Half Dumblator

[jazzbass]

Hi Stephen,

thanks for the video, and now thanks to you, Martin, Rootz, Erwin and many other friends in TAG I understand the working principle of the Dumblator. I finished the construction of what I started building many years ago, never finished. Now I have touched with my hand, or rather with my ear, what happens when it is placed between the preamp and the amp and I share my observations. Of the first (unsuccessful) attempt I used the TT-T47 toroidal transformer https://www.tube-town.net/ttstore/toroidal-47va.html and the casing.
I then bought a Dumbleator Kit and built a power supply. Assembled everything, solved an error and finally connected to my new creature, a 2nd generation ....... result: the beautiful sound of the amplifier has become rubbery, not ugly, but gives a beautiful, unique, well defined I got the sound of "any" amplifier.
I checked the voltages and they are correct, some "peculiarities" are questionable (if I have not mistaken the construction), for example the Stand-By does not work as it should and the sound disappears after a long time. I have no difference in sound if I activate or deactivate the capacitor on the switch in the return, I tried to increase its capacity without result.
Do you have some advice? I wish that its inclusion would really produce a positive change and not only serve to connect effects like Reverb, Echo ...
P.S. don't criticize the construction .... it's not finished yet
Thank you
Franco

[erwin_ve]

First, engaging the bright switch on the recovery out pot. The more you open this pot the less the effect of the bright cap. It helped open up my amp icw a dumblelator.
Second: is the lnfb on the recovery connected to the grid directly or as schematics here indicate: a lnfb at the entrance of the grid cap//resistor?
Connecting it directly to the grid will open up the the dumblelator soundwise.

[martin manning]

...some "peculiarities" are questionable (if I have not mistaken the construction), for example the Stand-By does not work as it should and the sound disappears after a long time.

Maybe nothing wrong here. With only ~2mA current draw the Dumbleator will run for quite a while on the energy stored in the power supply caps.

I have no difference in sound if I activate or deactivate the capacitor on the switch in the return, I tried to increase its capacity without result.

Hard to imagine how this could be, but of course the bright cap on any output pot will not have any effect unless the pot is turned down.

[jazzbass]

Hi Erwin,

the schematic of the board purchased as a Dumblator kit from Tubetown https://www.tube-town.net/ttstore/kit-dumbleator.html "Schematics".

Hi Martin,

The speech on the function of the capacitor on the switch of the Pot Recovery is now clear to me and the answer you gave earlier is also clear to me.

I believe that I will have to reset my expectations and look for a solution that does not alter the sound of the amp so heavily and at the same time can justify its presence between the preamp and the power amp to allow you to use the time base effects correctly. .
It's just my curiosity because at the moment the 2nd generation and the John Mayer are the two amplifiers that I prefer among those built on the Dumble project.
P.S. I love using 4x6V6 instead of 6L6.

Now begins a phase that I consider very interesting and constructive, the study of what has been written so far on the Dumblator.
thanks to Rootz, Martin, Drew, Erwin, Bepone......

Thanks guys, a hug
Franco

[Colossal]

I've attached the schematic here, for quick reference, and for when the link changes in the future.

TT_Dumblelator_Kit.pdf

[jazzbass]

Hi Colossal,

what do you think if I replace R4, which is now 10K, with a 27K? do you have any other suggestions to give?
Thanks, a hug.
Franco

[martin manning]

I believe 27k is the value shown in the schematic posted here on TAG.
A couple of threads that you might find interesting:
https://ampgarage.com/forum/viewtopic.php?f=4&t=35393
https://ampgarage.com/forum/viewtopic.p ... 73#p413673

[Colossal]

Hi Colossal,

what do you think if I replace R4, which is now 10K, with a 27K? do you have any other suggestions to give?
Thanks, a hug.
Franco

Hi Franco,

I'm sorry, but I don't have a suggestion here as I don't have experience with a Dumblelator

Best,
Dave

[Stephen1966]

Hi Colossal,

what do you think if I replace R4, which is now 10K, with a 27K? do you have any other suggestions to give?
Thanks, a hug.
Franco

Hi Franco, I've just finished building a Dumbleator into my amp and I can tell you that if you have your B+ voltages at 360V and 260V, you use the 27k tail AND a 12AX7, you are pretty much guaranteed to get the magical 30V on the cathode of the CF. Now, I'm only speculating but a 10k tail is going to alter the operating point of the tube and it may well be that a 10k tail and a 12AT7 are better suited to one another.

