A spiffy passive EQ with tube make up gain I knocked up in my spare time

[strangeandbouncy]

Hi,



i am contemplating a mastering switched version of the ultra pultec you have done, and was thinking about dual signal path, one tube one DOA( probably Pier Paulo's).


  I was just wondering, do you get more or less distortion with feedback? ANd does it increase or decrease with more or less feedback?



      Kindest regards,



      ANdyP



       

 

[Kingston]

With feedback you get less distortion of course. The output signal is sent in positive phase back to to the first inverting amplifier where their distortion products cancel out each other. The amount of feedback controls this, but it also controls gain. A drawback.

Without feedback the amp has about 0.4-0.6% THD at unity gain (RMAA), depending on the tube. Feedback takes this down to below even 0.1, but you might not have enough make up gain for EQ use.

The line amp I posted is somewhat low gain. ECC99 is not a great tube in this regard. Its strength lies in very linear amplification, and low output impedance for common-cathode configuration (needed for that 2:1 ratio output transformer). In other words, ideal for usage without feedback. Distortion products are practically pure 2nd order. Take 1% 2nd order distortion with a grain of salt. You might not even hear it, and when you do, it sounds superb with a fat triode like ECC99.

Experiment around. It's a very very simple amp.

You could also use ECC88 (or one of its numerous variants) with a 4:1 ratio output transformer for a bit different distortion spread. Or 12AV7.

Or 12AU7.

Or 6SN7.

Or.

well you get the idea, this configuration is flexible.

 

[strangeandbouncy]

Hi Kingston,



    As I was wanting two signal paths, one clean and one tubey, I guess I'll want a tad of warmth please! I most definitely will be playing about once I get it going, but I think your little line-amp is the place for me to start!

        . . . . . I also have a lovely pair of 6SN7's . . . . .


      Kindest regards, and thanks for the inspiration!


      ANdyP

 

[Moby]

Hey I missed this  :-\ Congratulations, looks great , I'm glad see see "my" PCB's inside  ;D

 

[telefunk]

ihana.

Congrats, R