2nd Generation 50w Period Correct ODS

[rooster]

The first amp shown has a different screen circuit than the first one. The first one has that 2.2K attached to pin 5 and then pin 4 gets a 470 to ground. The second one is a traditional Fender screen supply with pin for bridging to pin 6 - but no values so will assume 470 ohm. What's the deal here? Did Dumble create a different sounding amp originally and then move back towards the Fender direction? Certainly the slider switch Dumble (#1) is earlier, right?

[dbharris]

The first amp shown has a different screen circuit than the first one. The first one has that 2.2K attached to pin 5 and then pin 4 gets a 470 to ground. The second one is a traditional Fender screen supply with pin for bridging to pin 6 - but no values so will assume 470 ohm. What's the deal here? Did Dumble create a different sounding amp originally and then move back towards the Fender direction? Certainly the slider switch Dumble (#1) is earlier, right?

These are electronically the same as a fender circuit. The grid resistors (at pin 5) are tied to the unused pin 6 where bias voltage is delivered versus being tied to unused pin 1 in later lead dress with bias voltage delivered there.

The screen resistors are tied to separate terminal strips with screen voltage being fed from the PS board to the resistor on the right, then a wire carries it over to the strip on the left. It goes through each resistor and to pin 4. Rather than being tied to pin 6 in later lead dress with wires carrying the signal over to each pin 6. This would be a 3 terminal strip, where the resistor is not soldered to the ground lug.

-Dan

[rooster]

Ah, roger this, Dan. So, I'm left wondering, was Dumble trying to confuse ppl here? Or do you think he at one time thought this was a better way to attach the screen voltage?

[dbharris]

Ah, roger this, Dan. So, I'm left wondering, was Dumble trying to confuse ppl here? Or do you think he at one time thought this was a better way to attach the screen voltage?

We can only speculate...but I imagine he was trying different techniques to see what he liked best.

-Dan

[Matt J]

For those who have added a Ratio/Level control to a 2nd or 3rd Gen design like this, what is the recommended pot value you have used?
I've seen some hybrid designs with an 1MA but I wonder how it would work with an 100kL pot like some later ODS circuits have.
Matt J.

[erwin_ve]

For those who have added a Ratio/Level control to a 2nd or 3rd Gen design like this, what is the recommended pot value you have used?
I've seen some hybrid designs with an 1MA but I wonder how it would work with an 100kL pot like some later ODS circuits have.
Matt J.

The Hybrid 2nd gen design with ratio pot is set up like a HRM which means, seperate master for clean and drive channel. Thats why it has a 1M ratio pot.

When having a ratio pot going to the Overall master like #124, #102 , a 100k or 250k is appropriate.

Ans maybe move this to discussion area to keep the 2nd gen file thread clean?

[Matt J]

Ah, thanks for pointing this out, Erwin! That makes more sense now.
Agreed. Admins, if you want to erase this part of the thread to keep it clean go right ahead.
I'll post a 2nd Gen thread in the Discussion section once I start getting things together.
Matt J.

[martin manning]

A couple of updates for the 2nd Gen:
- Optional realay PS regulator
- Location of the pedal/manual switch arc suppression cap corrected and redrawn for clarity

Note in the 2nd Gen layout the ground lead from XLR pin 3 does not have the ground connection it needs for the relay to function. See here: https://ampgarage.com/forum/viewtopic.p ... 49#p383349

[Raoul Duke]

Awesome, thanks Martin!

What I did was break the wire from the switch to the DIN and put that ground lug in line. Would I then run the ground from the relay PS board to that lug as well? That’s how I’m interpreting this - but certainly correct me if I’m wrong.

IMG_0356.jpeg

The bias supply board then goes straight to the HV ground.

Am I still ignoring the solder lug at the top of the DIN plug and using pin 3 as in the layout? It appears that way but I just wanted to be sure.

That switch wiring seems significantly different (to my untrained eye) but your drawing clears it up perfectly. I’m guessing that the suppression cap doesn’t need to be 630v either?

Great stuff! Thanks again

[martin manning]

Correct, the only chassis ground point for the relay power supply is at the lug near the pilot lamp, or on the nearest transformer mounting bolt as Dumble did it in the photos above. Best practice is a dedicated bolt and ground lug, like on the later ODS's.

[erwin_ve]

A couple of updates for the 2nd Gen:
- Optional realay PS regulator
- Location of the pedal/manual switch arc suppression cap corrected and redrawn for clarity

Note in the 2nd Gen layout the ground lead from XLR pin 3 does not have the ground connection it needs for the relay to function. See here: https://ampgarage.com/forum/viewtopic.p ... 49#p383349

Depending on the chassis to use, mine have the same spacing and holes for the PS regulator as the later gen chassis.

[wsaraceni]

im not familiar with bumble terminology or any of that, but ive always liked the clips ive heard of the 2nd and 3rd gen dumbles Ive heard clips of. (I believe Mayer has one out on his solo tour, and Santana used one for a while). trying to compare these early layouts to something like 124 and later I notice the lack of master and presence controls and additional switches on the front panel. are they the majority of the functional changes (vs component value changes). I want to dip my toe into the dumble build and keep talking myself out of it because there is so much info.

im definitely following these two 50w 2nd gen threads closely.