Diplomat - Matchless DC30's EF86 Channel

[Neil_H]

If you have a link where R21 470k resistor should be you have increased the output of the pedal by about 30%, R21 limits the output of the signal.
If you add a 22k resistor across leg 1-3 on the volume pot you have also changed the tone of the pedal a lot, you have lost a lot of the low end of the signal.
I think it would be a lot safer for the tube if you install R21 at 470k or even higher if you want to drop the output level, and then you could place a switch across R21 to increase the output level when the switch shorts out R21.
You can use this calculator to see what changing the volume pot to less then 22k will do to the signal, CG is the capacitor you select with the rotary switch (390pF - 47nF) and RV is the volume pot 1000k or 22k if you add the 22k resistor across it. The "Control % Resistance" is where the volume pot is set and I just leave it set at 100%, and "Output Impedance" is the impedance of the tube output but it is not crucial in this case so I would leave it alone as well in this case (unless you really want to work it out just for fun).
I could be wrong but that is what I think is happening in this case.
Cheers
Mick

PS....a picture of your pedal would be nice to see as well.

Hi thanks for the reply, this build was a bit of a physical challenge as I am recovering from a serious infection in my hand and arm that kept me in Hospital for 9 days and has left my left hand very weak and with poor sense of touch. My circuit board didn't have and pads/holes for the resistor to the left of the 100uf cap which I think was R21 so to add one I'll have to get creative, It's a different pcb to the build docs, I'll try and work out where to tack in a flying resistor or maybe change the pot . Any clues would be appreciated.
thanks
Neil

 

[Neil_H]

Removed the resistor across the pot and added a 2M2 from the center pin of the tone switch to to 180p cap, hopefully it's in the right place. It certainly sounds better.

 

[Tassieviking]

You made me check my old build of the Diplomat and you are right, there is no R21 on the PCB's.
I just looked at the build doc when I answered before so I did not realise that it is missing from the PCB's.
That will be the right place to put a dropping resistor but it will only work if you make a small cut across the copper track that connects the pins together on the PCB.
There is a copper track on the front (component) side of the PCB that goes up from the tone switch to leg 3 of the pot, and there is another track on the back that connects leg 3 of the pot to C13.
You will need to cut the track somewhere under C2 and the tone switch, a sharp hobby knife or box cutter makes it easy to make a tiny cut to sever the track.
Here is a pic where you should cut the track so that the added resistor will work, where the pink X is on the drawing.
You might have to use less then 2M2 after you cut the track.

Cheers
Mick