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In Reply to: RE: Filters Done - Pictures posted by JimBop on May 11, 2010 at 14:47:56
Total removal of high frequency hash, increased clarity, increased detail, did I say clarity?
Seriously, I thought that the simple 0.01uF Multicap/10 ohm PRP made a nice improvement, but this is something much more. Any last trace of the Class D hardness that may have been present is gone (Gilmore Raptor monoblocks), and everything just sounds more real, from the midrange on up.
Note that the cap/resistor combo I'm using is optimized for the characteristic impedance of my speaker cables (Zu Ibis), which probably enhances my results.
I'm going ahead and potting these with MG Chemicals clear epoxy potting compound, which is not removable - that's how good they sound!
Follow Ups:
How do you optimize them for the characteristic impedance of your speaker cables?
JD
Well, first you need to determine what the characteristic impedance of your cables is. Perhaps your cable supplier can tell you. If not, you can calculate it if the supplier will tell you the series inductance (L) and shunt capacitance (C) of the cables. Then, the characteristic impedance (Z) may be calculated according to this formula:Z=sqrt(L/C)
In my case, Zu supplies the L and C values for their Ibis cables, so I was able to calculate it.
If you cannot get that information, the characteristic impedance may be measured, but you will need specialized high-frequency equipment for that, as we are now talking about the RF behavior of cables, which is governed by transmission line theory above roughly 100kHz. The key tenet of all transmission line theory is that the source impedance must be equal to the load impedance in order to achieve maximum power transfer and minimum signal reflection at the destination. In real world case this generally means that the source impedance is the same as cable impedance and the value of the receiver in another end of the cable has also the same impedance. What you are attempting to do here with the matching is to ensure that the maximum amount of RF is transferred into the filter and dissipated by the resistor, instead of being reflected back down the cable due to an impedance mismatch. What's cool (in my nerdy world!) is that when you match the impedance properly, the signal thinks it's in an infinitely long cable, because it never encounters anything that will reflect it.
Here's a nice little summary of the theory as applied to coaxial cables; the theory still applies to our speaker cables at RF frequencies, which is what we are attempting to filter out:
Edits: 05/13/10
Thank you for the detailed information.
The series inductance and shunt capacitance specs are not available for my cables. If I wanted to have them measured, what types of companies would have the equipment and experience to measure them for me?
Jim
Well, cable companies come to mind, although if it's not their cable they might not want to do it. You could ask them, though.
Telecommunications companies would have the equipment - know anyone who works for one of them?
So, now that you know the characteristic impedance of your cables (hopefully), all you need to do is to match the resistor value to that value - in my case it was 71ohms. Then calculate the amount of capacitance you need together with that resistance to achieve the -3dB corner frequency you would like, using the equation:
f=1/(6.28*R*C) , where resistance is in ohms and capacitance is in Farads
In my case, I wanted to get an f = about 500kHz, so I used 4.2nF of capacitance.
Do keep us posted on how the potting effects it, if at all, and how it burns in over time.
I'm assuming you are using the units on both ends.
I'm interested in your results that the grounding connection is best, but that either config works equally well. I did not try grounded to the (-) leg, as I recall, and those extra wires are not my favorite thing either!
Yes, I made four units, and they are located on each end of the speaker cables. I have them installed so that the spade of the speaker cable is between the spade of the filter and the amp/speaker, in other words the filter spade is furthest from the amp or speaker body. I did some extended listening last night and the clarity is really noticeable - on acoustic guitar I can hear the resonances of the guitar body and the decay of the strings more clearly.
The grounding experiments were interesting. Maybe my earth ground has a lot of RF noise on it from everything else in my house, but it did not sound better than simply grounding the shield to the (-) leg, in fact I thought it sounded a little worse (but not by much, it was close). To do that I simply alligator clipped the ground wire to the shield on one end and used an old cut off plug I had laying around to connect to the earth ground via the ground plug.
One thing I like about these units is their small size - they can fit right on the posts supported only by the silver leads; they look about the same size as the Walker units.
I potted them last night using MG Chemicals clear epoxy #832C. I'm not expecting any dielectric issues since there is very little wire exposed in the first place (only the solder joints, basically), and since the epoxy has a dielectric constant of ~3, which is better than polyester and PVC which many folks use as insulation on their wires. Since it is not a filled epoxy I don't need to worry about the dielectric properties of the filler. The epoxy flowed very nicely into the nooks and crannies of the box - I filled it to just below the top of the box, then bent the shield over and snapped on the lid. It's curing now and I should have pictures for you tonight. Besides the obvious benefit of rigidity and protection from shorting, the epoxy also has a higher thermal conductivity than still air, so it should help the resistor to dissipate heat (and thus RF) better. The hard epoxy combined with the Mortite damping layer may give some vibration control benefits as well.
I'll let you know how it works out.
I measured them after curing and they read the correct levels of capacitance and DC resistance (off scale) so the potting process did not destroy them (phew!). I took a listen to them after potting and they sound about the same to me as they did before; no changes that were obvious. They are now as hard as little blocks of granite, and pretty much indestructible. They are fastened to the speaker and amp ends of the cables and I don't think I'll be taking them out any time soon. Here's a picture, with a quarter for a size reference.
I used similar little potting boxes (though I confess that I didn't know that's what they are called.) Same reason: reduce size and weight, because the slim 20 AWG silver wire I was using wouldn't hold too much. I also used good silver solder and silver plated spades from Audioquest (?).
My amp end is a sigle R-C cascade, but still hooked up to both speaker cable posts. I never bothered to test out one for each cable and wonder if that might have made any difference.
I used the Microsorb recommended originally by cdc and didn't bother damping further.
I also surrounded the R-C with the grounded TI-shield. Mine don't cover the sides as well, but that was a very small difference from yours.
Yours do look more elegant and I appreciate all the careful trouble you went through, plus your detailed explanations and pix.
As you know, mine are grounded by 12 AWG wire to the power box, unlike yours. I run those through an updated AC rated version of the R-C filters of Al's design into my power strip. Works great this way for me.
Al calculated the values of C and R for me. It was difficult measuring my cables' values!
Sounds like like we did much of the same. I used WBT silver solder on mine. I haven't looked into the AC filters yet, but I'm using a PS Audio Power Plant Premier to power everything, so I think the AC is being filtered/regenerated pretty well.
AC filtering without any loss of dynamics is the key here. The AC versions (must be X- or Y-rated!!!!!) R-C array filters are yet another improvement. From others who have tried them, I gather that they are still an improvement even when you're using an active power filter/regeneration unit. So don't write these off.
But if you haven't yet tried Alan Maher's Infinity CBF units, you are really missing a sure thing!
These are passive devices using crystals (don't laugh, there's good science behind using piezoelectric crystals for filtering) that don't plug into anything. He sells them very cheaply and they are shockingly effective in improving sonics. Nobody has dissed them so far who has actually tried them. And they too work well with other AC filtering schemes.
If nothing else, I'd say try the Maher CBFs next.
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