Interconnect Inductance vs. Capacitance


How do the inductance and capacitance of ICs impact the sound? I have seen some ICs that have low inductance but high capacitance. On the other hand, some ICs have high inductance but low capacitance. One manufacturer even claims that his higher models have higher capacitance.

So can someone explain to me how they impact the sound?
vett93
Let me give an example to illustrate my point. I had a DIY preamp project recently. I used 0.68uF for the output coupling caps. Since my power amp has an input impedance of 500K, it yields 0.5Hz 3db cut-off freq. Then I changed the output caps to 10X value; i.e., 6.8uF. The 3dB freq. is now 0.05Hz. Interestingly, I can hear better bass. A couple friends can hear that too.

Interesting. 500K is pretty high for input impedance. Did you ensure their was a return path for input bias current on the power amp? (Charge can build up in coupling caps if you aren't careful)
I think in the end the best approach is to design for minimum capacitance AND minimum inductance (as well as minimum resistance). That is the approach I took when designing my interconnect cables. http://forum.audiogon.com/cgi-bin/fr.pl?fcabl&1243691470&openmine&zzRova&4&5#Rova

Of course it is not possible to do so perfectly and you must alway balance the compromises you must make. Ideally you want to pass the signal from one end of the cable to the other without loss, or change in any way.

As I said I tried my best to make the optimal balance of compromises while attempting to meet all requirements. I think I have made an interconnect that is on the right track. I'm very pleased with the results. (So are a few others who have built cables from my design).

ROVA
Good responses by all. Yes, I too was wondering about the 500K -- that seems unusually high, and I would imagine that parasitic impedances in the circuit could become significant relative to that value, at least at high frequencies. But more significantly, I suspect that Vett's capacitor experiment is most likely a good example of what Redkiwi was referring to when he said:

One of the problems in science is that when experimenting you need to assume certain variables are not relevant in order to observe the impacts of an experiment on what you believe to be relevant. You cannot screen out all other variables all of the time.

My guess would be that the differing results with the two capacitors were not the result of the different capacitance values (the variable being tested), but were the result of differences in the departure of each device from being an ideal capacitor. Dielectric absorption, ESR (equivalent series resistance), leakage, stray inductance, and other known and unknown parameters make every capacitor something other than a pure capacitor. Which is why it is fairly widely recognized that different makes of capacitor, of the same values, can sound different, especially when they are in the signal path.

Redkiwi, I certainly agree that digital cables can sound different in an audio system. It is fairly widely documented, both in this paper and in threads at this and other audio forums, that 1.5 meters is an optimal length for cd transport to dac connections, and significantly shorter lengths will increase jitter by causing the round-trip timing of reflections from the dac input, and re-reflections from the transport output, to be such that the re-reflection would arrive coincident with edges of the original waveform. Of course, the degree of that effect would be dependent on the degree of impedance mismatch at both ends, as well as on the rise and fall times of the transport output, and the jitter reduction capability of the dac (if any).

Re skin effect, I haven't performed or studied in detail any analysis of its relevance to audio frequencies, but based on what I have read I would not disagree that it could be marginally relevant in some cable configurations.

I do still feel, though, that inductance and characteristic impedance are not relevant to analog audio interconnect cables of reasonable length, particularly in the bass region. When you say
If the characteristic impedance of the cable is below the output impedance of the upstream component then phase errors can get audible, particularly in the bass, and is a major cause of the belief that interconnects can be system dependent.

my feeling is that something else must have been going on to account for the differences your testing revealed. Of course, as I noted previously, inductance certainly can be expected to be a significant factor in a speaker cable (as opposed to an interconnect, where source and load impedances are much higher than for a speaker interface). And since characteristic impedance is a function of inductance (and capacitance), there may be an indirect correlation between speaker cable characteristic impedance and performance, but not in the usual sense of impedance mismatch resulting in vswr effects.

Regards,
-- Al
Regarding the 500K input impedance, a common-cathode tube input stage can indeed have high input impedance levels. If you measure the resistance between the grid and the cathode of a tube, it is in the order of several mega ohms or higher. To lower it to 500K, one would need to put grid resistors to get that level.

Another concept to clarify is that it is the output impedance of the preamp that can cause the roll-off highs, instead of the input impedance of the power amp. This is because the capacitance of the ICs and the preamp output impedance form a low pass filter.

Regarding the experiments with two capacitors, the smaller value ones are actually the higher end model. The smaller ones are Mundorf Silver/Gold & Oil, and the larger ones are Mundorf M Caps.

TRL told me that they had experimented various capacitance levels of the same brand and same model of capacitors. Their findings were similar to mine. If you look at the Dude preamp, you will be amazed by the size of the output coupling caps.
Just out of curiousity, do you think that anyone selling cables has IC designs that would exhibit enough capacitance to grossly affect high end frequency response? Isn't this more an issue for the designer than the consumer?