So the the point with a tube preamp with a cathode follower is they will typically (nothing is always) have a higher output impedance or one that rises quickly and/or both typically and this will cause a poor impedance
match with a said matching ss amp.
So
with a preamp the output impedance rule of thumb is the lower, the better.
The simplified reasoning for this is the minimum of a 10 to 1 impedance match you want for your preamp to your amp.
There are many technical reasons for this but to make it easy to understand just know as a rule of thumb the minimum is 10 to 1 but to have more is better.
Why is this? Mainly to keep from having your bass roll off or other roll off issues.
So if the output impedance of a solid state preamp is 100ohm (SS preamps are typically lower than tubes) and the source (input) impedance of a solid state amp is 30k then you know you are good.
Why because 10 to 1 or 10 x 100ohm = 1,000ohm. 1,000ohm is much lower than amps input impedance of 30,000ohm or 30kohm.
In this event you will be covered and good to go.
You will have your 10 to 1 covered via (10 x 100ohm) being 1,000 which is well under the 30kohm (30,000ohm). Remember the more head room the better. Here your amp max is 30,000ohm and you are only at 1,000 so you are in great shape.
Now the idea is that a tube preamp with a cathode follower will have a much higher output impedance. Also, the impedance is not only much higher to start with but also rises much quicker also so its double trouble.
Lets say for this example this example the tube preamp with cathode follower output impedance is 3,000ohm ohm. The Solid State preamp was only 100ohm. These are common numbers of tube and ss.
Big difference here. My SS preamp has an output impedance of .5ohm which is nice and super low.
As a rule this is why SS preamps and SS amps work well together. Same said for tube preamps and tube amps. The output impedance of tube preamps is high but many times the tube amps source impedance or input impedance is equally high to form a good match as such as 80k or 100k so it can handle the tube preamps higher output impedance.
This is why people say that tube preamp and especially tube preamp with cathode followers can be tough match for ss amps. Because tube preamps with cathode followers typically have higher output impedance and many (not all) solid state amps do not have very high source impedance to cover the 10 to 1 delta.
So back to our tube preamp with cathode follower example that has an output impedance of 3,000ohm. Take the 3000ohm x 10 and that is 30,000ohm or 30k.
Your ss amp has a source impedance 30k and this puts you right up against the ss amps source impedance of 30k.
This you might be able to squeeze by with but not ideal. The problem is like I stated before tube preamp with cathode follower not only starts high but also rises. At some frequencies it could rise to 5,000 or 6,000 and now you do not have the 10 to 1 covered and you can get bass roll off and/or top end roll off or both and now for no other reason than a improper impedance match your rig will not provide anywhere near its potential. Never mind how great each preamp or amp may sound if they don't match electronically your rig will be flat and rolled off and has all kinds of problems.
I hope this hacked version helped clear some of this up.
Thanks
So
with a preamp the output impedance rule of thumb is the lower, the better.
The simplified reasoning for this is the minimum of a 10 to 1 impedance match you want for your preamp to your amp.
There are many technical reasons for this but to make it easy to understand just know as a rule of thumb the minimum is 10 to 1 but to have more is better.
Why is this? Mainly to keep from having your bass roll off or other roll off issues.
So if the output impedance of a solid state preamp is 100ohm (SS preamps are typically lower than tubes) and the source (input) impedance of a solid state amp is 30k then you know you are good.
Why because 10 to 1 or 10 x 100ohm = 1,000ohm. 1,000ohm is much lower than amps input impedance of 30,000ohm or 30kohm.
In this event you will be covered and good to go.
You will have your 10 to 1 covered via (10 x 100ohm) being 1,000 which is well under the 30kohm (30,000ohm). Remember the more head room the better. Here your amp max is 30,000ohm and you are only at 1,000 so you are in great shape.
Now the idea is that a tube preamp with a cathode follower will have a much higher output impedance. Also, the impedance is not only much higher to start with but also rises much quicker also so its double trouble.
Lets say for this example this example the tube preamp with cathode follower output impedance is 3,000ohm ohm. The Solid State preamp was only 100ohm. These are common numbers of tube and ss.
Big difference here. My SS preamp has an output impedance of .5ohm which is nice and super low.
As a rule this is why SS preamps and SS amps work well together. Same said for tube preamps and tube amps. The output impedance of tube preamps is high but many times the tube amps source impedance or input impedance is equally high to form a good match as such as 80k or 100k so it can handle the tube preamps higher output impedance.
This is why people say that tube preamp and especially tube preamp with cathode followers can be tough match for ss amps. Because tube preamps with cathode followers typically have higher output impedance and many (not all) solid state amps do not have very high source impedance to cover the 10 to 1 delta.
So back to our tube preamp with cathode follower example that has an output impedance of 3,000ohm. Take the 3000ohm x 10 and that is 30,000ohm or 30k.
Your ss amp has a source impedance 30k and this puts you right up against the ss amps source impedance of 30k.
This you might be able to squeeze by with but not ideal. The problem is like I stated before tube preamp with cathode follower not only starts high but also rises. At some frequencies it could rise to 5,000 or 6,000 and now you do not have the 10 to 1 covered and you can get bass roll off and/or top end roll off or both and now for no other reason than a improper impedance match your rig will not provide anywhere near its potential. Never mind how great each preamp or amp may sound if they don't match electronically your rig will be flat and rolled off and has all kinds of problems.
I hope this hacked version helped clear some of this up.
Thanks