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speaker cables are 17 foot with about 1700pf total capacitance with characteristic impedance ~18.5 ohms. Speakers are 8ohm. Does this diagram look about right?
Follow Ups:
nt
I tried wiring the TI-Shield directly to the earth ground using a Oyaide brass plug, 12ga. THHN wire and copper ring. Huge difference, not subtle. Although with tube gear, wiring the TI-Shield directly to the R-C network may prove to be more satisfying, depending on how the system sounds now. Wiring the TI-Shield directly to the earth ground instead of the network sounds very similar to tube gear. Meatier and thicker midbass through mid frequencies. Added a bit more inner detail, sweeter but a tad rolled off HF compared to grounding to the network. The network without the TI-Shield sounds thin but detailed (reminded me of Krell gear), with the TI-Shield a bit warmer with other benifits. Wired to the earth ground the presentation is completely different. I can report back after treating more of the system and then critically listening. Since I tried this on one speaker only and did comparisons with the rest of the system speakers, I will not know how the entire system will sound with this tweak in place yet.
Chris
Give the network a good week to adjust to the magnetic field created by the earth ground.
Alan
nt
The R-C networks provide damping for the normal mode ringing on the line. This is the mode where the ringing wave voltage is from the (+) to the (-) wire within the speaker cable.
The common-mode is where both wires act together as a single wire and the wave voltage is from both wires to the outside world, which is close to the AC safety-earth potential. The R-C networks do not provide any damping for this mode, and are carried along with it at the cable ends.
A grounded, isolated material with some resistance is able to provide common-mode damping without adding the circuit complications that would arise if one were to connect R-C networks from the speaker terminals to the AC safety-earth (DO NOT DO THIS!!!).
Another material that might work is carbon fiber cloth. TI Shield is easier to make a solid connection to safety-earth, but be careful of any acoustic resonances in it.
In reading some of your other posts on commmon mode ringing, you mention that wrapping the speaker cable in carbon fiber cloth and securing with Teflon tape, particularly near each end (but better for the entire length) addresses common mode issues. But I don't recall mention of grounding the fiber cloth. Is that an "extra step" one could take, or is this entirely different; here we are talking about TI shield or Carbon Fiber betw *only* the RC network and speaker?
TI Shield is conductive, and the reports here from others are that grounding a piece of it wrapped around the R-C networks provides a benefit. I thought about what advantage the grounding could have, and concluded that doing so should improve the common-mode damping. However, I have not yet done something like this myself (too many other projects).
My cables have carbon fiber sleeve on them as you described. Since the sleeve covers both conductors, it is relatively ineffective for normal-mode waves. However, it would be effective for common-mode waves. It would be difficult to make a secure and permanent ground connection to it, as it cannot be soldered. It seems to help just used as an ungrounded wrap. I can't say whether grounding it would make it work better.
Carbon fiber is conductive, but much more resistive than TI Shield material. I use it along most or all of the cable to improve the damping. Using TI Shield in the same way would be like adding a conventional shield, and increase the cable capacitance with little series resistance. This might upset the tonal balance or create problems for the power amp.
Another caution is that I believe the AC safety-earth wiring ("ground") is a carrier of RF noise. Adding another connection to the AC safety-earth may increase the amount of RF noise that gets into the audio system.
Microsorb backing will take care of any ringing concerns.
Alan
TI Shield is helpful in all electrical applications. In this one, the TI Shield is helping to damp the ringing character of the network....this is a very good thing. Becareful not to add too much ringing into the circuit.
Alan
So I will know how many to modify, what do you guestimate the change will be? Will it tilt more to the warmer side, more toward neutral or?
Thanks bro,
Chris
The three 3650 pF caps are to replace a single 10,000 pF cap which is no longer easily available. Either wire all three in parallel and then in series with a single 20-ohm resistor, or wire each cap in series with a 60-ohm resistor and connect the pairs as shown in your diagram.
There may be some interaction among caps wired in parallel, so the 60-ohm resistor method may give better results. I don't know, as I've not tried this.
Your orientation is correct regarding polarity (negative wired to the resistors, positive from the caps). The formula I used is based on Al Sekela's experimenting and suggestions. I am currently experimenting with these networks and have built 14 of them so far using different materials (other then the recommended caps and resistors by Al Sekela). By the way, using different wire, solder, damping, termination/spades, shielding vs non-shielded all makes a difference. Here is Al Sekela's cap and resistor recommendation and what you see in the pic:
* three 3650pf Silver Mica caps to one PRP 10ohm resistor
* one 360pf Silver Mica cap to one PRP 10ohm resistor
* one 36pf Silver Mica cap to one PRP 10ohm resistor
Chris
Thanks Chris for the validation. Yes, I'm basing this off Al's posts also, and am using silver mica's and prp's although I am going to reorder prp's in 18-20 ohm to match the characteristic impedance of my cable.I'm using the alpha core silver spades Al recommends.
May I ask:
- your pic shows all 3, 3650pf caps tied to just *1* resistor; mine shows 1 resistor for each of these 3 caps ??
- what type of wire you like to use?
- is that microsorb underneath the RC's?
- where might I pick up a plastic enclosure? That's a good ideaThanks
Here are the answers to your questions:
Q: your pic shows all 3, 3650pf caps tied to just *1* resistor; mine shows 1 resistor for each of these 3 caps ??
A: That is correct, this is what Al recommended
Q: what type of wire you like to use?
A: I have tried several including Gold alloy (gold, silver, copper mixure), 5N copper, 4N silver from two sources and Cardas 5N silver. I have not tried pure gold yet. So far the wire I like the best is Cardas 24ga. 5N silver from Percy. I also polish the Cardas wire.
Q: is that microsorb underneath the RC's?
A: Yes it is Microsorb. I tried the wrapping teflon tape as Al does. So far, I find that the Microsorb seems to work the best.
Q: where might I pick up a plastic enclosure? That's a good idea
A: Radio Shack, the dimensions are 1"H x 2"W x 3" long. $2.69. I use brass screws instead of the steel screws that come with the enclosure. I also use a brass bolt, nut and washer for the TI-Shield (see the lead with a loop coming off of the last resistor).
Chris
that is not shown? Yes I wondered what that wire was for. So you are grounding the TI shield...and the shield is between the RC network and the speaker drivers?
Yes, the TI-Shield is on the underside of the cover and not pictured. I probably have taken 10-11 pictures of the different R-C Networks I have built. If it helps I can post a pic or two of the TI-Shield. The TI-Shield is grounded to the resistors. With the TI-Shield installed, the presentation is a bit warmer/more organic then without. No noticable loss of information with the TI-Shield installed. I use cotton in between the TI-Shield and the rest of the network, to ensure that there will never be a short.
Chris
Chris
Remember we were talking about warmth....I got an idea....remove the internal TI Shield ground wire and earth ground the TI Shield back to the ac outlet...that should warm things up a bit. Use a good 12ga insulated copper wire for the ground....copper spade as well. Keep me posted.
Alan
...
Sorry....we had a DEXTERathon today in the Maher household....just got the dvd series in the other day. Check you mail...I sent my response.
Alan
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