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

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!

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

Registered: 01/21/07
Posts: 6498
It's a Zobel network used to ensure closed-loop stability by removing poles in the right s-plane.

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

Registered: 08/25/04
Posts: 6228
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:

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:


Edited by bridgman (03/15/17 12:58 AM)
M60ti, VP180, QS8, M2ti, EP500, PC+ 20-39
M5HP, M40
LFR1100 actives picked up Friday 13th

#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: 13629
Loc: Iowa
what he said
M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB SonyUBPX800

#424500 - 03/26/17 04:33 PM Re: Questions about the amplifier output voltage [Re: SirQuack]
Rjlitho Offline
old hand

Registered: 03/01/17
Posts: 89
Loc: Mississauga, ON
Is it recommended to have a seperate power for the amps I thinking of purchasing a set of pair mono blocks
M100 V4, VP180 V4,QS10s x2 QS8s V4 x2 EP500 V4 X 2,ADA 1500-3,

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

Registered: 01/21/07
Posts: 6498
You shouldn't even bother with audio unless you have two of these bridged per channel.
A-LFR/1000-8/500v4x2 coming
100,160,QS10x2,800,M5x2,M3,M50 v4
had v2
N2, N3 someday


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