Dumbleator circuit questions

[MKB]

Hi all, posted this in the Dumble Files forum a few days ago with no response, will try here.

I'm building a Dumbleator, and have noted some differences in the available schematics, as such:

1) In the recovery amp stage, some schematics have a 4.7uf cathode bypass, and others have a 47uf. Which would be correct for a Dumbleator II build? I am aware that this would simply change the low freq bypass point, and the 4.7uf is probably large enough.

2) Again in the recovery amp, some schematics have the 500pf/220k network inserted between the recovery stage grid and the 10meg/0.22uf/10meg network, and others have the 10meg/0.22uf/10meg connected directly to the recovery stage grid. Which is most like the Dumbleator, and does either way have any advantages?

3) Does the original have the recovery amp input grid circuit AC coupled to the recovery input pot wiper, or is it dc coupled?

I'm just trying to get the details of the original, as if I've learned one thing in my ODS build, the small details matter. Thanks for all replies.

[Structo]

Go with the 47uF bypass.

Key thing seems to get the cathode follower around 31v.

Power supply depends on what PT you are using.

I also installed a choke on mine.

Try to follow Dumbles grounding and use of shielded cable.

[jam-mill]

Go with the 47uF bypass.

Key thing seems to get the cathode follower around 31v.

Power supply depends on what PT you are using.

I also installed a choke on mine.

Try to follow Dumbles grounding and use of shielded cable.

Structo,

Can you please tell me what tube you use in your d-lator?

Thank-You,
-jack

[Structo]

I believe I have a vintage GE short plate, 12ax7 in mine.

[MKB]

Hi Structo, thanks so much for the reply, much appreciated. The grounding is indeed important, I had a strange issue with mine and it turns out I needed to ground the input to the recovery stage at both the input jack and pot case. Also I'm still getting a tiny bit of hum in the signal, not enough to be concerned with, but maybe a choke will help that as well. It's 120Hz and my supply grounds are carefully routed, also my PT has a low enough output so that the first dropping resistor only drops a few volts, so I'm sure its on the supply rail.

I'm surprised that he didn't AC couple the recovery input, any DC leakage from an effect output could cause significant bias issues with the recovery stage.

Thanks also for the pictures. Are two of those pictures (the rack case that is painted blue inside) from a real Dumbleator? If so, I wonder if the flux left on the PCB is important for the tone.

[Structo]

I think I also suffered hum/ ground loop on mine.

I remember cutting a shield on one of the cables but couldn't tell you which one is was now.