I am wrong about 100x higher gain, since only fraction is fed back to the summing junction, but it is in the same level as nominal amplifier’s input. It won’t be as sensitive because of lower impedance, but will still inject noise picked up by long unshielded speaker cable.
Math + Logic + Science = something completely mad...
So, I've done a metric fuckton of research, notwithstanding the clear bias the man who designed and built my Belles has against esoteric cabling. And here's the conclusion to which I arrived.
My monoblocks are sitting on top of the speakers. The distance from the amp to the speaker is barely a foot, which is exactly how long a run of wire I intend to use. Goal is to minimize the effect the wire has on the sound.
According to the calculations I've seen and done, the skin effect depth on copper wire at 20Khz is 461 micrometers. Meaning a 19-gauge copper wire (911 mics diameter) would reduce skin effect to zero. As in no impact whatsoever on the signal.
Of course, it's actually very difficult to find 19-gauge wire. 18-gauge (1024 mics) is much easier, and the skin effect is near zero, but not quite zero. Seems to be an acceptable compromise. Could go down to 20-gauge and eliminate skin effect entirely. If I could find insulated aluminum wire, 18-gauge would eliminate skin effect entirely, because skin effect depth on aluminum at 20khz is 580 mics.
12 inches of 18-gauge wire produces 0.006 ohms of additional resistance. 20-gauge = 0.01 ohms.
Frankly, I don't see the value in spending big bucks on esoteric, heavy-gauge wire for this application. I'd rather make the bigger investment in the 2m runs from the preamp to the blocks, because that's where the wire's going to have a hell of a lot more of an effect on the sound.
Stepping back to allow you all the opportunity to punch holes in my thought process here.
My monoblocks are sitting on top of the speakers. The distance from the amp to the speaker is barely a foot, which is exactly how long a run of wire I intend to use. Goal is to minimize the effect the wire has on the sound.
According to the calculations I've seen and done, the skin effect depth on copper wire at 20Khz is 461 micrometers. Meaning a 19-gauge copper wire (911 mics diameter) would reduce skin effect to zero. As in no impact whatsoever on the signal.
Of course, it's actually very difficult to find 19-gauge wire. 18-gauge (1024 mics) is much easier, and the skin effect is near zero, but not quite zero. Seems to be an acceptable compromise. Could go down to 20-gauge and eliminate skin effect entirely. If I could find insulated aluminum wire, 18-gauge would eliminate skin effect entirely, because skin effect depth on aluminum at 20khz is 580 mics.
12 inches of 18-gauge wire produces 0.006 ohms of additional resistance. 20-gauge = 0.01 ohms.
Frankly, I don't see the value in spending big bucks on esoteric, heavy-gauge wire for this application. I'd rather make the bigger investment in the 2m runs from the preamp to the blocks, because that's where the wire's going to have a hell of a lot more of an effect on the sound.
Stepping back to allow you all the opportunity to punch holes in my thought process here.
