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Book : Small Signal Audio Design - Douglas Self
Book : Small Signal Audio Design - Douglas Self
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Old 10th February 2016, 05:02 PM   #1
dearchap is offline dearchap  United States
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Default Book : Small Signal Audio Design - Douglas Self

Hi
I am looking at the figure in the book and had a couple of questions.

1. Is Vrms the RMS voltage of input signal ?
2. Distortion will have factors of the form Vpeak/Vt (square, cube and so on). So how can the distortion be so low for wide output swings as depicted in figure ?
3. Figure 3.4. How exactly is the data being measured in spice ? Is it instantaneous Vin vs (Vout/Vin) ?

TIA
DC
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Old 10th February 2016, 05:05 PM   #2
AndrewT is offline AndrewT  Scotland
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Are you allowed to post a pic of the diagram?
What does D.Self say on extracts from his books?
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regards Andrew T.
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Old 10th February 2016, 05:51 PM   #3
dearchap is offline dearchap  United States
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It is basically a unit gain buffer circuit with emitter resistance of 2K7 AC coupled to a load resistance 3K9. Base is connected to ground via a 22K bias resistor. Dual supply rails +/- 24V
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Old 10th February 2016, 06:39 PM   #4
Mooly is offline Mooly  United Kingdom
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Book : Small Signal Audio Design - Douglas Self
I think fig 3.4 is showing how the gain of the circuit alters with varying load impedances by taking a know Vin (along the x axis of the graph) and showing the gain along the Y axis and how that gain varies with differing load impedances. For example at 10 volt input and with a 10k load the gain is shown as approx. 0.990. At no load and the gain is 0.996. Vout isn't shown as such. So the values uses could be equally be peak, rms or even DC.

There are references to rms values in the but these are relevant to the specific topic and example being discussed.
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Old 10th February 2016, 07:19 PM   #5
dearchap is offline dearchap  United States
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Ok I think I understand Figure 3.4 now. A DC voltage Vin is presented at the input and the output Vout is measured at the load (with coupling capacitor removed ). The quantity plotted is dVout/dVin i.e the small signal gain when the voltage at base of BJT is Vin. Thats why it is referred to as incremental gain.
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Old 10th February 2016, 10:01 PM   #6
Mark Johnson is offline Mark Johnson  United States
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Book : Small Signal Audio Design - Douglas Self
The text says Because the distortion is mostly second harmonic, its level is proportional to amplitude, as seen in Figure 3.3.

And indeed Figure 3.3 shows amplitude on the horizontal axis, distortion on the vertical axis.

There are several curves plotted, each curve for a different value of Rload (schematic is Figure 3.2). As Rload decreases, distortion increases.

In the caption of Figure 3.3, the author is using "degraded linearity" as a synonym for "distortion". An alternate caption would be
  • Figure 3.3: How various external loads increase the distortion of the simple emitter-follower circuit in Fig 3.2.
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Old 12th February 2016, 01:59 PM   #7
dearchap is offline dearchap  United States
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I search diyaudio and couldnt find any threads dedicated to discussion regarding the book. Can we convert this thread to something like that ? I'd like to discuss some other circuits in the book too.
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Old 12th February 2016, 02:22 PM   #8
Mooly is offline Mooly  United Kingdom
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Book : Small Signal Audio Design - Douglas Self
The thread title can be changed easily enough.

(the material in Dougs book is under copyright and so it wouldn't be possible to start taking material and reproducing it here en-masse without Dougs permission)
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Old 12th February 2016, 02:37 PM   #9
dearchap is offline dearchap  United States
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Of course. I can simply refer to the chapter/figure and discuss based on that. How do I change the title ? I think a Moderator needs to do it correct ?
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Old 12th February 2016, 05:25 PM   #10
Mooly is offline Mooly  United Kingdom
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Book : Small Signal Audio Design - Douglas Self
What do you want it to be called ? I can change the title for you.
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