C3g Aikido Phono

[simon]

This is an old one! I thought there was a thread here but can't find it so it must date back to the WD or even the WAD board. This is where it ended up:

C3g Aikido circuit rev F.png (95.36 KiB) Viewed 41149 times

Andrew did some great work on this and it sounds really nice. But there was a bit of hum I could never get rid of, which I felt was a consequence of the layout. It's been on my list of things to look at for a long time and I've been thinking about it for a few weeks with some encouragement from Andrew. I found an earth loop I'd never seen before which helped but I think I need to deconstruct and reconstruct now.

The Aikido part is one of John Broskie's All in One pcbs complete with series regs for HT and heaters, and the C3g stage and RIAA filter are laid out on kite board with separate pcbs for Broskie's HT and heater regs. This doesn't make it easy to alter and amend and I've been playing with Eagle laying out some pcbs. I'm still learning how to use Eagle, and very much learning how to lay out pcbs so will be interested in the panel's thoughts on what I've done so far.

[simon]

Eagle's limit for the free version of 100mm x 80mm makes it an interesting challenge. My starting point is with the components currently in use - some of the caps are fairly large physically - and I've ended up with three boards: one for the C3g stage; flowing to the RIAA filter; then to the Aikido output stage.

Here's the C3g stage. There's a ground plane on the bottom (blue hatch) and small HT plane on top (red). And a honking big Clarity Cap SA 10uf cap.

C3g.png (66.26 KiB) Viewed 41146 times

Here's the RIAA filter and the 56nf coupling cap. The 47uF and 56nF caps are Russian K72P teflons and also surprisingly large. There's another ground plane on the bottom but no HT plane as there isn't any HT here.

RIAA.png (28.37 KiB) Viewed 41146 times

Finally the Aikido section. I tried to keep this to half size so I can get two on a pcb just for the extra challenge. This was only the first attempt and might benefit another look. Again ground plane on the bottom in blue, around the 3mm wide heater wires. I couldn't squeeze the Russian K40Y PIO in here so went with Clarity Cap 250V ESA.

Aikido.png (56.48 KiB) Viewed 41146 times

How do they look? Anything obvious amiss?

[simon]

And FWIW here are the renders

C3g render.png (94.23 KiB) Viewed 41146 times

RIAA render.png (52.87 KiB) Viewed 41146 times

Aikido render.png (99.18 KiB) Viewed 41146 times

There looks to be plenty of space on a big screen but some parts are quite tight at 100mm x 80mm.

[IslandPink]

Nice to see the circuit again.

Here's the RIAA filter and the 56nf coupling cap. The 47uF and 56nF caps are Russian K72P teflons and also surprisingly large.

I should think a 47uF teflon cap would be large !

[simon]

monster! 47nF!

[simon]

Layout of a phono on a pcb might be a bit niche.

Another question - just how important are the type of caps in the RIAA? The channels need to be well matched, and the values accurate for RIAA adherence of course, but are teflon the best? PP or PIO? Does it matter? Any good experience?

I have another layout using all Clarity Cap ESA PP which saves space over the big Russian teflons and fits on 2 boards rather than 3 but there's no point if they're not as good.

[Nick]

I would also consider the Mundorf ZN ones.

Exactly what load is that c3g going to be driving, it looks a bit harsh over 10kHz (<1k I would guess). Did you ever do a THD against frequency sweep for it?

[IslandPink]

On caps, I have found the Russian teflons to be a bit lacking in dynamics and maybe a bit of low-level signal. They are however very neutral across the midband. Bud Purvine told me they have a higher 'activation threshold' than polypropylene's, which would suggest they could distort more at low signal levels, but i haven't tried to do any measurements on this.
It's sometimes hard to get small values under 0.1uF on caps like the Mundorfs if you need them. I have found Rel PCU to work very well too, but they may be hard to find nowadays, I think I got them from Michael Percy in the US.

[simon]

I would also consider the Mundorf ZN ones.

I did wonder about the ZNs as I know a few here like them, never tried the personally. According to HiFi Collective they're discontinued now though they have remaining stock - get them now before they're gone. The smallest value they have is 100nF so I'd still need a 47nF.

Exactly what load is that c3g going to be driving, it looks a bit harsh over 10kHz (<1k I would guess). Did you ever do a THD against frequency sweep for it?

The intention is to reuse the E88CC Aikido. No I never measured THD against f as I don't have the kit.

[simon]

Interesting, thanks Mark.

Not much turns up for a quick Google of REL PCU caps. Parts Connexion have a 1uF 400V for $107 in the bargain basement sale, if it's the same thing.
https://www.partsconnexion.com/RELCAP-BB-62330.html

[IslandPink]

I did wonder about the ZNs as I know a few here like them, never tried the personally. According to HiFi Collective they're discontinued now though they have remaining stock

F*ck ! Now I need to think of all the values I might need in the future, this week.
I need a batch for Jonny's monitor speaker crossover, which isn't quite finalised....

[IslandPink]

Parts Connexion have a 1uF 400V for $107 in the bargain basement sale, if it's the same thing.
https://www.partsconnexion.com/RELCAP-BB-62330.html

That's the badger. Not cheap... shame they are discontinued ( too )

[Nick]

I would think tolerance is more of a issue in a riaa than any other consideration. I would be more thinking towards 10 or so cheap rs polystyrene and select matched pairs. Or measure and trim once built. Happy to help with the latter assuming you don't have the kit.

[simon]

Parts Connexion have a 1uF 400V for $107 in the bargain basement sale, if it's the same thing.
https://www.partsconnexion.com/RELCAP-BB-62330.html

That's the badger. Not cheap... shame they are discontinued ( too )

I've been surprised how much caps seem to have gone up since I last had a good look 10+ years ago. Way ahead of inflation.

[simon]

I would think tolerance is more of a issue in a riaa than any other consideration. I would be more thinking towards 10 or so cheap rs polystyrene and select matched pairs.

Yes, I'd wondered about this. I was going to see if HiFi Collective could perhaps match, but I haven't seen anything on the website to confirm this. There's not a lot around in polystyrene though, not at 47uF and over 180V. Digikey don't look to even have any PS, unless I'm looking at the wrong thing. Mouser, Farnell, RS and HiFi Collective have a few but nothing convenient.

PP on the other hand are much easier, something like this for instance?
https://uk.farnell.com/vishay/mkp183934 ... dp/1413925

Or measure and trim once built. Happy to help with the latter assuming you don't have the kit.

Thanks. Been a good while since I've been to Dr. Nick's