I would avoid the high output of the PL unit. With any passive pre amp you should keep your cable runs short and look for the lowest output impedance from the source and the highest input impedance in the amp.

Quote:
Considering a PrimaLuna tube cd player. It has a high output impedance. Understand how this works when dealing with preamps/amps. How does this work with a transformer based passive line stage like my Sonic Euphoria? I know of two tube units that will not work with the transformer line stage (EAR phono stage and Eastern Electric phono). EAR goes unstable. Don't think this is the same as bad impedance mismatch. Should I avoid all tube sources with this line stage?
just trying to understand the technical side of this.
thanks
barondla
1st post!

Hi Barondla,

As you mention it depends upon the output impedance (Z). The output Z of the tube stage can vary, depending upon the tube and mode (whether cathode follower or high voltage feedback), from a few hundred ohms to 50 ohms. Even at 2000 ohms, the IC cable has to have capacitance in the other of a couple of hundred pf to affect the sound.

Here is a link where I discuss some varying the IC capacitance and output Z. Of course we want to minimize the Ic capacitance.
http://forum.stereophile.com/forum/showf...part=3&vc=1

post #55873.

Hope this helps.

In general, the input impedance should be at least 5 times higher than the output impedance of the device feeding the signal to it, if you want to be sure to avoid problems.

Don't always believe the manufacturer's spec sheet!

A power amp I use said that the input impedance was 51K ohms, but after noticing some odd behavior driving it with an Audio Research LS1B preamp, I tested it on the bench and found that its input impedance was actually 1.6K ohms!!!!

I modified the amplifier to have an input impedance of 7.2K ohms; this required lowering the gain of the amplifier somewhat, but the overall system gain was quite adequate despite the change.