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Class AB Amp Questions.
Class AB Amp Questions.
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Old 26th July 2015, 08:16 AM   #1
FellCrustacean8 is offline FellCrustacean8  United States
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Default Class AB Amp Questions.

Im new to amp building. And i am wanting to build 4 class ab amps. Can someone please give a very clear explanation of how they work and some formulas to building them. I need 2 300w RMS amps and 2 150w RMS amps. I am bi-amping a pair of speakers i have designed. Any help is greatly appreciated! Thanks in advance.
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Old 26th July 2015, 05:45 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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They usually have a LTP front end into a VAS stage.
The VAS goes into a Vbe multiplier.
You can then have a driver stage or not.
Then you have the output pair(s) which can be quasi complimentary or just plain complimentary.
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Old 26th July 2015, 06:02 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Details of the speaker ? The power seems excessive.

There is a lot to amplifier design and no short, simple guide.

rgds, sreten.
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Old 26th July 2015, 10:31 PM   #4
Alan0354 is offline Alan0354  United States
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If you ask this question, you need to buy the Audio Power Amplifiers by Bob Cordell.

I am a newbie also, I spent like half a year and I am only at the stage to power up my first power amp in the next day or two. You need a lot more than just asking like this.
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Old 26th July 2015, 11:04 PM   #5
nigelwright7557 is offline nigelwright7557  United Kingdom
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Be careful which amplifier you decide to build.
While there are some good projects out there, there are also some very unstable designs which will just oscillate and burn up.
Some of the old designs but using modern transistors can be unstable.
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Old 27th July 2015, 02:01 AM   #6
CBS240 is offline CBS240  United States
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Quote:
Originally Posted by FellCrustacean8 View Post
Im new to amp building. And i am wanting to build 4 class ab amps. Can someone please give a very clear explanation of how they work and some formulas to building them. I need 2 300w RMS amps and 2 150w RMS amps. I am bi-amping a pair of speakers i have designed. Any help is greatly appreciated! Thanks in advance.
New to building amps, I would suggest starting with a smaller design or buy a pre-designed kit. Unfortunately many of these kits are not comprehensive do not have protection circuitry included nor a power supply circuit and thus requires another kit(s).

If you are going to start from scratch, make your own circuit, there are many little tricks you learn from building amps as to the best method. First, start small until you get the feel for how the circuit functions and understand how to control it. Then move on to a larger circuit. A wrong move during construction and test can cause power transistors to release magic smoke. This is not good, but if this is a small TO-220 that costs $1, it is much less of a kick in the wallet than if $20+ worth of outputs go "POOooffff-zzz-t". Believe me, I have smoked my share of power transistors. Always keep in mind building amps with no fault detection/protection circuitry is done at your own risk........possible speaker damage and such.
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Old 27th July 2015, 04:46 AM   #7
FellCrustacean8 is offline FellCrustacean8  United States
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Quote:
Originally Posted by sreten View Post
Hi,

Details of the speaker ? The power seems excessive.

There is a lot to amplifier design and no short, simple guide.

rgds, sreten.
The power isnt excessive. I'm powering 2 jbl woofers and tweeter. those are their rms ratings. im biamping.
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Old 27th July 2015, 08:08 AM   #8
DF96 is offline DF96  England
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Buy Horowitz and Hill. Read it. Buy Bob Cordell's book (or Douglas Self's book). Read it. In the meantime, build some low power kits. 300W is excessive for a newbie, who presumably has never designed and safely built a mains-powered PSU before.

Make a lamp limiter. Use it.
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Old 27th July 2015, 09:07 AM   #9
AndrewT is offline AndrewT  Scotland
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Originally Posted by FellCrustacean8 View Post
The power isnt excessive. I'm powering 2 jbl woofers and tweeter. those are their rms ratings. im biamping.
Ah, you're building a Public Address (PA) system for an audience greater than 200 people !
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Old 28th July 2015, 10:05 AM   #10
FellCrustacean8 is offline FellCrustacean8  United States
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Originally Posted by AndrewT View Post
Ah, you're building a Public Address (PA) system for an audience greater than 200 people !
Nope great sounding hifi speakers. They just need a redicoulous amount of power. Harman does that a lot. Like on the revel Salon 2. They need 500w per channel and they are studio speakers. They have a low sensitivity.
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