Based upon many very positive testreports, and because of the fantastic looks, I decided to buy a ML 320S, without giving it a try before bying.
I have a pair of Quad ESL´s plus a pair of ML20.6, everything, including CD and Turntable, connected with expensive MIT Oracle cables.
After breaking the 320S in for more than a week, I started listening.
It was not at all what I had expected. The sound was cool, and far from involving. Big disappointment so far.
I decided not to sell the 320S, but instead finding the cause of the laid back sound, knowing that this would violate the guarantee.
As a first step I replaced all AD797 op amps for the much more expensive OPA627. Four SMD's on the mainboard, and four DIP's on the little volume control boards.
This already gave me a sound much more to my liking, but I wasn't satisfied yet.
The last stage in this preamp is a buffer, without any feedback, with just 1 time amplification, being responsible for supplying the drive current to external loads.
From a technical viewpoint, the design of this buffer is an achievement of the highest order.
But sound and technics are following different ways.
For this reason, I have included the buffer in the feedback loop of the amplifier before this buffer.
In that way, the OPA627 is responsiblke for the good sound, and the buffer can supply whatever current is needed to the outside world.
The result to my opinion, is what the 320S should have been from the beginning.
It reproduces all emotions that should be there, it is involving and very detailed without a trace of being harsh.