#002 - my journey begins

[Bombacaototal]

It might be a issue, I'm not sure either.
Only thing I can say:HR3111-1032-ZINC-PL-HEX-KEP-LOCK-NUT-1_600x600@2x.jpg
When using these, the edges go right through the powdercoating.
I accidentally discovered it when checking if my tube sockets had a ground connection( for the pre amp tube cover).

Thanks Erwin, yeah I understand, good point indeed.

I wonder if the proximity of my FX loop return and the stand off may be causing a double ground. I bent it out a bit, but I will heat shrink everything just to be sure

[Richard1001]

Is your amp chassis shielded on the open side of not?
You could just be picking up hum from electro magnetic fields around you. (Just like the pickups of a guitar)

[Bombacaototal]

Is your amp chassis shielded on the open side of not?
You could just be picking up hum from electro magnetic fields around you. (Just like the pickups of a guitar)

Thanks for the contribution Richard. Further experiments, I floated fairly separately the B+ leads and the "1" wires from the shielded cables (pic attached). No audible difference. I also flam floating this group of cables about 1.5cm compared to the heaters.

I have unsoldered the supply ground at the power tube and the power supply ground which has its own ground. I have been moving them around, like one in FX loop and the other in the power supply/bias ground. No real difference

As far as your question, I have the amo sitting on my desk without a headshell (which is still being produced), so this could be a possibility although none of my other amps would have suffered from a similar issu

[Richard1001]

As you van see in the picture i posted, i tied the reverb feedback wire (blue greenish) to the powersupply wires with a tiewrap. No hum issues.

I do see a black ground wire comming from the effect send jack and going somewhere. There is also one on the return jack, but this wire is for the PI board ground (of should be)

Where is the black wire from the send / preamp out jack going?

[Bombacaototal]

Hi Richard, the ground wire on the fx loop send is grounding the reverb jack, similar to how the layout document is wired. I actually do not have the footswich jack connected to the circuit yet, as purposely, I leave this for last, once everything in the amp is perfect. So it should make no difference to the rest of the amp at this stage

[Bombacaototal]

Narrowing down the issue.

First I checked all grounds, pots and board by using an alligator clip and "re grounding" them at the pre amp ground point. No difference

Now I have grounded the filters return and the reverb return pot out at the board. Hum is still present and as loud as previously.

The mixer tubes and dry and wet LNFB are what is left as pre amp circuit

[Bombacaototal]

Now I have the filters return grounded at the board and the wet signal path before the 220k wet mixing resistor and hum is still here.

If I also ground before the 220K of the dry there is no hum. Issue is then between the filters and the 220k on the dry path

[Bombacaototal]

I think I found my issue. I didn't find a PCB trace for the empty pin 1 (attached) but it must go to the 100k for the supply, probably right there the issue

[Bombacaototal]

Just added the lead on that lug but not much difference. Here is the hum now with reverb return and volume at zero and master at max

[erwin_ve]

I think I found my issue. I didn't find a PCB trace for the empty pin 1 (attached) but it must go to the 100k for the supply, probably right there the issue

As in the layout, there is a wire going from pin 7 to pin 1. The "eyelet" for pin1 is optional, you could wire the lead from the pin7 eyelet to the pin 1 eyelet. Or omit it. Or use it as a measurement point.

[Bombacaototal]

I think I found my issue. I didn't find a PCB trace for the empty pin 1 (attached) but it must go to the 100k for the supply, probably right there the issue

As in the layout, there is a wire going from pin 7 to pin 1. The "eyelet" for pin1 is optional, you could wire the lead from the pin7 eyelet to the pin 1 eyelet. Or omit it. Or use it as a measurement point.

Got it Erwin, thanks. Yeah I had omitted before but now it's added for completion

By the way this is the full build as is

[Richard1001]

I looked at your picture.

Don't you use the isolation boards on the rectifier and Fet board? If so, i would install them!

I see a lot of components that don't seem to be soldered right or look like they have not been soldered at all.

Are you sure you wired the inputs the right way?

[Bombacaototal]

I looked at your picture.

Don't you use the isolation boards on the rectifier and Fet board? If so, i would install them!

I see a lot of components that don't seem to be soldered right or look like they have not been soldered at all.

Are you sure you wired the inputs the right way?

Hi Richard, no I don't use the isolation boards because of the thick powder coating which isolates the chassis. But I can try.

All components are soldered but from underneath like I mentioned before, but I can re tint the top. Does it make any difference?

What do you mean about the inputs?

Edit 1: soldered the power board from the top too, no change. Next up the isolation board

Edit 2: isolation board is in but no difference

[Richard1001]

I looked at your picture.

Don't you use the isolation boards on the rectifier and Fet board? If so, i would install them!

I see a lot of components that don't seem to be soldered right or look like they have not been soldered at all.

Are you sure you wired the inputs the right way?

Hi Richard, no I don't use the isolation boards because of the thick powder coating which isolates the chassis. But I can try.

All components are soldered but from underneath like I mentioned before, but I can re tint the top. Does it make any difference?

What do you mean about the inputs?

Edit 1: soldered the power board from the top too, no change. Next up the isolation board

Edit 2: isolation board is in but no difference

You can't trust on the paint for sufficient isolation! Even if it works, over time vibrations could Scratch through the paint. Paint thickness can vary and you don't know the properties of the paint.

Soldering the board, the solder should flow through to the other side.

The wiring of the inputs looks kind of messy.

[Bombacaototal]

Thanks for the constructive feedback. I have added both isolation boards for peace of mind

Noted in regards to the solder going through. To be honest this is my first time going PCB and I find it a bit nerve racking, due to the fragility and lack of flexibility. I bought some 0.7mm solder to minimise time and heat at the lugs and tried to be more "in and out", but maybe should have kept the heat a bit longer. I still prefer turret followed by P2P eyelets I think.

Input should be fine as my tests were all with volume at zero.

Thanks all for the help so far. I shall spend some time with the amp and shall report back if I manage a fix

Edit: and if anyone who has built this amp have a bit of time I'd love to have a phone recording of the noise floor of the amp with master at max and return and volume as zero for basis of comparison