This app note gives some some relevant stability considerations for feedback amplifiers with a capacitive load.
I always laugh when people post pics from hifi shows where you see speaker cable that looks like an Anaconda. 🙂
jeff
jeff
Which takes me back to the question: what is the proper way to measure capacitance for this cable?
I took the time to measure the capacitance of the cables as well as the length. I was just eyeballing them when I pulled them out of storage, so I thought they were 8 feet in length; in reality they're 13 feet long. Since they're intricately braided I should say they're technically longer than that. Using my B&K 815 and Rayma's advice, I got a value of .987nF from one cable and 1.017nF from the other. At the extreme length of these cables I'd say thats not too bad, based on the table given in the DIYAudio Projects cable page I referenced earlier.
Or is it? I don't understand this topic enough, I think.
Or is it? I don't understand this topic enough, I think.
... And it's sitting on little piers to keep it off the ground because apparently having the wire jacket touch anything but air or those little piers means that the sound is corrupted irretrievably. 😀
You should see the IEC power cables that came with my PS Audio Power Plant. 😳
To keep the impedance of the cable much less than the impedance of the speaker drivers. Its about damping factor, not necessarily max current handling.
Nope, microphones have completely different requirements from speakers. Use speaker cable for speakers, microphone cable for microphones - speaker wires require no shielding at all, but they carry large currents and need to be solidly constructed. Typical currents in a microphone circuit are a few microamps, speakers pull amps. Quality microphone cable will concentrate on shielding, flexibility, semiconducting foils to reduce electrostatic induced noise when the cable is handled while in use. Quality speaker cable should be low resistance with solid brass connectors to carry large currents reliably (and no iron or steel in the wire or connectors). Longer runs need thicker wire for speakers, not an issue with microphones.
Your cable probably just fused on loud sections leading to intermittent connection.
I checked with my friend about the wire he used. I had it wrong. He said "I do not remember exactly which wire I used when I made those for you. for a while I was using just extension cord 18 gauge wire". Now that I think about it I believe I asked him if he'd pulled any mic wire, based on something I'd read elsewhere that said it would be perfect for making speaker cables, and he said he'd just torn apart a huge system and had thousands of feet of discard high quality wire from various categories. I assumed he'd used mic wire but he didn't. He's out of town on another huge job right now but he's going to look into it when he gets back.
I'd say that's not actually very relevant, twisted pair is all about 70 to 120 ohms characteristic impedance, so when driving an 8 ohm load its pretty irrelevant - a good amplifier should be safe with a 100's of nF loading anyway, so unless your speakers are a few blocks away from the amp the capacitive reactance it presents shouldn't be bad news. And twin cable isn't too different from twisted pair - most (reasonable) cables are in the range 20pF to 150pF per metre, amps always have to be able to handle a few nF total, and with the normal inductor output network can handle any amount of capacitance...
I threw the cables off to the side while I work on some other things, but with some time to kill I looked over all my saved info and found more details. My friend works as the national lead tech for a major PA company, and he was the one who provided the raw wire stock for these. In an old text he described them as the "14ga wire we use". He's using a similar set of cables to run a very good system at his house using Canton speakers and a Bongiorno amp, I can't say which one at the moment.
I found a picture of the wires before I added banana connectors and the flexible jackets:
I found a picture of the wires before I added banana connectors and the flexible jackets:
I made speaker cables using 16 awg burial rated speaker wire that got a lot of "giant killer" buzz a decade ago because it was half the cost of usual pro grade wire. Worked, except for intermittent popping sounds. I could not measure a problem with my limited equipment, but both left and right cables behaved the same. Whatever insufficient insulation/oxidation/capacitance caused the problem was pervasive with that wire. I stick to dedicated speaker wire from trusted manufacturers and vendors now.
That reads a lot like whats happening with my wire, but I wouldn't say it's a popping sound, more like the scissors noise from a working barber. It's faint but noticeable and irritating.
I forgot to mention these wires didn't do this on the ground floor of my house, on two separate systems. But on the top floor they were passed around to several systems and several pairs of speakers and the clicking symptoms followed the wires.
I'm going to give these back to my friend and start over with proper wires, same as you. I don't have enough hours in my life to wonder about this stuff anymore.
I forgot to mention these wires didn't do this on the ground floor of my house, on two separate systems. But on the top floor they were passed around to several systems and several pairs of speakers and the clicking symptoms followed the wires.
I'm going to give these back to my friend and start over with proper wires, same as you. I don't have enough hours in my life to wonder about this stuff anymore.
UPDATE
You guys who suggested this was an amplifier issue were proven correct. I then pulled the Carver amp and preamp from this setup and put it with different wires and yet another pair of speakers, the results were interesting to say the least: entire swaths of the frequency band were missing. The preamp has already been serviced immediately prior to this experiment so it seems that the amp was the problem.
You guys who suggested this was an amplifier issue were proven correct. I then pulled the Carver amp and preamp from this setup and put it with different wires and yet another pair of speakers, the results were interesting to say the least: entire swaths of the frequency band were missing. The preamp has already been serviced immediately prior to this experiment so it seems that the amp was the problem.