Croft 25 Upgrade Advice

[OD1]

I am currently thinking about sending my preamp to Glenn to upgrade to "R" status, but have the following questions.

When my current pre was built by Glenn I was told that it had Zero gain, and that the line stage ECC82 valve was configured as a "cathode follower".
Could someone explain what this means please ?

Does zero gain mean that the line stage would NOT benefit (SQ wise) from the "R" upgrades unless reconfigured to produce gain (I am very happy with the gain as is, and would prefer not to change it)?

And finally, what SQ improvements should I expect to hear from the "R" ?

Oliver

[Firebottle]

When my current pre was built by Glenn I was told that it had Zero gain, and that the line stage ECC82 valve was configured as a "cathode follower".
Could someone explain what this means please ?

The 'gain' will actually be about x 0.95 as a cathode follower does have a small loss.
A cathode follower is circuit configuration that provides a buffer function, it effectively drives the next stage/amplifier.

[OD1]

Thanks Alan,
Does this mean the improved power supply of the "R" will influence the SQ of the line stage ?

[Firebottle]

Personally I doubt it buy I can't speak from experience on this one.

[Jimbo]

Thanks Alan,
Does this mean the improved power supply of the "R" will influence the SQ of the line stage ?

Oliver you can have the line stage upgraded at the same time to a 12Bh7a with better resistors similar to the line stage in the top RS. Definitely a worthwhile improvement if you use this more than phono although it does benefit the phono stage as well as it goes through line stage. The regulation will also tighten up the sound with more control and detail.

[OD1]

James,
Thanks to reading one of your earlier threads :), and getting confirmation from Adrian Parsons that it would work in my 25, I swapped my Mullard ECC82 line stage valve to a Sylvania 12bh7a about a year ago, and am very happy with it.

Does Glenn fit the mods you mentioned as part of the normal "R" upgrade, or do I need to specify them ?

I have set aside a modest 2016 "upgrade" budget that would enable me to either
a. Upgrade my pre & purchase 2x5m of TQ Blue speaker cable, or
b. Leave the pre as is, and get 2x5m of TQ Black

I am leaning more towards a. but was worried that the "R" mods would not make much difference due to the no gain config of my current pre.
I need to purchase 2x5m of speaker cable, due to rearranging my living room (SWMBO insisted the cables must be hidden :( )

Oliver

[Jimbo]

James,
Thanks to reading one of your earlier threads :), and getting confirmation from Adrian Parsons that it would work in my 25, I swapped my Mullard ECC82 line stage valve to a Sylvania 12bh7a about a year ago, and am very happy with it.

Does Glenn fit the mods you mentioned as part of the normal "R" upgrade, or do I need to specify them ?


I have set aside a modest 2016 "upgrade" budget that would enable me to either
a. Upgrade my pre & purchase 2x5m of TQ Blue speaker cable, or
b. Leave the pre as is, and get 2x5m of TQ Black

I am leaning more towards a. but was worried that the "R" mods would not make much difference due to the no gain config of my current pre.
I need to purchase 2x5m of speaker cable, due to rearranging my living room (SWMBO insisted the cables must be hidden :( )

Oliver

You would have to ask Glenn to change the line stage to work properly with the 12BH7a. I think you are probably currently just using this valve in the line stage as it reduces gain a little but it won't be working at its optimum. Glenn will make other changes to the line stage which involves non inductive resistors and a similar spec to the RS line stage. Sounds better than ECC82 Or ECC83 line stage ;)

[OD1]

Thanks for the advice James,
You have given me something concrete to discuss with Glenn, and made my mind up to go with plan a.

Regards
Oliver

[banjoman]

Thanks for the advice James,
You have given me something concrete to discuss with Glenn, and made my mind up to go with plan a.

Regards
Oliver

My 25R has been through several upgrades by Glenn Croft, including the cathode follower mod. So, it is definitely compatible with the 25R upgrade.
the Cathode follower reduces the gain of the 25R and allows it to work better with a wider range of power amps - I'd defnitely recommend it.
Mine has also been modded to work with a 12BH7A tube in the line stage