Document:

<PAGE>   1
                                                                  EXHIBIT 10.4.5

                       TRANCHE A NOTE EXTENSION AGREEMENT

      This Tranche A Note Extension Agreement (this "Agreement") dated as of
March 30, 2001 is entered into by and between CRL Systems, Inc., a Nevada
corporation ("Borrower") and Harman Acquisition Corp. (f/k/a/ Orban, Inc.), a
Delaware corporation ("Lender").

                                    RECITALS

      A.    The parties hereto entered into a Credit Agreement dated May 31,
2000 (the "Credit Agreement");

      B.    Pursuant to Section 2.1 of the Credit Agreement, Borrower agreed to
pay $250,000 of the principal amount of the Tranche A Note to Lender on March
31, 2001 (the "March 2001 Obligation");

      C.    Lender wishes to defer the payment of the March 2001 Obligation to
July 31, 2001 as more fully set forth herein;

      NOW THEREFORE, IN CONSIDERATION of the mutual covenants and agreements
contained in this Agreement and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties to this
Agreement hereby agree as follows:

                                    AGREEMENT

      1.    Lender hereby defers the payment of the March 2001 Obligation to
July 31, 2001 unless such payment shall otherwise become payable sooner as
provided in the Loan Documents.

      2.    Borrower acknowledges that failure of Borrower to fulfill any of its
obligations under this Agreement shall be deemed an Event of Default under the
Credit Agreement.

      3.    Borrower and Circuit Research Labs, Inc. (the "Company") agree that
the Obligations are valid and enforceable obligations of Borrower and hereby
confirm, acknowledges and ratifies the existence of the Obligations and
Borrower's obligations to Lender with respect thereto as set forth in the Credit
Agreement, and all other obligations of Borrower and the Company to Lender under
the Loan Documents.

      4.    Representations and Warranties of Borrower.

            a     The Borrower is a corporation duly organized, validly existing
and in good standing under the laws of the jurisdiction indicated at the
beginning of this Agreement.

            b     The execution, delivery and performance by the Borrower of
this Agreement are within the Borrower's corporate powers, have been duly
authorized by all necessary corporate action and do not violate, contravene or
create a breach, violation or default under (i) the Borrower's charter or
by-laws, (ii) any Requirement of Law or any Contractual
<PAGE>   2
Obligation binding on or affecting the Borrower, or result in, or require, the
creation or imposition of any mortgage, deed of trust, pledge, Lien, security
interest or other charge, encumbrance or preferential arrangement of any nature
(other than as contemplated by the Loan Documents) upon or with respect to any
of the properties now owned or hereafter acquired by the Borrower.

            c     No authorization, approval or other action by, and no notice
to or filing with, any Governmental Authority is required for the due execution,
delivery and performance by the Borrower of this Agreement.

            d     There is no pending or threatened action or proceeding
affecting the Borrower or any of its Subsidiaries before any court, Governmental
Authority or arbitrator, which could materially and adversely affect the
financial condition or operations of the Borrower or any Subsidiary or which
purports to affect the legality, validity or enforceability of this Agreement.

      5.    THIS AGREEMENT AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL
AGREEMENT OF THE BORROWER AND THE LENDER WITH RESPECT TO THE SUBJECT MATTER
HEREOF, AND THERE ARE NO PROMISES, UNDERTAKINGS, REPRESENTATIONS OR WARRANTIES
BY THE LENDER RELATIVE TO THE SUBJECT MATTER HEREOF NOT EXPRESSLY SET FORTH OR
REFERRED TO HEREIN OR IN THE OTHER LOAN DOCUMENTS.

      6.    This Agreement constitutes a one time extension of the Borrower's
repayment obligations under Section 2.1 of the Credit Agreement. Except for the
extension specifically contained herein, the terms, conditions and obligations
contained in the Loan Documents remain in full force and effect and are hereby
ratified and confirmed. The execution, delivery and effectiveness of this
Agreement will not, operate as a waiver of any right, power or remedy of Lender
under any of the Loan Documents, nor constitute a waiver of any provision of any
of the Loan Documents.

      7.    This Agreement will be deemed to be a contract made under the Laws
of the State of New York and for all purposes will be governed by and
interpreted in accordance with the laws prevailing in the State of New York,
without regard to principals of conflict of laws.

