Recommend me the Blackface type amp grounding method please.

[psychepool]

I made a single channel Blackface type amplifier.
Made the circuit based on the AX84 California Dreamer and the Mesa Rectoverb clean channel.
There was a slight change during make it, but the overall circuit diagram is roughly like this.

F7A3CB7C-4011-43A5-BE66-262FB6AE1A48.jpeg

All functions work well and has good sound.
One problem is background noise.
If uses it with high volume, it's not a big problem to use, but it seems to be a problem that can be solved and I ask for your help.

I applied Lar/Mar PPIMV.
When PPIMV is reduced, there is almost no noise even if increase the preamp volume.
However, when PPIMV is fully opened, there is many noise even in preamp volume 0 as well.
Of course there is noise that occurs as preamp volume is raised, but it is distinct from the noise mentioned above.
It is a feeling that the noise generated by raising the preamplifier volume is overdubbing with the noise mentioned above being basic.

There may be many causes, but I would like to find the cause in the grounding first.
The amplifier I built had a lot of difficulties in following the references because the chassis was so narrow and the structure was unusual.
(Don't ask me why I made like this structure. I want to recycle the head cabinet, and the story was very complicated.)

This is the whole picture of the chassis,

E45A5F3B-7074-44F0-AD07-7E4468094178.jpeg

7C0E6C69-EF68-4E90-8267-062330B17FF9.jpeg

and I have drawn a structural diagram to help understand.

220A1C87-33E7-4920-97E1-E142F8C6C770.jpeg

It is largely divided into a top plate where the control panel is located and a bottom plate into which the main parts are mounted.
The horizontal size is 330mm.

Ground was connected like this way.

8C591F5F-B1D6-4271-9D99-366D5A0C73C0.jpeg

The ground method is very different from each other, so I don't know which is right.
I grounded PT 2nd main center / heater center / Powersupply ground(JJ Tesla 40/20/20/20uF multicap ground) / bias circuit ground / preamp ground to PT bolt together
The preamp ground includes an input jack, a reverb transformer, a reverb jack, and presence (PI ground).
The ground of the power jack was grounded to the PT bolt near the power jack.
The ground of the output jack (OT ground) was grounded to the OT bolt near the output jack.(Far away from main ground)

What's the proper ground work for my chassis?
Would it be Better to separate the presence from the preamp ground and connect it
to other PT bolt with the bias ground?
Would it be better to ground the preamp to the input jacks?
I heard that the output jack ground should be separated, but would it be better to join the main ground?
Is it better to disconnect the reverb transformer and jacks from the preamp and ground to chassis nearby?

There are various causes of background noise.
But first, I want to think about the other reasons after I put the ground wiring correctly.
Please give me proper grounding method for my amp.

[Malcolm Irving]

It looks like you are using a metal-body input jack. I think there may be a 'ground loop' created by grounding the preamp to the main chassis via the transformer bolt and also to the chassis via the input jack. If so, you could try removing the preamp ground that goes to the transformer bolt and just keeping the input jack ground.

The same thing could be happening with the reverb jacks, which might be creating another ground loop through the chassis.

Might be worth considering plastic-body jack sockets, so you can control where grounding to the chassis occurs. Generally it is a good idea to only have one signal ground connection to the chassis for the whole amp. (There is also the separate safety ground connection to the chassis, of course, which should be close to the mains inlet.)

[psychepool]

It looks like you are using a metal-body input jack.

Sorry, The input jack is insulated type. And the Reverb Jacks also have plastic washer for insulate.

[M Fowler]

Nice, I've dreamed about that style of chassis and there it is, good job.

As long as all the panels are bolted together there should be no problem there.

I would ground all preamp sections together near the input jack.

The PI, CT's, filter cap, and speaker jack ground together.

I realize the preamp filter cap is in that can cap so we can't do anything about that but I've had good luck before with can caps.

The reverb jacks grounding depends on your reverb pan so you have to look up the number of your pan and compare to reverb pan data sheet on antigue electronic supply dot com page.
I just ground my reverb driver transformer right at the RCA jack ground tab.

Mark

[psychepool]

Nice, I've dreamed about that style of chassis and there it is, good job.

As long as all the panels are bolted together there should be no problem there.

I would ground all preamp sections together near the input jack.

The PI, CT's, filter cap, and speaker jack ground together.

I realize the preamp filter cap is in that can cap so we can't do anything about that but I've had good luck before with can caps.

The reverb jacks grounding depends on your reverb pan so you have to look up the number of your pan and compare to reverb pan data sheet on antigue electronic supply dot com page.
I just ground my reverb driver transformer right at the RCA jack ground tab.

Mark

The PI GND is presence pot pin1 in my amp.
I will try to remove the presence pot1 from circuit board GND and move to main GND first.
And other preamp GND move to nearby input jack.

It is also unreliable that the output ground is around the input. I will move it to Main GND also.

One last concern is the ground of the filter cap.
I search many articles and I found that the first filter to the OT center and power tube screen was sent to the main ground, and the remaining filter caps correspond to the preamp so sent it to the input ground with the preamp ground bus.
However, my filter cap is multi type so grounds are tied and shared.
Is it necessary to change the filter cap to separate the ground?

[labb]

This works well....Don't recommend attaching to back of pots, run a buss bar instead.and a separate ground connection for the ac incoming power. ...http://el34world.com/charts/grounds.htm

[psychepool]

http://el34world.com/charts/grounds.htm

I saw it many times. However, since the chassis structure is different from me, so I had difficult to applying it, and even there were something that could not explain.

I am trying to modify the grounding of the filter portion using an individual capacitor instead of a multi-cap. Is it ok to change the first parallel 16/16uF that to the OT center and the screen to 33uF one? If use the same brand, which is the better choice?

[psychepool]

I separate preamp ground from main ground and move to input, and send speaker out ground to main ground but no change.
I will try to replace multicap to indivisual 22uF caps and then seprate the ground of the filtercaps.

If after done it there is no change then I will look for other causes other than ground.

[psychepool]

If the noise disappers by turn down the PPIMV, could it be because the shield cable is not applied?
I don't have 2 conductor shielded cable. Just have single conductor.
I didn't apply it because 4 single conductors may makes the chassis inside too messy.

[psychepool]

I applied shield cable but no change.
I will change the power supply caps and if there’s no change, I’ll stop to try reduce the noise.

[psychepool]

Change the PSU caps and seprate the grounds but no change.
The cause of the noise seems to be not a bad grounding.

I will look for other causes such as lead dressing etc.
There is a bit more noise than other non-master volume amps I've made,
but it could be normal noise level.

Later, I will upload a noise sample and ask you to let me know what kind of noise it is.
Thanks for your replies!

[sluckey]

Referring to your schematic... The PI tube can't possibly work. The cathodes have no dc path to ground. Maybe that's just a drawing error?

I'm thinking that your unusual chassis design and overall layout are factors in your noise?

[psychepool]

Referring to your schematic... The PI tube can't possibly work. The cathodes have no dc path to ground. Maybe that's just a drawing error?

I'm thinking that your unusual chassis design and overall layout are factors in your noise?

Yes it's just a drawing error. The capacitor that has no value is not exist one.
I think chassis layout seems to be a problem too. The cause of the other part is hard to find.