Diy preamp for Amplifier IRFP240/IRFP9240

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you'll question the value of opamps as preamps.

I don't question their value at all. They can sound really good if you know which ones to use and implement them properly.

I've built and listened to a couple of the JC-2 clones. They sound okay for the money...nothing spectacular.

While I don't like bright-sounding amplifiers, I find the 6SN7 to sound a little too dark.
 
I want to clarify ; I completed this pre with BC550C and BC560C ( unknown brand ) as required by progetto.Esso does not provide an output capacitor, try this can be dangerous for the presence of DC , but it can be unvantaggio for sound. The power amplifier , however , provides a coupling capacitor of 1uF input . As I said at the top , the sound of this preamp is really very interesting , but I "only" a limit , I think my only , at low frequencies ..... them feel not very deep . Can be due to use of BJT unmarked ...?

Bearing in mind this is a dc-coupled line amp with 4.3 gain, the only reason of being "not very deep" at low frequencies I can imagine is impedance matching with your power amplifier. Try to add a follower at the output of the preamp in order to achieve a low output impedance.
 
Bearing in mind this is a dc-coupled line amp with 4.3 gain, the only reason of being "not very deep" at low frequencies I can imagine is impedance matching with your power amplifier. Try to add a follower at the output of the preamp in order to achieve a low output impedance.

... Thanks for your advice , but what do you mean by "add a follower" ?...
I have to lower the output impedance of the preamp ?
I have to add such a buffer ... ?
 
... Thanks for your advice , but what do you mean by "add a follower" ?...
I have to lower the output impedance of the preamp ?
I have to add such a buffer ... ?

Exactly - you need to lower the output impedance.
Here is a top quality buffer for your purpose.

Cheers,
Valery
 

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