      8.    This Agreement may be executed in several counterparts each of which
when so executed will be deemed to be an original and all of which will together
constitute one and the same agreement. this Agreement will become effective when
this Agreement is executed by each of the parties hereto.

      9.    Capitalized terms used but not defined in this Agreement have the
meanings ascribed to them in the Credit Agreement.
<PAGE>   3
      IN WITNESS WHEREOF, Borrower and Harman Acquisition Corp. have executed
this Agreement as of the first date written above.

                                    CRL SYSTEMS, INC.

                                    By:  /s/ Charles Jayson Brentlinger
                                         ---------------------------------------
                                    Name:  Charles Jayson Brentlinger
                                           -------------------------------------
                                    Title:  President, CEO, Chairman
                                            ------------------------------------

                                    HARMAN ACQUISITION CORP.

                                    By:  /s/ Frank Meredith
                                         ---------------------------------------
                                    Name:  Frank Meredith
                                           -------------------------------------
                                    Title:  Chief Financial Officer
                                            ------------------------------------

Agreed to and accepted by

CIRCUIT RESEARCH LABS, INC.

By:  /s/ Charles Jayson Brentlinger
     -------------------------------------
Name:  Charles Jayson Brentlinger
       -----------------------------------
Title:  President, CEO, Chairman
        ----------------------------------<PAGE>   1
                                                                  EXHIBIT 10.4.6

              TRANCHE A NOTE AND TRANCHE B NOTE EXTENSION AGREEMENT

      This Tranche A Note and Tranche B Note Extension Agreement (this
"Agreement") dated as of April ___, 2001 is entered into by and between CRL
Systems, Inc., a Nevada corporation ("Borrower") and Harman Acquisition Corp.
(f/k/a/ Orban, Inc.), a Delaware corporation ("Lender").

                                    RECITALS

      A.    The parties hereto entered into a Credit Agreement dated May 31,
2000 (the "Credit Agreement");

      B.    Pursuant to Section 2.1 of the Credit Agreement, Borrower agreed to
pay $250,000 of the principal amount of the Tranche A Note to Lender on March
31, 2001, June 30, 2001, September 30, 2001, December 31, 2001 and March 31,
2002 (the "Quarterly Payments");

      C.    Pursuant to Section 2.2 of the Credit Agreement, Borrower agreed to
pay the full principal amount of the Tranche B Note to Lender on September 30,
2000 (the "Tranche B Maturity Date");

      D.    The parties hereto entered into a Tranche A Note Extension
Agreement, dated March 30, 2001 (the "Tranche A. Extension Agreement"), pursuant
to which the payment of the March 2001 Obligation was extended to July 31, 2001;

      E.    The parties hereto executed a First Extension Agreement, a Second
Extension Agreement, a Third Extension Agreement and a Fourth Extension
Agreement, dated February 22, 2001 (collectively, the "Tranche B Extension
Agreements") pursuant to which Lender extended the Tranche B Maturity Date to
May 14, 2001; and

      F.    Lender wishes, subject to the conditions set forth in this
Agreement, to (i) defer the payment of the Quarterly Payment, including the
March 2001 Obligation, to April 30, 2002, and (ii) further extend the Tranche B
Maturity Date to April 30, 2002.

      NOW THEREFORE, IN CONSIDERATION of the mutual covenants and agreements
contained in this Agreement and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties to this
Agreement hereby agree as follows:

                                    AGREEMENT

      1.    Lender hereby defers the payment of the Quarterly Payments to April
30, 2002, unless such payment shall otherwise become payable sooner as provided
in the Loan Documents; provided, however that on or before September 30, 2001,
Borrower shall pay $250,000 to Lender in satisfaction of the September 30, 2001
payment required to be paid by Borrower to Lender in accordance with Section 2.1
of the Credit Agreement.
<PAGE>   2
      2.    Lender hereby extends the Tranche B Maturity Date to April 30, 2002.

      3.    Borrower acknowledges that failure of Borrower to fulfill any of its
obligations under this Agreement shall be deemed an Event of Default under the
Credit Agreement.

