C3g Aikido Phono

[simon]

Well that's quite amusing. No wonder it wasn't simming well. Sometimes you can't see for looking.

[simon]

I don't think I should be allowed to play with spice really. As far as I can see nothing's changed after fettling Q2, so there must be something fundamentally wrong in the model somewhere.
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TubeCAD Simple Pre-Preamp 2.png (108.5 KiB) Viewed 1399 times

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TubeCAD Simple Pre-Preamp Sim 2.png (177.63 KiB) Viewed 1399 times

[Nick]

Are you using AC on the input? if so, whats the 1.4V

[simon]

These are the settings. The 1.4V was a relic of another sim I modded. I didn't give it much thought as I figured I was interested in relative gain. I've tried 10mA and it didn't seem to make any difference.

I'm not sure though what the small signal AC analysis is though?
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TubeCAD Simple Pre-Preamp Voltage.png (231.06 KiB) Viewed 1358 times

[Nick]

The small signal section is for AC analysis of fr and phase. It may be you need to set that depending on the analysis you are showing. The left hand side is for voltage/current against time.

[Mike H]

Just a thought, take the 'V' out, after both the numbers.

I never use 'V' here, by default the field is a Voltage value.

On the graph, green should be 0 dB, if 'AC 1'.

[Mike H]

Whoah I've just noticed something, R2 is 1 milliohms!

That's a virtual short circuit.

I presume you meant 1 Megohms, so you have to write '1meg' or '1Meg' (can't be an 'M' on its own, and no spaces).

[Mike H]

Second problem, you've got '-12V' for V3 (and you don't need the 'V'), but you're already using its negative terminal for the supply rail, so you've inverted it and made it +12V. As it is, just needs '12'.

V2: again don't need '+12V', just '12'. The text box value is a Voltage by default, so don't need the 'V', and the object has positive and negative terminals, so don't need the '+'.

HTH.

[simon]

Great spots Mike, thanks! I'll see what difference they make.

[Mike H]

I took the liberty of having a play with it - didn't take long - so this is my tidied up version - yes it has a Voltage of X4 (12 dB).


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TubeCAD Simple Pre-Preamp-3.png (22.6 KiB) Viewed 1251 times

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Screenshot 2024-02-14 192036.png (38.52 KiB) Viewed 1251 times

[simon]

You're a genius Mike .
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TubeCAD Simple Pre-Preamp 3.png (109.65 KiB) Viewed 1249 times

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TubeCAD Simple Pre-Preamp Sim 3.png (190.84 KiB) Viewed 1249 times

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Yes, 4x gain, f-3 under 2Hz. Probably a bit low. I think what happened with the 1M resistor is that 1M is interpreted as 1m, which I missed.

[simon]

Screenshot 2024-02-14 192036.png

What's this analysis you did Mike? (The sine wave jobbie.)

[simon]

Now the sim's working (thanks Mike!) it's been interesting to have a play. Reducing the coupling cap to 20nF gives a f-3 of 9Hz. I suppose one might want to go even higher to filter warp/rumble maybe.

But playing with the two resistors, R1 and R6 was interesting. The sim suggests there is a practical maximum difference between the two. 9x was the most I could squeeze out until the gain went screwy. Whether that would be achievable in reality I don't know. I guess this is what Nick was referring to?
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TubeCAD Simple Pre-Preamp 4.png (91.65 KiB) Viewed 1239 times

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TubeCAD Simple Pre-Preamp Sim 4.png (194.81 KiB) Viewed 1239 times

[simon]

As I'm on a roll here's a sim of Boozehound Labs MC preamp
https://cdn.shopify.com/s/files/1/0289/ ... PrePre.pdf
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BoozehoundLabs Pre-Preamp Circuit.png (64.71 KiB) Viewed 1236 times

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Uses 2SK170 or LSK170s. Similar 9x gain. Who knows which one sounds best.
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BoozehoundLabs Pre-Preamp.png (129.88 KiB) Viewed 1236 times

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BoozehoundLabs Pre-Preamp Sim.png (175.36 KiB) Viewed 1236 times

[Nick]

You can play with the source resistor in the case of the jfet to alter the gain, and also try paralleling up 2 or more.