Croft "Vita" Line (6SL7) & RIAA (3x 6N9S/6H9C) Phono Preamplifier - Schematic here

[tiefbassuebertr]

Croft "Vita" Line (6SL7) & RIAA (3x 6N9S/6H9C) Phono Preamplifier - Schematic here

According post #8 under
Croft Vitale
this model is short-lived and thus rare.
Check also this thread:
Croft pre-amps differences.

Test review is here:
Croft Vita | zStereo

Here the datasheets of the used tubes:
''GSTube.com''. Tubes, sockets etc. Parameters and characteristics 6H9C
6SL7-GT pdf, 6SL7-GT description, 6SL7-GT datasheets, 6SL7-GT view ::: ALLDATASHEET :::

In the attachment sketched schematics which I have create and various images of this pre-amp device.

Follow deficiencies I discovered at first look:
1) No capacitor for input load of connected MM cartridge (phono input)
2) No bypass capacitor at input and no capacitor at whole at output of 12V voltage regulator (go to image No 8, post #2)

I would like to convert the line gain stage into a cathode follower without gain (buffer) and enhance the idle current from 1,4mA to 6-8mA. Is this possible with this tube without reducing life time ?

 

[tiefbassuebertr]

Croft "Vita" Ser.-No 691

Croft "Vita" Ser.-No 691

 

[Alex M]

Others more knowledgeable than me may differ, but I don't think 6SL7 makes a good cathode follower. In the circuit above, it is used as an inverting "anode follower" (a little like an op-amp with negative feedback).

In the octal version of the Super Micro A that I have come across, Glen Croft used a 6SN7 for the line stage buffer. If you google "6SN7 cathode follower", you might get a few hits.

Alex

 

[tiefbassuebertr]

Yes you are right - this is basically the same different than between ECC83/12AX7 (1mA idle current) and ECC81/12AT7 (for 10 mA).
go to schematic in post #1 under
The complete 6SN7 preamp

OTOH, EAR's integrated amplifier model "V20" use the ECC81 in a power amp stage
EAR V20 integrated amplifier Measurements | Stereophile.com
EAR V20 Schematic wanted.

 

[tiefbassuebertr]

Modifications was realized as in follow:
1) Bypass capacitor (40uF) in parallel to the last electrolytic of the power supply (left in the front of the attached image)
2) Additional MKP capacitors in parallel to the output caps (5uF each - in the middle of the attached image)
3) Ordinary low cost pot replaced by a Khozmo attenuator - go to the attached images in the follow post

 

[tiefbassuebertr]

Images concerning the new implemented Khozmo attenuator

 

[tiefbassuebertr]

Others more knowledgeable than me may differ, but I don't think 6SL7 makes a good cathode follower. In the circuit above, it is used as an inverting "anode follower" (a little like an op-amp with negative feedback).

In the octal version of the Super Micro A that I have come across, Glen Croft used a 6SN7 for the line stage buffer. If you google "6SN7 cathode follower", you might get a few hits.

Alex

some URL's for cathode followers:
http://soundmovements.co.uk/diyaudio/Croft_preamps.htmlhttps://www.pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Broskie_John/1999/01_08_Oct_99.pdfhttps://www.tubecad.com/2010/06/blog0188.htmhttps://www.diyaudio.com/community/threads/6sn7-mu-follower-or-cathode-follower.334106/
this cathode follower circuits I favour in the moment:
http://www.valvewizard.co.uk/accf.htmlhttps://www.diyaudio.com/community/threads/the-complete-6sn7-preamp.7761/ (post #1)

 

[analog_sa]

Thanks for the pics. I keep forgetting how good the Brits were with their garage work. As long as it didn't involve cars 🙂

 

[fdegrove]

Hi,

Happy New Year all.

Thanks for the pics. I keep forgetting how good the Brits were with their garage work. As long as it didn't involve cars 🙂

ROTFLMAO.

Cheers, 😉

 

[analog_sa]

Happy New Year Frank!

Great to hear from you!