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)
Amp-section:
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
(To quote Joe, "all this iron is used only to make sure the amplifiers can't fly away...")
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