Charles1dad, I tried real hard but I could never get those MIT caps to sound right to me, if I used them as a coupling cap. If I am not mistaken though, the MIT uses several caps in parallel in a single package. I have found that to be a bad move in a coupling cap (although it can be just fine as a bypass in a power supply)- whenever there is a bypass in a coupling cap, smearing occurs, and causes troubles in the high frequencies.
So I figure you use one cap and give it your best shot. The problem is that in tube preamps, you often have to have a very large cap at the output, and even if its the best Teflon or paper and oil, its still going to have an adverse effect due to the size required. So I came up with a direct-coupled circuit, basically side-stepping that problem.
Another, rather surprising way to get around that problem is to go with an electrolytic! I know, I know, most audiophiles think electrolytics are terrible and they have good reason to think so. The problem is an electrolytic will not function correctly unless it is polarized with a voltage. In a tube preamp this is easy (you should try it!), but in a lot of solid state designs the designer neglects to polarize the caps and so they introduce distortion when the waveform charges the cap in the wrong direction! **That** is where electrolytics got their bad reputation.
If I have not made the point clearly in this post, the bottom line is that as a designer you have to watch what you are doing with caps. The MIT above is a great example- a good cap, but don't use it for coupling. Same thing with electrolytics, but make sure that the DC across them is always more than the total AC waveform they will pass if you do that they will easily give good quality film caps a run for the money!). See what I mean?
So I figure you use one cap and give it your best shot. The problem is that in tube preamps, you often have to have a very large cap at the output, and even if its the best Teflon or paper and oil, its still going to have an adverse effect due to the size required. So I came up with a direct-coupled circuit, basically side-stepping that problem.
Another, rather surprising way to get around that problem is to go with an electrolytic! I know, I know, most audiophiles think electrolytics are terrible and they have good reason to think so. The problem is an electrolytic will not function correctly unless it is polarized with a voltage. In a tube preamp this is easy (you should try it!), but in a lot of solid state designs the designer neglects to polarize the caps and so they introduce distortion when the waveform charges the cap in the wrong direction! **That** is where electrolytics got their bad reputation.
If I have not made the point clearly in this post, the bottom line is that as a designer you have to watch what you are doing with caps. The MIT above is a great example- a good cap, but don't use it for coupling. Same thing with electrolytics, but make sure that the DC across them is always more than the total AC waveform they will pass if you do that they will easily give good quality film caps a run for the money!). See what I mean?