audio-talk

That's a good idea! Presumably a corner frequency of say 20kHz would be adequate and keep part values low?

I had wondered if the C3g gridstopper (220R) might be a bit low - I don't have any carbon composites to hand but I could try say 1k carbon film. Or would oscillation be much more audible?

Both seem worth doing to me.

Well, progress, of sorts.

820R and 10nF worked nicely and the light doesn't appear to be affecting the results now. This is good - it's a lot easier poking around a live amp with the light on... That said the light has just crashed and burned - the tube's gone .

This didn't resolve the issue though. But a 1k carbon film made a good difference. For some reason it only worked on one channel not both. I tried upping the other channel to 1k5 and if anything it was worse. I swapped the C3gs over but nothing changed.

Can grid stoppers be too large?

The channel affected is closest to the power supply. I could look out a larger board and see if some separation helps?
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Can grid stoppers be too large

Possibly, eventually the resistor means the grid is less controlled so free to do what it wants.

Maybe worth earthing the c3g can?

Okay maybe I'll try 820R and 680R and see what happens.

Interesting suggesting to earth the cans. Even with pcbs gotta love clipleads

BTW I reckon the difference in volume between channels is at least 3dB, maybe more. The "good" channel is maybe liveable with now, though I'd like to hear the other channel at a similar volume to see.

I also got quite a surprise when I was hot plugging the phono leads from the phono that they were incredibly microphonic. They were cheap ebay jobs so it might be worth me experimenting with some better ones.

The microphonic cables may be a symptom. The capacitance of the cable will be the thing that's is picking up the movement (there will also be some triboelectric going on). That varying capacitance may be interacting with the pentode to demodulate the varying C into audio.

I'm sure it's not doing any good at all, but I've usually tested with nothing connected to the output phonos. They're quite long leads so I can leave the phono on the bench.

My mistake I thought you meant the input ones.

Ah yes, I wasn't very clear. The input phonos have always been grounded.

simon wrote: ↑Sat Apr 29, 2023 10:03 am Ah yes, I wasn't very clear. The input phonos have always been grounded.

I've never had any luck grounding the input sockets.

In certain wiring layouts, usually a busbar system, many folk do this with success. I've never built a bus bar grounding system as IMHO, there are better wiring layouts.

My usual approach is to build and leave off the ground and then clip lead one in experimenting with best place. So far, that's never been the inputs.

YMMV and all that.

We might be at crossed purposes? I meant I clipleaded the phono pin to the earth tag for measurement purposes, as opposed to the permanent grounding regime. Interesting feedback though.

Maybe its worth clarifying that. I have a pair of phono plugs with a 100R resistor wired internally to plug into the input of a phono stage when checking for noise. Thats not strictly speaking grounding the input, as in most cases the output from a cartridge and tonearm is floating, so the relation to the outer of the input phono socket is connected to the inner by the 100R but the relationship to ground is defined by the phono stage.

Literally grounding the input will probably create a loop that at worst will look like an aerial.

I normally build the input of a phono stage that goes from the RCA to the PCB without a connection to ground. I have a 10nf cap between the input phono outer and the actual ground point, and then I connect the output phono outer's to ground via a pair of 100R resistors. I find that gives the best noise avoidance.

In the above sentence ground is defined by the grounding post of the phono stage which is connected via 40A cable to ground on the input IEC and the casework.

On the actual phono PCB I use a ground plane to connect everything together but that "ground plane" is only connected to actual ground via the 100R resistors on the output.

simon wrote: ↑Sun Apr 30, 2023 10:48 am We might be at crossed purposes? I meant I clipleaded the phono pin to the earth tag for measurement purposes, as opposed to the permanent grounding regime. Interesting feedback though.

That may or may not be a good thing depending on what "earth tag" means.

Whooaaaaah! Lots of really good stuff here, clarification definitely worth while.

I meant that I clipleaded from the signal pin of the input phono to the earth tag/outer of the input phono. I can see that this might cause an aerial. Would this be for higher than audio frequencies though?

Nick wrote: ↑Sun Apr 30, 2023 10:56 am Maybe its worth clarifying that. I have a pair of phono plugs with a 100R resistor wired internally to plug into the input of a phono stage when checking for noise. Thats not strictly speaking grounding the input, as in most cases the output from a cartridge and tonearm is floating, so the relation to the outer of the input phono socket is connected to the inner by the 100R but the relationship to ground is defined by the phono stage.

I will make some up to try.

Nick wrote: ↑Sun Apr 30, 2023 10:56 am I normally build the input of a phono stage that goes from the RCA to the PCB without a connection to ground.

Do you still use screened wire, screen connected to ground at the pcb end but to nothing at the phono socket?

Nick wrote: ↑Sun Apr 30, 2023 10:56 am I have a 10nf cap between the input phono outer and the actual ground point, and then I connect the output phono outer's to ground via a pair of 100R resistors. I find that gives the best noise avoidance.

Actual ground point is grounding post? One 100R per phono socket? Screened wire, screen only connected at one end?

Nick wrote: ↑Sun Apr 30, 2023 10:56 am In the above sentence ground is defined by the grounding post of the phono stage which is connected via 40A cable to ground on the input IEC and the casework.

That's a fat piece of wire!

Nick wrote: ↑Sun Apr 30, 2023 10:56 am On the actual phono PCB I use a ground plane to connect everything together but that "ground plane" is only connected to actual ground via the 100R resistors on the output.

Isn't ground also connected via the HT PS?

For clarity I have the phono wired up like this currently.

Raw HT PS ground connected to chassis ground (via earth lift resistor).

Two shunt regs (HT and ground) connected to each channel's C3g pcb and then to Aikido pcb.

Input and output phonos signal and ground connected to pcbs by screened wire.

Grounding post connected to the earth lift resistor.

It's a long way from yours.