Time for an update as there have been further developments at my end around the issues of gain through the Vida.
it is interesting re-reading the thread to date as i think there is a pattern emerging that also ties up with my own findings.
Gain on the MC input of the Vida is 64dB, this is a fairly typical figure for phono stages. However, gain on the MM stage is down at 38dB which is somewhat lower than normal. In practice, this means that provided you are using a medium output MC cart - say in the range 0.4 - 0.7mV (as Baggawire does) - then the output from the Vida will be in the range of 0.7V to 1V. This should be adequate for a wide range of pre-amps.
Challenge starts to come when using lower output MC's such as my Ortofon at 0.25mV, which through the Vida's MC circuit would only output 0.4V - below the ideal input sensitivity range of many pre-amps. As the MC gain in the Vida is typical, this is no different to what could be expected from other phonos and use of an SUT or head amp would be needed. This is where the lower gain on the MM input needs to be factored in. Using a 1:20 step up SUT then plugged into the MM input would normally be about right for my cart, but due to the Vida's below average gain this would still result in an output of 0.4V, no better than through the MC stage alone.
In fact, what is needed is a 1:40 SUT or a headamp with 32-34dB gain to start to get to a adequate level of output. Of course, what this means is that instead of the typical MM cart output of 5mV being fed to the Vida's MM inputs, the boosted MC is putting around double that amount. Fortunately, the Vida has generous overload margin on the MM input of over 160mV, so even with a 10mV input there is 24dB of headroom (against recommended 18dB).
Whist I am quoting specific figures for cart outputs, it is worth bearing in mind that these are only typical outputs at a set frequencies. The actual figure will differ significantly based on the programme material and the record pressing itself. I fact I think it is the latter that has caused me some frustration and is possibly what Speedracer was describing as well. An LP that has been pressed 'hotter' in effect increases the output from the cart and overcomes some of the issues with gain through the Vida - hence, sometimes the system doesn't have the same flatness.
So, a bit of a ramble but suffice to say I have now installed a Denon HA1000 head amp set to 32dB gain and the sound has been transformed, the flatness has gone and replaced with real dynamics, without being LP pressing dependent (in fact even LP's that were acceptable previously have benefited).
Two takeaways for me for Vida users or prospective users to consider;
- I am not convinced that a standard MM cart with 5mV output will be a successful combination with quite a few pre-amps
- If using an MC cart below 0.4mV output then do your calculations carefully and don't underestimate the step up gain required to overcome the lower gain of the Vida MM input.
Hopefully helpful and IMO, of course.