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by simon
Fri Feb 16, 2024 7:24 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Doubling the voltage to 24V adds another .7dB, hardly worth it.

I suppose I should add another fet to see what the effect is, it's a bit of an effort with LTSpice though as I don't think you can copy groups.
by simon
Fri Feb 16, 2024 7:20 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Nick wrote: Fri Feb 16, 2024 1:59 pm I can send you some LSK170's if you want to try that circuit.
Well I think it would be rude not to, thanks :-D. I'm kinda fascinated to find out how this sounds now.
by simon
Fri Feb 16, 2024 7:18 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Well, the gain had dropped around 3dB. Changing the lower resistor R9 to 20R was about optimal for gain, but the gain drops really quite quickly below this so I used 22R for a little safety margin in sim inaccuracy. This sims as a gain of 28dB, so just over 9x. Then I tried increasing the coupling c...
by simon
Fri Feb 16, 2024 1:51 pm
Forum: Assorted Stuff
Topic: Nothing In Particular
Replies: 16439
Views: 4652652

Re: Nothing In Particular

Even though the meter was plugged in at the wall? That sounds like a bit of a design flaw.
by simon
Fri Feb 16, 2024 1:48 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Updated for the shorted 40R resistor, a little light relief at lunch. Interesting results that needs more investigation. Noise was better with the shorted common resistor, but maybe gain was affected?
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Noise2.png
Noise2.png (162.59 KiB) Viewed 776 times
by simon
Fri Feb 16, 2024 9:12 am
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

So it is. Nuts, it took ages to read off the noise levels.
by simon
Thu Feb 15, 2024 10:32 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

And finally the paralleled Boozehound noise . Boozehound Parallel Noise.png . It's a bit tricky comparing them so I scaled off the plots and graphed in Excel . Noise.png . It's been really interesting investigating noise. Paralleling the fet makes a big difference, presumably the law of diminishing ...
by simon
Thu Feb 15, 2024 10:24 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

The gate resistor will be needed for each one. in case you don't know, its job is to protect the fet if the input is sent too +ve. The gate/source junction will become a forward biased diode (as shown in the symbol) and its to prevent excess current in that case. This is one of these bits of inform...
by simon
Thu Feb 15, 2024 10:04 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Thanks Mike. There's a lot to Spice, I've only scratched the surface so far. Just spent some time looking at noise...
by simon
Wed Feb 14, 2024 10:38 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Presumably to parallel the fet each will need a gate and source resistor? I can't quite work out in my mind before simming this whether it will increase the gain, or improve noise. Possibly both?
by simon
Wed Feb 14, 2024 10:36 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Here's R3 with a stepped load from 30R to 70R in 10R steps.
30R green
40R blue
50R red
60R cyan
70R magenta
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BoozehoundLabs Pre-Preamp Sim 2 stepped Source resistor.png
BoozehoundLabs Pre-Preamp Sim 2 stepped Source resistor.png (194.95 KiB) Viewed 942 times
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Interesting that much less than 50R dramatically reduces gain, increasing it doesn't change (decreases) it much.
by simon
Wed Feb 14, 2024 8:14 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

As I'm on a roll here's a sim of Boozehound Labs MC preamp https://cdn.shopify.com/s/files/1/0289/4153/files/BoozhoundLaboratoriesJFETMCPrePre.pdf . BoozehoundLabs Pre-Preamp Circuit.png . Uses 2SK170 or LSK170s. Similar 9x gain. Who knows which one sounds best. . BoozehoundLabs Pre-Preamp.png . Boo...
by simon
Wed Feb 14, 2024 7:56 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

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 practica...
by simon
Wed Feb 14, 2024 7:37 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

Mike H wrote: Wed Feb 14, 2024 7:30 pm Screenshot 2024-02-14 192036.png
What's this analysis you did Mike? (The sine wave jobbie.)
by simon
Wed Feb 14, 2024 7:35 pm
Forum: Everyones Projects
Topic: C3g Aikido Phono
Replies: 319
Views: 81553

Re: C3g Aikido Phono

You're a genius Mike :-D.
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TubeCAD Simple Pre-Preamp 3.png
TubeCAD Simple Pre-Preamp 3.png (109.65 KiB) Viewed 929 times
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TubeCAD Simple Pre-Preamp Sim 3.png
TubeCAD Simple Pre-Preamp Sim 3.png (190.84 KiB) Viewed 929 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.