DK Design VS.1 Reference mkII - Optimization

By removing the cover you will have changed the mechanical mass of the entire chassis.Vibration and it effects on the circuitry will also have been changed. Vibration influences can greatly alter the spectral balance. The amp has been retuned within its own environment. Tom

Tom, Your explanation is as good as any I've seen for the reason this amp sounds best with the top off. Tubes are microphonic to some degree and the less vibrations (from any source) the better. Removing the top would certainly eliminate one potential source of vibrations. I've done this with some CDP's/Dac's and pre-amps.

I just don't understand these electro-magnetic 'waves'comments.

Apparently the amp generates a lot of EMI which must then be disappated in some fashion and taking the top off facilitates that disappation. But if the amp is creating the EMI in the first place, and its harmful to the signal, it seems to me as if the damage is already done.

If the EMI is externally produced it seems that having a non-ferrous case, including top, would be beneficial in keeping it out of the amp. I also don't understand the 'wave' concept, I can understand EM fields of changing intensity, but 'waves' which bounce back and forth off some surfaces but not others? Are you aware of any science which supports this?

Tvad, Audioaril, Tom, anyone - please help me to understand this.

Tvad, I'll take a stab at the vibration/top issue, by way of example. I have a CDP with case vibrations induced by the transformer. These vibrations are sufficient to rattle the tube innards which increases any potential they have to be microphonic. When I take the top off the CDP I'm eliminating one of the surfaces which facilitate the transmission of the vibrations. Often the audible (as well as physical) frequency (pitch if you will) and intensity of the vibration changes - usually lessens. Mass loading can have a similar effect.

If you have the best LN tubes and your unit has a low noise floor you might not actually change anything except reduce the audible transformer hum (not a bad thing at all), but if you have borderline tubes and a highish noise floor these vibrations can induce tube microphonics which can be audible. FWIW, I think there are better ways of getting 'spacious and open' than using microphonic tubes. :-)