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I'm still waiting for the TX2575 resistors from Texas Components, but in the meantime I've done some experimentation using PRP resistors, Multicaps and Silver Mica caps. I feel that the best sounding capacitor combination on my system is a cascade of 4 silver mica caps, so that is what I'm going with. The cascade will be 2200pF, 1800pF, 180pF and 18pF, all connected to a 71 ohm TX2575 resistor to match the characteristic impedance of my speaker cables, giving a -3db point of ~530KHz, right at the bottom of the AM band, and far enough away from the audio band to cause no concerns.
I have built 4 small boxes of TI-shield which fit inside an ABS plastic potting box about 1 3/16" X 1 3/4" x 1/2" OD (Mouser Electronics). The attached picture shows an empty potting box with lid, the TI-shield box alone, the TI-shield box inside a potting box, and the cascaded caps. Once I get the TX2575 resistors I will assemble it all and experiment with grounding arrangements for the TI-shield, i.e. none, grounded to the (-) leg of the speaker cable ala Walker, and grounded to earth ground at an outlet ala our own cdc. I will also need to decide how I will damp/insulate the circuit from the shield - right now I'm leaning toward potting the entire assembly with epoxy potting compound.
The whole completed assembly is only 1 3/4" long and will fit very nicely either over or under the speaker and amp binding posts. Also, putting the TI-shield inside the box gives IMHO a nicer exterior appearance, and prevents the shield from ever shorting across the binding posts.
Stay tuned.
Follow Ups:
Sold in Ace Hardware stores, at least in earthquake country, this clear paraffin wax is meant to stick expensive tchotchkes down to shelves so they don't fall over in the event of earthquakes.
It works well for me to stick capacitors together to avoid acoustic chattering.
You don't want springy material, as it does not absorb acoustic energy. Instead, it allows the treated objects to resonate.
I'm thinking that I might stick the caps to the box and to each other with Mortite, then pot the entire assembly in epoxy. The caps are coated with hard epoxy as is, so adding mortite and then hard epoxy around that should make a type of constrained layer damping system around them. That ought to keep them quiet, no?
Damping materials are also dielectrics, and some of them give poor sonic results depending on where one puts them and the taste of the user. The late lamented Microsorb was one of them. I have one friend who likes it and another who cannot stand it. There are also some folks who do not like the effects of Teflon. Cotton batting is a benign dielectric but a weak damper unless it is compressed to some degree.
Mortite would be excellent for vibration damping, but might cause a noticeable change in the tonal balance compared to the undamped caps. I would try your idea in stages, so that you can change plans if you find the sonic effects of the Mortite to be not to your taste. An alternative would be to wrap the caps tightly in cotton batting and compress it further by wrapping tightly with Teflon thread-seal tape.
Thanks, Al. The TX2575 resistors just arrived in the mail today, and the wife is going out tonight to a cooking class, so I will be working on these tonight. I will certainly proceed in stages as you suggest, with the epoxy potting being the last stage, of course.
Well, the filters sound excellent with the Mortite on the caps and the back of the TX2575 resistor - it is only applied to the exterior of the component bodies, not to any wires. I'll let it break in for a while and then I plan to pot the whole assembly with clear potting epoxy and pop a lid on the box. For now I just bent the shield closed and used it that way.
By the way, I tried no grounding, grounding to the AC outlet earth, and grounding to the (-) leg of the circuit, after the resistor. I could hear no difference between the earth ground and the ground to the (-) leg, and they both sounded a little better than no ground, so I went with the ground to the (-) leg, since it is simpler and requires less wires to be run around the room. You can see the ground wire soldered to the shield and connected after the resistor. The wires in and out are DH Labs solid core silver with teflon jacket and the spades are Audioquest gold over copper. Here are some pictures:
:)
Can you tell me what sonic changes/improvements you hear with these filters?
Thanks,
JD
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!
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.
nt
Yeah, that museum wax is a bit harder to find out here on the east coast (no earthquakes). The GelWax looks like it would be very good for vibration isolation, and I think it is a similar material to what is in gel pads in shoes and gloves, handlebars, etc. for isolation. It must absorb some vibrational energy as it compresses and rebounds, but it is more like a spring than a shock absorber, I guess.
Edits: 05/09/10 05/09/10
Great resistors & caps. For RC I have been using FT-1 teflon cap with Mills resistor, and have been intending to substitute SSG silver mica cap with Duelund resistor. Are you using several TX2575s in series for this? If so, how many?
Just one resistor per filter. I want to be able to keep the resistance constant and equal to the characteristic impedance of my cables (71 ohms), and that cannot be done with parallel RC networks since branches of the circuit roll in and out as the frequency increases. I suppose several resistors in series may offer some advantages but those TX2575 are kind of pricey, and there is not a whole lot of room in the potting box, so for now I'm sticking with one per filter. They are rated for 0.6W per resistor - plenty to filter residual RF frequencies from your speakers. It takes a couple of weeks to get them from Texas Components, but the nice thing is they will custom make any value you want for no extra charge, so you can get the exact values you need and don't have to settle for stock values.
