Upgrade for old Dahlquist DQ LP1 Crossover


I have been using this old Dahlquist DQ Lp1 crossover to send the LFE to my passive VMPS Larger sub. To me it sounds ok but I have not had anything to compare it with. There must be an upgrade to this unit seeing that it was made in the early 1980's.
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Have you seen this link? http://www.regnar.com/cgi-local/SoftCart.100.exe/online-store/scstore/p-DQLP1CRUK.html?L+scstore+rhvk5229ff794b79+1051030992
At one time, Frank Van Alstine modified these units. Cost unknown. You can reach him at 952-890-3517.
It was a Van Alstine modified DQ LP1 that Harry Pearson used in his writings about one of his then listening room system which consisted of Quad ESL63's with Maggy Timpani panels for the low end

This is an old post but I am responding to it as I am still using my LP1.  I did modify mine to it is now singled ended from a +30Vdc supply, rather than the +/- 15Vdc.  That meant putting polypropylene caps on the output to block the DC.   The design did add significant bass impact as it eliminated the sensitivity of the op amp to noise on the negative rail.  

Definitely use polystyrene caps on the upper pass region.