Stephen

[Edit: why not try them both? I think the TT kit is asking for lower B+ voltages and that could explain their choice of a 10k tail but there are nothing like your ears! Also, if you fancy doing the maths, check this out: https://www.valvewizard.co.uk/accf.html]

[jazzbass]

Hi Stephen1966, hi everyone,

I made "peace" with my Dumblator derived from a TT kit, first of all I built a PS board by obtaining the two voltages that Martin Manning's diagram indicated: B + 1 360 V and B + 2 260 V by feeding the side with these values the Recovery and the CF side of the 12AX7 valve. I then replaced the recovery input potentiometer which was indicated with the value 500K in the TT schematics with a 50K potentiometer. I swear, I thought I had read the 500K value in the potentiometer but I probably hadn't had the third morning coffee yet and I inserted a pot of ten times less value but ..... miracle, the dumbulator started to work great with every amps I have at home. I don't know why but it has truly become an irreplaceable component (for now ) in my very short effects chain.
Thanks for all your answers.

A hug

Franco

[Stephen1966]

Hi Stephen1966, hi everyone,

I made "peace" with my Dumblator derived from a TT kit, first of all I built a PS board by obtaining the two voltages that Martin Manning's diagram indicated: B + 1 360 V and B + 2 260 V by feeding the side with these values the Recovery and the CF side of the 12AX7 valve. I then replaced the recovery input potentiometer which was indicated with the value 500K in the TT schematics with a 50K potentiometer. I swear, I thought I had read the 500K value in the potentiometer but I probably hadn't had the third morning coffee yet and I inserted a pot of ten times less value but ..... miracle, the dumbulator started to work great with every amps I have at home. I don't know why but it has truly become an irreplaceable component (for now ) in my very short effects chain.
Thanks for all your answers.

A hug

Franco

Great news! Perhaps if you have time, you could pin up a revised schematic with your mods to the TT kit? There seems to be plenty of interest in the TT version here on the forum and anyone considering it as an option in the future, if they haven't installed one already, might be very interested to see why you are so happy

[jazzbass]

Hi Stephen 1966,

I'd like to report to ALL the small and lucky changes I've made but I don't know anyone in TT. I don't know who to turn to.

Franco

[Stephen1966]

Hi Stephen 1966,

I'd like to report to ALL the small and lucky changes I've made but I don't know anyone in TT. I don't know who to turn to.

Franco

Hi Franco,

I'm not sure what you mean. As I see it though, these are your mods, to a TT circuit which after all said and done, isn't proprietary. They copied the Dumbleator topology. But that itself, is nothing especially innovative. Blencowe's Practical FX loop has many similarities. I'm not sure if you spoke with TT they would offer any technical support anyway. They are actually great guys and do great business, but when you modify their products they quite rightly say they can't be held responsible for the changes you made, or support you technically for a product they haven't produced themselves.

Anyhow, I don't have any stake in this, and it isn't for anyone to tell you what you should do. I'm just thinking there is a possible learning opportunity here.

Stephen

[jazzbass]

Hi Stephen,

I have no doubts or requests to TT technicians, at least a couple of questions regarding the valve power supply and maybe try to understand why the project works better with the 50K mix-pot instead of 500K as indicated by them, or in Martin Manning 250K scheme.

The fact remains that I don't know anyone at TT to ask questions. Perhaps (certainly) some guy trained here in TAG could answer these little curiosities.

What matters to me is that everything is working great now and with all the Dumble clones I've built.

Un abbraccio

Franco

[martin manning]

I see on the TT schematic it says "original no return pot," so it looks like they started from a different version of the D'lator than the "3-knob" version we have documented here.