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Old 1st October 2013, 09:06 PM   #11
hewo is offline hewo  United States
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maybe cd4049 low noise version IC would be a better avenue to go?
does it exist "low noise version", equal or better?
each stage is fet in the cd4049 - separate discrete low noise jfet like 2sk170 would be equivalent to cascading inverters of cd4049?
otherwise maybe noise can be attenuated by tempering inverter stage gains, like under 5 per stage?
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Old 1st October 2013, 09:11 PM   #12
kevinkr is offline kevinkr  United States
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No such thing as a low noise CD4049, it is an digital inverter IC that just happens to work as mediocre inverting amplifier. Now you could try a few different vintages and vendors and see if any just happen to be quieter. Note that the CD4049 uses complementary mosfets, not jfets - not in any sense equivalent.

Build something and see if you can get it to work.

References:
http://www.generalguitargadgets.com/...do/distortion/

http://www.muzique.com/schem/tubesnd.gif
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Old 1st October 2013, 09:31 PM   #13
hewo is offline hewo  United States
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okay cd4049 is not fet but instead mosfet complementary topology - but mosfet is soft clipped just like jfet discrete.
this noise business must be from impurity doping within control channel (gate?)
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Old 1st October 2013, 09:35 PM   #14
kevinkr is offline kevinkr  United States
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Largely irrelevant, these devices were not designed as anything but fast switches - not intended for linear use, but with care you may be able to get things quiet enough to do the job. The geometry/doping of those mosfets is optimized for speed and low power consumption - the things that matter for the intended application.
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Old 1st October 2013, 10:09 PM   #15
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Don't run the stages at too high a current. If you run them near 3V, the gain is higher, the noise and bandwidth are lower. Connect gates in parallel for lower noise. I've used up to 12 (two packages piggybacked). You must use an "unbuffered" part, usually with a U suffix as in CD4069U. The only problem running low current is that you can't drive much. Use an opamp or JFET as a buffer. You can use one inverter in a package to set the bias for the other gates. Just connect input to output and that voltage can be used to bias the other gates.

Don't use a voltage regulator right on the supply pin. Use a higher voltage like 5V and then use an RC network between the regulator and IC. Use the resistor to set the current, something between 1K and 100K.

The CD4007 can also be used but you have to connect the MOSFETs up to make inverters. You can also connect the 4007 up to make NOR or NAND gates for more distortion.

Last edited by Loudthud; 1st October 2013 at 10:16 PM.
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Old 2nd October 2013, 12:00 AM   #16
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Old National AP note: http://www.qsl.net/l/lu7did/docs/QRP...fier_AN-88.pdf
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Old 2nd October 2013, 12:42 AM   #17
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Here's some data I took on a 4069U with all 6 inverters biased linear. There is a lot of variation between parts.

3V 25uA
5V 2.3mA
6V 5.0mA
7V 8.3mA
8V 12.5mA
9V 17mA
10V 22mA
12V 37mA
14V 44mA
15V 47mA

The inverters look more like tubes at low voltages. At higher voltages the top and bottom of the waveform looks extremely rounded unless you use lots of feedback. You can easily get a gain of 10 (20dB) per stage with feedback.
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Old 3rd October 2013, 07:18 AM   #18
alayn91 is offline alayn91  France
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Hello,

http://pdf.datasheetarchive.com/data...-5/X106-27.pdf
Attached Files
File Type: pdf CMOS_InvertAamp1.pdf (7.2 KB, 12 views)
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Old 3rd October 2013, 04:11 PM   #19
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@ alayn91, thanks for posting. The CA3600 has the same pinout as the CD4007. It's not clear if there is actually any difference in the parts. The CA3600 may be impossible to find.

The pdf file shows how gain, bandwidth and current change at different supply voltages. 47K is pretty low impedance. At low currents it needs to be much higher, something like 1 to 10 Megohms.

The attached file below shows some design ideas.
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File Type: gif CMOS_linear.GIF (5.7 KB, 52 views)
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Old 10th October 2013, 03:30 PM   #20
shanx is offline shanx  Canada
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Quote:
The CD4007 can also be used but you have to connect the MOSFETs up to make inverters.
Very good chip suggestion, Loudthud. The Craig Anderton circuit was a bit too limited , literally I found it quite a compressed sound with the 4049.
The 4007 has some access to individual Mosfets, which I had been meaning to fool around with, but became a backburner project. Like you said you need to build up the inverter etc, but allows one to ''build down'' to a simple common source amp stage, and also add Drain limiting on individual stages, which could be interesting. So maybe time to go back to the breadboard and see what I could come up with.
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