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From: rsd@sei.cmu.edu (Richard S D'Ippolito)
Newsgroups: sci.electronics
Subject: Op amp for audio applications -- roll your own!
Message-ID: <5605@aw.sei.cmu.edu>
Date: 27 May 88 17:44:23 GMT
References: <3601@pasteur.Berkeley.Edu> <1196@neoucom.UUCP>
Sender: netnews@sei.cmu.edu
Reply-To: rsd@ae.sei.cmu.edu.UUCP (Rich D'Ippolito)
Organization: Carnegie-Mellon University, SEI, Pgh, Pa
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In article <1196@neoucom.UUCP> Bill Mayhew writes:

    An integrated operational amplifier that would probaly perform
    quite well for audio (hifi?) applications might be the Analog
    devices AD318K.  This chip can be characterised as a wideband, low
    drift, FET input opamp.
    
    Here is a synopsis of its characteristics:
    
    open loop gain:		100,000
    
    output:			+/-12v (+/-10 min) at Rl=1K
    			20 mA short circuit output current limit
    
    dynamic:
    	unity gian, ss	5 MHz
    	full power bw	500 KHz
    	slew rate	30v/uS
    	.1% settle	700 nS
    	.01%		1.2 uS
    
    input bias current:	10pA avg, 50 pA max
    
    imput impedances:
    	differential	1E12 ohms in parallel with 7 pF
    	common mode	1E12 ohms in parallel with 7 pF
    
    input volrate range:
    	differential	+/- 20 v  (maximum safe limit)
    	common mode     +/- 12 v (+/-10 min)
    	CMR		80 dB minimum
    
    noise figures:
    	0.1 - 10KHz	2 uV peak-peak
    	10 Hz		70 nV/Hz^.5
    	100 Hz		45 nV/Hz^.5
    	1 KHz		30 nV/Hz^.5
    	10 KHz		25 nV/Hz^.5
    
    case style:		TO-99

Why not make your own? After all, a hundred bucks is a small price to pay
for perfection! (Seriously, these make good QUIET mike preamps.)


		The JE-990 discrete op amp(*)

	Open loop gain			125 dB
	Gain error @ 100-dB gain	0.4 dB
	Noise voltage spectral dens.	1.13nV/root Hz
	Equiv input noise voltage,
	 20Khz bandwidth, shorted input 160nV
	Noise index, 1000 ohm source	0.6dB
	THD @ 20KHz, at 12.3V output
	 (+24dB)
	  Load = 75 ohms, gain = 40dB	0.06%
	  Load = 75 ohms, gain = 20dB	0.005%
	  Load = 600 ohms, gain = 40dB	0.015%
	Unity gain small sig bandwidth	10MHz
	Large signal bandwidth
	  Load = 150 ohms		145Khz
	Supply voltage			+/- 24V

(*) Parts list and full description is in the Journal of the Audio
Engineering Society, Vol 28, No. 1/2, Jan/Feb 1980. The article is entitled
"JE-990 Discrete Operational Amplifier" by Deane Jensen of Jensen
Transformers. You can buy them already assembled.


Rich