Give Ric Schultz at EVS a call. He worked at Audible Illusions for awhile, and was at one time offering a mod for the Modulus 2 pre-amps.
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My M3A was having attenuator issues and I was told that its five years of use required the attenuators to be replaced. The manufacture then suggested to have the sonically superior 2000 main printed wire board upgraded which included the attenuators.
They assured me they had the parts necessary to make the upgrade and it would take two or three weeks. I sent the pre off with a check. After five months of difficult communication and parts availability issues I demanded the unit be returned immediately regardless of its condition. Almost three weeks later it arrived upgraded.
Unfortunately, my acoustic memory couldn't discern such a slight, if any, improvement and sold it.
If you find the dual mono volume and the general layout acceptable the Bruce Moore preamplifier is a substantial improvement.
I have had my M3A for quite a number of years and it has been modified several times by Bob Backert of RHB Designs in Richboro, PA.
Bob puts his own design circuits in which really open up the clarity and resolution of the unit. Go to his website to get information on exactly what he does, it's too involved for me to explain. The mod is not terribly expensive and I feel has really improved what is already a great pre amp.
The comments by Mb D are really interesting to me. My unit is now with Bob after my right channel went dead out of the blue. Bob called me to report that the right attenauter had malfunctioned and not only killed the pre but also my amp and right speaker. This has turned into a very expensive malfunction of the attenuated, I wish I had known about the upgrade before this from AI. Bob has ordered a replacement board for me from them, who knows when it will arrive. When I ordered new tubes from AI it took very long to get them and the communication was very spotty.
Anyway, I am still a firm believer that these are great preamps and worth the upgrade cost.