dumble with Fender tone stack

[rutledj]

Just wondering if anyone has tried this combination before and how it sounded. I prefer the clean sound of the scooped fender. I suppose that would screw up the OD tone though.

[Stevem]

Yup!
Have you ever played a Dumble?

[wpaulvogel]

The tonestack in a Dumble is one of the main modifications he performed in transforming the donor Fender components into the Dumble circuit.

[rutledj]

Yup!
Have you ever played a Dumble?

Yes. I built one from this site. It sounded very nice, particularly the smooth thick od. I would just like to have that smooth od with the Fender scooped clean.

[Stevem]

Then you need to layer things as in two different preamp sections in parallel.

[roberto]

Instead of having two preamps in parallel, if you just need a dedicated EQ for the clean and another for the OD, you can simply switch EQ+VOL through a relay together with the channel switch, keeping one single preamp.
Just use two 2M2 resistors to give voltage reference to the EQs and avoid unwanted pops when switching.

[10thTx]

I prefer the clean sound of the scooped fender.

There are other factors involved getting that scooped Fender tone besides the tone stack such as 100k plate resistors, 3 gain stages (AB763), and 22uf cathode caps. The tone stack alone is not going to create a Fender tone.

I think using two parallel tone stacks would perhaps be something of a challenge in switching between them on the fly? You'd need to also lift the ground connections of the tone stack not being used as well as a switch to engage which tone stack you're wanting prior to the 2nd clean gain stage.

OR have 2 DPDTs in the tone stack switching. One prior to and one after the tone stack. In which case then you would need 3 relays switched simultaneously to go from AB763 midscooped to Dumble clean into OD. And keep in mind that attempting this would put voltage on the prior to tone stack DPDT since there would be no capacitor prior to that switch.

So, in both of these, you'd need to have 3 switches engaged simultaneously for this to work.

OR ............................

You could build a 3 gain stage AB763 clean and a paralleled Dumble clean preamp (both with input jacks) and use an A/B box to switch between them. The advantage of this is you can have the 100k/1.5k/22uf gain stages of the Fender and the 220k/3.3k/5uf & 150k/2.7k/5uf Dumble. This would make the most sense to me.

Just thoughts to consider ............................ with respect, 10thtx

[10thTx]

I'll offer a thought for consideration. This may or may not be worth trying in regards to getting you closer to the Fender clean tone?

This could be considered a Fender clean/ Dumble clean tone stack hybrid. Not capturing the best of either but offering a possible compromise that might be useful?

150k/2.2 and 120k/1.8k ............ instead of 220k & 150k

100k slope resistor

10uf or 22uf & 5uf cathode .............. instead of 5uf or 5uf

R2a relay switches mid cap sort of between Fender and Dumble values

R2b engages the PAB simultaneously with R2a as the R2 relay is a DPDT. This would obviously increase the OD tone. I would certainly anticipate a contrast between clean and OD using this.

With respect, 10thtx

[roberto]

One single DPDT relay:
- plate to EQ1 or EQ2 (with a 2M2 resistor to keep the caps at the average plate voltage and avoid pops);
- Vol1 or Vol2 to second stage's grid (with a 1M resistor to keep the grid at ground potential and avoid pops).

[10thTx]

One single DPDT relay:
- plate to EQ1 or EQ2 (with a 2M2 resistor to keep the caps at the average plate voltage and avoid pops);
- Vol1 or Vol2 to second stage's grid (with a 1M resistor to keep the grid at ground potential and avoid pops).

Can you please post a schematic of what you are referring to? Maybe I am not understanding this but if you have two paralleled tone stacks and they are BOTH connected to ground even though only one of the is sending signal to the V1-b grid ................ wouldn't that be problematic in that it would be impacting the other tone stack signal?

And again, this still doesn't have the 100k/1.5k & 22uf Fender triode values.

With respect, 10thtx

[10thTx]

Now I think one could consider this but it would involve another dual triode? Then ......... you could use one DPDT and the other tone stack still connected to ground would not matter. And since the tone stacks have NO shared connection to a V1a triode, then it would not be problematic in my thinking?

This also would allow 100k plate resistors with 1.5k cathode resistors with 22uf cathode caps.

However, the Fender clean would be more like a Deluxe non-reverb with only two triodes and not the typical Fender AB763 three triodes.

With respect, Tubenit

[ChopSauce]

Just out of curiosity: how about an HRM-alike OD-only tonestack with typical blackface values?

NB: there have been some experiments around various OD tone stacks, amongst which the Vox one, leading to poor tone and I also could read that the rich content in the medium band is one reason for the "strong" feedback of Dumble amp - as a side note -

Please let us posted with whatever result for your experiments ...

[10thTx]

I've tried a handful of different tone stack approaches in an overdrive topology. I have found the James tone stack to be the best to my liking. It allows a "faux" mid boost or a mid scooped option. See Duncan Tone Stack calculator for an example: http://www.duncanamps.com/tsc/

With respect, 10thtx

[ChopSauce]

Interesting, thanks!

[JD0x0]

My suggestion would be to wire the PAB to the OD switch, so in OD mode, it automatically bypasses the BF style tone stack, and basically gives you a stock PAB tone on the OD side.
You could do low plate values on the clean, with a BF tone stack, it's basically a non-reverb Fender at that point.