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Old 11th February 2011, 04:41 PM   #1011
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that would be a typo/transposition error.

Also see the LTSpice wiki here: Common Issues Encountered By New Users - diyAudio

where a lot of this stuff is already captured. Also buy a copy of Bob Cordell's excellent new book on designing power amplifiers, there is a lot of terrific material in there on using spice (LTspice specifically) for amplifier simulation.
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Old 11th February 2011, 05:01 PM   #1012
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OK thanks, that helps. I think I'm getting the hang of it. One observation, the numcycles/dlycyc people are using is too low if you model your PSU with series resistance because it does not give the PSU time to sag.

Last edited by Buckeye; 11th February 2011 at 05:03 PM.
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Old 11th February 2011, 05:47 PM   #1013
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I used keantoken's number and hadn't spotted the typo !
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Old 11th February 2011, 08:17 PM   #1014
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Allright, making good progress now & have a question about the pearl script ltspdisto. It's not what you're thinking, I was able to finally get it to work. The big trick there was to run the script from where my netlist/schematic were located. But now that I have all the data, how to interpret the results?

I was hoping to get a %THD plot vs frequency but that's nowhere to be found. I see voltage plots and such. My disto.thd and disto.raw have all the FFT point values but not the THD. I know that the plot viewer can draw expressions using data from the raw file. Is there a simple expression that will draw the THD in % as a function of frequency (or whatever the disto variable I choose)?

thanks
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Old 11th February 2011, 11:38 PM   #1015
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You are right, I typed it wrong! Use my up-to-date example command set, the wiki entry is slightly old. I will change it back again and see if the FFT works any better.

Just for completeness, here is the updated example schematic.

- keantoken
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File Type: txt ampsim2.asc.txt (3.3 KB, 32 views)
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Old 11th February 2011, 11:44 PM   #1016
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The LTSpice plotter is missing some important features. There are some 3rd party tools which can do some of these things, but I could never get them to work. You will have to ask on the yahoo group about that.

I used Openoffice/excel to make THD plots, but I had to input the data manually.

- keantoken
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Old 12th February 2011, 03:05 AM   #1017
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I just thumbed through Helmut's pearl source and it looks like the percent THD is written into the raw file as V(THD). I checked the value that's written against what I get when I run .four at that same frequency and they are the same.

So the %THD data are there, but the Y-axis units are shown as Volts (mV in my case). I have searched and can't find a way to change the displayed units to a percentage. Is there a way to do this?

The easiest way is to edit the raw file, and the line that has the V(THD) in it:

0 F1 param
1 V(THD) voltage
2 V(AC_1) voltage
3 V(DC) voltage


Alas, I tried a variety of different things and can't make % appear on the Y axis.

Any ideas? If there's a way to put % on the axis, it would be easy to modify the script to write it automatically.

I just noticed that all of the Voltage values are most likely percentages. Look at V(k1). That's the normalized voltage at the fundamental frequency. It's always 100.
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Old 15th February 2011, 07:18 AM   #1018
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Hey Buckeye, here is OS's Mongrel AX simulation file. Questions about the amplifier design should be asked in this thread:

The MONGREL (supersym II)

This is a thoroughly modern amplifier. When I wondered if there was a better example for you to use, rather than mostly obsolete designs, this instantly came to mind.

- keantoken
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File Type: txt mongrel_AX1.3.asc.txt (15.9 KB, 28 views)
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Old 15th February 2011, 01:43 PM   #1019
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Yeah, that's a fine amp design. I'm mostly looking for quick & simple, while learning to use LTspice. Hate to say it but as for modern goes, class D is where it's at. Did anyone see the article about class D in the IEEE Spectrum January issue? The Spectrum staff picked class D as one of the top 11 technologies of the decade for their 2011 New Year issue. Class D is up there on the pedestal with technologies like smartphones, social networking, VOIP, LED lighting, etc. Here's the link: IEEE Spectrum 1/2011.

Anyway, my simulations are working fine and I'm using Helmut's disto Pearl script. There are some other very cool THD analysis tools on the LTspice Yahoo group.

But you are right. The amp I'm working with is not audiophile quality. I call it the Cheap150, and It's got a bit of distortion. The key word here is Cheap, not audiophile. I posted some info about my simulation results in the forum where this amp concept was first described. It's here:

Cheap 100 to 150 Watt Amp
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Old 15th February 2011, 02:09 PM   #1020
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Quote:
Originally Posted by Buckeye View Post
Yeah, that's a fine amp design. I'm mostly looking for quick & simple, while learning to use LTspice. Hate to say it but as for modern goes, class D is where it's at. Did anyone see the article about class D in the IEEE Spectrum January issue? The Spectrum staff picked class D as one of the top 11 technologies of the decade for their 2011 New Year issue. Class D is up there on the pedestal with technologies like smartphones, social networking, VOIP, LED lighting, etc. Here's the link: IEEE Spectrum 1/2011.

Anyway, my simulations are working fine and I'm using Helmut's disto Pearl script. There are some other very cool THD analysis tools on the LTspice Yahoo group.

But you are right. The amp I'm working with is not audiophile quality. I call it the Cheap150, and It's got a bit of distortion. The key word here is Cheap, not audiophile. I posted some info about my simulation results in the forum where this amp concept was first described. It's here:

Cheap 100 to 150 Watt Amp
Hi Buckeye,

You're right about class D - it is the wave of the future and in fact it is here now for many important applications, including HT receivers and professional audio amplifiers. It has a ways to go for high-end audio, but great progress has been made in that department as well, especially in the last 5 years.

You may be interested in the class D section in my book, which goes from the basics to some in-depth technical discussion of the various types of class D amplifiers. There are four chapters devoted to class D:

28 - Class D amplifiers
29 - Class D design issues
30 - Alternative class D modulators
31 - Class D measurement, performance and efficiency

The detailed table of contents can be found on my web site at CordellAudio.com - Home.

Cheers,
Bob
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