Edits: 05/08/10 05/08/10
I ran across something called GelWax (made by Yaley) today in a crafts store, and it might just be perfect for potting the RC filters. It is actually mineral oil which is gelled with the addition of a polymer - the grade I bought has the consistency and resilience of firm gelatin ( but is stronger), yet it melts easily on a stovetop and can be poured into a mold. I can press my finger about 1" deep into it without it breaking apart, and when I release the pressure it springs back to its original form; it is also non-conductive and clear. Apparently it is used to make candles containing inclusions like glitter, etc. I'm thinking it might be perfect for this application as it will absorb vibrations, is non-conductive and can be removed for later tweaking (as opposed to epoxy!).Once I give it a try I'll share the results.
Edits: 05/08/10 05/08/10 05/08/10 05/09/10
you try getting it in 1/2" pvc without burning yourself :) Seems like it would be easy but I never pulled it off.
Anyhow, that produced some great cables and now it makes more sense as to why.
THough long term the gelwax always seemed to change colors or absorb them or leach them from other things. So I would be worried about the longterm effects on the materials it is around.
FWIW, I havent used it in say 6 years.
Thanks for the info. I gave up on the GelWax idea for various reasons, probably the biggest was that the melting point of the GelWax is higher than the melting point of the ABS containers I was going to pour it into! It is also a bit too springy to absorb vibrations optimally - I went with Mortite pressed onto the caps and resistor instead.
First, try it without a vibe damping compound. I suggest this for a reason!
Mineral oil has its uses, but while it is non-conductive, it does convert electrical energy to heat energy. This is not the application I'd use it with at all, though who knows what might work....
What you should try, if you can still find it, is Microsorb. If you can't get that anymore, then try blu-tak or cotton balls. The latter are very good to use between between the components and the TI and also between the TI and box if you need it.
You will want to connect the TI into a roll. Ask Al how you should do this. Make sure that you fit the TI so that it doesn't short out your components (Rs and Cs).
A la CDC, I tried different grounding schemes, as I told you before. None, grounded to outlet by separate wire, and various AWGs of wire. As CDC said, the 12 or 14 AWG grounding to the outlet by separate wire DOES work best in my system too.
As per Al, silver mica caps do work best in my system for speaker cable filters. I also use a 3 or 4 R-C array here.
Thanks for the tips. Mineral/paraffin oil and waxes are used in capacitors all the time, where they can encounter much more electrical energy than the GelWax will here, so I'm not too worried about that, in fact I have PIO caps in my tube preamp getting way more voltage. Waxes are used all the time for electronics potting - the guitar guys like a 80/20 mix of paraffin and beeswax for potting pickups, and I was actually looking for paraffin wax when I stumbled upon the GelWax, which has a higher melting and ignition point than paraffin. As for converting that energy to heat - great! That's exactly what I want the resistor to do with the RF energy, so the more the better. The advantage I see with GelWax over paraffin/beeswax is its rubber-like consistency; it's very resilient and should make an excellent damping compound - next time you're in a crafts store check it out, it's pretty cool stuff.All that said, I wouldn't use it in an AC line filter - too much energy there.
Edits: 05/08/10 05/08/10 05/08/10
Maxamillion, bartc, Al a couple of us have sucessfully used linseed oil, but you need to wrap caps in silk or cotton and load it with oil, which eventually has a lovely gel like feel. I scalped all the caps in my cdp and pre prior to linseed oil damping, but never again prob, as its too time intensive - works nicely on opamps etc. Think I'll look into blu-tak or mortite and equivalents. Thanks for the posts.
You realize that it does eventually solidify sort of, not just gel. Linseed oil has been used for centuries in oil painting as a medium. That means that it does eventually dessicate or El Greco's work would be running off the canvas! Al has cautioned in the past about using organic materials that harden like that.Meantime, mineral oil is good for turning vibes into heat (or so I read and have found in using it) and does not dessicate quickly at all.
Frankly, I like Max's solution of mortite and then potting. Makes most sense to me.
I'm using either Microsorb or Al's cotton batting solutions for the damping and both work fine.
Edits: 05/19/10
Hope you see this bartc.
Didn't have (easy) access to Microsorb (I don't live in the US) so moved on and tried Blu-tak, Power Tack actually, but I suspect there's not a large difference - it met what I figured was required.
I used it to damp the backs of my speakers Beryllium drivers, the woofers aluminium spiders/frames, the crossover. You need to know that I used boat loads of the stuff - you also need to know that its been terrifically successfull.
I suspect it'll be like Mortite and will harden somewhat over time - I'll check in 5yrs!
Last was the crossover - late last night I compared a finished speaker ie all drivers HEAVILY damped, crossover HEAVILY damped, with the speaker that had the drivers damped only. The undamped crossover is the only difference.
Well I'm stunned at the difference I can hear - it ain't subtle. Worst case scenario I guess - crossover directly behind the woofer.
Yes points well made - but according to my test pot, it'll be a long time before its a problem - my cdp and pre will have departed! I rather like the prospect I read via DIY I think > oil based modelling clay. One poster used it in speakers in the 70s and it is still fine - seemingly it never hardens. Well suited to the backs of drivers apparently.
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