There are five standards and of course lots more.... In no particular order:
1) Placette passive - very highly regarded, excellent support - resistor based as opposed to transformer based - this is the big decision you get to make
2) Sonic Euphoria - PLC for passive line controller - transformer based
3) Bent TAP is the new generation product using autoformers - design change was required when the transformer provider stopped providing, the previous version is also highly sought after
4) Promitheus TVC - for transformer volume control preamps - quite a full line - built offshore so high price/performance ratio
As far as I know all these suppliers will build balanced or single ended, multiple inputs and remote volume control
5) Probably the simplest units out there are by Channel Island Audio - they have a passive/active unit and a two source passive - small form factors and very clean
Full disclosure - I run my Keces 151 DAC into my Sonic Euphoria passive and then onto my Graaf. As the Brits like to say, "brilliant".
1) Placette passive - very highly regarded, excellent support - resistor based as opposed to transformer based - this is the big decision you get to make
2) Sonic Euphoria - PLC for passive line controller - transformer based
3) Bent TAP is the new generation product using autoformers - design change was required when the transformer provider stopped providing, the previous version is also highly sought after
4) Promitheus TVC - for transformer volume control preamps - quite a full line - built offshore so high price/performance ratio
As far as I know all these suppliers will build balanced or single ended, multiple inputs and remote volume control
5) Probably the simplest units out there are by Channel Island Audio - they have a passive/active unit and a two source passive - small form factors and very clean
Full disclosure - I run my Keces 151 DAC into my Sonic Euphoria passive and then onto my Graaf. As the Brits like to say, "brilliant".