Valve cascodes for Phono input.

[atmasphere]

The Daniel preamp was published by Curcio in the Audio Amateur years ago. It used 6DJ8s in a cascode configuration driving a passive EQ network.


The loading of the network is not of great consequence. This is because the EQ network has a series resistor of fairly high value as an input to the rest of the network.

 

[Herrmann]

The Daniel preamp was published by Curcio in the Audio Amateur years ago.

Years ago, yes. Mid eighties.

 

[Sodacose]

I've been itching to try a shunt cascode (a la Rod Coleman) in a phono preamp. I used it as LTP in a two stage PP amp and am very happy with the result.

It will probably look something like Rod's post #7 with a good sturdy tube or Mu follower on the output.

 

[Bigun]

Thanks for the references. I tracked down a very handy website which talks about the successor, Daniel-II and their description of how they went about improving it. The end result was still a cascode front end, but a hybrid SS-tube cascode. A schematic is freely available on their website. However, it's also no longer a zero feedback design and I consider the new topology so different from an all-tube zgfb that was the original that it may as well be a completely different beast altogether.

DANIEL II REFERENCE PREAMPLIFIER SPECIFICATIONS

 

[Bigun]

I haven't found details of the original yet, but here's a nice photo of the main board from an original Daniel

 

[Bigun]

ah, I was a bit hasty, it turns out that there is in fact a successor to the Daniel that retains the all-tube spirit of adventure. The reason I missed it was that it's called 'Sarah'.


CURCIO AUDIO: SARAH - VACUUM TUBE PHONO PREAMPLIFIER

I didn't know these guys have such interesting kits available - I'm not affiliated etc. etc. but they look pretty nice.

 

[atmasphere]

Thanks for the references. I tracked down a very handy website which talks about the successor, Daniel-II and their description of how they went about improving it. The end result was still a cascode front end, but a hybrid SS-tube cascode. A schematic is freely available on their website. However, it's also no longer a zero feedback design and I consider the new topology so different from an all-tube zgfb that was the original that it may as well be a completely different beast altogether.

DANIEL II REFERENCE PREAMPLIFIER SPECIFICATIONS

That was my thought as well. Interesting that in the Sarah, they took the same approach we did- paralleling the bottom tubes in the cascode so as to more easily drive the top tube. I found that was a good solution to noise and gain issues. But we did everything differential and so got rid of a bit of noise and improved power supply immunity as a result.



A bit of a side issue is that nearly all cartridges (and arms) are balanced sources anyway so we also use an XLR input.

 

[Bigun]

in the Sarah cascode, why r109?

 

[atmasphere]

I can't think of a good reason for it, unless oscillation of the input circuit was a problem. I've tried with and without, and in our circuits its only been a detriment.

 

[Bigun]

I remember in some solid state designs this resistor affects the sound, it acts as degeneration at the cathode input for the common grid upper tube.

 

[Adams_Leo]

Cascode is extremely useful in building networks with unusual frequency responses as its output impedance is precisely the load of the upper device.

Here is the example of the MM project I am currently working on, it has been fully prototyped and it set the bar for the quality of a phono preamp for me at a new hight. Using Lipschitz RC correction circuit it produces 0.2dB max deviation in full audio range. Output stage is also a powerful SIT with a choke load.

any update for 2SK79 sit phono preamp.I have found some pair of the 2sk79 and also plan to use it for the riaa