200W Amp Simulation Advice

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mexmike

Member
Joined 2018
#1
I am trying to simulate an 200W amp in Ltspice and measure its THD but do not know how to proceed.

Thanks to dadod for the input from his thread. The attached asc file is using his directives and the models files are from his post. I added the missing models to the Cordell-Models file.

The input section was copied from the SC200 https://www.diyaudio.com/forums/chi...ordell-super-gainclone-sc200-post5731705.html and the output of the circuit was copied from an amp by dadod. https://www.diyaudio.com/forums/solid-state/253039-unique-cfa-120-230w-amp-post3858433.html

Can anyone provide any easy to understand insight? I have tried Google and YouTube but nothing really straightforward.

There are also various errors flagged "Node N031 is floating", which I cannot understand as the connections appear complete to me.
 

Attachments

  • My SC200 and Unique 200W-Hybrid.jpg
    My SC200 and Unique 200W-Hybrid.jpg
    723.5 KB · Views: 430
  • Cordell-Models.txt
    Cordell-Models.txt
    21.9 KB · Views: 122
  • dadomodels.txt
    dadomodels.txt
    29.5 KB · Views: 89
  • 200W Amp.asc
    200W Amp.asc
    16.9 KB · Views: 119
#8
indianajo said:
There is no connection dot between r2 and c16 the input cap. Nor between c16 & c1. also on the input if I read the # wrong. Why have 2 input caps in series anyway?
Click to expand...

Hi indianajo. I think you mean R2 and C19 and C19 and C1. I believe there would only be a 'dot' junction with three or more components. I have 'Mark Unconn Pins' selected in the 'View' menu and no unconnected pins are highlighted. I believe LTspice doesn't like the back to back caps. When I remove one, the error disappears.

The reason for having two back to back caps comes from the SC200 design.
Quote from Silicon Chip magazine "The signal passes through an RF attenuating RC low-pass filter (100 Ohm/1nF plus ferrite bead) and is coupled to the base of PNP transistor Q1 via a pair of series connected 47μF 25V electrolytic capacitors ( which are together more compact and cost less than an equivalent non-polarised capacitor)." I don't have the ferrite bead in my circuit.
 
#9
indianajo said:
There is no connection dot between R130 & C100, the zobel on the output. The R & C right before the output inductor.
Click to expand...

I believe you are wrong, the components are connected; again, unless I'm missing something obvious, there would only be a 'dot' junction with three or more components. I checked the connections in LTspice on multiple occasions and they appear good.
 
Last edited:
#12
dadod said:
No, Unique use triple OPS, means predrivers, drivers and output transistors, your amp use just drivers and output bipolar transistors. In 200W CFA output transistors are mosfets.
Click to expand...

Hi Damir. Sorry, I'm confused. The amp I meant was the one I have attached below, which I downloaded from your post #39 which has 4 MJL4281C and 4 MJL4302C Complementary NPN-PNP Silicon Power Bipolar Transistors.
 

Attachments

#15
Rallyfinnen said:
Check Sandro's videos on how to simulate (and much more). You can download the models he uses from his thread here on the forum, links are in the comments for the video's.

SW Audio - YouTube
Click to expand...

Hi Rallyfinnen,
Thanks for the great video recommendations. I watched the THD one's and managed to copy down the spice directives and add them to my schematic 🙂
There's a lot to learn but very well explained tutorials.
 
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