# Special Overdrive Dumbloid



## rectifier (Apr 30, 2020)

Hi everyone, I just built a Special Overdrive which is basically the dumbloid. The pedal works great but I kinda don't get the sound of it. Although its based on the tuibescreamer it sounds nothing like it. When you enable the pedal you lose all the highend in your guitar. The accent knob works more like a tone control, and the other real "tone control" is more a character knob. The distortion overall is quite fizzy and warm, I would even go so far and say it reminds me of a big muff. It's cool for leads but completely unusable for rhythm guitar.

So far:
- Everything works great, all knobs, jazz / Rock switch etc.

I just wanted to ask the community if someone also had the same experience with that pedal. I've built this one for my friend and I don't want him to be dissapointed and I'm also not sure if mine is really similar to the original or if I made a mistake somewhere with the components


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## rectifier (Apr 30, 2020)

Just measured all the capacitors and resistors nothing odd, other than R18 and R17 being 6.7k instead of 10k. Maybe the multimeter is tripping because of the two 47 uF caps

For tone I used 25k instead of 20k like in the schematic but I think that shouldn't make a difference


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## GenoBluzGtr (May 1, 2020)

The one I built sounds fine... you're correct it sounds very little like a TS circuit, but it has a pleasing, yet different, character. I do NOT get fizz from mine, although I will say I do prefer it at halfway or less on the gain control.  I also tend to prefer it in Jazz setting for Teles and Strats and the Rock setting only with my Les Paul.   Your description above sounds like you may be on the Jazz setting with the Accent control set too high? Play around with different settings and switch position and see what you get, but it should sound at least semi-"normal" unless something is off in the circuit.


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## GenoBluzGtr (May 1, 2020)

Here is mine in the Jazz setting when I first did a Pre-Enclosure wiring test.  Sounded the same after wiring it up.  This is a Les Paul through a vintage Pro Reverb w/ Neo Creamback speakers at VERY low volume.


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## rectifier (May 21, 2020)

Had to take a break from that circuit. Now started to experiment with it again. When my accent pot is set low the tone pot doesn't work at all. The tone pot only starts working when accent is set above 11 o clock





Also that whole Fat PReamp setting thing doesn#t work and why is the tone control at 5-8 when accent is at zero. Makes no sense with my build as the tone control doesn't do anything with the accent set on zero


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## GenoBluzGtr (May 22, 2020)

Have you checked the voltages on the Op Amp?  Lowering the resistance of R17 and R18 could potentially cause VRef to be higher voltage than intended... this could, in turn, drive your Op Amp harder causing that "Fizzy" clipping you referenced.  Just a volt or two increase on the biasing of the opamp can cause it to drive into higher levels of saturation.  Just a thought.    Changing those without changing the two capacitors in parallel may impact the V-Ref?

I just went through this with a Blues Breaker Clone where I inadvertently used an incorrect resistor in the power generation section and it caused Op Amp Clipping at levels that were too much to sound right.  It sounded kinda ratty and fizzy.  Fixed the resistor in the power section, brought my voltage levels down to the correct level and it sounds perfect now.


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## rectifier (Apr 2, 2021)

GenoBluzGtr said:


> Have you checked the voltages on the Op Amp?  Lowering the resistance of R17 and R18 could potentially cause VRef to be higher voltage than intended... this could, in turn, drive your Op Amp harder causing that "Fizzy" clipping you referenced.  Just a volt or two increase on the biasing of the opamp can cause it to drive into higher levels of saturation.  Just a thought.    Changing those without changing the two capacitors in parallel may impact the V-Ref?
> 
> I just went through this with a Blues Breaker Clone where I inadvertently used an incorrect resistor in the power generation section and it caused Op Amp Clipping at levels that were too much to sound right.  It sounded kinda ratty and fizzy.  Fixed the resistor in the power section, brought my voltage levels down to the correct level and it sounds perfect now.



This is really some good help / advice. Finally, found some time today to check all the resistors. Will report back.


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## rectifier (Apr 2, 2021)

Measured all the resistors and all the valuies are ok other than 6.95k and 6.96k for R17 and R18 which are in the supply chain. Their color code says that they should be both 10k resistors. Why does my multimeter show 6.95k ?

Here's the schematic part

Voltages Opamp:
1: 4.43V
2: 4.65V
3: 4.42V
4: 0V
5: 4.43V
6: 4.43V
7: 4.43V
8: 8.89V

Voltages Transistors:

C: 8.89V
B: 4.21V
E: 3.67V

C: 8.88V
B: 4.28V
E: 3.72V


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