, transformers everywhere and lots of iron. (To quote Joe, "all this iron is used only to make sure the amplifiers can't fly away...")       ©The Audio Eagle 2005-2009• All Rights Reserved • Disclaimer