C3g Aikido Phono

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Nick
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#181 Re: C3g Aikido Phono

Post by Nick »

I would either make up some phono plugs with 100R resistors in them to make up some shorting plugs to put into the input of the amp, or solder some 100R resistors across the input phono to make sure you are chasing hum in the phono stage not from the inputs floating (which they can, certainly with 47k loading).

I would then see if the hum first appears on the c3g anode, the first ecc88 grid or after the first stage of the akido.

Certainly moving the transformers around and watching the scope trace is worth doing to see if its induced.
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#182 Re: C3g Aikido Phono

Post by Nick »

Looking at the picture of the breadboard. You seem to have lots of purple wires coming together on the dual cap, I would not treat the -ve teminal of the cap as the earth point, as that will move WRT the output of the regulators if the current in the 0ve line of the regulators in move. I would treat the 0v output of the regulator as the signal star earth point. I am alway weary of current in 0v lines inducing voltages where you may not expect them. And the input 0v point need to be rock solid WRT the rest of the phono stage and its power supply.
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#183 Re: C3g Aikido Phono

Post by Nick »

And going back to the circuit of the regulator. I don't like the way that's drawn. In theory its fine, but in practice, the F0 and S0 need to be bonded together at the common 0v point and the ground connected there not somewhere back on the nominal 0v line. Any The regulator will regulate WRT 0v at the S0 point and it wont see any voltage induced in the ground line between that point and where the ground symbol is drawn. If your phono input is referenced to that ground symbol, that voltage induced in the 0v line will look like (and be) a signal.

https://www.audio-talk.co.uk/phpBB3/vie ... 93#p203293
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#184 Re: C3g Aikido Phono

Post by simon »

Nick wrote: Mon Mar 13, 2023 10:15 pm
Which suggests things are fine up to the Aikido?
Maybe, is the circuit of the amp in this thread somewhere (will go and look)? It certainly makes me think that its not a issue with HF thats causing the wide trace. I think its just induced hum.
First Post, think you've found it. The only differences are instead of the E88CCs I've bodged it with ECC83 first valve and 12AY7 second valve.
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#185 Re: C3g Aikido Phono

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Nick wrote: Mon Mar 13, 2023 10:20 pm I would either make up some phono plugs with 100R resistors in them to make up some shorting plugs to put into the input of the amp, or solder some 100R resistors across the input phono to make sure you are chasing hum in the phono stage not from the inputs floating (which they can, certainly with 47k loading).
l had the inputs shorted, would the 100R make a difference? I've read about larger values of resistor, like 1M, being used in this way permanently but I presume the 100R would be just a temporary thing?
Nick wrote: Mon Mar 13, 2023 10:20 pm I would then see if the hum first appears on the c3g anode, the first ecc88 grid or after the first stage of the akido.
It wasn't in my list above but tomorrow I intended to have a poke around the Aikido to see if I can narrow it down any.
Nick wrote: Mon Mar 13, 2023 10:20 pm Certainly moving the transformers around and watching the scope trace is worth doing to see if its induced.
Similarly I intend to do this too.
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#186 Re: C3g Aikido Phono

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Nick wrote: Mon Mar 13, 2023 10:30 pm Looking at the picture of the breadboard. You seem to have lots of purple wires coming together on the dual cap, I would not treat the -ve teminal of the cap as the earth point, as that will move WRT the output of the regulators if the current in the 0ve line of the regulators in move. I would treat the 0v output of the regulator as the signal star earth point. I am alway weary of current in 0v lines inducing voltages where you may not expect them. And the input 0v point need to be rock solid WRT the rest of the phono stage and its power supply.
I think those purple wires are the voltage reference for the heater regs. They're taken off the raw DC ground reference lift. I thought this would be adequate for the heater references?

The raw DC supplies the shunt regs, the shunt regs supply the audio circuit HT and ground, which is what you're saying I think. I'll sketch a block diagram type thingy tomorrow for clarity.
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#187 Re: C3g Aikido Phono

Post by simon »

Nick wrote: Mon Mar 13, 2023 10:36 pm And going back to the circuit of the regulator. I don't like the way that's drawn. In theory its fine, but in practice, the F0 and S0 need to be bonded together at the common 0v point and the ground connected there not somewhere back on the nominal 0v line. Any The regulator will regulate WRT 0v at the S0 point and it wont see any voltage induced in the ground line between that point and where the ground symbol is drawn. If your phono input is referenced to that ground symbol, that voltage induced in the 0v line will look like (and be) a signal.

https://www.audio-talk.co.uk/phpBB3/vie ... 93#p203293
Yes, I think I have it connected as you say. The S0 and F0 wires are both squeezed into the ground solder pad, and the S+ and F+ wires in the HT solder pad.

