Exhibit 10.4

     FOURTH AMENDMENT (the “Amendment”) dated as of November 30, 2009 (the
“Amendment Effective Date”) by and between ADVANCED PHOTONIX, INC., a Delaware
corporation (the “Company”) and ROBIN F. RISSER, an individual (“Holder”), to
that certain SECURED PROMISSORY NOTE (the “Note”) dated as of May 2, 2005, as
amended by the Amendment dated May 1, 2008, the Second Amendment dated November
26, 2008 and the Third Amendment dated April 1, 2009.

     The Company and Holder have agreed to amend and modify the Note in
accordance with the terms and conditions hereinafter set forth. Unless otherwise
defined herein, capitalized terms shall have the respective meanings assigned to
them in the Note.

     NOW, THEREFORE, in consideration of the foregoing, the parties, intending
to be legally bound, hereby agree to replace in its entirety Section 1 of the
Note as follows:

(1) PAYMENT OF PRINCIPAL. The Principal shall be payable in annual installments
of ONE HUNDRED SIXTY SIX THOUSAND SIX HUNDRED SIXTY SEVEN DOLLARS ($166,667) on
the first anniversary of the Issuance Date, ONE HUNDRED EIGHTY THREE THOUSAND
THREE HUNDRED THIRTY THREE DOLLARS ($183,333) on the second anniversary of the
Issuance Date, ONE HUNDRED FIFTY THOUSAND DOLLARS ($150,000) on December 1,
2008, ONE HUNDRED FIFTY THOUSAND DOLLARS ($150,000) on December 1, 2010, and a
final installment of THREE HUNDRED SIXTEEN THOUSAND EIGHT HUNDRED THIRTY THREE
DOLLARS ($316,833) on March 1, 2011 (the “Maturity Date”).

Except to the extent amended hereby, the Note remains in full force and effect
in accordance with its terms and the Interest Rate (as defined in the Note) will
continue to be paid at the rate prescribed in Section 2 of the Note. The terms
and conditions of this Amendment shall be construed together with the terms of
the Note as a single agreement, provided that, to the extent any terms and
conditions of the Amendment are inconsistent with the terms and conditions of
the Note, the terms and conditions of this Amendment shall govern.

     IN WITNESS WHEREOF, this Amendment has been executed by the Parties as of
the Amendment Effective Date.

  ADVANCED PHOTONIX, INC.           By:  /s/  Richard D. Kurtz    Richard D.
Kurtz, Chief Executive Officer        /s/ Robin F. Risser    ROBIN F. RISSER

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