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Old 9th January 2004, 12:09 PM   #1
rulezzz is offline rulezzz  Lithuania
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Default parallel connection

What is the best parallel amplifier connection ?,please post image.
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Old 9th January 2004, 04:24 PM   #2
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it one way to connect them...

[edit]: i have used the resistors in blue (0.1R). they help share the load between the chips.
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Old 9th January 2004, 04:34 PM   #3
macboy is offline macboy  Canada
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The 0.1 Ohm resistors are absolutely essential. It is also very important to use tight tolerance (1% or preferably 0.1%) gain-setting resistors and/or to hand-match the resistors (the 10k/220k resistors). This ensures that both/all amps have the exact same gain, so that their output voltages will track as closely as possible. Imagine the current that would flow from one amp straight into the other one if their output voltages were off by just 1 Volt: 1 V / 0.2 ohm = 5 Amps !!! Matching is very important in a parallel connection.
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Old 9th January 2004, 05:04 PM   #4
rulezzz is offline rulezzz  Lithuania
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Yap i see that it is not very easy to connect 2amps in parallel mode.The thing is that i have same 2 microshem and 4 ohm speaker.Maybe it would be easier to make bridge connection and on load near speaker put 4Ohm 10w resistor?What you think about this?
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Old 9th January 2004, 07:10 PM   #5
macboy is offline macboy  Canada
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No, bridging will not work into a 4 ohm load. And forget about putting a 4 ohm resistor in series with the speaker to make a 8 ohm load. Half of the output power would be wasted in the resistor, which completely eliminates any benefit of bridging in the first place.

Building a parallel amp is not really all that difficult. Even if you do not have access to 1% resistors, it is not difficult to measure several cheap 5% resistors to find two that are a close match.
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Old 9th January 2004, 08:22 PM   #6
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wouldn't this work?
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Old 9th January 2004, 08:48 PM   #7
macboy is offline macboy  Canada
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Quote:
wouldn't this work?
No.
This does not guarantee which amplifier IC is going to supply the current necessary to provide the desired output voltage. The amps will probably end up fighting against each other. Each amp must have its own feedback path and input resistance. It is the only way.
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Old 9th January 2004, 09:34 PM   #8
rulezzz is offline rulezzz  Lithuania
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one thing i want to ask if i put 10k resistor to the input of the amplifier do i need to connect straight to amp(like in chip amps before microshem input there is usualy one electrolithic capacitor or etc...) or to normal input (before capacitors or smth else where preamp is connected?
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Old 9th January 2004, 09:57 PM   #9
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Quote:
Originally posted by macboy
No, bridging will not work into a 4 ohm load. And forget about putting a 4 ohm resistor in series with the speaker to make a 8 ohm load. Half of the output power would be wasted in the resistor, which completely eliminates any benefit of bridging in the first place.

Building a parallel amp is not really all that difficult. Even if you do not have access to 1% resistors, it is not difficult to measure several cheap 5% resistors to find two that are a close match.
Bridging into a 4ohm load would give each chip an 8ohm load to work with, (says national spreadsheet)
Either design is pretty easy, search for the file AN-1192.pdf on Nationals site for some great simple plans of both bridged and parallel amp circuits.
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Old 9th January 2004, 10:06 PM   #10
rulezzz is offline rulezzz  Lithuania
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what preamp should i use because those 10K resistor can realy lower a lot my input
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