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Author Topic: DIY PERSPECTA SOUND INTEGRATOR Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-26-2016 02:52 PM                     I don't have any info of the exact nature of the insides of the boxes not do I remember that the patent has any info. I can tell you that it is a tuned resonant deal of some sort, possibly a tank circuit that affects the bias on the stage after it thus controlling gain. A friend in Portland had a working Perspecta unit that he recapped but still wouldn't work properly and it turned out that those tuned resonant tank circuits had capacitors inside the tops of the cans that had drifted. So it is some sort of RC tuned LF band pass circuit. His father in law who happened to be an engineer at Tektronix at the time melted the wax out of the transformers and took the guts and put them on a spectrum analyzer. Then he put in new caps to tune each band pass filter back to its center frequency again. Then resealed them back in the cans in the original wax again. The results were spectacular. So making these filters will take some ingenuity on your part to either duplicate what they originally used, or to engineer something else that does the equivalent job at 30,35, and 40 hz. It might be sort of a brick wall problem and was no doubt why others did this in Solid State. Mark  |  IP: Logged Mikael Christensen Film Handler Posts: 13 From: Vejrup, Bramming, Denmark Registered: Oct 2015 posted 09-27-2016 01:07 PM                     Hi Thanks for the reply :-) My theory is that the first "filter" A, is the bandpass filter. and the second B is some sort of transformer coupled driver stage, for the 6AL5 tube, due to the fact that there is a negative voltage of -20V. http://i283.photobucket.com/albums/kk294/dfmsbofa/ft1.jpg  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-28-2016 10:14 AM                     I believe that A is a low pass filter and that there are three of B, one for left, Center and Right. Or one B for each frequency. Filter A would cut off all frequency just above the highest control frequency of 40 hz. Filter B's output feeds the 6AL5 dual diode which rectifies the AC voltage output from the B filter and the resulting DC voltage is used to control the gain and phase of main audio stage for that channel. You can see from the following schematic (204 and 208) what is inside those eight band pass filters on these units. They would be quite difficult to produce and very expensive because they are going to have to be custom made and tuned. 208 is a high pass filter by the way. These units are VERY simple with the exception of these RCL filters. I spent about ten minutes on line looking for a company that can manufacture low frequency band pass filters to no avail. You might want to contact a company like Lundahl Transformers in Sweden to see if they might be of any assistance. They make the best audio transformers on the planet! They are also a small enough company that they might be interested in making something like this. You are gonig to need to kow the original specs of the filters as designed though. They were very steep filters. http://www.lundahl.se/ If I were going to do this today I'd do it all with Digital DSP. It would actually be easier to do and no filters involved because it would all be done in the digital domain. Mark  |  IP: Logged

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