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PostPosted: 21 May 2020, 03:13 
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Joined: 13 Jan 2018, 21:33
Posts: 313
Location: australia
I have been tinkering with microcap plugging in my amp's components mainly to have a neat circuit diagram. I have had a play running the transient analysis under quiescent conditions and different levels of volume and see voltage and levels similar to my actual measurements. For those that use it, is it worth going in deep and learning more? I haven't learned how to do a frequency response yet, so that's a possibility. I noticed it has a stepping function and distortion analysis etc. but no idea how to use it yet.

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PostPosted: 05 Jun 2020, 19:47 
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Joined: 13 Jan 2018, 21:33
Posts: 313
Location: australia
Hardly know what I am doing, just having some fun. It would be cool if it was useful particularly for trialling my next amp project (when I get around to it), have the parts except for the costly transformers. Wish there were more value for money transformers in Aust.

Not exactly the circuit I use now but intend to go back to if it works ok. I used the Ayumi 6sn7 model, Duncan model for the 300b and Immler model for the GZ34. I tried the Immler 6sn7 model but try as I might I couldn't get it to work.

The i
Immler models are fairly recent and he posts on AK but has his own site, http://adrianimmler.simplesite.com/440932026, worth a visit, an interesting guy. A few popular hifi/guitar/radio tubes so far.

The transformer models were created using an excel spreadsheet based calculator "elecalc" https://www.diyaudio.com/forums/softwar ... kbook.html.

I haven't been able to get the frequency response function to work yet, there must be something I am doing wrong or have overlooked. I am trying to follow the example circuit in Microcap for the EL34 and 6L6 which do work, but it comes out wierd when I use my circuit.

If I use a simpler circuit and use the battery 300v and 440v battery supplies to power the signal tubes directly rather than including the transformer and GZ34 rectifier, it looks more like the usual frequency response although the 3db points I am not sure of. If I can find that I will include it here for comment.


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Last edited by Woodo on 05 Jun 2020, 21:59, edited 2 times in total.

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PostPosted: 05 Jun 2020, 21:27 
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PostPosted: 09 Jul 2020, 23:00 
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Joined: 13 Jan 2018, 21:33
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Location: australia
I swapped over to LTspice with reservations but more help seems to be available with it and Adrian Immlers tube model for the 6sn7 seems to at least work. With @koonw 's of diyaudio help i had a play with the simplified model of the xpwr144 transformer (separately). And for the amp model I just used the estimated B+ from the psu model. Its kind of fun to do and would be worthwhile knowing more if I i were planning to build many more amps but having a scope would probably be more useful. Attached are frequency and distortion estimates. I was expecting a wider response but could be limited to my choice of OPTs (or something I have done wrong). I'll need to dig out my notes but I attempted to calculate the distortion of the amp in its current form using the manual method by Steve on this site and the number was much higher I recall so there could be something amiss there.


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