Gibson GA50 clone issues

[bepone]

I thought a sketch of the current Power Distribution might be helpful.

Pretty self explanatory.

this is not good. it is not following any rule. for the beginning try to make this, we will se after how to proceed

Power Distribution.jpg

[Phil_S]

Try what LoudThud and/or Bepone suggest. I suspect what either one said will improve things. The problem, as I understand it, is that bank of components to the left of C4. Those mix up parts from various stages and the layout makes it difficult to separate the grounds by stage. I also think that the pot grounds should not be routed directly the input jack like you did. Because of the layout, it may be challenging to sort this out.

[didit]

Hello --

Sensing common ground in advice. Filter capacitors C3 & C4 should be grounded at the input jack with the rest of amp front end. The suggested long flying connection illustrated works but suggest unnecessary, and instead short jumper onto the grounded end of R7 would be fine.

I hope this resolves all or at least most of the hum. Contrary to (my interpretation of) this advice --

[..] if this is correct there is no any humm for some normal valve.

-- as hum can and does creep in from other sources than just flawed preamp grounding. Octal small signal pentodes have deserved reputation for heater induced hum. Output transformers can have coupling to power transformers, etc. These both would be heard down at 60Hz though.

Best .. Ian

[bepone]

I took some time to correct again this layout, this should be the best noise wise, separated all the currents , not mixing everywhere in the gnd buss bar, chassis ground only at the input jack!

This topology became now local star gnd daisy chained .

When all of this is done, and there is still humm, then we can discuss about electromagnetic coupling from the power transformer , and leaking thru the heater/cathode lines.

X- means remove/break this line

Power Distribution 2.jpg

[didit]

This topology became now local star gnd daisy chained .

Theoretical correctness but the real-world existence proofs point to some needless fuss. ..

Be patient, I'm a (retired) mechanical engineer.

Take a bit of time going through the "Grounding" chapter that Blencowe generously shares off this page --

https://www.valvewizard.co.uk/Grounding.html.

If you plan on going deeper then order his preamp book too, to get the rest of his sound engineering advice.

Best .. Ian

[bepone]

?
i just corrected your layout, so who need to take lessons?
btw all the books i read in first week when they have been published so this one cca 10yrs ago.

[Duck Dodgers]

Did the changes suggested by bepone....

Completed the board grounding changes but left the pot grounds. (They're attached to the buss wire soldered to the backs of the pots and go to the chassis ground at the input jack.) In other words everything but the skinny rectangle at the top of the diagram. Much quieter but not gone.

Did the pots. RP1 is closest to the input jack. Daisy chained pot ground lugs and went to C3 from RP3. No improvement from the above grounding work.

So quieter, think good condition Fender Brown Face Princeton.

I did not remove the pot buss going to the input jack.

Thoughts?

[LOUDthud]

How do the plates of the 6SN7 look ?

[Colossal]

The pot buss is an antiquated and bad idea. It would be best to remove it.

[Phil_S]

I did not remove the pot buss going to the input jack.
Thoughts?

As Colossal says, get rid for the pot buss. Only RP1 and RP2 get grounded. Run a ground wire between the two ground lugs and run wire from the closer one to the ground of C3.

[Duck Dodgers]

Removed the pot ground buss. No change.

LOADthud asked about the 6SN7 plates......nothing significant. Voltages measure 185 and 187. (Don't remember which is which.)

Phil_S on pot grounding. I'm missing something (not surprising). Schematic shows end of RP1 to wiper and end of RP3 then to ground. RP2 at top of schematic shows one end grounded.

Playing with my ancient O'scope...vertical grid 5mv horizontal 2ms; V2P2 and V2P5 look waaay different than my first post. Output jack has a low frequency ripple (my Fluke says it's 10Hz) with a lot of noise and some spikes that look like 120Hz. Don't know if this is useful/interesting, LMK.

First pic is chassis. I did the new ground wiring in blue so it would be easy to see. (There is an additional blue wire C2+ to V3,4 P4 not part of the changes.) Lead dress looks a little haphazard to me at this point.

Thanks gang!
Cheers

[Phil_S]

Phil_S on pot grounding. I'm missing something (not surprising). Schematic shows end of RP1 to wiper and end of RP3 then to ground. RP2 at top of schematic shows one end grounded.

Yes, I missed that. There is a dot on the schematic, junction of RP1 wiper, RP3 wiper and downside lug, C9, and ground. This ground belongs to C3 ground.

[Duck Dodgers]

So the daisy chain you can see in the chassis pic is OK?