From ???@0x00001014 Thu Aug 10 12:04:51 2000 Path: pitt.edu!newsflash.concordia.ca!sunqbc.risq.qc.ca!newsfeed.cwix.com!chnws02.mediaone.net!chnws05.ne.mediaone.net!24.128.44.7!typhoon.ne.mediaone.net.POSTED!not-for-mail Message-ID: <3992B930.98D5BB6E@mediaone.net> From: Win Hill Organization: Rowland Institute for Science X-Mailer: Mozilla 4.73 [en]C-CCK-MCD NSCPCD47 (Win98; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: sci.electronics.design Subject: Re: Super-Low-Noise Microphone Preamp, Advice needed References: <965762624.150168@news2.cybercity.dk> <3990C9B8.CE7A7665@mediaone.net> <8ms1s1$cev$1@serv1.iunet.it> <965899401.997171@news2.cybercity.dk> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 63 Date: Thu, 10 Aug 2000 14:17:28 GMT NNTP-Posting-Host: 24.147.185.92 X-Complaints-To: abuse@mediaone.net X-Trace: typhoon.ne.mediaone.net 965917048 24.147.185.92 (Thu, 10 Aug 2000 10:17:28 EDT) NNTP-Posting-Date: Thu, 10 Aug 2000 10:17:28 EDT Xref: pitt.edu sci.electronics.design:201040 Status: N Rune Baeverrud wrote: > > Thank you everyone - for all the good answers - you have all definitely > guided me in the right direction, I may be able to pave my way through > the jungle of low noise design from here. I'm also helped by some books > I purchased a long time ago - with special credits to Robert A. Piece, > Jim Williams and Horowitz & Hill for their excellent literature. > > A consumer device with 2 pcs 9V batteries (or more) that runs out of > power after 10 hours use would be considered as not being very practial > at consumer level. Unfortunately - all the high-quality opamps suitable > for microphone use that has been mentioned so far seems to draw current > in the 8-15mA range - no exception. The discrete transistor solution I posted a few days ago for you equals the performance of the opamp circuits, but draws only 2mA from a single 9V battery and works to 6V end-of-life. OK, here's another one, fresh off mt drawing pad, this time with a dual BJT input instead of a JFET. This one also draws 2mA, although I hasten to point out that the parts values in both circuits can be scaled for operation at 1mA. That's 500 hours for one alkaline 9V battery. ,----+-----+--------+------+------+------- +9v | | | | | | BATT | 1.10k | | 470 75k | | | e | | 30k +---------+- b Q2 +--||--+ 2.2uF | | | | c pnp | | | | | | | c | ,--+ | | 47pF +--- b | R10 | | Q1 | | | 5.6k e Q3 | G = 1 + --- = 50 1.0M | LM394CH | | | | | R9 | | | | '----+------+ | 0.1 | | c c | Vx | 1 uF In -||-+---- b b -+--, ,--+-+--------||---+--- Out | e -+- e | | R10 | | | Zin 27k | 47u 1M 2430 c | | 1meg | c | | | b -+ | 20pF +---- b Q5 '--+----' e | 47k | e R9 | Q4 | diode | c | 49.9 ,---+ | | Q6 b ----+ | | | 4.7k | e | 470uF 22uF 1.0k | | | 453 | | | | | GND -----+-------+----------+-----+---+----+--------+-- GND The amplifier should have an input noise level of about 1.5nV/rtHz. Like the JFET circuit, this one features constant-current operation for _each_ transistor in the signal path, including the output drive, resulting in very low distortion. Also, note that the White follower output can drive more load current (during peaks) than its quiescent bias level. Thanks, - Win Winfield Hill Rowland Institute for Science 100 Edwin Land Blvd Cambridge, MA 02142-1297