Grounding questions on tube reverb unit

[bieworm]

hi guys
I built a reverb unit and after some troubleshooting I still have hum.
Maun circuit properties are:
- 1x 12VAC plugpack to feed the filaments
- 1x TX 240VAC to 12VAC , reverse placement back to back with the plugpack, so the 240VAC gets rectified for B+
-1x 12ax7 : 1st triode pre powertube, 2bd triode recovery after tank
- 1x 6AU6 tank driver pentode
- high impedance reverb tank, due to the constant current driven reverb nature of the beast

The final grounding layout is as follows:
- all compontents on the tubes are PTP and the ones that go to ground are grounded on the central ground in the middle of the tube socket. ( both tubes separately ofcourse) .. from that middle ground lug I wired it directly to star ground. All other stuff is directly wired to star ground. So I have only got 1 grounding point. The wallwart has ground lifted I guess?

Questions:
- Is there in this situation a possibility for ground loops?
- I have the ground for the rca jacks going from outputjack ground to inputjack ground to star ground. Should they he separately going to star ground?
- I twisted the central ground of the filamentwiring around that wiring, ending up in star ground.. is that a problem?

[maxkracht]

Check out Merlin's grounding article. http://www.valvewizard.co.uk/Grounding.html You can minimize the potential for a ground loop between your amp and reverb with a hum-loop blocking circuit.

[bieworm]

I understand the value of that... I have read it before. But the device being fed by a walwart should already react as a ground loop lift, no?
I ordered a toroidal tranny and see if that gives some relief.
I moved the output jack further away from the rectifier. That helps some bit..
I rewired the whole thing and moved the rca jacks really away from the tranny. I followed Merlins guidelines, except for the ground loop lift as you sent..
I also added more filter caps. I think of replacing the diodes too because in the beginning I had higher voltages.. so maybe that has messed them up...

15951827364344227883294043770935.jpg

[maxkracht]

I didn't catch the wallwart part. Yes, lifting a ground that isn't there won't do much... It's hard to tell from the picture, but it looks like one end of the heater is tied to ground. You could try putting in an artificial center tap with a couple 100R resistors.

[bieworm]

The heaters are wired in series for 12VAC. That way you can use a smaller current feed. The tubes need half the current...
Running the verb through the fx loop makes it quiet enough, more quiet than my digital reverb pedal, but I want to find the source of that hum anyway..and maybe run it in front of my amp.
I hope for better results with the toriodal TX .

[TUBEDUDE]

Haven't seen the schematic, but would it be safe to elevate the heaters?

[bieworm]

https://valveheaven.com/2016/10/the-lam ... omment-539

Here is all the info...maybe it can ve helpfull

[maxkracht]

You can also test to see if it is heater hum by swapping in a 12v DC supply if you have one with sufficient current. If it is magnetic interference from the power transformer, changing its location would change or eliminate the hum. A torrid in the wrong spot will still make noise. Changing the location of the reverb tank could help or at least eliminate a variable. There is also the obvious: bad cables, jacks, bad solder joint, etc. Using a jumper from chassis ground to various ground points can eliminate more variables.

[bieworm]

The tank is 2 feet away from the unit while experimenting. I sure ain't that hum... I held the tank closer and I could notice the difference in hum doing that. It increased...

Things I have tried before are:
- another tranny with full length wires attached, with the tranny 20cm away from the chassis. Same hum..
- i rewired the entire unit like 3 times. Always the same hum. So it is not a bad connection or solder.

The output jack is suspicious though... I moved it because when it was 2 inches away from the rectifier the hum was worse .. whenever some metal part is close the hum increases.. but I can't see anythung wrong on it..

[bieworm]

Soundclip finished product

https://www.dropbox.com/s/wxfty9ucjbj9g ... t.m4a?dl=0

[Bombacaototal]

Sounds great, I am wondering how you managed to fix it?

[bieworm]

I didn't.. I judt run it throug the loop. Its mire quiet than my digital pedal...

[martin manning]

Something you could try:

[bieworm]

Will try that...thx
But you must know, I first had only 2 100uf electrolytic caps, just like the schematic says. But on my quest for tracking down the source of that hum I added 2x 47uf parallel caps before those two. Will it still make any difference moving that ground wire like you point out?

FWIW... when I put a 100nfd cap from the 3rd lug of the dwell pot to ground, the hum was substantially reduced. But also the amount of reverb...maybe that tells something? I also tried smaller czps like .022 and .01uf .. it brought the reverb back more but also the hum. Does that mean it's not ground hum?

[martin manning]

Still worth a try. More capacitance will reduce the ripple, but you don't want that ground return current flowing through your ground bus.