Document:

<PAGE>
                                                                   Exhibit 10.23

                     Jiangsu Electronics Industries Limited
                       c/o Koss Audio & Video Electronics
                           11733 Missouri Bottom Road
                           Hazelwood, Missouri 63042

                               December 28, 2001

Mr. Michael J. Koss
Koss Corporation
4129 North Port Washington Avenue
Milwaukee, Wisconsin 53212

     Re: Seventh Amendment to License Agreement

Dear Michael:

     Koss Corporation, a Delaware corporation ("Licensor"), and Jiangsu
Electronics Industries Limited, a British Virgin Islands company ("Licensee"),
are (by way of assignment) parties to a certain License Agreement between
Licensor and Trabelco N.V. dated November 15, 1991, as amended (as amended, the
"License Agreement"). Licensor and Licensee now desire to further amend certain
terms and conditions of the License Agreement and agree as follows:

     1.  The first sentence of Section 1.2 of the License Agreement (as amended
by the Fourth Amendment to License Agreement dated May 29, 1998 and Fifth
Amendment to License Agreement dated March 30, 2001) is hereby revised such that
all references to December 31, 2001 shall be deleted and replaced with December
31, 2002 and all references to January 1, 2002 shall be deleted and replaced
with January 1, 2003, but ONLY to the extent such dates relate to the sale of
DVD players and/or recorders added to the License Agreement pursuant to this
letter agreement as reflected on EXHIBIT B and EXHIBIT D to the License
Agreement (modified in accordance with item 3 below).

     2.  As of the date hereof Licensee agrees that Licensor shall have the
right to manufacture, distribute and sell personal AM/FM and TV band radios with
headsets for use with specially outfitted automobile audio and video systems.
Licensor agrees that all such radio and headset units shall comply with the
specifications of the automobile original equipment manufacturer (i.e. Ford,
General Motors) and be distributed directly through such manufacturer to its
respective automobile dealers as well as sold direct to consumers through
Licensor's internet site.

     3.  EXHIBIT B and EXHIBIT D to the License Agreement are hereby deleted in
their entirety and the EXHIBIT B and EXHIBIT D attached hereto shall be inserted
in their place.
<PAGE>
Mr. Michael J. Koss
December 28, 2001
Page 2

     4.  The parties hereto agree that this letter agreement has been jointly
drafted by the parties, that the language used in this letter agreement
reflects their mutual intent, and that no term or provision shall be construed
more or less favorably to either party hereto on the grounds that it was
drafted or authorized by such party.

     5.  Except as hereby amended, the License Agreement shall remain in full
force and effect.

     To evidence your agreement with the provisions set forth in this letter,
please execute this letter below.

                                       Very truly yours,

                                       JLANGSU ELECTRONICS INDUSTRIES LIMITED

                                       By:  /s/ Poon Ka Hung
                                            ------------------------------
                                            Name:  Poon Ka Hung
                                            Title: Chief Executive Officer

Agreed to this 28 day of December, 2001

KOSS CORPORATION

By:  /s/ Michael J. Koss
     --------------------------
     Michael J. Koss, President
<PAGE>
                                   Exhibit B

<Table>
<Caption>
MOBILE PRODUCTS*                                                       ROYALTY
---------------                                                        -------
<S>                                                                      <C>
Audio systems of any nature (excluding clock radios and
audio systems incorporating clock radios) with a
cassette player but without a compact disc player                        2.0%

Audio systems of any nature (excluding clock radios and audio
systems incorporating clock radios) with a compact disc
player and/or a CD changer                                               1.5%

Power amplifiers                                                         1.5%

Power inverters                                                          1.5%

Receivers                                                                2.0%

Audio and video systems of any nature incorporating a DVD
player and/or recorder                                                   1.0%

</Table>

<Table>
<Caption>

HOME AND PORTABLE PRODUCTS**                                            ROYALTY
----------------------------                                            -------
<S>                                                                      <C>
Clock radios                                                             2.0%

AM/FM radios (excluding clock radios and audio systems
incorporating clock radios) without a cassette or compact
disc player                                                              3.0%

Audio systems of any nature (excluding clock radios and audio
systems incorporating clock radios) with a cassette player but
without a compact disc player                                            2.0%

Audio systems of any nature (excluding clock radios and audio
systems incorporating clock radios) with a compact disc player
and/or a CD changer                                                      1.5%

Power amplifiers                                                         1.5%

Receivers                                                                2.0%

Audio, video and home theater systems of any nature incorporating
a DVD player and/or recorder                                             1.0%

</Table>
-------------
* All products listed under Mobile Products in this Exhibit B shall
  mean only those products which are designed for use in automobiles
  only.

