[happyrabbit]

Just finished my ECC99 Cathode Follower w/ Servo.  It’s a tube buffer built to drive my 2a3. I found this crazy cool design on - https://tubecad.com/2007/04/blog0102.htm

Operating the ECC99 @ 94v / 15ma.  DC Offset is ~0.2mv. Configured as Series Filament - 12.6v @ 400ma. THD% @ 0.03 with no high order harmonics. Startup / Shut down muting + 45sec delay circuit.   No DC protection..  Khozmo 10k  ladder attenuator.

















Blue is b+ (ac coupled) Red is output (dc coupled).  4mv/2s for scale.   






Dwight

[poseidonsvoice]

Dwight,

Did you etch your own boards too? That's fantastic. You are just one step away from mass manufacturing! Excellent job, and thanks for the measurements!

Give us your subjective feel on the pre since you have pretty much provided everything else!

Best,
Anand.

[DaveC113]

Looks good!

I use the ACF-2 Octal Aikido buffer currently, have used ECC99 as a driver in the past as well. Good tube! How's it sound?

[happyrabbit]

This design adds a healthy dose of realism.   I found the 2a3 SET to be a more enjoyable partner than the AVA 120 SET (aka SS amp).  I hate to say this but the design is ‘too clean’ ?    Maybe I need more break in time..  I can understand why the ecc99 is recommended as a driver for a dht tube.   Dave113 & Poseidon - I can send you the preamp if interested ? I am going to be gone for the next couple weeks.

Not sure I want to continue this design any further..  I am leaning towards this approach :

https://www.tubecad.com/2011/08/blog0212.htm

I found this design while looking up White Cathode Followers.   

See attached images for actually design.   The article has a bunch designs to pick from...

I get my boards made here :  https://www.4pcb.com/

It’s an 6 layer 2oz FR-4.   SIGNAL / GND / PWR / PWR / GND / SIGNAL.   ALL PLANE FILLS ARE TIED TOGETHER AND THEN CONNECTED TO EARTH.

Dwight

[DaveC113]

Yeah, ACF measures and sounds super clean as well, which is what I'm going for... if I were to do it over I'd probably still use the ACF circuit just with a tube rectified PS and no electrolytic caps at all. Last time I rewired my EL34 SET amp I did it PtP w/ 5AR4 and CLC filter, the Aikido noise canceling scheme and all Clarity film caps, turned out sounding really nice! I actually use a previous Aikido preamp w/ 6SL7 > 6SN7 for the driver, the Aikido circuit makes for a far better driver than anything I came up with using a single ECC99, even with CCS loading, the Aikido simply blew it away as far as a clean, clear noise-free result.

Thanks for the offer to try out the pre but I'm too far behind on work, I should be working and not posting right now, lol.

[poseidonsvoice]

Dwight,

Thanks again for the offer, but I'm with Dave on this one. I have TOO many designs in my little workshop that still need to be completed before I take on another design, even though this looks plenty simple. At this time, I also have no need for a preamp. I'm just happy to see your completed work.

All the best!

Anand.

[happyrabbit]

Here is the latest attempt 

Additional B+ Source to achieve a dual mono approach.
Moved Toroid to front and centralized power distribution layout. 
Removed Sonic Imagery Op Amps and replaced with TI OPA196
Different servo circuit. 

Attached a couple pics.  I should have a couple measurements very soon.   I still need to add the attenuator. 

Dwight

[happyrabbit]

Picked up some 120hz noise but dropped the THD% to 0.007.  No free lunch with tubes..   running the tubes a bit hotter - 115v @ 20ma.

[DaveC113]

Wow, nice! 

How's it sound?

[happyrabbit]

Excellent.   I rolled another pcb to correct for 120hz crap and in the process , the 3rd order dropped too .. go figure  see attached