I have just finished researching Fosgate units for synthesizing surround from stereo, of course with lots of seperation, and a real quad like experience.
The Tate 101a used the first DES, directional enhancement circuitry. This was a huge advance for SQ decoding, and also for processing stereo. The first circuits were slow, however, and can lead to pumping type artifacts. Most of the time they would only be obvious to critical listening, especially of one or two channels at a time. Sometimes it is downright unlistenable.
The 3601 was not a step forwards, as nearly I can tell, and I haven't auditioned one. They have nearly universal negative reviews, at least for our purposes.
The Fosgate models 1 and 2 were an advance, and have powered back channels.
Model 3 and 3a, and then 4 and 5 have very excellent performance, as I think they aproach the performance of a Tate, but with very minimal pumping. The 3a was the most expensive of this sequence, and commands a higher price. Harman Kardon bought Fosgate Audionics, and rebranded these units, as did their subsidiary label JBL. I have a model 4, and love it. It has replaced my Tate for synthesizing surround, as the pumping is nearly negligble for most music, and it gives 5.1, not just 4.0.
The next step in Fosgate's design was 6-Axis. I just received a Citation pre-amp which has the 6-axis circuit. I believe only Citation 5.0 and 7.0 preamps had 6-axis. There was also the car decoder, the Harman Kardon CSP-1, and possibly the same unit branded as an Infinity. I have not hooked my 7.0 up, but in research, including lengthy conversations with Bob Popham, who worked for Fosgate, this is the ultimate Fosgate synthesizer. It is even faster, which should reduce pumping even more than the models 3-5, and boasts a much better seperation between channels. It also has lots of parameter controls. I will be posting reviews of the Citation 7.0 in the near future. The 5.0 came later, and used cheaper components. I do not know if this affected the 6-Axis circuitry, though. The 5.0 did offer Dolby digital and optional DTS however. It is interesting that the reviews at the time said the lack of digital decoding on the 7.0 was not a handicap, because the reviewers felt that 6-Axis sounded better. One other note on the 5.0, is that it offered the digitally decoded dolby digital and DTS through a 6-Axis Encoder to be recorded on the stereo analog outputs! The primary drawback to both units is the lack of external inputs. MSB technology offers a $400 5.1 input upgrade to the 7.0.
Now to the interesting part, that I have just uncovered. Just before the launch of Dolby ProLogic II, there was a media blitz, at least in audio circles, of this new wonder to be released. The extremely glowing commentary of DPLII was mouthwatering at the time. The thing I most focussed in on was its purpose to convert stereo music into 5.1 surround. It was said to be Fosgate's ultimate acheivement, as it incorporated a new concept of feedback logic to acheive incredibly accurate decoding, even better than 6-Axis. Well, after more research, at first it seemed that DPLII was an improvement of 6-Axis. I bought one of the very first receivers that offered DPLII, and I liked it, but it didn't ring my bell like I thought it would. The Tate was much more satisfying. Unfortunately, I did little surround listening for the last year and a half until recently, as I was building a dedicated home theater, and music listening room. After setting up the Tate again, finally, it just was so much more pleasing to me as a quadgeek than DPLII. What's the deal here? DPLII was supposed to be so awesome in its abilities as Fosgates ultimate, yet his ancient Tate ran dircles around it (pun intended). Well to make a long story a little shorter, Roger Dressler of Dolby Labs finally admitted that they wanted some accuracy and dynamics issues resolved for the new DPLII, and to accomodate them, Fosgate reduced the front to rear seperation. I do like DPLII, but if you are like me, and like an aggressive surround experience, DPLII should not be confused with Fosgates' earlier designs. This is why I just bought the 7.0, and again, I'll let you quaddudes know the score. I haven't heard much about the 6-Axis design in quad circles, but I think it's probably because the Citation units were so expensive, about $4k. Now they run about 10-15% of their original price.
Thanks for listening!
Dan in Spokane
