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hi all
I have an XM44 crossover on order. have a balanced unit ordered. are there any REAL enhancements that you wish you had ordered ?
Thanks
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Ask Phil to customize the filters to match the OEM filters as close as possible. Do not use the Magnepan recommended xo points for active biamping as they are only a gross approximation. For the 20.1 The mid HP filter is first order at 360 Hz and a 20k resistor and 22 nf cap on Phil's module will be near perfect. The LP filter is 3rd order at 110 Hz but is not quite an orthodox Butterworth although fairly close. From my spreadsheet I got the following values: R4=39K C5=39nf R6=27K C7=27nf R9=27K C10=100nf. You can have Phil confirm those.
One other suggestion, get the three way model just in case you decide to tri-amp in the future.
Edits: 04/19/15
A couple of things I'm planning, but haven't done yet, is to upgrade the power supply (PS10 for my XM9s) with better capacitors and replace standard diodes with FREDS.
Mark in NC
"The thought that life could be better is woven indelibly into our hearts and our brains" -Paul Simon
I don't know about FREDS. What about simply using CAPS in parallel with each diode in the bridge to reduce noise / switching hash?
Too much is never enough
That is not a bad idea but FREDs are what my modster friend uses as they do the job better than old style diodes.
In what way 'better'?
I'd love to take a SCOPE and see the swithcing noise generated by various diodes.
Too much is never enough
I never asked him so I will have to ask when I get a chance.
He does use a scope to help track down problems and to see what "changed".
I don't know how much of what a FRED does over a traditional diode is less switching noise, but switching noise would not be eliminated by a parallel cap or cap to ground.
Even with FREDs he adds chokes everywhere in the PS where feasible.
Copied from the PASS DIY site.
Per Pass DIY SITE.
Rectifiers.
Yeah, sure, rectifiers are important, after all, the AC has to get converted to DC, but I don't like the fast recovery types that some audiophiles have raved about. Fast recovery means that they withstand many amps and volts in a tenth of a few nano-seconds, something we don't see very often on the old 60 Hz AC line. They are essential element in switching power supplies, but for regular "linear" power supplies, I much prefer SLOW diodes, and we create them by placing small capacitor circuits across the diodes, which greatly reduces radiated noise.
This is the reason I asked. Believe your guru? Believe Pass? I have no idea. Just asked a question:
Too much is never enough
I can say that is a reason some use tube rectification and gas diodes but my modster friend does like his FREDs. I don't doubt that Pass is right about switching noise reduction with slow diodes, I also don't expect my modster friend has the slightest issue with existing noise levels in his tubed and vinyl centric system. Those are way below what is inherent in this source and gain devices. His main noise reduction step was to use a MM cartridge. A step I readily took myself.
He dud have a hum issue that he traced back to the filament power supply on his preamp's phono stage which he powers separately through a separate tranny and regulator board.. So he put a choke on it and got a cleaner regulator and it solved the issue. He says it easily covered the cost of the scope that showed him where the hum was coming from.
Nelson is of course correct. Standard diodes are just fine....you can use RC snubbers on the diodes if you like, but even those are not really necessary with line-frequency applications.
These are not SMPS supplies we're dealing with here.....just simple linear-regulated +/- supplies delivering low current.
Dave.
I don't know enough about this in-depth to evaluate your question. I found the FRED sub idea on an old AA post. Perhaps someone with deeper electronics background can comment.
Mark in NC
"The thought that life could be better is woven indelibly into our hearts and our brains" -Paul Simon
I would second those though I had not done that myself as they were beneficial in other components. I would also upgrade the caps in the XO cards to better foil types. Made a significant difference in imaging and clarity and major in taking some electronic edge off. note that foil caps are far larger for the same values.
Most likely that would be a downgrade not an upgrade. Phil has been supplying excellent capacitors in the frequency modules of his crossovers for years now. Either polypro or usually polystyrene types. These are small value capacitors.....a couple of nanofarads usually.
Dave.
I am not saying they are bad but the foils are better - particularly noticeable with high order filters. Even the cheap Dayton foils sound smoother and fuller while not robbing you of detail. This was not trivial.
Also Burson op amps in the input section are a plus by some reports
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