<PAGE>
                                                                    EXHIBIT 10.8


                               AMENDMENT NO. 1 TO
                             NOTE PURCHASE AGREEMENT

AMENDMENT NO. 1 TO NOTE PURCHASE AGREEMENT ("Amendment") effective as of October
15, 2004 (the "Effective Date") by and among CALAMOS HOLDINGS, INC., a Delaware
corporation (the "Company"), and the purchasers listed in Schedule A hereto (the
"Purchasers").

                                    RECITALS

WHEREAS the Company and the Purchasers have entered into an Note Purchase
Agreement dated as of April 29, 2004 (such Note Purchase Agreement, as amended
from time to time, the "Note Purchase Agreement"); and

WHEREAS the Company desires to amend the Note Purchase Agreement as provided
herein.

NOW, THEREFORE, in consideration of the material promises and agreements herein
made and intending to be legally bound, the parties hereto hereby agree as
follows:

All capitalized terms used herein and not defined herein shall have the meaning
specified in the Note Purchase Agreement.

1. Amendment. Section 10.8(a) of the Note Purchase Agreement is amended by
replacing the word "corporation" with the words "corporation or limited
liability company" wherever it appears in that section. The text of Section
10.8(a) prior to the amendment and subsequent to the amendment is attached as
Exhibit A hereto.

2. Effectiveness. Pursuant to Section 17.1 of the Note Purchase Agreement, this
Amendment shall be effective upon its execution by the Company and the Required
Holders. Upon such execution, this Amendment shall be deemed effective, and the
Note Purchase Agreement shall be deemed amended as herein provided, as of the
Effective Date.

3. Ratification. Except as amended hereby, the Note Purchase Agreement is
ratified and confirmed and shall continue in full force and effect.

4. Governing Law. This Amendment to the Agreement shall be construed and
enforced in accordance with, and the rights of the parties shall be governed by,
the law of the State of New York excluding choice-of-law principles of the law
of such State that would require the application of the laws of a jurisdiction
other than such State.

5. Counterparts. This amendment may be executed in one or more counterparts,
each of which shall be deemed an original but all of which shall constitute one
and the same instrument.


                                       1
<PAGE>
In witness whereof, the parties hereto have executed this Amendment as of the
Effective Date.

                                  CALAMOS HOLDINGS, INC.

                                  By: /s/ James S. Hamman, Jr.
                                  Name: James S. Hamman, Jr.
                                  Title: Executive Vice President, General
                                         Counsel and Secretary


                                       2
<PAGE>
ALLSTATE LIFE INSURANCE COMPANY

By: /s/ Jeffrey J. Cannon
Name: Jeffrey J. Cannon


By: /s/ Jerry D. Zinkula
Name: Jerry D. Zinkula
      Authorized Signatories


ALLSTATE INSURANCE COMPANY

By: /s/ Jeffrey J. Cannon
Name: Jeffrey J. Cannon


By: /s/ Jerry D. Zinkula
Name: Jerry D. Zinkula
      Authorized Signatories


                                       3
<PAGE>
THE TRAVELERS INSURANCE COMPANY

By:  /s/ Matthew J. McInerny
Name:  Matthew J. McInerny
Title:  Investment Officer

CITICORP INSURANCE AND INVESTMENT TRUST, BY TRAVELERS ASSET MANAGEMENT
INTERNATIONAL COMPANY, LLC

By:  /s/ Matthew J. McInerny
Name:  Matthew J. McInerny
Title:  Investment Officer

PRIMERICA LIFE INSURANCE COMPANY

By:  /s/ Matthew J. Inerny
Name:  Matthew J. Inerny
Title:  Investment Officer

THE TRAVELERS LIFE AND ANNUITY COMPANY (ON BEHALF OF ONE OF ITS SEPARATE
ACCOUNTS)

By:  /s/ Matthew J. Inerny
Name:  Matthew J. Inerny
Title:  Investment Officer

THE TRAVELERS INSURANCE COMPANY (ON BEHALF OF ONE OF ITS SEPARATE ACCOUNTS)

By:  /s/ Matthew J. Inerny
Name:  Matthew J. Inerny
Title:  Investment Officer


                                       4
<PAGE>
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY

By:  /s/ Mark E. Kishler
Name:  Mark E. Kishler
Title:  Its Authorized Representative


                                       5
<PAGE>
TEACHERS INSURANCE AND ANNUITY ASSOCIATION OF AMERICA

By:  Angela Brock-Kyle
Name:  Angela Brock-Kyle
Title:  Managing Director


                                       6
<PAGE>
MIDLAND NATIONAL LIFE INSURANCE COMPANY

By:  /s/ Adrian Duff
Name: Adrian Duff
Title:  Managing Director


                                       7
<PAGE>
THE GUARDIAN LIFE INSURANCE COMPANY OF AMERICA

By:  /s/ Ellen I. Whittaker
Name:  Ellen I. Whittaker
Title:  Director, Fixed Income


THE GUARDIAN INSURANCE & ANNUITY COMPANY, INC.

