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My attempts at a design of a 3 stage amplifier
My attempts at a design of a 3 stage amplifier
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Old 13th August 2018, 05:41 PM   #41
Mooly is offline Mooly  United Kingdom
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My attempts at a design of a 3 stage amplifier
Simulating power supplies can be done a couple of ways. One method is to set each rail up as a voltage source that appears like ripple. The three images show the settings for a - and + 45 rail of fixed ripple. This can be useful for evaluating power supply rejection.

A second method is to add an AC voltage source and bridge rectifier to the simulation. Here I have used just 1000uF reservoir caps to highlight the ripple.
Attached Images
File Type: jpg V3 +45 Volt Rail.JPG (74.5 KB, 185 views)
File Type: jpg V4 -45 Volt Rail.JPG (75.9 KB, 181 views)
File Type: jpg Capture.JPG (187.8 KB, 179 views)
File Type: jpg Capture2.JPG (287.7 KB, 169 views)
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Old 13th August 2018, 05:45 PM   #42
Mooly is offline Mooly  United Kingdom
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My attempts at a design of a 3 stage amplifier
One thing to note, the ripple simulation is now exclusively a 'transient' type meaning that DC analysis (the .op command) does not work. This is because there is no fixed DC rails powering the circuit, they are derived just like the real thing from an AC source.

If you right click the two voltage sources feeding the bridge you will see how they are set up. Note the 180 degree phase shift for one of them. Here is the sim file. If you are using LTXVII then the 30 amp rectifiers may not be included in the model library... just pick something else that is.
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File Type: asc Draft2.asc (13.9 KB, 8 views)
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Old 13th August 2018, 09:04 PM   #43
edbarx is offline edbarx  Malta
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In KiCad I used PWR_FLAG and the error did not appear anymore. However, there is still one remaining problem before I can proceed to successfully process my schematic. KiCad is telling me transistor footprints like To-92, To-225, To-3PL, etc are legacy and that I must enter their modern equivalents manually. I tried good-old-google, but it seems, at google they are more interested in giving links to commercial sites rather then giving me a link to a site that can help me.

Does anyone know of a list listing these legacy footprints and their modern codes?
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Old 19th August 2018, 03:50 PM   #44
edbarx is offline edbarx  Malta
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I am reading tutorials about using LTSpice, and in fact succeeded to produce charts for a simple circuit diagram, but I am still stuck to produce meaningful output from ltspice. The reason is I cannot make heads or tails of how nodes of a circuit are represented in the list of variables displayed whenever I try to draw a new chart.

What is the meaning of these?
V(p001)
V(n001)
V(n002)
V(n003)

I assume the meaning of Ie(Qn), Ic(Qn), Ib(Qn) are for the emitter, collector and base currents of Qn respectively.

How are nodes numbered? Is there a way of avoiding this ambiguity?
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Old 19th August 2018, 04:12 PM   #45
EssB is offline EssB  United Kingdom
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Nodes are numbered automaticaly by LTSpice when you make connections on your schematic. If you hover the mouse over a connection you can see the node number in bottom left of window.
You can label nodes with meaningful names if you want: put mouse over connection -> Right click -> label net.

If you want to plot the voltage at node n007, you just select V(n007) from the list in the plot dialog.
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Old 20th August 2018, 10:40 AM   #46
edbarx is offline edbarx  Malta
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I am using LTspice to simulate a simple amplifier which I am designing for learning purposes. Feedback and suggestions are welcome and appreciated.

These are the screenshots from LTSpice.
Attached Images
File Type: png freq-response.png (42.1 KB, 126 views)
File Type: png trial-cct.png (43.7 KB, 58 views)
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Old 20th August 2018, 03:05 PM   #47
edbarx is offline edbarx  Malta
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These are my results after increasing key resistors for the circuit to use +/- 60V DC. The simulation amplifier has been added an output stage that drives directly from the VAS. I know driving a large output stage directly from the VAS is rather naive, but there is nothing wrong in simulating an amplifier like that if it helps undestanding of key concepts.

The blue and red plots are currents from the power supplies. The blue plot is the output voltage developed across the output load resistance of 25 Ohms. The simulation frequency is 4500Hz. The thing that is exciting me is the 'nice' looking sine wave, which suggests distortion should be low, but how do I tell LTspice analyse for distortion?

The next step will adding more workhorses in the output to drive a proper 8 Ohm load and a driver stage.
Attached Images
File Type: png cct-with-added-output-stage.png (44.8 KB, 58 views)
File Type: png output-with-added-power-stage.png (35.1 KB, 41 views)

Last edited by edbarx; 20th August 2018 at 03:11 PM.
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Old 20th August 2018, 05:16 PM   #48
Mooly is offline Mooly  United Kingdom
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My attempts at a design of a 3 stage amplifier
Have a read at posts 19 and 20 here:

Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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Old 20th August 2018, 05:25 PM   #49
EssB is offline EssB  United Kingdom
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Quote:
Originally Posted by Mooly View Post
Mooly,
Thanks for that link, I was looking for that thread of yours the other day and couln't find it - don't know why, probably my rubbish eyesight.
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Old 20th August 2018, 05:29 PM   #50
Mooly is offline Mooly  United Kingdom
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My attempts at a design of a 3 stage amplifier
Lol its also a clicky on my signature line.
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