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Re: RIAA EQ software

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Wed, 27 Aug 2008 10:16:21 -0400

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 ```At 08:16 AM 2008-08-27, you wrote: >Thanks for the tutorials, folks... > >Hi, [Richard] > > > You don't want to double-terminate the cartridge. > >Ok... I just thought that would get me a lot closer to Z = 47k, since the >combined Z would be what the cartridge actually "saw" (no?); the sum would >be about 50k Ohms, tops. What causes the difficulty? i.e., Why not "y-"? It sounded as if you are paralleling resistors. When resistors are paralleled, the value goes down. The formula is 1/(1/R1+1/R2+1/R3...). So if you have an input impedance of 25 K ohms, it is already too low, and there is no "negative resistance" that will increase it above 25 K by paralleling. If you place the resistor in series, you would throw away 6 dB of level and hence the same in noise performance where you can least afford it. Now capacitors add directly in parallel (and resistors in series). So if you have a 30 pF input capacitance and 120 pF of cables and want a 200 pF load, adding a 50 pF capacitor will work. >And here I thought that the capacitance (in the cabling, and entire network) >was merely something to try to minimize (due to the LPF effect of the R-C >network)... Yes, generally, but not in this case as the whole system needs to be matched to be flat. >If I were to use the 14 pF/foot Mogami 3080 cable, could I get to the target >loading value by merely making the interconnects 10 feet long? ]: (14 x 10 >= 140 pF) No, because the input has some capacitance so you need to subtract that from the Mogami capacitance. Ideally, you should have a preamp that has a variable capacitance and variable resistance to load the cartridge. Using the capacitance to smooth out square waves might be a good idea however, the CBS test records were cut with ringing on the square waves and that biased a whole generation of engineers including one of my mentors until I saw an article (which I don't have--but I think it was in audio) where someone did scanning electron micrographs of the CBS test record and it showed the ringing. It would be interesting to view one of these on an ELP laser turntable. >Or is it actually better (for other reasons than cap and Z, alone) to use >cabling which is as short as physically possible with a small tuning cap >hung off the ends? Preferred as the tolerances of everything seem that an adjustment range would be beneficial. Since I don't really DO this other than for my own listening enjoyment, I would caution that my advice may not be totally in keeping with what the people who DO discs for a living do. In fact, I know just enough about what I don't know about discs to be dangerous...one of the reasons I don't do discs is I know a good deal of what I don't know and don't have time to learn or budget to acquire what I need as I'm swamped with tapes and don't see the need to branch out. Cheers, Richard Richard L. Hess email: [log in to unmask] Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX Detailed contact information: http://www.richardhess.com/tape/contact.htm Quality tape transfers -- even from hard-to-play tapes. ```