Dumbleator for #124. Made a layout and schematic. Please C&a

[Joost]

Ok, guys, I finished my preliminary layout and schematic for a built-in Dumbleator in my #124. I pieced together all this from many hours of searching and studying different layouts and schematics from the original Dumbleator, Normsters layout, and a 124 bassman conversion with built in loop.

I have found different values used for many parts and even more strangely, B+s mixed up. (in one schematic the send gets a higher B+ than return and in other schematics vice versa)

Anyway. Here are the files. Can you PLEASE give me any and all feedback?

I will be ordering a bunch of different values for the dropping string to get the B+ voltages right.

I WOULD ESPECIALLY LIKE YOUR FEEDBACK ON THE BEST PLACES TO GROUND THE DIFFERENT GROUND POINTS. DO I JUST USE THE CLOSEST ONE, OR....


THIS IS MY CURRENT CHASSIS
[img:900:600]http://www.familieassink.com/documents/toorock001.jpg[/img]


Now I plan to insert a board on top of 5 of the bolt/standoffs of the current boards, using these 5mm M3 female/male Hex standoffs:
[img:85:140]http://www.familieassink.com/documents/140.jpg[/img]

That will put the Dumbleator Eyelet board 5mm higher than the preamp and power boards.

So here is the schematic I came up with, based on different posts. I will take the power from the grid supply node B+2.



[img:439:600]http://www.familieassink.com/documents/ ... cjoost.gif[/img]



And then this is my layout:

[img3142]http://www.familieassink.com/documents/ ... tJoost.jpg[/img]

And here it is, projected inside my chassis:

[img2073]http://www.familieassink.com/documents/ ... ection.jpg[/img]



SO I AM LOOKING FORWARD TO ALL YOUR FEEDBACK AND SUGGESTIONS[/list]

[David Root]

Most ingenious Joost!

I just used Normster's simple design, and grounded the tube related grounds to the #1 ground point by the input jacks, if I recall correctly. I will check that.

I have done this on two amps, my '70s ODS and my Bluesmaster HRM, but not on my 124, which I built without the fourth tube.

I have never compared the "Full Monty" Dumbleator with Normster's built in design. I use a 12AT7 tube and it sounds and operates fine with Normster's design and layout, so based on my experience I don't see the need for the massive secondary power supply with choke and many e-caps which makes it much more intrusive than I believe it needs to be.

If I had the room for a fourth preamp tube in my 124 I think I would just build a small board like an HRM board and put Normster's parts on it.

Your layout is comprehensive all right and for all I know maybe it will sound better than Normster's, but it is going to make servicing the amp much more difficult and time consuming I think.

Even so, my hat is off to you! You have done a remarkable job of making it all fit and saved some people a lot of design work.

[Joost]

Thank you! Took a bit of time researching and planning.

Yeah, servicability will suffer a little, but it's better than degooping an amp to service it Plus, you'll be able to reach all parts. No parts will be covered up by the new board, just some wire.

As for the power supply node, there were some threads on this and they were all clear that this was the way to go, so I'll try this. I am not getting an extra choke for this. Everything to the right side of the B+2 in my schematic is the current situation. I am adding three resistors and three el-cos for B+6 and B+7, tapping from the screen grid supply node (B+2)

Most ingenious Joost!

I just used Normster's simple design, and grounded the tube related grounds to the #1 ground point by the input jacks, if I recall correctly. I will check that.

I have done this on two amps, my '70s ODS and my Bluesmaster HRM, but not on my 124, which I built without the fourth tube.

I have never compared the "Full Monty" Dumbleator with Normster's built in design. I use a 12AT7 tube and it sounds and operates fine with Normster's design and layout, so based on my experience I don't see the need for the massive secondary power supply with choke and many e-caps which makes it much more intrusive than I believe it needs to be.

If I had the room for a fourth preamp tube in my 124 I think I would just build a small board like an HRM board and put Normster's parts on it.

Your layout is comprehensive all right and for all I know maybe it will sound better than Normster's, but it is going to make servicing the amp much more difficult and time consuming I think.

Even so, my hat is off to you! You have done a remarkable job of making it all fit and saved some people a lot of design work.

[Fischerman]

Did you consider just going point-to-point on a few of those parts? For example, the .1uF and .47uF caps from the socket to the Send/Return pots?

FWIW, I just made two extra nodes off of the screen supply, the first node is unused and the second node is for the whole loop. This allowed me to mount the 100k plate resistor right on the socket but the voltages are not like a real D'lator. This was in a Bandmaster Reverb chassis and the doghouse was getting full!

[ElectronAvalanche]

Hi Joost,

I have come full-circle concerning FX-Loops incoorperated into the amps. I would rather opt for a stand-alone Dumbleator since the amp is pretty cramped with the added Loop.

I used point-to-point in one of my amps and went for a simplified and rather transparent loop.

Yet I think having the separate loop gives you more flexability.

There are some 9.5" Dumblelator builds described here and these could fit nicely inside the head-shell.

But none-the-less great layout and planning! I would of course take great care not to get too much cross-talk from the Loop to the TS-controls....

Cheers,

Electron

[martin manning]

I don't think you need three RC filters for the loop, two should be fine. Tap the screen node in your amp with a resistor that is (Vscreen-360)/0.0022 since you want 360V for the recover stage supply, and the total current draw should be about 2.2mA. So e.g. for 440V screen 80/0.0022=36k, then 22u cap to ground, then 100k and another 22u cap to ground.

[Joost]

Hi Electron,

What would you change in this layout to minimize the chances of cross-talk?

