C3g Aikido Phono

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simon
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#136 Re: C3g Aikido Phono

Post by simon »

The gerbers have now been uploaded, phew. Something went screwy with the C3g board I was working on and I ended up having to rewire the schematic and start the board from scratch which has delayed things a little.

So, 5 boards for the C3g were £1.66, 5 boards for the RIAA were £3.32, and 10 boards for the Aikido were £4.15 - an additional 5 boards were 83p so I took a punt on them working and having a use for them in the future. Customs and taxes were £3.35 and shipping £7.60. A grand total of £20.08.
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#137 Re: C3g Aikido Phono

Post by simon »

Here are the "final" versions of the three boards

The first C3g stage:
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C3g render final.png
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The RIAA filter:
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RIAA render final.png
RIAA render final.png (101.61 KiB) Viewed 3296 times
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And the Aikido stage:
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Aikido render final.png
Aikido render final.png (145.17 KiB) Viewed 3296 times
Andrew
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#138 Re: C3g Aikido Phono

Post by Andrew »

They look great, Simon!

I also found it useful to increase the size of the default pads on some of the resistor and capacitor models, making the diameters as large as the width's of the tracks they sat upon.
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simon
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#139 Re: C3g Aikido Phono

Post by simon »

Yes I found some if the default sizes a bit narrow previously. A lot of the components I've used I've created myself so they've got decent pads. Part of having these fabbed is to get some more experience with what comes and what could be improved.
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#140 Re: C3g Aikido Phono

Post by simon »

Whilst I'm waiting for the boards I need to order some caps and resistors. Thinking about matching in the RIAA how close is close enough?

I was going to use Takman metal films as they're 1%.

Measuring the caps I have, the two Mundorf ZN caps are 474.6nF and 474.9nF which is 0.06% difference. I could add a 300pF to the lower but is this feels like overkill?

Similarly the 4no. 47nF teflon caps I have measure at:
48.49nF
difference 120pF/0.25%
48.61nF
difference 70pF/0.14%
48.68nF
difference 70pF/0.14%
48.75nF

I could add 2no. 70pF caps to the third on the list and one 70pF to the fourth (not sure it's a good idea to bypass just one teflon with a PP film) but is it likely to be worth it?
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#141 Re: C3g Aikido Phono

Post by simon »

I could look for some 0.1% resistors, or buy a number of cheaper 1% and match them?
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Nick
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#142 Re: C3g Aikido Phono

Post by Nick »

Similarly the 4no. 47nF teflon caps I have measure at:
48.49nF
difference 120pF/0.25%
48.61nF
difference 70pF/0.14%
48.68nF
difference 70pF/0.14%
48.75nF
The problem I see is assuming your meter is accurate (which unless its calibrated you don't know), while they are very closely matched, they are all about 3% away from 47nf. So either trust your meter and recalculate the resistors to match a 48.5nf cap or don't but that would make me less worried about the resistors at the moment.
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#143 Re: C3g Aikido Phono

Post by simon »

Mmm, that had occurred to me. The meter isn't calibrated so I'm guessing as to absolute values. I'm not sure what the way around this is though, apart from buying 1% parts.

Even if I asked HiFiCollective to match them I don't know that their meter's calibrated either.

Nor do I know how absolutely accurate the 470nF ZNs are, though percentage wise it may (or may not) be smaller.
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Nick
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#144 Re: C3g Aikido Phono

Post by Nick »

Yep, you end up chasing your tail. Building and measuring is the only way (other than calibration) I know out of this. We can measure frequency and amplitude using a PC close enough to compare to the simulation model. Its why I think matching channels first is the best we can do without absolution calibration.
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#145 Re: C3g Aikido Phono

Post by simon »

That makes sense.

HiFiCollective have just replied and their meter is calibrated so a couple of 47nF from them might be the way forward.
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Nick
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#146 Re: C3g Aikido Phono

Post by Nick »

Sounds like a good plan. You can also use them to check your meter as well.
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#147 Re: C3g Aikido Phono

Post by simon »

Yeah.

I thought about asking for say 46.9nF, if they have them, on the basis it's easier to add some more capacitance than take some away.
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#148 Re: C3g Aikido Phono

Post by izzy wizzy »

simon wrote: Mon Feb 20, 2023 4:42 pm That makes sense.

HiFiCollective have just replied and their meter is calibrated so a couple of 47nF from them might be the way forward.
When they say calibrated, what exactly does that mean?

Calibrated to what? What is the accuracy of their meter? What is the accuracy of the standard it's being calibrated to?

I'm only asking so that you might know what you're dealing with otherwise you're straight back to Nick's suggestion of the only sure answer is measurement.

AFAIK, riaa eqs accuracy depends on the ratio between the caps being accurate to the formula and the resistors altered to get the thing flat. Usually only the low end one needs fiddling with while the other can usually be the calc'd value unless the caps aren't the calc'd ratio. Works like that in the sim and seems to IRL as well. IME I think.
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Nick
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#149 Re: C3g Aikido Phono

Post by Nick »

When they say calibrated, what exactly does that mean
Well, it normally means its been through the devices calibration process against a standard that can trace its calibration back to a UK standards lab and comes with accreditation such as UKAS.
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#150 Re: C3g Aikido Phono

Post by simon »

The pcbs have just been delivered. The valve sockets fit with a little encouragement, which is a bit of a relief. 5 days from pressing the upload button to the arriving in the UK, 4 days from the airport to me.
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