Interestingly, TRL told me that Blue Jeans Cables RCA interconnects are good enough. Paul may be right as these BJC ICs have the lowest capacitance that I can find anywhere! This man has integrity!!
TRL's cables are not cheap though. So I am exploring all options. It would be great if manufacturers can offer in-home trial. Then I'll find out if they can beat BJC's $50 10-ft ICs. :-) |
I recently changed the preamp, from BAT VK-3iX to the Dude from TRL. I also had to get a new pair of RCA ICs between preamp and amp, as the new preamp is single ended and the previous preamp used balanced connections.
So I got a 10ft pair of Blue Jeans RCA interconnects. They seem to work fine. Another owner of the Dude preamp suggested the top line model from Audio Horizons. Their website indicated that the cable capacitance went higher and higher with their higher end models. This does not give me a warm and fussy feeling to try them.
The Dude preamp has extremely high output impedance, as the volume control is at the output. The volume attenuator has a max resistance around 100K! So I am reluctant to use ICs with higher capacitance for the reasons Al stated.
Thoughts are welcome.
PS. The Dude preamp sounds very very good even with the high output impedance. |
The Cable company offers only standard length cables for loan. They also charge 10% of the list price of the cables as the fees.
I do have various 1M ICs and I have tried them between the CDP and preamp. I do hear differences among them and I like the Reality Cables the best. But, the difference between Reality Cables and BJC 1M ICs is quite subtle.
The Reality Cables use a twisted pair design for the ICs, which would increase the capacitance. It works great with a short 1M run and the CDP which has a low output impedance. I am not sure that it would work well for the Dude preamp and at a longer length.
I have tried Anti-Cable's speaker cables. I know that they have a lot of fans. But they don't work well in my setup. I heard some artifical coloring to the sound which was un-natural to my ears. |
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. |
Thanks all for the great comments. I understand that the capacitance and the inductance are not the whole picture for most high-end audio gears. Like what I said earlier, I have a preamp that uses a 100K attenuator at the output and I need 10 ft of ICs between preamp and power amp.
Let me use an example to illustrate my point. Take Cardas Golden Cross ICs as an example. According to its website, the capacitance is 25.5 pF/ft. For 10 ft ICs, it yields 255pF.
Since the preamp attenuator has 100K max resistance, let's assume 50K ohm output impedance. With these two numbers, let's compute the 3dB roll-off freq, Fc.
Fc = 1/(2*Pi*R*C) = 12.5 KHz
As you can see, the highs are significantly rolled in this configuration! Hope it all makes more sense now. |
A gap between theory and reality is that there is no theory (that I am aware of) explaining how human being would perceive various specs in high end audio. I have never seen any EE courses relating human perception and technical specs in any length of details, even after my 3 EE degrees.
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.
I am not sure that there is any theory that can explain it!
Back to ICs. Redkiwi, your postings are interesting. Can you tell us the specs of your ICs after you improved the skin effect?
Thanks. |
Thanks Al for the comments. Let me further clarify two points.
If you think 6dB attenuation is not enough, a higher level of attenuation will actually lower the 3dB freq. A higher level of attenuation means that you will have a larger R value in series with the output. So at a lower sound volume, the highs will be rolled off even more and yields a narrower bandwidth!
The 2nd point is that my power amp needs 4V RMS to achieve full power, 100W/8ohm. The preamp has 12dB of gain. Most CD players have max outputs between 1V-2V. So the 6dB setting assumption is quite appropriate for my setup. I usually set the volume control knob anywhere between 10 to 3 o'clock, and I don't listen very loud....
Mathematics R us! lol...
|
The interactions between human and machine are always fascinating to me. A lot of them are beyond textbooks. Shadorne's example of dynamic and lively sound is a good one. I am not sure what electric characteristics can be used to describe it.
I also think that a system is only as good as its weakest point. In my example, if I get a pair of ICs that have higher capacitance, it can never sound good in my system. This is, of course, assuming that I still have good hearing.... lol...
A fellow Dude preamp owner likes the top line model from Audio Horizons the best. AH's website states the higher end models have higher capacitance. This seems odd to me. He is testing Blue Jeans Cables' ICs now. It will be interesting to see what he thinks.... |
You were right, Al, as Thevenin was on your side. :-)
It is the parallel of the two resistors that determines the output impedance. Good memory!!
Cheers! |
Hello again. Sorry that I was away with my other new toy...
I was a beta tester for a cable maker and tested about 10 versions of his ICs. This guy is quite interesting. He told me that he would never share any findings from his IC experiments with others. This is similar to a good friend of mine from Kansas. He makes the best BBQ that I have ever had. He told me that his grandpa would not pass the recipe to his own family until he was *very* ill...
My point is that EE courses only teach the basics. A lot of know-hows, tuning, refinement, and/or tweaking are the accumulation of experiences in the said field. Most companies' whitepapers most likely will not reveal their secret ingredients.
Bill, have you had the chance to find out the capacitance of your AH ICs? Note that Bill's configuration needs 5ft of ICs and mine needs 10ft. Bill's power amp is more sensitive and so his Dude preamp needs to have higher attenuations and thus lower output impedance. (Review Al's note about 75/25 vs. 50/50, using Thevenin's Theorem.) Consequently, the requirement for his setup is not as strict as mine.
Thanks all for the contribution. |