Hi Joost,

...............I would of course take great care not to get too much cross-talk from the Loop to the TS-controls....

Cheers,

Electron

Did you consider just going point-to-point on a few of those parts? For example, the .1uF and .47uF caps from the socket to the Send/Return pots?

yes, I thought of that, and I don't know if my logic is flawed, but, I thought it would be smart to keep all those parts away from the heater wires. But if you say it would be better to put them point to point around the socket, I could change the layout.

I don't think you need three RC filters for the loop, two should be fine. Tap the screen node in your amp with a resistor that is (Vscreen-360)/0.0022 since you want 360V for the recover stage supply, and the total current draw should be about 2.2mA. So e.g. for 440V screen 80/0.0022=36k, then 22u cap to ground, then 100k and another 22u cap to ground.

thank you for that! Here's where I got the idea for a third resistor/elco: https://tubeamparchive.com/viewtopic.ph ... or+builtin

this came from the venerable dogears

[Structo]

Use shielded cable for the signal runs.

I think the general consensus here is that the cathode bypass capacitor should be 47uF for full spectrum bypass.


That is a very nice layout by the way.

What did you use to draw that?

[img:400:332]https://tubeamparchive.com/files/thumbs ... rd_186.jpg[/img]

[martin manning]

I don't think you need three RC filters for the loop, two should be fine. Tap the screen node in your amp with a resistor that is (Vscreen-360)/0.0022 since you want 360V for the recover stage supply, and the total current draw should be about 2.2mA. So e.g. for 440V screen 80/0.0022=36k, then 22u cap to ground, then 100k and another 22u cap to ground.

thank you for that! Here's where I got the idea for a third resistor/elco: https://tubeamparchive.com/viewtopic.ph ... or+builtin
this came from the venerable dogears

Well, you already have the filtering of the main power supply at the screen node, then adding one more RC of 36k and 22u should reduce any remaining 120Hz ripple by 56dB before the recover stage. I can't see the need... anybody disagree?

[Joost]

Thanks. I dont have a dedicated program for this so I just use Adobe Illustrator. I used that for all the drawings of my chassis as well.

47 uF? that's going to be one huge cap. Are you sure?

So how far would you go with the coax? Every single bit the signal runs through?

Also, do I need to move any caps off the board to put them around the socket?

thanks so much

-Joost

Use shielded cable for the signal runs.

I think the general consensus here is that the cathode bypass capacitor should be 47uF for full spectrum bypass.


That is a very nice layout by the way.

What did you use to draw that?

[img:400:332]https://tubeamparchive.com/files/thumbs ... rd_186.jpg[/img]

[Structo]

What Martin is saying (I think) is that you can use the B+2 for your voltage at B6 on your drawing.
Then you need to drop the voltage from there for the plate of the cathode follower (B7)
The added resistor and cap will further decouple the circuit from the power supply.

Voltages aren't too critical but you want around 30v on the cathode of the follower for best sound.

So adjust the voltage accordingly.
You may have to adjust the 27K value to achieve that.

I also think you can wire this point to point to and from the tube socket and the Send and Return Jacks and the pots.

You can eliminate a lot of wiring that way and may not even need to use shielded cable.

Check out this layout that Normster made.

It had a lot of stuff on it but I wanted to show you the built in Dumbleator.

He uses a couple different values but it is virtually the same circuit.

Notice he takes the power from B3 (the PI power) and drops it with resistors.
It depends how much voltage you have there.

This is how I would do it.

[David Root]

That layout shows a .47 uF, not a 47 uF. I know the real Dumbleator uses the 47 uF but a 400V 47uF cap is a horse of a different color sizewise! That arrangement is similar to Normster's layout, which uses a 0.1, an 0.22 and an 0.47uF.

You can easily fit those into that space and into a smaller space too if you use Solen black (aluminum, not tin) non polar 630V caps. They are pretty neutral I think and very small compared to, say Mallory 150s.

I also agree about the PS from the screen node. I use a 22uF 450V cap and a 22 to 24K resistor from screen to the cathode buffer and a 2k2 from there there to the recovery stage with a second 22uF 450V cap. Never thought about the choke but a small one wouldn't hurt. You could probably drop to 10uF on the node caps then.

Tom is right about 30V or so on the CF cathode. Doesn't have to be exact, I have run between 30 and 35V, seems to sound OK.

[martin manning]

47 uF? that's going to be one huge cap. Are you sure?

Tom is talking about the cathode cap on the recover stage. You show 5uF on your layout, that should be 47uF at 10-25V... tiny cap.

The schematic you have is not the best one. Look here: https://tubeamparchive.com/viewtopic.php?p=53893#53893

[kevster]

Awesome looking layout!! Illustrator looks great, but it would be a little combersome for me. My wife could do something with it in a flash (years of advertising art and design using Illustrator for 75% of it).

Cool concept!

[Joost]

47 uF? that's going to be one huge cap. Are you sure?

Tom is talking about the cathode cap on the recover stage. You show 5uF on your layout, that should be 47uF at 10-25V... tiny cap.

The schematic you have is not the best one. Look here: https://tubeamparchive.com/viewtopic.php?p=53893#53893

Thanks for all the feedback everybody. I am working on an alternative layout that I'll post soon. Yes, you're right, they only have to be 25v, I have a few of those, They're small. I have changed it. Also changed the dropping string. Working on the other suggested changes in the layout.

BTW, Martin, I had exactly 440V on the screen node, so I am using your suggested resistor values in the new dropping string. Thanks so much.