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REALISTIC MPA-20 120V/12V SOLID STATE P.A. AMP N/R!!
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Time left: |
(8/24/2008 5:26:27 AM) |
Seller: |
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Bids: |
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caldizny |
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Current Bid: |
USD 0.99 |
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Hi here is a Used Realistic MPA-20 P.A Amplifier. It is missing the fuse and Cap So I couldnt try it out. I am selling it with No Reserve Packed up it weighs around 10-11lbs. This week Only!! No Gas fees.All International bidders Must pay with PayPal Only!!Buyer pays for shipping and handling. U.S. Bidders Pay with Paypal or U.S. Postal money orders Only!! All sales Final and are sold AS-IS!!No Reserve!! Please check out my other auctions.Heres some info I found online.
The amplifier is a Realistic MPA-20 Solid State Amp. This is used instead of an old stereo receiver due to longevity of operation. This unit must remain powered on 24/7 to facilitate as the amplification for the alarm siren as well as serving as a PA, Audio, and Intercom system.
Contents[hide] 1 Functions 1.1 Alarm 1.2 Public Address and Music 1.3 Intercom 2 Amplification 3 Speaker System 3.1 Multiple Speaker Handling 3.1.1 Without Line Transformers 3.1.2 With Line Transformers 3.1.3 Examples of 20W 70V Line Transformers 3.2 Speakers Staged in PA System 3.2.1 Marine Horn Speakers 3.2.2 Three Way Outdoor Speakers 3.3 Speaker Volume Control 3.3.1 Linear and Audio Taper 3.3.2 Some popular audio Attenuators 3.3.3 key points which may be worth considering [edit] Functions [edit] Alarm
The Alarm component will produce a siren loud enough to resinate though an entire city block. If an intruder breaks into the residence, the alarm will cause enough attention that the intruder will surely leave before police arrive as the result of someone phoning the police in the neihgborhood. [edit] Public Address and Music
Audio from various sources can be piped into the system. These sources include satilight TV audio, MP3 music, or a stereo receiver. [edit] Intercom
This is tied into the home intercom system so that from any intercom station within the residence someone may be paged that is outdoors near the house. [edit] Amplification
The Realistic MPA-20 is a 20 watt Solid State PA Amplifier sold by Radio Shack at one time. This is a good choice as the unit can run constantly powered on for years without problem. A less reliable amp or standard home audio receiver would burn up after such extended use without being powered off. This unit must remain constantly powered on and ready to amplify whatever line level signal it receives.
Originally there were only two speakers in the speaker system. These could be wired either series or parallel, thus doubling or dividing the total resistance rating.
The back of the MPA-20 supports a single connection to the "com" common ground and any one of the positive posts.
16 Ohms
8 Ohms
4 Ohms
There is a 70 Volt connector for using with line transformers.
Originally there were only two speakers in the speaker system. These could be wired either series or parallel, thus doubling or dividing the total resistance rating. Two 8 Ohm speakers wired in Series can be connected to the 16 Ohm post on the back of the MPA-20 amp. Two 8 Ohm speakers conencted in Paralle thus would have to be connected to the 4 Ohm post on the back of the amp. A resistance value too low can cause damage to the amp. A resistance value too high will result in low volume audio.
Series and
Parallel
Illustrated
[edit] Speaker System
There will be a hybrid of outdoor horn speakers, outdoor 2-way speakers, and indoor speakers all powered by the MPA-20 amplifier. Different audio levels will be needed for the various speakers.
The loudest speakers need to be the outdoor horn speakers, which serve as the main volume when the alarm siren is activated. The horn speakers are also ideal for voice, easy to hear over the sound of a lawnmower when being paged.
Moderately loud will be the 2-way outdoor speakers. Their purpose is to supply some level of musical fidelity as horn speakers are not able to produce a wide range of sound. However, they need to be limited as to prevent damage when the high powered siren is sounded.
The relatively quiet indoor speakers serve only to supplement the alarm and also music. These speakers not only need to be volume limited, but also require an off function.
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