By:  /s/ Ellen I. Whittaker
Name:  Ellen I. Whittaker
Title:  Director, Fixed Income


FORT DEARBORN LIFE INSURANCE COMPANY
By: Guardian Investor Services LLC

By:  /s/ Ellen I. Whittaker
Name:  Ellen I. Whittaker
Title:  Director, Fixed Income


                                       8
<PAGE>
THE OHIO NATIONAL LIFE INSURANCE COMPANY

By:  /s/ Jed R. Martin
Name:  Jed R. Martin
Title:  Investment Vice President
         Private Placements


                                       9
<PAGE>
                                                                       Exhibit A

Unamended Section 10.8(a):

10.8  Merger, Consolidation, etc.

            The Company will not consolidate with or merge with any other
      corporation or convey, transfer or lease substantially all of its assets
      in a single transaction or series of transactions to any Person unless:
      (a) the successor formed by such consolidation or the survivor of such
      merger or the Person that acquires by conveyance, transfer or lease
      substantially all of the assets of the Company as an entirety, as the case
      may be, shall be a solvent corporation organized and existing under the
      laws of the United States or any State thereof (including the District of
      Columbia), and, if the Company is not such corporation, (i) such
      corporation shall have executed and delivered to each holder of any Notes
      its assumption of the due and punctual performance and observance of each
      covenant and condition of this Agreement and the Notes and (ii) shall have
      caused to be delivered to each holder of any Notes an opinion of
      nationally recognized independent counsel, or other independent counsel
      reasonably satisfactory to the Required Holders, to the effect that all
      agreements or instruments effecting such assumption are enforceable in
      accordance with their terms and comply with the terms hereof;

Amended Section 10.8(a):

10.8  Merger, Consolidation, etc.

            The Company will not consolidate with or merge with any other
corporation or limited liability company or convey, transfer or lease
substantially all of its assets in a single transaction or series of
transactions to any Person unless: (a) the successor formed by such
consolidation or the survivor of such merger or the Person that acquires by
conveyance, transfer or lease substantially all of the assets of the Company as
an entirety, as the case may be, shall be a solvent corporation or limited
liability company organized and existing under the laws of the United States or
any State thereof (including the District of Columbia), and, if the Company is
not such corporation or limited liability company, (i) such corporation or
limited liability company shall have executed and delivered to each holder of
any Notes its assumption of the due and punctual performance and observance of
each covenant and condition of this Agreement and the Notes and (ii) shall have
caused to be delivered to each holder of any Notes an opinion of nationally
recognized independent counsel, or other independent counsel reasonably
satisfactory to the Required Holders, to the effect that all agreements or
instruments effecting such assumption are enforceable in accordance with their
terms and comply with the terms hereof;


                                       10
<PAGE>
                                   SCHEDULE A


<TABLE>
<CAPTION>
                                                                        Principal Amount of
Name of Purchaser                                                      Notes to be Purchased
-----------------                                                      ---------------------
<S>                                                                    <C>
ALLSTATE LIFE INSURANCE COMPANY ....................................        $13,800,000
 ...................................................................          9,200,000

ALLSTATE INSURANCE COMPANY .........................................        $ 5,000,000
THE TRAVELERS INSURANCE COMPANY ....................................        $15,900,000
CITICORP INSURANCE AND INVESTMENT TRUST, BY TRAVELERS ASSET
MANAGEMENT INTERNATIONAL COMPANY, LLC ..............................        $ 1,000,000
PRIMERICA LIFE INSURANCE COMPANY ...................................        $ 2,000,000
THE TRAVELERS LIFE AND ANNUITY COMPANY (ON BEHALF OF ONE OF ITS
SEPARATE ACCOUNTS) .................................................        $ 6,800,000
THE TRAVELERS INSURANCE COMPANY (ON BEHALF OF ONE OF ITS SEPARATE
ACCOUNTS) ..........................................................        $ 2,300,000
THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY .....................        $28,000,000
TEACHERS INSURANCE AND ANNUITY ASSOCIATION OF AMERICA ..............        $28,000,000
MIDLAND NATIONAL LIFE INSURANCE COMPANY ............................        $15,000,000
MIDLAND NATIONAL LIFE INSURANCE COMPANY ............................        $ 3,000,000
THE GUARDIAN LIFE INSURANCE COMPANY OF AMERICA .....................        $10,000,000
THE GUARDIAN INSURANCE & ANNUITY COMPANY, INC. .....................        $ 2,000,000
FORT DEARBORN LIFE INSURANCE COMPANY ...............................        $ 1,000,000
FORT DEARBORN LIFE INSURANCE COMPANY ...............................        $ 1,000,000
THE OHIO NATIONAL LIFE INSURANCE COMPANY ...........................        $ 6,000,000
</TABLE>


                                       11