C3g Aikido Phono

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Nick
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#211 Re: C3g Aikido Phono

Post by Nick »

It can still be connected to the power supply and working, just not connected to the output of the riaa bit.
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#212 Re: C3g Aikido Phono

Post by simon »

I dug out one of the spare Aikido pcbs and attacked the heater tracks with a Stanley knife and the corner of a small flat bladed screwdriver. Pretty it ain't but it worked and the heater pins are now isolated and connected by wires.
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Didn't make any difference though.

But I did notice there was something odd going on as the amplitude of the trace with the probe in free air varied greatly depending on where I was holding it. At first I though it was something to do with the magnetic field of the heater transformer but I eliminated that.

Scratching my head a bit more I tried turning off the work light (one of those ring tube jobs with a large magnifying lens in the middle) and blow me the trace cleaned up. I think the worst of that odd trace might have gone on the first triode's anode, problem is with the light off it was a little dark to be poking around live electricity so I don't really know what's going on yet.

Maybe that's why it wasn't too noisy when I listened to it, if I'd turned the light off.

Pesky high gain valves.
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#213 Re: C3g Aikido Phono

Post by simon »

Nick wrote: Tue Mar 21, 2023 6:43 pm It can still be connected to the power supply and working, just not connected to the output of the riaa bit.
Even easier!
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#214 Re: C3g Aikido Phono

Post by Nick »

Sounds like a big step. I always remember to turn off the soldering iron when trying to find hum. The worst one I has was the jfet phono. While checking for noise I spent ages trying to find the source of low frequency (say 1hz) wandering on the output. I was trying to find the source blaming the power supply when I found waving my hands around caused the problem to get worst. Finally twigged it was air currents around the jfet altering it's temperature. Putting the lid on the box cured the problem.
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#215 Re: C3g Aikido Phono

Post by simon »

I seem to recall seeing something similar with the iron when I was round at yours a very long time ago now you mention it. Phonos really are a step beyond the average amplifier.
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#216 Re: C3g Aikido Phono

Post by Andrew »

simon wrote: Tue Mar 21, 2023 7:43 pm I seem to recall seeing something similar with the iron when I was round at yours a very long time ago now you mention it. Phonos really are a step beyond the average amplifier.
indeed 60db of gain is not to be trifled with.
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#217 Re: C3g Aikido Phono

Post by simon »

I'm having a few days away from it, to see what percolates. When I checked it in daylight the noise for want of a better word is still there on the first triode's anode. But it occurred to me whilst unable to sleep that I'd wired the heaters up for E88CC rather than ECC83. Silly boy. So that noise is there with or without the valves conducting... Which strikes me as a bit odd.

I'll try the E88CCs again to see if they make any difference, and try disconnecting the signal from the RIAA too.
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#218 Re: C3g Aikido Phono

Post by Nick »

When they are not conducting the anode is a high impedance point, it may be less noise when they are conducting. It could be that you are seeing noise on the power supply line.
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#219 Re: C3g Aikido Phono

Post by simon »

Maybe, but I can't resolve any noise on the HT, beyond the low level mush that's present all the way from the grounded input phono and HT all the way up to the first triode's anode. Or have I misunderstood what you meant about noise on the power supply line?
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#220 Re: C3g Aikido Phono

Post by Nick »

Ahh, hang on, with the heater disconnected the top valve is also off, so the lower valve anode is floating, so its just noise pickup I would expect on a high impedance. There is a lot of noise about in the ether now.
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#221 Re: C3g Aikido Phono

Post by simon »

Yes, I wondered that. I even brought the phono and scope downstairs for a completely different environment. But there's no guarantee the kitchen is any better the upstairs with the modem router. The noise looked similar FWIW.
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#222 Re: C3g Aikido Phono

Post by Nick »

Yep, I have to turn off Ethernet over mains if I want to see into the noise floor. The noise on ground is enough to show up on the scope. I assume various inductance on leads and stuff is enough to generate signal voltages that the scope see's
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#223 Re: C3g Aikido Phono

Post by simon »

Right after a bit of a break from this I've had another play.

To recap, the scope has some kind of "mush" even when the probe tip is earthed, but I was picking up noise on the anode of the Aikido's first valve's lower triode.

I butchered the heater tracks so I could put the E88CCs back in, but the buzzy hum seemed similar volume as the ECC83, which perhaps suggests it's not directly as a result of the first valve as I would have expected more gain to give more noise.

Next I tried disconnecting the signal from the RIAA to the Aikido with good success - there was just a trace of ripple. Another gold star for Nick :-D.

So I grounded the Aikido input and as far as I could tell the ripple went.

Is it reasonable to deduce then that the Aikido per se isn't at fault? The noise doesn't appear at the grid of the first triode though so I'm not so sure about this.

Any ideas what's going on and what might be worth trying next?

The RIAA board is very close to the Aikido so I don't think it's picking noise up in the connection. I could try some screened wire I suppose, but it would be fiddly it's so short.
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#224 Re: C3g Aikido Phono

Post by simon »

Trying to think this through I think the scope and/or probe's inability to resolve the lowest level is impeding me.

Scoping the signal as far as the anode of the first Aikido triode gives low level "mush" for want of a better word, not a flat signal. Whilst the hum didn't seem notably decreased when changing from ECC83 to E88CC it would perhaps make sense that whatever noise there is entering the triode is amplified, I just can't see if it's there before with my scope/probe.

Does this seem a reasonable hypothesis?

If so I guess the culprits are either the C3g stage or the RIAA section. Any thoughts on amending either? The RIAA would be easy enough to point-to-point.

Could there be an issue with the probe? I have two, both the same, with the same results - any recommendations if I got another?
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#225 Re: C3g Aikido Phono

Post by Nick »

I think you may need to separate the idea of the mush and hum. Maybe add a RC low pass filter before the probe, you may be getting confused about the RF hash that is all over the place and may be seeking in via the ground and every other line.
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