Dumbleator in Bassman

[half_smith]

*edited,
here's the layout with minimal changes from AA864 with Dumbleator instead of Bass Ch.

I included some alternate values provided by Martin (for long cable runs to the pedal board) in this thread:
https://ampgarage.com/forum/viewtopic.p ... r&start=60

I'm really curious how this will sound, and how the Dumbleator drive/recover pots interact.
In any case, I hope to get a good effects loop for my delay, tremolo, and reverb pedals.

Thanks for the help!

[dmoose5835]

I'm not quite seeing the path from Input to Send, and it looks like Return comes back to the Send node (red rectangle).
Then again, I'm far more comfortable reading schematics than layouts.
Hope this helps!

[half_smith]

hi dmoose, I'm fairly sure I've got the input and send wired right.

[half_smith]

*deleted (to declutter the thread)

[Olomert Brever]

I'm not super familiar with this loop buffer circuit and am not sure what actual benefits it will provide that you can't get from a low cost modern device. If this is more about building a circuit for the sake of building and learning, then that is a great motivation. With all this in mind, I would seriously consider trying the project in another platform. This much modification to a vintage Bassman that will have uncertain benefits seems better suited to project chassis, IMHO. Bassman and absolutely top-tier amplifiers and there are a finite number of them in existence. I'm always supportive of modifications to increase reliability and functionality, especially to professionals who use the gear to earn a living but in this case my gut says maybe save it for a Hammond box. Just my two cents, FWIW.

[half_smith]

... If this is more about building a circuit for the sake of building and learning, then that is a great motivation.

Yes this is my project amp and I've been using it to experiment and learn.

[GAStan]

One suggestion, on the Dumbleator Send Jack maybe consider rather than using the switched contacts have it unswitched to the Return switched contact. This would still provide preamp signal to the power amp if nothing plugged into the Return jack.

[half_smith]

thanks Glenn, that makes sense.

[half_smith]

guys, it's incredible.

It gives you so many options.
It makes the standard Bassman into a big broad raging monster or gentle chimey whispering angel
And the effects loop is so much better for reverb etc.

* I had to add another .1uf 600v AFTER the MV, I think it was interacting with the next stage (it had 14v DC on the pot and very noisey).
all good after the additional coupling cap.

[martin manning]

Sounds interesting. Can you post a schematic of what you ended up with?

[half_smith]

Hi Martin, here's the schematic.

I've only made a few changes from the posted Dumbleator schematic.
* 4k7 Grid resistor on input (was unstable, I'm not sure if this was the ticket, but the problem went away after I installed it so I left it)
* 50K DRIVE pot and bigger resistor (ala Martin)
* Send jack not switching (ala Glenn's suggestion)
*I apparently used .1 (instead of .01) on the input cap by accident, I might change that, it's a little bassy.

Any further suggestions?

[martin manning]

...here's the schematic.

Thanks. I was referring more to the way it is integrated into the Bassman. I think you said you were moving it to the normal channel?

[half_smith]

I decided to put it in place of the BASS Ch (as pictured in first post) after all, for a proof of concept.
Now that I know how it works I wish it was swapped, my sense of feng shui is a little thrown having the signal path wrap around itself, but I'll leave it for now.

[half_smith]

It occurred to me to DC Couple the V2 stage straight into the Effects Send - I've tried a few arrangements and this is working well now.

- At the moment I have two unused triodes and I will either rebuild the circuit and just remove a tube, or think of something to do with the available triodes...
- I have tried making V1b a DC Coupled CF into the TS, I appreciated the tonal change but it sapped the gain of the stage too much.
- I have tried an additional DC Coupled CF on V3 (recovery of the Dumlbeator, sending low impedance to the PI) but the amp was getting noisy (probably some sketchy birdnest joints) so I pulled it out for now.

Any suggestions for the unused triodes on V1, V3?
- I want the amp to stay "clean" more SS than ODS, so not looking to add more gain stages
- I've tried some different voltage dropping Rp on V3, is there a target B+ for that stage I need to consider?

Thanks!

[dbharris]

You could add the Hi and Low filters from the SSS or add the driver from the SSS to the power amp.

-Dan