D´Lator and ground loop hum

[hans-jörg]

Hello,

I would like to know if you have simmilar problems like me with ground loop hum.
When I pull the in/out connection to D´Lator the amp is deadly quiet. But connected there is hum which I can regulate with the Recovery pot. When the pot is at 0 its ok.

I have 2 grounding points: one for the power suply and heater (100R/100R) and one for 12Ax7 circuit and jacks. ok, one seperate more for ground of AC inlet.

Should I use a auto ground lift?

How are your expereance with that?

My built is following the orig. schematic from here.

Best
Hans-Jörg

[bluesfendermanblues]

Hans-Jörg,

I have build a couple of D-lators and followed the layout in the files section
(https://tubeamparchive.com/download/file.php?id=14586) closely. And have no hum issues. I think you have to use jacks (switchcraft or Neutrix) like the ones in the layout as well. I have done that.

For built-in d-lator, I ground everything at the loop tube socket - its also completely silent.

[martin manning]

If the hum is silenced with the return pot at zero, then your problem is not an Amp-D'lator ground loop. The hum is in the signal being fed to the return pot.

My D'lator power supply grounds are split. The reservoir cap is grounded with the power transformer center taps near the power inlet, and the other filter grounds are tied together and then grounded with the circuit grounds. The pot housings do need to be grounded to the chassis, and the sleeve terminals on all four jacks should be tied together and then grounded with the circuit grounds.

[hans-jörg]

Hello,

I`m shur I have no heater problem because I can dial the hum with recovery in and out.
Also, when I ground the tube socket which is mounted on the on the board (horizontal) the hum goes a bit down but not much.
It sounds like a classical ground loop but I can´t see one.
Like the loop is generated by connecting with the main amp via In/Out.

I have a stand alone D´Lator which is mounted at the bottom of the head - under the hanging 102 Dumble clone.

I found out that because of the close mounting a (very small) hum is generated even when the Loop is not AC powerd. Perhaps through the amplifying of the small amount the hum grows.
If I pull the in/out connections its quiet.

Maybe a poor magnetic shielding between the two - though why I can regulate it by recovery pot. This should not work when the shielding is the problem.

Or both together: poor shielding and poor grounding

Best

Hans-Jörg

[hans-jörg]

If the hum is silenced with the return pot at zero, then your problem is not an Amp-D'lator ground loop. The hum is in the signal being fed to the return pot.

My D'lator power supply grounds are split. The reservoir cap is grounded with the power transformer center taps near the power inlet, and the other filter grounds are tied together and then grounded with the circuit grounds. The pot housings do need to be grounded to the chassis, and the sleeve terminals on all four jacks should be tied together and then grounded with the circuit grounds.

Ah I see. As I wrote above: poor grounding.
I will rewind all and build up a new grounding structure.

Thank you

Hans-Jörg

[ayan]

One more consideration for you. Do you use "Cliff style" isolated jacks? When I built my first Dumbleator clone I had a terrible hum problem. Separating grounds, as already explained, and using isolated jacks cured the problem. To this day, I don't know how Dumble managed without isolating the jacks.

Cheers,

Gil

If the hum is silenced with the return pot at zero, then your problem is not an Amp-D'lator ground loop. The hum is in the signal being fed to the return pot.

My D'lator power supply grounds are split. The reservoir cap is grounded with the power transformer center taps near the power inlet, and the other filter grounds are tied together and then grounded with the circuit grounds. The pot housings do need to be grounded to the chassis, and the sleeve terminals on all four jacks should be tied together and then grounded with the circuit grounds.

Ah I see. As I wrote above: poor grounding.
I will rewind all and build up a new grounding structure.

Thank you

Hans-Jörg

[bluesfendermanblues]

One more consideration for you. Do you use "Cliff style" isolated jacks? When I built my first Dumbleator clone I had a terrible hum problem. Separating grounds, as already explained, and using isolated jacks cured the problem. To this day, I don't know how Dumble managed without isolating the jacks.

Cheers,

Gil

If the hum is silenced with the return pot at zero, then your problem is not an Amp-D'lator ground loop. The hum is in the signal being fed to the return pot.



My D'lator power supply grounds are split. The reservoir cap is grounded with the power transformer center taps near the power inlet, and the other filter grounds are tied together and then grounded with the circuit grounds. The pot housings do need to be grounded to the chassis, and the sleeve terminals on all four jacks should be tied together and then grounded with the circuit grounds.

Ah I see. As I wrote above: poor grounding.
I will rewind all and build up a new grounding structure.

Thank you

Hans-Jörg

In two stand-alone dumbleators I have used the same jacks as used in the original Dumbleators in the file section ...and don't have hum issues. It's not a problem as long as they have ground connection to the same reference point. No mystery.

[ayan]

It may have to do with whether you rack mount your Dumbleator, what unit(s) you put through the loop, whether you defeat the AC ground connection, etc. On a non Dumble-related note, just the other day I was messing with my band's PA since we had got a new reverb (Lexicon of sorts). Inserted in the Mackie's main loop, the Lexicon hummed like crazy unless the AC ground was defeated. Inserted in the auxiliary loop that feeds the monitors, it hummed if the ground was lifted and did not if the ground was left alone. The predecessor didn't hum in either configuration, go figure.

