The VAS website does not describe the turns ratio, but I have managed to tease out the desired information from Steve Leung. What it says is:
![[IMG]](https://drmoss.ca/Web%20Images/VAS_MC_One.jpg "[IMG]")
I asked him a while ago about the turns ratio, and he replied "1:15." So another enquiry today about the two inputs, whether they represented different taps and thus different turns ratios and he said that they are different taps. The high impedance input is 1:10, for a nominal impedance of 100Ω and a gain of 10.9dB, whilst the low impedance input is 1:15, with a nominal impedance of 47Ω and a gain of 17.3dB. I write "nominal" as this means nothing until you consider the turns ratio and the impedance of the MM stage it feeds into. For a 47kΩ MM stage, the low impedance input provides 47000/15²=208Ω, and the high impedance input provides a load of 47000/10²=470Ω.
This explains why the low output cartridges I run through it (LP-S, Ruby 3, Sussurro MkII ES) sound best with the high impedance/470Ω input, and extra bassy with the low impedance/208Ω input. I had got to the point of wondering whether to buy a 1:10 SUT, but now I know I have one!
My phono stage was designed by Tim deParavicini, and accepts MM or MC inputs, BUT its MC input is loaded with just 10Ω. Using the MM input and this VAS SUT is just so much better. That's probably down to appropriate loading, but maybe in part to Quad making compromises in the components used versus those Tim specified.
Anyway, potentially useful knowledge for owners.
Chris
I asked him a while ago about the turns ratio, and he replied "1:15." So another enquiry today about the two inputs, whether they represented different taps and thus different turns ratios and he said that they are different taps. The high impedance input is 1:10, for a nominal impedance of 100Ω and a gain of 10.9dB, whilst the low impedance input is 1:15, with a nominal impedance of 47Ω and a gain of 17.3dB. I write "nominal" as this means nothing until you consider the turns ratio and the impedance of the MM stage it feeds into. For a 47kΩ MM stage, the low impedance input provides 47000/15²=208Ω, and the high impedance input provides a load of 47000/10²=470Ω.
This explains why the low output cartridges I run through it (LP-S, Ruby 3, Sussurro MkII ES) sound best with the high impedance/470Ω input, and extra bassy with the low impedance/208Ω input. I had got to the point of wondering whether to buy a 1:10 SUT, but now I know I have one!
My phono stage was designed by Tim deParavicini, and accepts MM or MC inputs, BUT its MC input is loaded with just 10Ω. Using the MM input and this VAS SUT is just so much better. That's probably down to appropriate loading, but maybe in part to Quad making compromises in the components used versus those Tim specified.
Anyway, potentially useful knowledge for owners.
Chris