<PAGE>
                                   Exhibit D

                   Calculation of Quarterly Royalties Payment

<Table>
<Caption>
                                        Total Sales    Returns     Net Sales    Royalty Rate   Subtotal
                                        -----------   ---------    ---------    ------------   --------
<S>                                      <C>           <C>         <C>              <C>         <C>

MOBILE PRODUCTS*

Audio systems of any nature              ---------    ---------    ---------        2.0%
(excluding clock radios and
audio systems incorporating
clock radios) with a cassette
player but without a compact
disc player

Audio systems of any nature              ---------    ---------    ---------        1.5%
(excluding clock radios and audio
systems incorporating clock radios)
with a compact disc player and/or
a CD changer

Power Amplifiers                         ---------    ---------    ---------        1.5%

Power Inverters                          ---------    ---------    ---------        1.5%

Receivers                                ---------    ---------    ---------        2.0%

Audio and video systems                  ---------    ---------    ---------        1.0%
of any nature incorporating
a DVD player and/or recorder
</Table>
<PAGE>

<Table>
<Caption>
                                        Total Sales    Returns     Net Sales    Royalty Rate   Subtotal
                                        -----------    -------     ---------    ------------   --------
<S>                                     <C>            <C>         <C>             <C>         <C>
HOME AND PORTABLE PRODUCTS**

Clock Radios                            -----------    -------     ---------       2.0%

AM/FM radios                            -----------    -------     ---------       3.0%
(excluding clock radios
and audio systems incorporating
clock radios) without a cassette
or compact disc player

Audio systems of any nature             -----------    -------     ---------       2.0%
(excluding clock radios and audio
systems incorporating clock radios)
with a cassette player but without
a compact disc player

Audio systems of any nature             -----------    -------     ---------       1.5%
(excluding clock radios and audio
systems incorporating clock radios)
with a compact disc player and/or
a CD changer

Power Amplifiers                        -----------    -------     ---------       1.5%

Receivers                               -----------    -------     ---------       2.0%

Audio video and home theater            -----------    -------     ---------       1.0%
systems of any nature
incorporating a DVD player
and/or recorder

    Subtotal                                                  $                    Subtotal    $
                                                               -------                         --------

    Less 2% of itemized discounts, rebates
    and shipping costs                                         (      )
                                                               -------

    ROYALTIES PAYMENT                                         $
</Table>

*  All products listed under Mobile Products in this Exhibit D shall mean only
   those products which are designed for use in automobiles only.

** Home and portable products listed in this Exhibit D shall not include
   products designed for use in automobiles.<PAGE>
                                                                   Exhibit 10.25

                        AMENDMENT & EXTENSION AGREEMENT

     THIS AMENDMENT & EXTENSION AGREEMENT is made as of the 1 day of May, 2001,
by and between KOSS CORPORATION, a Delaware corporation with its principal place
of business at 4129 North Port Westington Avenue, Milwaukee, WI 53212 (the
"LICENSOR") and LOGITECH ELECTRONICS INC., an Ontario company, with its
principal place of business at 60 Bell Farm Road, Barrie, Ontario L4M 5G6 (the
"LICENSEE").

          WITNESSETH:

          WHEREAS LICENSOR and LICENSEE are parties to a certain License
Agreement dated the 30th day of June, 1998 (the "LICENSE AGREEMENT") and are
furthermore parties to a certain Addendum Agreement dated the 30th day of June,
1998 (the "ADDENDUM") with respect to the License Agreement;

          AND WHEREAS the parties now desire to amend and extend the terms and
conditions of the License Agreement and the Addendum as hereinafter provided;

          NOW THEREFORE for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

     1.   AMENDMENT TO ROYALTY.

          Section 6.1 of the License Agreement is hereby amended to replace the
          definition of "Royalties" as "an amount equal to ten percent (10%) of
          net sales" to read "AN AMOUNT EQUAL TO SIX AND ONE-HALF PERCENT (6.5%)
          OF NET SALES", said amendment to be effective as of the 1st day of
          July, 2000.

     2.   AMENDMENT TO MINIMUM ANNUAL ROYALTIES.

          Section 6.2 of the License Agreement is hereby amended to replace the
          "annual minimum Royalties" as referred to therein, for the period from
          July 1, 2000, to June 30, 2003, as follows:

                   "Contract Year                          Minimum Royalties
                   --------------                          -----------------

                   July 1, 2000 - June 30, 2001               U.S. $210,000
                   July 1, 2001 - June 30, 2002               U.S. $220,000
                   July 1, 2002 - June 30, 2003               U.S. $230,000"
<PAGE>
     3.   EXTENSION OF LICENSE AGREEMENT & ADDENDUM.

          It is agreed that the License Agreement and Addendum shall be renewed
          and extended for a further five (5) year term from the 1st day of
          July, 2003, to the 30th day of June, 2008. It is furthermore agreed
          that Section 6.3 of the License Agreement is hereby amended to replace
          the "Minimum Royalties for the first renewal period" as referred to
          therein, for the period from July 1, 2003, to June 30, 2008, as
          follows:

                   "Contract Year                          Minimum Royalties
                   --------------                          -----------------

                   July 1, 2003 - June 30, 2004               U.S. $241,000
                   July 1, 2004 - June 30, 2005               U.S. $252,000
                   July 1, 2005 - June 30, 2006               U.S. $265,000
                   July 1, 2006 - June 30, 2007               U.S. $278,000
                   July 1, 2007 - June 30, 2008               U.S. $292,000"

     4.   MISCELLANEOUS.

          Save and except as amended and extended herein, the License Agreement
          and Addendum shall remain in full force and effect, binding upon the
          parties thereto and hereto in accordance with the terms therein.

          IN WITNESS WHEREOF the parties hereto have caused this Amendment &
Extension Agreement to be executed as of the date set forth above. The
effective date of this Amendment & Extension Agreement is the 1st day of July,
2000.

                                       KOSS CORPORATION

                                       By:  /s/ Michael J. Koss
                                            ---------------------------
                                            President and CEO

                                       LOGITECH ELECTRONICS INC.

                                       By:  /s/ Greg Bell
                                            ---------------------------
                                            President and CEO

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