ROG Umble

[AndyG]

Hi I built the umble and it works but sounds pretty bad. There is some type of high end that I cant dial out.
Has anyone experenced this same problem?

Andy

[modsquad]

Built it a while back and was underwhelmed with the end result.  One thing is to make sure you bias all the fets.  Otherwise is sounds even worse.

[bigstomper]

Built one and was also underwhelmed with the result.  It sounds OK.  Something tells me putting (slightly modified) Fender circuit in a pedal isn't going to do the Dumble thing.  However...maybe I'm off here.  Would like to hear from some other people as to what their results were.

[d95err]

Redesigning the Umble more likethe newer ROG circuits (e.g. the Thor) might produce a better result.

EDIT: The first thing I'd try is to replace the Volume pot with fixed resistors (most Dumble players say they just keep it at 12 o'clock anyway). Then put a gain pot in place of the 180k/100k voltage divider towards the end instead (like the Drive pot in a Dumble). I would also remove the source capacitors to lower the overall gain of the circuit. A small capacitor between the source and drain of the overdrive stages (just like the anode-cathode caps on Dumbles) might also help control the high-end.

[stm]

High end can be tamed by performing one or more of the following simple steps:

1) Remove the 47p treble bleed cap in the Volume (Gain) control.
2) Remove the 330p cap in parallel with the 220k going into the gate of the 2nd stage.
3) Add a 220p or 330p cap from gate to GND in the third stage.  Adjust cap to taste.
4) Ditto but for the fourth stage.
5) Reduce a bit the overall gain by removing the source bypass cap in the first stage.

Ideally you should try one change at a time and check if it goes in the right direction.  Remember this is DIY... don't be shy to experiment and tune the circuit to your liking!

[Bucksears]

I built one a few years ago, but it had that typical low-end fuzziness that I found with almost all of the ROG circuits I've tried when you turn up the gain. Otherwise, it sounded ok.
dschwartz came up with the suggestion of reducing the .022uF caps between gain stages (he used .0022uF) and worked most of that out.

[stm]

Low end buzz can be reduced by replacing the 4.7u cource bypass caps with a lower value, like 0.47u, 0.68u or 1u.  This chould be done in order fcrom 1st to 4th stage, untilobtaining the desired effect.