parallel connection

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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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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.
 
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.
 
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?
 
macboy said:
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.
 
Re: A stupid question

soundNERD said:
Just a stupid question about parallel/bridge:

I know bridged mode doubles the power. Does parallel only double the current output, or also double the power output.

I know this is a stupid question, please don't laugh.

-Mike

It actually depends on the load impedance in both cases.

For bridging it is only true that it doubles the power if the
load impedance is high enough so the amps can supply the
necessary current.

For paralleling, you get the double power if the load impedance
is low enough so you can put twice the current into it without
hitting the max output voltage of the amps.

Basically it is just Ohms law as usual. In reality things are
always more complex due to reactive loads, frequency
dependent impedance etc. but that is a complication also in
the case of single non-bridged non-paralleled amps.
For this reason it might still make sense to parallel amps to
get better current capacity even if you don't have the voltage
swing to increase the power.
 
the situation im in is 2 lm3886 and 1 4-ohm speaker. will parallel increase power output?

another situation is 2 lm1875 and a 4-ohm speaker.
Yes, you can get get double the 8 Ohm power rating into 4 ohms by using a parallel connection.

It is very important to use the proper power supply voltage, in order to provide enough voltage to the chip to give high output power, but at the same time, to avoid providing too much voltage to the chip, which will result in excessive heat (power dissipation). That will cause SPiKe protection to kick in, killing the sound quality, and of course resulting in less output power than with lower voltage rails.

In order to choose the power supply voltage, you need to know the load impedance for the amplifier. In the case of a parallel amplifier, the effective load impedance for each of the amps is equal to the real load impedance (4 ohms in your case) multiplied by the number of amps that you are connecting in parallel (two in your case). So the effective load for each amp is 8 ohms. Design your power supply and heatsink with that in mind.
 
paulb said:

No. Wrong. Bridging means each amp sees half the impedance; it is essentially a series connection.
A Parallel connection (if the load is shared evenly) means each amp sees twice the impedance.

Not trying to be a jerk here ;), but I’m inclined to trust a National product sheet over you. Can any third party weigh in on this topic? (Honestly I’ve never thought that their calc was right either, but I’ve just trusted it, and figured their engineers must know more then me. :clown: )

http://www.national.com/appinfo/audio/files/Overture_Design_Guide13.xls
 
Officeboy, I think that you are getting confused between what the Overture Design Guide spreadsheet is telling you, and what paulb has said.

The Overture design guide will indicate the "Bridge Load" and "Parallel Load". What you see in either of these cells is the actual speaker (load) impedance that you should be using with the amp, given the other design data that you have plugged into the spreadsheet. The most important of this other data which you supply is the load impedance, RL, in cell D10. This is actually the effective load impedance seen by each amplifier chip that you are using in the overall design (whether normal, bridged, or parallel). It is not the true impedance of the speaker. That is indicated by the Parallel Load or Bridged Load cells.

You may benefit from reading the How to Use the Overture Design Guide document from National.
 
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