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Old 18th May 2007, 01:32 AM   #31
Tim__x is offline Tim__x  Canada
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Like I said, bipolar input amps like the NE5332 will work for the filter stages too, you don't need to use a fet input opamp like a 2134 or TL072.

The input impedance is increased to approximately Rin*Av*Bf, where Av is open loop gain, Bf is the gain of the feedback network (always less than 1), and Rin is much greater than the parallel impedance of the feedback network.

P.S. This is coming from quick in my head analysis, so it may not be mistake free. Simply put, one can usually regard an opamp's input impedance as infinite so long as the closed loop gain is reasonably low.
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Old 27th May 2007, 10:52 PM   #32
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I was looking at the various designs that people use, and I am looking at the dirt cheap capacitors being used. In the tube world, A small change in capacitor quality has a large change on sound quality. I was going to use orange drop capacitors for this, does capacitor quality matter? what kind does everybody seggest?
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Old 28th May 2007, 12:20 AM   #33
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The low value/voltage caps in active XOs are a lot cheaper than the relatively huge caps in passive XOs. Quite nice caps can be had for under a couple of dollars.

I've build my share of active XOs. The first was a dirt cheap experiment, using polyester caps and NE5532s. It sounded decent. I used polypropylene caps in the next XO - it sounded better, but the caps weren't the only change. I have also used Panasonic stacked polypropylene film, Wima MKP and FKP as well as some of Mouser's dirt cheap polystyrene caps. The 10% parts need to be chosen carefully from a large lot, so it ends up costing a bit more than you'd think.

Although I have never done a direct comparison without changing something else, I prefer polystyrene slightly over the stacked polypropylene caps which in turn I like better than the polyester. I still end up using cheaper polystyrene caps in the low end, due to space constraints. YMMV, etc.
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Old 2nd October 2007, 12:03 AM   #34
RyanW is offline RyanW  Canada
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Default Adding volume control to P09

Can anyone recommend a good method of adding volume control to the P09? I was thinking of cutting a few traces and installing a dual gang 10k log pot between U1 and U2/U5... Would this work? If not, I will likely build a P88 or P97 but it seems that this would add unnecessary opamps to the signal path.
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Old 2nd October 2007, 07:55 AM   #35
Eva is offline Eva  Spain
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Extra op-amps are always worth when their purpose is to do some useful task (particularly when they add correction to make loudspeaer response more ideal ) Exotic expensive components are just not worth the effort. Speaker THD is usually above 0.1% at any listening level.
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