Matching Solid State Amp w/ Tube Preamp

[esldude]

Not quite trial and error. 

 

Some tube preamps have high output impedances.  Some solid state amps have lower input impedances.  You don't want a tube preamp with 1 k ohm output impedance feeding a solid state amp with a 10 k ohm input impedance.  Well it might barely be okay.  A tube preamp with 1 k ohm output impedance feeding a solid state amp with 47 k ohm input impedance should be just fine. 

 

Related tube pre-amps may typically use an output capacitor to couple to the amplifier.  Again keep plenty of impedance in the solid state amp so this doesn't cause a roll off in the bass. 

 

One final area that used to be a problem.  Tube preamps might be asked to deliver 2 volts or so yet be able to output 20 volts or more.  This can lead to running the tube pre-amp at a very low volume setting if it has more gain than is needed.  This doesn't get the best sound from the tube circuit in some designs. 

 

So use a solid state amp with 47 k ohm or higher input impedance.  Use a tube pre with a lower output impedance (not hard to find one with only 300 ohms), and don't get a tube preamp with lots more gain than you need for the power amp.  I would suggest not going over a preamp gain of 12 db in general.  

[esldude]

1 hour ago, DancingSea said:

What part do tube buffers play in this?

 

Well a tube buffer would have no gain.  Provide some high input impedance and low output impedance.  Might impart a bit of the tube sound.  Though often if well designed they sound about the same as solid state device.  Though if you are wishing for the tube sound maybe that isn't well designed for the purpose.  

 

BTW, it is often assumed tube amps have a good musical sound, and tube preamps in front of solid state amps are a way to get some of this flavoring.  Usually doesn't work out that well.  I prefer the color of tube amps myself (specifically triodes).  Pre-amp circuits are different however in that they don't have transformers, and handle the loads they are connected to so well that some of the more musical aspects of a tube amp never come into play.  Other than using tubes they aren't really the same effect as push pull amps running thru transformers. 

[esldude]

8 minutes ago, mourip said:

 

That is what I said...

 

Here is a quote from a good company that manufactures David Berning circuits. This would apply to tube preamps without muting circuits.

 

 "...you must turn on the MicroZOTL2 before you turn on your power amp, and turn your power amp off before you turn off the MicroZOTL2. The MicroZOTL2 should therefore be the first thing on and the last thing off."

Have not tried the Micro line of products.  But the original Berning preamp was really something.  More than 200 khz bandwith flat.  Used FETs with Tubes. 

 

I seem to recall the amps were something like modern switching amps.  Can't remember if the preamp worked the same way or not (I don't think it did).