Dumble Preamp with 12AU7 Output section

jaymenon · August 2023

It's a dream of mine to have a low output Dumble...

So I thought of going with a 12AU7 output section
Single ended (0.5W) or push pull (1W)

A question please for you knowledgeable folk:

When Ceriatone made a lower output (20W) amp they changed to a new preamp configuration.
Does that mean the preamp from the 50W amp will not work nicely with a lower output power amp?

Image: https://tfb-user-images.eu-central-1.linodeobjects.com/1a4b14ef9635a2c20da8bb780b13d01f63f2ffb4a3738dfd34

(I take it that the lower the value of the mid pot - the more mid-scooped the tone will be?)

ICBM · August 2023

A lower-value mid pot value gives less maximum mid, yes - although turning down a higher-value one cuts mid just as much when it's down to zero, but may also boost bass slightly depending on how it's wired. A higher-value mid pot gives not only more maximum mid, but also a more middy character and less insertion loss for the whole tone stack. (Which is why Mesa - incorrectly - say that their mid control acts as a gain control.)

The bass pot value simply determines the maximum amount of bass.

RiftAmps · August 2023

jaymenon said:

Does that mean the preamp from the 50W amp will not work nicely with a lower output power amp?

Not necessarily...you need to use your ears rather than simply copying what someone else did.

jaymenon said:

(I take it that the lower the value of the mid pot - the more mid-scooped the tone will be?)

What are the other tone stack values (caps/resistors)?

Is it Cathode or Anode follower?

Is there a Volume control immediately after the treble pot?

What is the PI configuration and operating conditions?

What voltage swing do you require to drive the 12AU7 PP OP stage?

Lots to think about

jaymenon · August 2023

the 12AU7 power amp will be single ended
So no phase inverter

I hope the pic below will help...

Image: https://tfb-user-images.eu-central-1.linodeobjects.com/212bd173ebbd7d4d3de071fa53a0c8c9e6099219182c3eb783

jaymenon · August 2023

From the replies thus far I'm guessing isn't a straightforward job to place a simple low output power amp section after this preamp...

ICBM · August 2023

jaymenon said:
From the replies thus far I'm guessing isn't a straightforward job to place a simple low output power amp section after this preamp...

Well, just doing that is

. The question is whether it will give the result you expect or want.

Just for one potential difference - bear in mind that the full-size amp uses negative feedback from the output to the phase inverter... if you omit or alter that, it will change the sound significantly.

Modulus_Amps · August 2023

Sounds like you need to go do a deep dive over at ampgarage.

But from what I know the 100k mid pot was used earlier and the 250k pot came later - possibly with the skyline mod.

ICBM is right in that you need the negative feedback to smooth things out. I was always of the impression that a part of the Dumble sound was the high headroom power amp.

You can use a different power section easily, but once built you will probably have to tweak things to make it all work the way you expect. That's part of the fun of it.

pluckbuddy · August 2023

Bluesmaster tonestack configuration is much more like a black panel Fender, hence the lower value. The mid control is set up in a different arrangement in many earlier Dumbles, according to info shared on the interwebz anyway; so the different value has to be understood in that context.

In short, different circuit, means there isn't necessarily an equivalence in the values of components.

Bare in mind as others have said, the Dumble ethos is a powerful clean power amp and they are complex builds too. You risk putting in a great deal of time and effort into building something that never sounds like you want it to because you've messed with the recipe.

For example, would being single ended get away from what makes a Dumble sound like a Dumble.

A push pull 20 watt Dumble might be a compromise with 2x 6v6s for home/low volume use... or even a 12au7 set up in push pull? Just ideas... be interested to see how it works out.

pt22 · August 2023

There’s a dumble clone in the classifieds. Add an attenuator and you’re golden?

Airmiles · August 2023

I claim no knowledge beyond Google -fu, but would some combination of the Rob Robinette Tweedledee mod
https://robrobinette.com/5e3_Modifications.htm#Other_5E3_Modifications
And his Deluxe Micro 1 watt

https://robrobinette.com/Deluxe_Micro.htm

Get you close? It may depend which Dumble you had in mind, ofc.

Airmiles · August 2023

Ah - I see from your other post you're already familiar with Rob's site

jaymenon · August 2023

Airmiles said:

I claim no knowledge beyond Google -fu, but would some combination of the Rob Robinette Tweedledee mod
https://robrobinette.com/5e3_Modifications.htm#Other_5E3_Modifications
And his Deluxe Micro 1 watt

https://robrobinette.com/Deluxe_Micro.htm

Get you close? It may depend which Dumble you had in mind, ofc.

Thank you @Airmiles ;

…that is exactly what I had in mind

Except that rather than the Tweedledee, I’m going to go for a ‘proper’ front end of a Dumble overdrive special #124

PhilKing · August 2023

I have a Ceriatone Overdrive Special and it sounds glorious when the volume is about 50%, however it is really loud, so I spoke with Nik about reducing the volume and he said that I could use the JJ 6V6's, as they can take the voltages and I can adjust the bias to match them. Tbh, even though I got the 6V6's, I haven't tried it, as I haven't been using the amp much for a while.

jaymenon · August 2023

PhilKing said:

I have a Ceriatone Overdrive Special and it sounds glorious when the volume is about 50%, however it is really loud, so I spoke with Nik about reducing the volume and he said that I could use the JJ 6V6's, as they can take the voltages and I can adjust the bias to match them. Tbh, even though I got the 6V^'s, I haven't tried it, as I haven't been using the amp much for a while.

Using 6V6 valves would drop it to something like 20W

...which is 76% of the volume of a 50W job...

PhilKing · August 2023

I will have to try it. I'm not gigging anymore, so haven't had need for the amp (also having 16 amps means that I really don't use a lot of them). My main amps nowadays are some McIntyre recording amps that I have had for years.

hywelg · August 2023

PhilKing said:

I have a Ceriatone Overdrive Special and it sounds glorious when the volume is about 50%, however it is really loud, so I spoke with Nik about reducing the volume and he said that I could use the JJ 6V6's, as they can take the voltages and I can adjust the bias to match them. Tbh, even though I got the 6V6's, I haven't tried it, as I haven't been using the amp much for a while.

I tried Russian 6P6S Black glass 6v6's in my OTS. Capable of handling the 429v (IIRC) without problems They are darker and the breakup is earlier, just. They are nice but different. I also use a Hotplate on -6dB and run it though a 4x10 cab with Jensen p10R's in (95dB ish). So I am able to manage the output quite well.

Still sounds better loud tho'

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Dumble Preamp with 12AU7 Output section

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