[west]

"Eeyore" wrote in message
...


west wrote:

I built a typical phono amp with 3 12AX7s, the last tube a cathode
follower
(low impedance). It has plenty of gain (70db) and can easily drive any
amp
directly. I like using a 100k step resistor volume control instead of a
line
amp.
My problem is that when I use any of my tube amps, the sound has limited
bandwidth. A SS amp does not exhibit this problem, if fact the SS sound
is
rather impressive to me (for silicone).
With my limited know-how, I'm swagging that an impedance mismatch is the
culprit.
If my contention is correct, is there a simple cure besides using a line
amp? Perhaps some kind of buffer is called for. All comments welcomed
and
thank you.

You're using a 100k 'pot' effectively to drive a cable.. With as little as
1 nF
of cable capacitance that forms a low pass filter at 6kHz !

The transistor amps will have a lower input impedance that loads this
which will
push the turnover frequency out of the audible area (just).

You should never drive a cable from a pot or attenuator of high value.

Try using a 10k stepped attenuator instead. The whole point of cathode
followers
is to drive lower impedances.

Graham

Your answer is what I suspected but not having much experience, I asked this
NG. I was looking for a Tube Basic 101 generic answer that I did not find in
my reference books. I don't understand where Patrick is coming from. I have
never asked for specific help. That's the most enjoyable aspect of this
hobby (for me), is rolling your own, having some problem, and ultimately
solving it. Thanks again Graham.

west