Now, on a Dumble-related note, Brandon told me many years ago that Larry Carlton's Dumbleator ended up literally in the trash can. The reason for that, as relayed by Brandon, was that the unit killed dynamics and highs and hummed like a son of a bitch. Again, why he would isolate the amp's inputs but not the Dumbleator's is a mystery to me.

To elaborate a bit more on the hum issue I had experienced, the culprit in my case was the Dumbleator's return stage only; I could have lived without isolating the other 3 jacks. If you count the ground loops you introduce with the Dumbleator when using something in its loop, I think it's easy to see why hum could be easily injected into the amp.

Cheers,

Gil

In two stand-alone dumbleators I have used the same jacks as used in the original Dumbleators in the file section ...and don't have hum issues. It's not a problem as long as they have ground connection to the same reference point. No mystery.

[hans-jörg]

Hi Gil,

thank you for explanation.

I had no time till now to check but I think its my PS grounding.
All my amps are death quiet because I seperate the ground of first (loading) cap and the following filter caps. What I didnt in the Lator with whatever reason, .. I don`t know.
But I will fix at first the grounding schem and than follow a possible wireing problem at the grids. Thats a possibility too because the signal is very hot there and you need a proper layout. As I said, I can dail the hum in with recovery pot.
The weekend will give me a chance.

Thanks for your support

Best

Hans-Jörg

[bluesfendermanblues]

It may have to do with whether you rack mount your Dumbleator, what unit(s) you put through the loop, whether you defeat the AC ground connection, etc. On a non Dumble-related note, just the other day I was messing with my band's PA since we had got a new reverb (Lexicon of sorts). Inserted in the Mackie's main loop, the Lexicon hummed like crazy unless the AC ground was defeated. Inserted in the auxiliary loop that feeds the monitors, it hummed if the ground was lifted and did not if the ground was left alone. The predecessor didn't hum in either configuration, go figure.

Now, on a Dumble-related note, Brandon told me many years ago that Larry Carlton's Dumbleator ended up literally in the trash can. The reason for that, as relayed by Brandon, was that the unit killed dynamics and highs and hummed like a son of a bitch. Again, why he would isolate the amp's inputs but not the Dumbleator's is a mystery to me.

To elaborate a bit more on the hum issue I had experienced, the culprit in my case was the Dumbleator's return stage only; I could have lived without isolating the other 3 jacks. If you count the ground loops you introduce with the Dumbleator when using something in its loop, I think it's easy to see why hum could be easily injected into the amp.

Cheers,

Gil

In two stand-alone dumbleators I have used the same jacks as used in the original Dumbleators in the file section ...and don't have hum issues. It's not a problem as long as they have ground connection to the same reference point. No mystery.

Gil, I forgot that in my country we don't use the (3rd leg) on AC plugs on consumer electronics. We only ground equipment in kitchen and bathrooms and we use grounding in computer networks private and in companies.

Consequently, we don't have ground loops stemming from AC ground reference.

Therefore, you are right about it being a mystery how Dumble managed to avoid hum issues with US, AC ground.

[Structo]

I had a ground loop hum in the first Dumbleator I built.
I ended up clipping the ground on the shield of one of the pots.
Can't remember which it was but I think it was ground to the wiper lug of the Return pot.

Later I rebuilt the D'ator in a different chassis and this time I soldered the shields to the pot backs ala Dumble.

I also use a choke in the power supply.

No hum this time.

My PT is a Fender Reverb PT without a center tap so it is a full wave bridge rectifier that may also help reducing hum.

[ayan]

Since we're at it, I built my first couple of Dumbleators without chokes and with AC filament supplies. Out of boredom, at some point, I "upgraded" both of my personal units with a choke (generic Fender Champ, I think), and I changed the filament supply to regulated DC. Well, doing that entertained me to a couple of hours and set me back about $10, but it didn't change anything at all. The D-lator clones were almost dead quiet before the change, and just as almost dead quiet after.

Cheers,

Gil

I had a ground loop hum in the first Dumbleator I built.
I ended up clipping the ground on the shield of one of the pots.
Can't remember which it was but I think it was ground to the wiper lug of the Return pot.

Later I rebuilt the D'ator in a different chassis and this time I soldered the shields to the pot backs ala Dumble.

I also use a choke in the power supply.

No hum this time.

My PT is a Fender Reverb PT without a center tap so it is a full wave bridge rectifier that may also help reducing hum.

[hans-jörg]

Hello Gentleman,

hum is history.

I wired the grounds like in all my amps and hum is gone - which leads me to the question why I didn`t done it before that way. Maybe because it looked so simple
That means: filament symetry and load cap at one pont and the second ground point for pots, jacks, cathodes and ... filter caps. The third and alone grounding near the AC inlet is the yellow/green wire from AC in (Euro norm).

I have a choke in too and a turodial 30VA PT with full wave recti. and no filament CT.

Best

Hans-Jörg