62 responses Add your response
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Negative feedback increases the bandwidth w.r.t. the definition of bandwidth as the -3db point. However, it does not increase gain at that frequency. We are both going off memory but I am almost certain an amplifier in 1969 didn’t have the IMD numbers you are quoting. I wouldn’t guarantee it didn’t but I highly doubt it. Can you please confirm that in some manner?No, I remember year and even the store (spending vacation in London) but don’t remember model number or brand. You are right about lack of excessive gain at the high frequencies but I’m not sure how bad amplifiers in 70s were. Rectification phenomena is not even specific to electrical processes. It applies to thermal processes as well and can cause non linear electrical effects modulating back into the electrical signal, typically low frequency, but you can actually detect it in switching MOSFETs.Rectification phenomena, as it was described by Analog Devices, at their seminars is an electrical process. Uneven positive/negative slew rates combined with limited bandwidth result in DC proportional to amplitude of high frequency signal (hence demodulation) - at least that’s what I remember. You will easily find few opamps advertised as rectification phenomena free. I’m not sure if slew rate difference is the only reason for rectification, but you can find more here: https://www.analog.com/media/en/training-seminars/tutorials/MT-096.pdf The emitted RFI from switching supplies for consumer electronics is fairly low and the efficiency of conduction into a speaker cable would be low. You are correct the feedback gain is high, but still usually bandwidth limited, and while there are RFI noise sources, the efficiency of local wiring and audio wiring for picking up RFI from an antenna standpoint.It depends on switching supply. Some of them, like resonant mode SMPS, are extremely quiet while crude high current computer supplies pollute everything around. Amplifiers are bandwidth limited (not limiting already rectified/demodulated signal), and antena (speaker cable) has very low gain for <1/10 of the wavelength. It means that interference will be greatly reduced but not eliminated. I assume we can hear -60dB down from nominal signal level (equivalent to 1mV signal level). As for the standards - you can find them for everything. Bearingless torquemeters (that I used to design electronics for) digitally communicate from rotor to stator by high frequency pulses and two sets of coils. We had to lower frequency from 20MHz to 9MHz because field intensity was violating standard. Our competition almost lost business (had to stop production) because of that (Navy complained). In the proces we purchased NARDA calibrated EMF measurement device (scope). |
Ohm said: “Yes and if you can manage, cold press the ends, no solder. Treat the bare wire before you install it into the bore with a good enhancer. Graphite dust works great. If you have to solder, use GREAT solder, that is another boo boo, people make. They solder ends instead of tinning and using and enhancer with a cold press or HEAVY hammer strikes will work. 20-30 tons with 2 of my hammer strikes..” My question is how does that square with the fact the inside every component are hundreds of solder points. Why would a couple more on the ends of the connecting wires make any difference? |
@dletch2 this has been a great discussion and as a technically conversant DIYer I learned a lot. In particular this statement of yours: “We end up where we started R, L, C. Take a cable with low R and high L, and it will sound warm, the bass even muddy as it is too loud. Take a cord with high R, and high L, and the mids and vocals will pop out and be emphasized. Take a cord with high R, but low L, and the cable will come across comparatively bright. Have a high enough C, and some amps will be unstable and can come across as bright, potentially distorted.” ...was just the kind of distillation a relevant information that I have been looking for. Could you just go a few steps further and Define what you mean by high and low with regard to R,L and C. I have a Proster BM4070 LCR meter and I’ve actually been measuring some of the cables that I own to see if I can correlate numbers to sound and your statement helps tremendously in setting up a model of what to expect. The Proster was not an expensive instrument, about $40, do you think it is sufficiently accurate to make the kind of measurements we are talking about here? |
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bruce19 I replaced banana plugs with spades by crimping them first and then soldering with WBT 4% silver solder. I applied heat to end of the wire first to prevent spade expansion and loosing oxygen free connection. That way it's oxygen free and won't move. Plain crimper worked poorly so for my AQ spades I borrowed from local HiFi store AQ crimper and it worked great. Both look exactly the same - likely difference in quality. https://www.audioquest.com/accessories/tools/aq-ratchet-crimper 4% silver solder is probably overkill, but it is doesn't cost much. Measuring cable's inductance or capacitance with your LCR meter might be inaccurate since you measure distributed inductance or capacitance. One affects another. I believe there is a way of measuring it, by doing it at two different frequencies and then using formula to calculate it (inductive reactance is proportional to frequency, capacitive reactance is inversely proportional to frequency) . Unfortunately your meter measures at one frequency only. |
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"Here is the really funny thing for me. On here, I am considered this uber objectivist. When I deal with my technical colleagues, I am a bit of a pariah, because I always relate things back to subjective experience, and take a different more human centric view on accuracy. I have proven that humans are more sensitive to differences than was previously thought based on some specific variances. Because of that, I probably know more than most what we can and cannot detect. Hence why I am very confident about what happens with cables." There we have it. You are quite simply, a contrarian... |
