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15th April 2018, 23:18 #21
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16th April 2018, 00:26 #22
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Re: Damping factor of amplifier in LTSpice simulation
Since the open loop gain of an amplifier drops at high frequencies, the damping factor is highest at low frequencies that are the resonance of a woofer and/or its enclosure. You might not hear a difference between a damping factor of 20 or more.
Here is a good damping factor:

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16th April 2018, 06:50 #23
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
I've done it right now? Probably not
It seems you missed to calculate with AC voltages only.
Note: As written in the book and in my post: You need to know about your amplifier's nominal_load_impedance but there is no need that your measurement_resistor is of the same value. You might use 8Ohms, but you might use 800 Ohms...It won't harm the DF result.
Circuit:
Shorted_input  amplifier (DUT)  measurement_resistor  excitation AC source (sine waveform).
The excitation AC source is important. It introduces (via the measurement_resistor) measurement_current into the amplifier output.
This current causes some (small) AC voltage at the amplifier's output.
With these both values you are able to calculate the amplifier's output impedance: V_amplifier / measurement_current.
And DF = nominal_amplifier_load_impedance / amplifier_output_impedance.
(Here nominal_amplifier_load_impedance comes into account)
Btw: the DF depends on excitation frequency. Thus you should do several tests with different frequencies (or use the specified frequency). Usually DF decreases with higher frequencies.
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

16th April 2018, 07:15 #24
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Re: Damping factor of amplifier in LTSpice simulation
Last edited by northumber82; 16th April 2018 at 07:36.

16th April 2018, 11:42 #25
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
V_out is the amplifier output (voltage). > V_out1 is not of interest.
Please verify your measurements:
Voltage swing is 3uV, current is 130mArms.
Is it asking too much to do the calculations on your own?
With these both values you are able to calculate the amplifier's output impedance: V_amplifier / measurement_current.
And DF = nominal_amplifier_load_impedance / amplifier_output_impedance.Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

16th April 2018, 12:11 #26
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Re: Damping factor of amplifier in LTSpice simulation
It's because I have not yet understood if I have done well the measurements that I continue to ask, I understood the formula, but I still do not understand if the measurement_current is the current that passes throught the measurement_resistor(or load), and if the V_amplifier is the V(out).
If it's so, then why i don't have 130mArms? In the image I have a swing of +130mA and 130mA. Then I have a swing at V(out) of 1uVrms (because the amplifier without input and without an output source voltage have 366uV of DC output).
It's that not true? I'm still confusing.

16th April 2018, 12:35 #27
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
R17 is directely connected to the amplifier output. Thus it should be obvious that R17_current = amplifier_output_current.
Not to offend you, but if this isn´t obvious to you then I recommend to stop designing amplifiers and start to learn electronics basics.
If it's so, then why i don't have 130mArms? In the image I have a swing of +130mA and 130mA.
Please learn basics: A sinewave with +/125mA peak has an amplitude of 125mA .. has an RMS value of 125mAp/sqrt(2) is about 88.4mA RMS.
But this value doesn´t meet the 1VRMS you are talking about.
****
Then I have a swing at V(out) of 1uVrms (because the amplifier without input and without an output source voltage have 366uV of DC output).
Don´t use DC voltages for DF calculations. You have to look at AC voltages only.
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

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16th April 2018, 12:50 #28
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Re: Damping factor of amplifier in LTSpice simulation
This is the voltage of the source:
Are you saying that is 1Vpk and not 1Vrms? That is 0.707Vrms?
Please explain where your 1uVRMS comes from. I can´t find it.

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16th April 2018, 13:15 #29
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
Are you saying that is 1Vpk and not 1Vrms? That is 0.707Vrms?
* it is 2Vpp
* it is 0.707V RMS
It´s not "me" that says this, it´s the common definition.
> google for "RMS sinewave"
If you see the graphic you'll find that the voltage swing betweet 365uV and 367uV.
I refer to the upper picture of post#24.
There it is:
365.97uV ... 367.28uV which is 1.31uVpp = 0.655uVp = 0.463uVRMS
Don´t you agree? Even if you round it, it is not 365uV.
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

16th April 2018, 13:36 #30
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Re: Damping factor of amplifier in LTSpice simulation
Then wait, set voltage to 1.414Vp (to obtain 1Vrms), obtained:
 175mAp = 123mArms
 365.6uV367.5uV = 1.9uVpp = 0.95uVp = 0.67uVrms
In calculation:
0.00000067Vrms / 0.123Arms = 0.00000544715
DF = 8 / 0.00000544715 = 1468657.922
absurd I have failed again.

16th April 2018, 14:15 #31
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
No, you did not fail.
Well done. Everything is correct now. (except the simulation results. 0.67uV at 123mA is not realistic  my assumption)
If possible: do the measurements on the real circuit.
****
The simulation shows an output impedance of about 5.5uOhms. Every piece of trace, wiring, every connection will cause way more series impedance.
But even if the simulation doesn´t care about wiring or connections.... it needs a huge open_loop_gain inside the amplifier to get such low output_impedance.
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

16th April 2018, 15:02 #32
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Re: Damping factor of amplifier in LTSpice simulation
Sorry but a DF of over 1.4million it's really impossible, right? Or should I look at this value in db?
The distortion is really low: 0.000030%@50W  1kHz, at least in the simulation. I used double CFP differential input with a complete Wilson mirror and cc generators, a buffered VAS, two pole compensation and mosfet power output.
How much I can consider the simulation correct, knowing I'm using Bob Cordell's spice model and 5% tolerance resistor?

16th April 2018, 15:23 #33
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Re: Damping factor of amplifier in LTSpice simulation
Your damping factor and distortion numbers are not correct. Build the circuit and measure them, the simulation is missing something.

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16th April 2018, 15:58 #34
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Re: Damping factor of amplifier in LTSpice simulation
The simulation isn't missing anything. This amplifier required 8 months of design, the initial distortion was 0.1% at 1kHz with the same power, now it's 0.000030%. It seems strange, but looking in different volumes such as Self's and Cordell's books, seems like I built a very nice amp: I do not have the precision tools to measure the real it, though.

16th April 2018, 16:10 #35
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Re: Damping factor of amplifier in LTSpice simulation
Hi,
again: These values are not realistic. They are decades away from the real circuit.
Do tests on the real circuit.
I´m curious: What is the simulation DF with an excitement frequency of 100Hz and 10,000 Hz?
KlausPlease don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.

16th April 2018, 16:21 #36
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16th April 2018, 17:06 #37
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Re: Damping factor of amplifier in LTSpice simulation
The resistance of a short piece of wire or a drop of solder is much more than 8/1,645,613 ohms. The distortion that is inaudible is probably 0.003%, not 0.00003%.
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