Solid state tube amplifier

Here's a no feedback solid state tube amplifier;) for that rich warm sound, let comments flow
Schema.png

Fourier.png

freq.png
 
Member
Joined 2011
Paid Member
So what I see is basically you have
  • input network filters
  • class A VAS
  • 2EF output stage with three transistors in parallel

Questions:
How do you define gain without the feedback?
Did you do LG analysis?
What are the THD numbers?
With the feedback version, is it better to use LTP to compare input and output signals?

I wonder is there can be a way to adjust “tubeness” of the sound? So how much of a second harmonic is created?

Also, adjusting the extent of the feedback applied?

That would be cool 😎
 
  • Like
Reactions: 1 user
So what I see is basically you have
  • input network filters
  • class A VAS
  • 2EF output stage with three transistors in parallel

Questions:
How do you define gain without the feedback?
Did you do LG analysis?
What are the THD numbers?
With the feedback version, is it better to use LTP to compare input and output signals?

I wonder is there can be a way to adjust “tubeness” of the sound? So how much of a second harmonic is created?

Also, adjusting the extent of the feedback applied?

That would be cool 😎
  • Gain without feedback operates in the voltage domain and its the ratio of 20*logbase10(R22/R20 +1), drain resistor / source resistor
  • Without feedback upto 2%, we are running that output stage mostly in class A to improve that THD
  • Introducing the LTP raises challenges we don't need at this fun level, the Pathos sounded really good didnt it? Why do people still look for those really vintage amps? We are trying to stay true to our theoretical tube
  • Its that dominant second harmonic
 
Congratulations on rolling yur sleeves up and actually designing.
Bonus points if you actually build it :)

That said:

1) on the non NFB original version, you should split and bootstrap R22 (which you did in the second one).

2) an enhancement MosFet gain stage (Vas here) is notoriousy non linear/unsymmetrical by itself.
The NFB version shows quite unsymmetrical waveform at 20kHz, I´d love to see same out of the non NFB one.
Would expect even higher assymetry.
Same at, say, 1kHz and 100Hz.

Intermodulation would also be strong, any numbers available for it?.
 
  • Like
Reactions: 1 user

Attachments

  • 20kSQ4v2.png
    20kSQ4v2.png
    9.4 KB · Views: 55
Last edited: