Balancing my Hifi: Croft Super Micro Pre amp with QUAD 606

[dobson156]

(Mods: feel free to move this post if it's the wrong place, it doesn't neatly fit into tube or solid state as it's about the balance between them both!)

Hi everyone, I have the following hifi setup.

Turntable w/ AT440mlb cartridge & stylus
Preamp: Croft Super Micro
Amp: Quad 606mk2

The noise floor is getting quite high and it periodically makes weird crackling sounds. I suspect the valves in the pre have had their day and the 606 could do with recapping (1 of the 4 main caps is different to the others - suggesting it's been half(quarter?)-jobbed at some point before my ownership.

I want to take this opportunity to make any worthwhile modifications to it, specifically:

1. I'd like to match the Output Sensitivity of the Pre to the Input Sensitivity of the Amp.
2. Ensure their is appropriate loading for the stylus
3. Balanced the difference in gain between between the line level inputs and the phono input.

One, is balancing the sensitivities a simple case of matching the numbers together? I keep reading that Croft Pre-amps have a high gain however I can only find the stats online for the Croft Micro 25 which has a states output sensitivity of 0.5mV and the Quad 606's input sensitivity is also 0.5v. So is there anything to do here?

1. https://www.dadaelectronics.eu/uplo...vice-Manuals/Quad-606-Service-Manual-V2.0.pdf
2. (this is for the Micro 25) https://web.archive.org/web/20210922142521/http://www.croftacoustics.co.uk/micro25.html

Two, the AT440mlb cartridge apparently has a recommended load impedance of 47k ohms; I am not an EE person, but according to this schematic the Croft Super Micro has a 47k resister on the phono input - does that mean the pre amp is ideally suited to the stylus as is? What about input capacitance, is that "tuneable"?

1. http://soundmovements.co.uk/diyaudio/Croft_SM_III_circuit.gif

Three, when I play from the phono sources the output level is considerably higher than if I play the same music from a line in source. For all of my sins, this usually a line in from the headphones out of my iPhone for casual/background listening - I promise!

I have no intention of carry out these modification myself, I have an amp tech I have used before - but he tends to do what you instruct him and no more, so I want to be quite specific about the work I want carried out.

Thanks for any advice in advance!