C3g Aikido Phono

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simon
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#196 Re: C3g Aikido Phono

Post by simon »

Thanks Phil, they look interesting and much cheaper than Farnell et al.

(Am I wrong to be a bit nervous about the legitimacy of high voltage rating of stuff made in China? Probably.)
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#197 Re: C3g Aikido Phono

Post by simon »

A little progress today.

PS reworked to two stages with ground reference taken to the output of the shunt reg at the C3g pcb.

Heater voltage reference sorted. I'd had the bright idea of changing the referencing of the C3gs to ground rather than elevated the same as the Aikidos. But there's only one transformer so this was dragging the Aikido valves down to ground too... Silly boy.

HT and ground to the Aikido pcb now taken directly from the shunt reg output where it attaches to the C3g pcb.

I did try supplying HT and ground to the Aikido from the second filter cap rather than the same reged supply feeding the C3g but this made no difference to the noise on the first triode's anode. I think the shunt reg should be able to supply both the C3g and Aikido without a decoupling cap but wanted to eliminate this.

I need to fix the other shunt reg, but this is a job for another day when I have the patience and concentration.

I think it will be worth testing an Aikido pcb in isolation, nothing else attached, to see what happens.

And then I wonder if it's worth building up another Aikido pcb to test to see what happens. It's a bit odd what's going on with the Aikido, I've built a number over the years and never had this problem. I've never built one with my pcb before though.

I'll probably sketch things out again as it helps me clarify and visualise things - today is treatment day at the hospital though and it might be a few days before I'm bright enough to do some more.
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Nick
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#198 Re: C3g Aikido Phono

Post by Nick »

Earthing is often a case of try everything and keep what works.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#199 Re: C3g Aikido Phono

Post by Andrew »

Nick wrote: Wed Mar 15, 2023 6:39 pm Earthing is often a case of try everything and keep what works.
+1
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#200 Re: C3g Aikido Phono

Post by IslandPink »

Best keep that posting to ourselves, for the sake of your company stock value, Andrew !
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#201 Re: C3g Aikido Phono

Post by Andrew »

IslandPink wrote: Wed Mar 15, 2023 6:51 pm Best keep that posting to ourselves, for the sake of your company stock value, Andrew !
:lol:

Shh, don't tell anyone ;)
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simon
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#202 Re: C3g Aikido Phono

Post by simon »

Fortunately it was just Q3 (IRF840, the shunt element) that was fried, everything else tested okay. For a sanity check I plugged it in for a listen to make sure it was okay and was pleasantly surprised the noise was much reduced.

The reworking of the raw DC PS feeding the shunt regs and the rewiring to the pcbs has made a positive difference. It's a useful lesson in something that appears nasty on a scope isn't always audibly horrid.

If I can't track the Aikido issue down it's probably just about liveable with now. I'm curious what's going on though so will press on.
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Nick
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#203 Re: C3g Aikido Phono

Post by Nick »

May not be the case but remember that the scope will show the signal between the scope's earth and probe tip, so worth considering where the scope earth is and what affect the earth is on the amp and any potential induced voltage on that.
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#204 Re: C3g Aikido Phono

Post by simon »

To recap, as far as I can tell given the hash that seems to be on the scope/probe when earthed, the noise first appears on the anode of the lower triode in the first valve, circled green below:
.
Aikido layout schematic.png
Aikido layout schematic.png (13.52 KiB) Viewed 6768 times
.
I don't know what's causing this but it's the same on both channels. Looking at the layout of the pcb there's a track that runs from the lower triode anode to the grid of the upper valve (pins 1 to 7) crossing the heater track, again circled green below (top and bottom copper pours not shown for clarity).
.
Aikido layout.png
Aikido layout.png (178.5 KiB) Viewed 6768 times
.
There's c300mA in the wide blue heater track - any views on whether this might be causing the noise?

I'm considering trying to hack the pcb to sever the heater track and run a replacement wire to provide some distance. But would it help? (I can then use the E88CCs again too.)

Does anyone have any experience of cutting tracks on a pcb? I don't have one but a Dremel-type drill with a cutting disc would probably make short work of it, though I think there would be a high chance of collateral damage of adjacent tracks/copper pours. Alternatively a craft knife, make a couple of parallel cuts and try to remove the solder mask between and the copper beneath. Not sure how feasible this is though.
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#205 Re: C3g Aikido Phono

Post by simon »

Nick wrote: Tue Mar 21, 2023 9:47 am May not be the case but remember that the scope will show the signal between the scope's earth and probe tip, so worth considering where the scope earth is and what affect the earth is on the amp and any potential induced voltage on that.
Hmm, yes I don't think I've ever had the probe earth in the Aikido, it's worth a play around to see if anything changes.
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Nick
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#206 Re: C3g Aikido Phono

Post by Nick »

simon wrote: Tue Mar 21, 2023 10:13 am
Nick wrote: Tue Mar 21, 2023 9:47 am May not be the case but remember that the scope will show the signal between the scope's earth and probe tip, so worth considering where the scope earth is and what affect the earth is on the amp and any potential induced voltage on that.
Hmm, yes I don't think I've ever had the probe earth in the Aikido, it's worth a play around to see if anything changes.
Ok, in that case all bets may be off.
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#207 Re: C3g Aikido Phono

Post by IslandPink »

Aaaarg !
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#208 Re: C3g Aikido Phono

Post by simon »

Probe earth connected to the Aikido earth where the shunt reg attaches - no difference. Perhaps I have tried this previously, can't remember now.
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Nick
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#209 Re: C3g Aikido Phono

Post by Nick »

Does it do the same if the input to the Aikido is unconnected and its input connected to ground by the input resistor.
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simon
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#210 Re: C3g Aikido Phono

Post by simon »

I haven't tried that yet - the Aikido needs about 3mA compared to the C3g which is around 35mA so the shunt regs will need resetting.
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