C3g Aikido Phono

[simon]

Next sim is with a 15k series resistor before the RIAA, and the RIAA values changed as discussed previously.
RIAA new 1.png
Now there appears to be 1.6dB difference, but it looks nicer above 1kHz

By adding the series resistance you have made it an easier load but the bass now rolls off, doesn't it?

Yes, this has been a really interesting and illustrative process learning to play with Spice.

[Nick]

One thing to remember is that there are some caps hidden in the driving source (the valve anode and so on). Having a resistor in series with that can allow us to create a eq that is more isolated from those caps. The valve that's driven also has its grid capacitance that gets involved in the process. If it wasn't for those, then it would be possible to make a perfect RIAA network with caps and resistors (assuming the caps and resistors were perfect caps and resistors).

[Andrew]

If you are feeling a tad masochistic, Simon, then this is probably worth a read re: pentode's capacitance.

http://www.r-type.org/articles/art-004c.htm

[simon]

That's an interesting link Andrew, thanks. I've tried a few times to read it but had mental block, I will persevere.

I've been tweaking a few things on the pcbs. Curiosity has the better of me and I'm going to get them fabbed to see a) if they actually work, b) whether it sounds any better or worse, and c) what it does to the hum.

In addition to the ground plane on the Aikido pcb I added a ground place to the top also. I don't know whether this is a good idea though. I'm wondering if it might be beneficial to add an additional ground plane to the top side of the C3g stage also on the basis that the signal is at its smallest here and any benefit, however small, will be magnified by the second stage.

So, ground planes on the top side as well as the bottom side - good, bad or indifferent?

[Andrew]

The trick I was taught was to try and keep as much of the copper as possible, take a look at one of the DC heater boards, oh, and keep the connections as short as you can, tho' I appreciate some compromises are often required.

I also tend to switch of the thermal reliefs for thru hole components. Roughly speaking this... https://electronics.stackexchange.com/q ... s-in-eagle

I have been limited by the size of the PCB the freeware Eagle can process, same as you.

I have used multiple ground planes across top and bottom, provided they are connected via a low impedance, but again, this was a practical necessity, rather then something I consciously designed.

[Andrew]

The other bit of advice I would give is that you shouldn't assume caps are evil, or any other component, I think I was of that opinion, it's coloured thinking, it's all about a balances of compromises. All components have inherent weaknesses and strengths, the evil bit is not recognizing that and making poor design choices as a result. I struggled implementing the LCR coz I couldn't drop the idea that the coupling cap needed to be as small as possible.

Thorsten promoted low caps and large grid leak resistors in some of his designs, nowadays, I think, he was either misguided or taking the wee wee, perhaps to see who would follow his lead so he could 'have a giraffe' at them. We'd probably say he was an 'influencer', in modern parlance.

[simon]

Thanks Andrew.

I've tried to keep connections as short as practicable, the physical size of some of the caps makes this a bit tricky though, particularly the 10uF on the C3g and the 47nF teflon in the RIAA.

Interesting you mention the thermal reliefs. I've left them switched on - I struggled to get the solder to flow a little with your boards even with a temperature controlled iron. If it gives a better result though I'll switch them off.

[simon]

Whatever happened to Thorsten? He's another I haven't heard of in a long time. I remember being on an old Analogue Addicts email list with him in around 1995/6ish.

[Andrew]

Thanks Andrew.

I've tried to keep connections as short as practicable, the physical size of some of the caps makes this a bit tricky though, particularly the 10uF on the C3g and the 47nF teflon in the RIAA.

Interesting you mention the thermal reliefs. I've left them switched on - I struggled to get the solder to flow a little with your boards even with a temperature controlled iron. If it gives a better result though I'll switch them off.

That can happen, you just need a bigger tip

[Nick]

Thanks Andrew.

I've tried to keep connections as short as practicable, the physical size of some of the caps makes this a bit tricky though, particularly the 10uF on the C3g and the 47nF teflon in the RIAA.

Interesting you mention the thermal reliefs. I've left them switched on - I struggled to get the solder to flow a little with your boards even with a temperature controlled iron. If it gives a better result though I'll switch them off.

That can happen, you just need a bigger tip

A better solution IMHO is to use a hot air gun (SMT or paint stripper) to warm the board up before soldering to the pads without thermals. At a extreme I find a small amount of solder paste and then heat with a gun before soldering with a iron makes a great job of making a good joint.

If you are using ground plains on both sides, link them all over the place with vias to prevent isolated current flows.

[Andrew]

The hot air gun is a good idea, tho' in practical terms, if you have a paint stripper sized gun, then a small nozzle adapter would give more precise and controlled results, sort of a low tech rework station.

[simon]

Well this is rather frustrating.

I'd intended to get the gerbers uploaded today but something seems to have happened when I tried to panelize the Aikido board - the board outline is no longer recognised.

The lines are still there, still 0 width, still on layer 20 Dimension, but clicking on Manufacture the board is wider and taller than the 100mm x 80mm allowed.

Aikido render - no board outline.png (93.62 KiB) Viewed 2679 times

I'm guessing the milling slot is no longer recognised because of the lack of board outline info.

This was the previous render I posted of how it should look, for ease of reference.

Aikido render.png (99.18 KiB) Viewed 2679 times

I've even tried uploading the gerbers to see what happens and whilst successful it reports that the board outline can't be found.

I think it must be a setting in Eagle somewhere but Googling hasn't suggested anything. I'm resisting reinstalling at the moment.

[simon]

Chuffing well just found it! I've spent the last couple of hours looking for it. It's in Control Panel, under Options - User Interface - Layout - Detect Board Shape.

[simon]

If you are using ground plains on both sides, link them all over the place with vias to prevent isolated current flows.

Been thinking about this. On the screenshot below I've marked the existing "vias" between top and bottom ground planes with yellow dots (the yellow circle is only linked on the bottom side), and I've dobbed on some mauve dots where I thought might be appropriate. Does it look reasonable? Obviously the vias themselves would be much smaller than the dots.

Vias.png (80.79 KiB) Viewed 2641 times

[Nick]

You can make the vias any size you want.