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Questions about the amplifier output voltage
#424072 03/13/17 09:26 AM
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minie Offline OP
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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!


Re: Questions about the amplifier output voltage
minie #424082 03/13/17 07:04 PM
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axiomite
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It's a Zobel network used to ensure closed-loop stability by removing poles in the right s-plane.

Re: Questions about the amplifier output voltage
minie #424122 03/15/17 04:46 AM
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axiomite
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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

Last edited by bridgman; 03/15/17 04:58 AM.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
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Re: Questions about the amplifier output voltage
minie #424363 03/23/17 04:27 PM
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shareholder in the making
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what he said


M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB SonyUBPX800


Re: Questions about the amplifier output voltage
SirQuack #424500 03/26/17 08:33 PM
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Is it recommended to have a seperate power for the amps I thinking of purchasing a set of pair mono blocks
RJ


M100 V4, VP180 V4,QS10s x4 V4 EP500 V4 X 2,ADA 1500-3, N3
Re: Questions about the amplifier output voltage
minie #424508 03/27/17 04:05 AM
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axiomite
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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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