Croft 25 pre and 7 Power - adjusting the gain by changing the valve.

[loonytunes]

If I was considering the Croft 25 pre along with the 7 power amp, line level only (not interested in the phono stage), can I check with you the following:

The integrated is a passive pre design, I understand though that the dedicated pre at line level uses a valve - are you able to change the valve in the preamp to tweak the gain (ECC81, 82 or 83) without the need to modify or change any resistors?

In the Croft 7 power amp, (not the 7R), can you change the valve in the power section to affect gain in a similar manner?

I just want to know how configurable the gain can be using the 25 pre / 7 power - if in fact you can do that at all.

[Arkless Electronics]

AFAIK they are not zero feedback designs and so no you can't change the gain like this.

[loonytunes]

OK I always thought it possible to change the pre section to either an ECC82 or 83 at least... but if not fair enough - best leave as is.

[Arkless Electronics]

They have the same pin-out and so both will work but the biasing etc will only be right with the correct one.

[PhilofCas]

Chris,

Send an email to Glenn (Croft), he will advise all there is to know. I emailed Glenn a while ago , he came back to me quickly with a definitive answer.

All the best,

Phil.

[loonytunes]

He said you could use either an ECC81, 82 or 83 in the preamp stage - but it's optimised for use with an ECC83

[Arkless Electronics]

Like I said.....

[rubber duck]

Glenn replaced one of my ECC83 with a Mullard 81 or 82 to reduce the gain (and hiss) and this it certainly did. It also killed the sound stone dead. Took me a couple of days to work out why it sounded flat and lifeless. Similar effect to when I tried some RCA in-line attenuators. Glenn had warned me about these but I guess one only really learns from experience. The solution? Send it to Glenn for a simple mod.

[worrasf]

As others have said changing the valves has little or no difference in gain up or down (direct from the horses mouth). My NWA DL103 has lower output than standard so I sent the 25RS off to Glenn for a circuit mod (resistor changes +MOSFET) - perfect now
Steve