To be fair to Salas the short user guide describes this.

Thanks for thinking this through and checking my workings.
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#188 Re: C3g Aikido Phono

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I think those purple wires are the voltage reference for the heater regs. They're taken off the raw DC ground reference lift. I thought this would be adequate for the heater references?
Maybe, but every little helps, if the reference is moving WRT the amp 0v there will/may be some coupling via the heater cathode capacitance.
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#189 Re: C3g Aikido Phono

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simon wrote: Mon Mar 13, 2023 5:41 pm Question for Andrew - how much scope is there for increasing the distance of the heater modules from the audio circuit? Could they go in a separate PS box with umbilical wires to the audio box? This might be preferable to passing AC through wires between boxes? Or would this not matter if the umbilical had only the 6no. heater wires? I imagine they could radiate EMF that could be picked up by the DC umbilical for the HT maybe?
No reason why not. You'll get a bit more of a voltage drop across the longer wires, but you could easily compensate by changing the potential divider that sets the voltage for the regs.

Bear in mind, longer wires, in themselves, aren't always a good thing.
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#190 Re: C3g Aikido Phono

Post by simon »

Thanks Andrew. The alternative is to have the rectifiers and first caps before the IC reg in the PS box and the rest of the reg in the audio box, which wouldn't be too much hardship.
Last edited by simon on Tue Mar 14, 2023 5:14 pm, edited 1 time in total.
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#191 Re: C3g Aikido Phono

Post by simon »

Today has been a bit one step forwards and two step backwards. But without the step forwards.

I managed to kill one of the shunt regs. I was trying some HT decoupling at the Aikido and I think the capacitance must have been too much for the reg. The reg CCS seems to be okay so it's presumably one or all of the IRF840, KSA1381 and 2SK117GR parts. So that's a job to fix.

For reference here's a block diagram thingy of how it's built
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#192 Re: C3g Aikido Phono

Post by simon »

I did scope all the nodes on the good channel and the noise starts on the anode of the first triode.
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I'm not sure what's causing this. There should be half the HT ripple on the first triode anode which is cancelled out at the anode of the bottom triode of the second valve. Cancelled out might not be the right way to describe it.

I moved the voltage lift for the heaters to the reg output rather than raw DC but something's not right as it's at ~0V rather than 60-oddV. I've checked both resistors and the cap across the lower resistor individually and they measure fine. I gave up for the day but I'll have to make another one and see if that works.

This won't be doing the valves much good but I don't think this is causing the noise as I'm pretty sure it was elevating when I first commissioned it.

I moved the two trafos too but apart from making the trace dance a little when moving them it didn't make any difference.
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#193 Re: C3g Aikido Phono

Post by Nick »

Probably wont make much of a difference but I would not pass the gnd through the boards like that, I would take them all to the same point where the F&S0 connection comes in from the regulator.

And I would move the ground point in the power supply at least to the other side of the smoothing caps (between the caps and the shunt regs). Where you have drawn it will see the charging current passing by.
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#194 Re: C3g Aikido Phono

Post by simon »

Nick wrote: Tue Mar 14, 2023 7:05 pm Probably wont make much of a difference but I would not pass the gnd through the boards like that, I would take them all to the same point where the F&S0 connection comes in from the regulator.
Yes, I did consider this when designing the boards. I went with trying to mimic one contiguous pcb but added the functionality to star back to the shunt reg. Just wish I'd added a few more solder pads in a few places. But this is part of the learning process :-).
Nick wrote: Tue Mar 14, 2023 7:05 pm And I would move the ground point in the power supply at least to the other side of the smoothing caps (between the caps and the shunt regs). Where you have drawn it will see the charging current passing by.
Yeah, it was a bit of a dirty build and the two section Mundorf cap probably isn't the best choice here, better as a second cap probably. I'll see what caps I have and try to make the earth connection in a quieter position.

TBH I wish I could find a decent cheap multiway connector, good for say 300VDC, so I could easily have two boxes. Milspec connectors are a small fortune and I'm always concerned I'm looking at the correct matching parts whenever I've researched them. Recommendations welcomed!
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#195 Re: C3g Aikido Phono

Post by pre65 »

These are rated @ 250v, but they may have some leeway ?

https://www.ebay.co.uk/itm/224927449842 ... 3800407772

Edit

These are 400v

https://www.ebay.co.uk/itm/382852468715 ... 6020103814
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