C3g Aikido Phono

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simon
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#151 Re: C3g Aikido Phono

Post by simon »

Some progress. With the smaller physical size of the caps I've used in the RIAA filter I reckon I could probably have squeezed it all on to 2 boards rather than 3, but the real estate might yet be useful.

Learning points so far:

The general resistor I used is phyiscally right on the limit, it could have done with being a little larger for the half watt resistors I used.

It could have done with a larger solder pad too, as Andrew mentioned previously I think, particularly where it's attached to a large copper pour.

It wasn't too bad soldering to the large copper pours - I had to leave my iron on longer than felt comfortable for the solder to flow properly though. Larger pads helped heat the plane quicker.

The wire of the carbon comps I used for the C3g G1 stopper were a very snug fit.

HiFiCollective were out of stock of a number of resistor values and I had to use a 1W in the RIAA filter - the resistor on the pcb was nowhere near big enough and I had to bodge it with some cut off resistor leads.
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simon
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#152 Re: C3g Aikido Phono

Post by simon »

Some further learning points:

Don't trust Eagle parts found on the Web

Check everybloodything

So the large tubes lib I found and looked good had a ECC88 part which I used. If I'd used the alternative 6DJ8 I'd have been okay. The ECC88 part had the series/parallel heaters that the ECC83 et al have and I never twigged. So when I plugged it in I had 6.3V on on the E88CC heater pins, but unfortunately the nets run to the wrong pins for a 6.3V valve. So no heaters. Nuts. So these Aikido boards only works for 12.6V valves.

I looked in my small 9 pin novel stash and found 2 ECC83s and two 12AY7s so at least I could get up and running. Here it is in all it's gory.
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The first and most important thing is it works! At least after I tracked down why the left channel was very feint with loud buzzing. Even broke the scope out! So another learning point - it really helps if the phono lead at the step ups is fully plugged in... :lol:

Some initial impressions, bearing in mind there's only about an hour on it.

The hum is still there but improved. It's a little tricky to evaluate against the original as the Aikido valves have changed. There's more gain now, which is nice.

It perhaps doesn't sound quite as smooth as before. The ECC83s are Tungsram which may be Mullard-made but I've some 5751s in PHONO II I might need to try. There's decent detail and tone. I might find it difficult to spot the difference if someone were to blind swap them for me TBH.

One problem I do have is the shunt regs aren't supplying enough current for some reason - I can't get more than 46mA from one and 30mA from the other. I'm shooting for 60mA. Need to think about this.
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izzy wizzy
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#153 Re: C3g Aikido Phono

Post by izzy wizzy »

Looks like a good first go.

I realise a mangled PCB wasn't the plan but a few links for the heaters to get the right valves in wouldn't be wrong now that you got it going.

Hopefully your hum is down to regs not going quite right.
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#154 Re: C3g Aikido Phono

Post by simon »

Thanks for the encouragement Stephen :-).

Having thought about this a little I think I may have found the problem - the mains trafo secondary is too low at 220V.

The shunt regs are Salas' SSHV2
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SSHV2 circuit.png
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It requires at least 20mA and 20V for the reg, so 270V HT and 58mA.

The HT PS is 220v - UF4007 bridge - 100uF - 195R - 100uF and was only giving me about 250V. Linking the 195R out gives me nearly 260V, so I wound the reg down to 235V output and the current shot up to nearly 100mA, which I then wound down to 60mA.

235V is close enough for jazz, and no doubt valves. Another 20V or 30V on the secondary would have been nice though.
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#155 Re: C3g Aikido Phono

Post by simon »

izzy wizzy wrote: Fri Mar 10, 2023 6:54 pm Looks like a good first go.

I realise a mangled PCB wasn't the plan but a few links for the heaters to get the right valves in wouldn't be wrong now that you got it going.

Hopefully your hum is down to regs not going quite right.
It sounds a bit more "buzzy" than "hummy" but I'll need to battle with a scope to try to work out what's happening.

I haven't touched the pcb, it would be very difficult because of the size of the tracks. I could have a go at severing the track between pins 4 and 5 and jumping with a wire but I reckon there's a good chance I'd knacker it as it's pretty tight.
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#156 Re: C3g Aikido Phono

Post by Andrew »

Nice work, Simon.

PCB are highly rigid and inelastic, I used to write off the price of the first iteration when doing the heater boards as there was invariably room for improvement.

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#157 Re: C3g Aikido Phono

Post by simon »

Thanks Andrew. Yes, in the end I felt I could play with layout in Eagle for ever but until I actually built something I would never know if it actually worked, and what didn't. For a first proper pcb (or 3) I'm pretty pleased :-D
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#158 Re: C3g Aikido Phono

Post by simon »

Okay I've had a play with the scope, but I'd appreciate some expertise as I'm not sure what's going on.

The probe is 10x (no 1x switch) and the square wave is good. Please don't assume I have any idea what I'm doing...

This is raw DC, earth and probe on 100V+100V filter cap.
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Raw DC.jpg
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Looks to be 3.4V peak to peak. But as the probe is 10x is this actually 34V?

I think the raw DC could do with some more filtering but I'm struggling for voltage.
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#159 Re: C3g Aikido Phono

Post by IslandPink »

I'd assume it's 0.34 V, if the probe is 10x.
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#160 Re: C3g Aikido Phono

Post by simon »

Looking first at the left channel, probe earth on the ground of the C3g pcb for all measurements.

First the regulated HT
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Reg DC Left.jpg
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Looks to be about 8mV p-p, but with the 10x probe is this 80mV? Either way it's a lot more than I would expect. EDIT 80mV

This is with the probe on the input phono, input shorted to earth.
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Noise looks to be c12mV (or 120mV). As the phono is grounded I don't understand why this would be so but it implies there's a lot of nastiness on the ground I think? EDIT 120mV
Last edited by simon on Mon Mar 13, 2023 3:58 pm, edited 1 time in total.
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#161 Re: C3g Aikido Phono

Post by simon »

IslandPink wrote: Mon Mar 13, 2023 3:34 pm I'd assume it's 0.34 V, if the probe is 10x.
Ah okay, I've gone the wrong way. That would make it 0.8mV on the reged HT and 1.2mV on the grounded input phono. Still too much.
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#162 Re: C3g Aikido Phono

Post by simon »

This is after the C3g coupling cap, around 0.8mV EDIT 80mV
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After C3g coupling cap L.jpg
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And this is after the RIAA filter, still left channel. Looks similar, around 0.8mV. EDIT 80mV
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After RIAA L.jpg
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Last edited by simon on Mon Mar 13, 2023 3:59 pm, edited 1 time in total.
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Nick
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#163 Re: C3g Aikido Phono

Post by Nick »

Hang on, a x10 probe is a 1:10 attenuator, not a probe with gain. If the scope is set at 1v per div, and its not a scope that talks to the probe, then that is indeed 3.4v displayed on the scope, the applying the x10 probe, that means that the actual supply has 34v P/P ripple.
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#164 Re: C3g Aikido Phono

Post by Nick »

Its also hard to read any values from the scope. I would try turning the brightness down and try and play with the focus.
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#165 Re: C3g Aikido Phono

Post by simon »

Now it gets a bit more interesting. This is after the Aikido output cap
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After Aikido coupling cap Left.jpg
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And similarly at the output phono
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Output phono L.jpg
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Not sure what's going on here but I wonder if it's an issue with the Aikido board layout?
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