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#424072 - 03/13/17 05:26 AM Questions about the amplifier output voltage
minie Offline
newbie

Registered: 02/08/17
Posts: 2
I have to use a LM384 amp circuit (shown below) for a school project and need to explain how it works.

I've read the LM384 datasheet,and thus have a guess about some components but others remain a mystery.

Vin potentiometer is only a voltage divider to adjust input voltage
.1uF capacitor (above) is a decoupling capacitor to avoid noise in the power supply
5uF capacitor has the same purpose
RC branch + 500uF capacitor : That is the question. I don't really get the purpose of this.

Is the 500uF capacitor combined with 8 Ohm load just making a high pass filter with a cutting frequency of 1/(2*piRC) = 40 Hz ? Then what would be the point of this parallel RC branch?

Any help appreciated, thanks a lot!


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#424082 - 03/13/17 03:04 PM Re: Questions about the amplifier output voltage [Re: minie]
Mojo Online   content
connoisseur

Registered: 01/21/07
Posts: 4915
It's a Zobel network used to ensure closed-loop stability by removing poles in the right s-plane.

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#424122 - 03/15/17 12:46 AM Re: Questions about the amplifier output voltage [Re: minie]
bridgman Offline
axiomite

Registered: 08/25/04
Posts: 6142
Loc: Bowmanville, Ontario, Canada
Is it fair to say that the Zobel network is just the 2.7 ohm resistor and 0.1uF cap, while the 500uF cap is to AC-couple the output of the amplifier and remove the DC offset from having only a positive power supply ?

EDIT - never mind, minie already figured that out and was only asking about the RC portion. Sorry, couldn't see original email while responding...

I wondered for a minute why there was no input capacitor but checking the data sheet I found:

Quote:
A unique input stage allows ground referenced input signals. The output automatically self-centers to one-half the supply voltage.

AFAICS the 5uF cap does not directly filter the power supply, instead it filters a "half supply voltage" reference generated on the chip. If you look at the National data sheet you can see the internal schematic of the chip:

LM384 http://pdf1.alldatasheet.com/datasheet-pdf/view/8886/NSC/LM384.html


Edited by bridgman (03/15/17 12:58 AM)
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#424363 - 03/23/17 12:27 PM Re: Questions about the amplifier output voltage [Re: minie]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13579
Loc: Iowa
what he said
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#424500 - 03/26/17 04:33 PM Re: Questions about the amplifier output voltage [Re: SirQuack]
Rjlitho Offline
buff

Registered: 03/01/17
Posts: 54
Loc: Mississauga, ON
Is it recommended to have a seperate power for the amps I thinking of purchasing a set of pair mono blocks
RJ

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#424508 - 03/27/17 12:05 AM Re: Questions about the amplifier output voltage [Re: minie]
Mojo Online   content
connoisseur

Registered: 01/21/07
Posts: 4915
You shouldn't even bother with audio unless you have two of these bridged per channel.

http://www.pknc.com/3phase_eng.html

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