      4.    Borrower and Circuit Research Labs, Inc. (the "Company") agree that
the Obligations are valid and enforceable obligations of Borrower and hereby
confirm, acknowledges and ratifies the existence of the Obligations and
Borrower's obligations to Lender with respect thereto as set forth in the Credit
Agreement, and all other obligations of Borrower and the Company to Lender under
the Loan Documents.

      5.    Borrower represents and warrants to Lender as follows:

            a     The Borrower is a corporation duly organized, validly existing
and in good standing under the laws of the jurisdiction indicated at the
beginning of this Agreement.

            b     The execution, delivery and performance by the Borrower of
this Agreement are within the Borrower's corporate powers, have been duly
authorized by all necessary corporate action and do not violate, contravene or
create a breach, violation or default under (i) the Borrower's charter or
by-laws, (ii) any Requirement of Law or any Contractual Obligation binding on or
affecting the Borrower, or result in, or require, the creation or imposition of
any mortgage, deed of trust, pledge, Lien, security interest or other charge,
encumbrance or preferential arrangement of any nature (other than as
contemplated by the Loan Documents) upon or with respect to any of the
properties now owned or hereafter acquired by the Borrower.

            c     No authorization, approval or other action by, and no notice
to or filing with, any Governmental Authority is required for the due execution,
delivery and performance by the Borrower of this Agreement.

            d     There is no pending or threatened action or proceeding
affecting the Borrower or any of its Subsidiaries before any court, Governmental
Authority or arbitrator, which could materially and adversely affect the
financial condition or operations of the Borrower or any Subsidiary or which
purports to affect the legality, validity or enforceability of this Agreement.

      6.    THIS AGREEMENT, THE TRANCHE A EXTENSION AGREEMENT, THE TRANCHE B
EXTENSION AGREEMENTS, AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT
OF THE BORROWER AND THE LENDER WITH RESPECT TO THE SUBJECT MATTER HEREOF, AND
THERE ARE NO PROMISES, UNDERTAKINGS, REPRESENTATIONS OR WARRANTIES BY THE LENDER
RELATIVE TO THE SUBJECT MATTER HEREOF NOT EXPRESSLY SET FORTH OR REFERRED TO
HEREIN OR IN THE OTHER LOAN DOCUMENTS, THE TRANCHE A EXTENSION AGREEMENT OR THE
TRANCHE B EXTENSION AGREEMENTS.

      7.    Except for the extension specifically contained herein, the terms,
conditions and obligations contained in the Loan Documents, the Tranche A
Extension Agreement and the Tranche B Extension Agreements remain in full force
and effect and are hereby ratified and
<PAGE>   3
confirmed. The execution, delivery and effectiveness of this Agreement will not,
operate as a waiver of any right, power or remedy of Lender under any of the
Loan Documents, the Tranche A Extension Agreement or the Tranche B Extension
Agreements nor constitute a waiver of any provision of any of the Loan
Documents, the Tranche A Extension Agreement or the Tranche B Extension
Agreements.

      8.    This Agreement will be deemed to be a contract made under the Laws
of the State of New York and for all purposes will be governed by and
interpreted in accordance with the laws prevailing in the State of New York,
without regard to principles of conflict of laws.

      9.    This Agreement may be executed in several counterparts each of which
when so executed will be deemed to be an original and all of which will together
constitute one and the same agreement. This Agreement will become effective when
this Agreement is executed by each of the parties hereto.

      10.   Capitalized terms used but not defined in this Agreement have the
meanings ascribed to them in the Credit Agreement, the Tranche A Extension
Agreement and the Tranche B Extension Agreements.
<PAGE>   4
      IN WITNESS WHEREOF, Borrower and Harman Acquisition Corp. have executed
this Agreement as of the first date written above.

                                    CRL SYSTEMS, INC.

                                    By:
                                         ---------------------------------------
                                    Name:
                                           -------------------------------------
                                    Title:
                                            ------------------------------------

                                    HARMAN ACQUISITION CORP.

                                    By:  /s/ Frank Meredith
                                         ---------------------------------------
                                    Name:  Frank Meredith
                                           -------------------------------------
                                    Title:  Chief Financial Officer
                                            ------------------------------------

Agreed to and accepted by

CIRCUIT RESEARCH LABS, INC.

By:
     ----------------------------------
Name:
       --------------------------------
Title:
        -------------------------------

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