Croft Gain

[Bianco]

Hi All,
I have a Croft 25r and 7 power with Wilson Benesch Arc speakers, all cables are Mark Grant.
With vinyl it sounds great but, with my Isis CD player I have very little movement on the volume.
I contacted Glenn and he said - easiest way, change valve in power amp to a Ecc99, which I did.
What more can I do, I'm thinking about moving away from vinyl but need this sorted first.

 

[eastone]

https://www.hifiwigwam.com/forum/topic/113114-croft-micro-25-prephono/

Have a look at the image in this thread above ^^^

There’s a simple resistor swop to vary gain.


“If the 2 resistors per channel are 100K it is zero gain.
If 220K and 100K, it has gain reduced roughly by half. Standard ratio is 100K/470K”

 

[ampedup]

with my Isis CD player I have very little movement on the volume.

If you are saying that you have too much gain from that input with your Croft combination, use a pair of attenuators on the CD ouput to the preamp. I use 'GoldenJacks'. Apparently, there are different designs of their attenuators, depending on whether they are placed after a source, or at an input to the power amp.

Myself, I use attenuators on the input to my power amp, from the valve preamp, to reduce overall gain from all sources, not just CD. It yields a reduction in the noise floor too.

 

[Vinny]

Generally speaking, changing valves achieves, at best, very little. Gain is way more a product of circuit design that valve gain.

As for swapping rsistors............................... Beware - there are near countless different circuits used in Croft amp's.

Just by way of illustration - my TT uses an SUT into the Croft MM stage and it and my CD and tuner need something very close on the volume knobs - in the case here, off/minimum is at 12-o-clock and I have the volume setting anywhere between around 2, and 5-o-clock, 2 to 3 being normal.

 

[Darren L]

Attenuated plugs or Attenuated interconnect ? I use one between my CD player and preamp, very effective.

 

[eastone]

Just to echo what Vinny said... I didn’t mean to recommend diving in blindly with your soldering iron. But do investigate with Glenn about modding, it should be quite simple and affordable.

IME where there is feedback used in the preamp that is going to determine the gain and swapping valves around won’t give you the result you need.

I’ve never got on with attenuating plugs personally...

 

[paulfromcamden]

I had a Croft dealer do the resister change for my Micro 25 Basic pre. It reduced the gain a bit but not loads.

I have a phono integrated now and use attenuator plugs on the CD player output to give a bit more travel on the volume - especially as living in a flat I tend to listen a fairly low levels.

 

[Bluedroog]

Adrian Parsons at Audio Flair reduced the gain on mine, very simple job.

 

[Bianco]

Hi all,
Thanks for your help, it's going back to Glenn.

 

[Vinny]

The problem lies with a lot of CDPs and DACs, which, for reasons far beyond my ken, have output volts that are way high compared to "traditional" front-end units. Hence the "common" use of attenuators in the CD input.

I would love an explanaition from someone who knows the circuits involved, how the gain on the line stage can be reduced without dropping output from the phono output, and thus avoiding the volume "problem" elsewhere.