Tube Pre-amp CT-9H

I have gone though 2 upgrades since the release of the CT-11H preamp. However, I finally decided to create a new model based on the CH-11H with all the upgrades implemented and some changes in the actual circuit design. It's amazing because a very low level of distortion is achieved by LTspice simulation.

 

In the new circuit, the cathode follower now has a cathode resistor connected directly to ground and feedback is taken from the grid of the cathode follower with an added capacitor in the loop. Also made change is the output from the second stage which is now taken from the cathode of the top tube ,  making the second stage a typical mu-follower. The top and bottom tubes for the mu-follower are now separated in two triodes by the new PCB design. An ECC88 is employed for the cathode follower instead of 6BQ7A,  running at around 8ma current. In the chats, THD is 0.000061%, and second, third harmonic distortion are all below -120db.

Although simulation can hardly reflect exact the same thing in reality, but simulation results for the original circuit were never so good. Listening experience also tells me that it's absolutely worth the change. The sound is much more refined and I can feel more timber/body like with piano. Bass is also fuller and richer.

The main PCB has been re-designed in order to reflect all the changes and improvement.

UPDATE: 

Some reality measurements using ARTA software and Focusrite Scarlett 2i2 USB sound card.

Frequency Response

FFT Chart

2nd/3rd Harmonic Distortion 

At -3db output, second harmonic distortion is -80db, the third is about -100db. then the rest of  are all less than -100db. This could explain the preamp sounds very natural, no harsh across entire audible range. 

----------------------------------------------------------------------------------------------

Tube used 

3X  JJ802S new production

1X  Beijing 6n11  NOS

1X  6X4 Sylvania NOS

Filament Arrangement:

12.6V regulated for 2 X  JJ802S

6.3V   regulated for 6n11 and JJ802S

Output Noise level

0.1mv~0.12mv when input shorted to ground

Gain:

21.5GB

Power Input:

AC: 230V~240V

Connectivity:

3 set of RCA for input signals.

1 set of RCA for output (output signal can be muted by a mute switch in the front panel and automatic delayed for appox. 100 seconds on start-up)

For more info please contact peter@consoletronics.com