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Nad 2100PE in Spice - Can't get protection circuit to work
Nad 2100PE in Spice - Can't get protection circuit to work
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Old 16th July 2019, 10:40 AM   #1
AldoR is offline AldoR
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Join Date: Mar 2016
Default Nad 2100PE in Spice - Can't get protection circuit to work

Hi Everyone,

Don't understand the over-current protection scheme on this amp. Q4 needs to be forward biased to switch on once a threshold (measured across R33) has been reached. It all goes pear shaped after R8 (all references are my part numbering), marked B on the attached waveform. ER+ (emitter resistor high side) is what I would expect to see, minus some loss after going through the 1K5. E, the emitter of Q4 is also shown. I know next to nothing about Spice - if you have any suggestions, parameters / settings I've done wrong, please share. Transistor models are not for the original devices, I have listed these in blue text. If anyone can improve on them and re-upload, that would be great

Interestingly, if D4 is reversed, then the circuit works, even on a real amplifier. Unfortunately it's a bit too sensitive then.

Q1 approximates the protection circuit IC, we want the junction of Q1 and R27 to stay below pin 1 threshold of approx .7v under normal operating conditions.

Also attached is a partial of the original 2100 service manual. The full manual is available as a free download from Hi-Fi Engine.

Not related, attached is an image of the waveform as Class-G kicks in, for anyone interested.
Attached Images
File Type: png Nad_2100_Protect.png (357.4 KB, 36 views)
Attached Files
File Type: asc Nad2100_Rev1.asc (29.3 KB, 3 views)
File Type: pdf Nad2100_Rev1.pdf (31.0 KB, 4 views)
File Type: pdf Nad2100wave_Q4.pdf (35.6 KB, 3 views)
File Type: pdf Nad2100wave_PE.pdf (29.2 KB, 4 views)
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Old 16th July 2019, 10:52 AM   #2
AldoR is offline AldoR
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Join Date: Mar 2016
Forgot to add the .asc file will want to access a txt file in c:\ for some of the models. I used a zip file posted by Mooly in 2018. I see the file contains Cordel models and is copyrighted so didn't attach it. I'm sure there will be an updated version by now available for download on diyaudio.
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