Dominator II Build (Dumbleator II)

[rccolgan]

Hey all!

I know some of you have been following along in Charlie's Dumbleator II thread and I was working on a PCB since one was not openly available (to my knowledge).

I'm using Hammond 229B transformers so the end-user can choose between 120vac or 240vac mains simply by utilizing the jumpers. Everything is going well except I could use a second set of eyes on my power supply board. My variac gets up to ~26vac and pops the 500mA slo-blo fuse. (My wall mains in the US is 120vac so I jumped J1 and J2). When I start rotating the variac, the transformers start to hum before the eventual pop of the fuse. I have disconnected B+1/2/3 and it still popped. I am attaching a few build photos and a schematic/board layout.

A second set of eyes is appreciated! I must be missing something simple...

-Ryan

[martin manning]

Are you sure you have the phases of the dual primaries right?

[rccolgan]

Are you sure you have the phases of the dual primaries right?

I'm not sure but I'm Googling right now....

Edit.. I think you're right, Martin. Ugh.. I'll get a new PCB made

[martin manning]

Maybe you can cut some traces and add some wires to get it working?

[rccolgan]

Maybe you can cut some traces and add some wires to get it working?

Yup! That's my thought while new PCBs are being fabricated. Thanks for pointing this out!

[sluckey]

Have you seen this...

https://www.hammfg.com/files/parts/pdf/229B120.pdf

[rccolgan]

Have you seen this...

https://www.hammfg.com/files/parts/pdf/229B120.pdf

Yes. I see where my mistake was made. I got lost while trying to be clever. I'm directly wiring primaries tonight/tomorrow morning per the PDF. If this is the only mistake, I'll be really happy!

[rccolgan]

clipped the leads on the primaries from the PCB and wired up directly for 120vac mains. So far no popped fuse however I'm not getting voltage on the secondaries I'll try to figure it out tomorrow morning. Time for bed

[sluckey]

clipped the leads on the primaries from the PCB and wired up directly for 120vac mains. So far no popped fuse however I'm not getting voltage on the secondaries I'll try to figure it out tomorrow morning. Time for bed

Your secondary is wired wrong. As is, pin 7 and 5 are same phase so you will read zero volts between those pins. (Kinda like putting two batteries back to back.) You need to put a jumper between pins 8 and 5. Then take the output between pins 6 and 7.

[rccolgan]

Ah! Thanks so much for pointing this out... A few growing pains/life lessons here, for me. New, new PCB designed and sent to the printer. Meanwhile, I'll hack up the proto board and reply with the results.

[rccolgan]

It's alive! ~368VDC B+1 & B+3, ~251VDC B+2. I changed the 15k dropper to 1.5k and that seemed to raise the voltage appropriately with this power transformer. Sounds great! Now it's the usual figuring out if humming is introduced via ground loops or lead dress. Oddly, the bright switches can make the hum come and go depending on the combination. I'm getting 14VAC for the heaters but I don't thin that's causing anything because I lowered the voltage via the variac and there was no change.

I also really like the blend feature I added with just one of the Send/Returns. I can see that being useful with delays, reverbs, etc.

More to come!

[erwin_ve]

It's alive! ~368VDC B+1 & B+3, ~251VDC B+2. I changed the 15k dropper to 1.5k and that seemed to raise the voltage appropriately with this power transformer. Sounds great! Now it's the usual figuring out if humming is introduced via ground loops or lead dress. Oddly, the bright switches can make the hum come and go depending on the combination. I'm getting 14VAC for the heaters but I don't thin that's causing anything because I lowered the voltage via the variac and there was no change.

I also really like the blend feature I added with just one of the Send/Returns. I can see that being useful with delays, reverbs, etc.

More to come!

Brandon from Bludotone mentioned in one of his " Dumblelator how to build" tutorial the grounding of the pots to avoid hum. See: https://ampgarage.com/forum/viewtopic.p ... 625#p37625

[rccolgan]

It's alive! ~368VDC B+1 & B+3, ~251VDC B+2. I changed the 15k dropper to 1.5k and that seemed to raise the voltage appropriately with this power transformer. Sounds great! Now it's the usual figuring out if humming is introduced via ground loops or lead dress. Oddly, the bright switches can make the hum come and go depending on the combination. I'm getting 14VAC for the heaters but I don't thin that's causing anything because I lowered the voltage via the variac and there was no change.

I also really like the blend feature I added with just one of the Send/Returns. I can see that being useful with delays, reverbs, etc.

More to come!

Brandon from Bludotone mentioned in one of his " Dumblelator how to build" tutorial the grounding of the pots to avoid hum. See: https://ampgarage.com/forum/viewtopic.p ... 625#p37625

Thanks, Erwin!! This is very helpful. I'll try grounding the pots tomorrow in addition to using isolation transformers to make sure I'm not getting weird interactions between my amp & this unit.

[rccolgan]

Ok, good news! I figured out where most of the hum/ground loop issues were. I also ended up grounding the input & output of the "B" loop if no jack was plugged in. This reduced one source of hum. I grounded the front pots but that didn't make much of a difference in my build.

Another source of hum/noise was coming from B+2 wire. It was super sensitive and the extra noise would magically disappear if I, safely, pinched the wire with my fingers close to V1. A trick I learned from building pedals is adding .1uF cap CLOSEST to the component that's consuming the voltage to eliminate any parasitic noise introduced along the wire routing. I added a .1uf 400v cap at the tube and the noise floor dropped dramatically and any weird noises while bringing the drive/recovery pots down to zero were also gone after this trick. I don't think it will affect tone with such a low capacitance value.

I also dropped my heater voltage from 14.4vac to 13.4 (within +/- 10% of 12.6vac) by using the opposing diode pair in series with one of the heater wires method. I probably need a weaker power transformer however, I have other plans with this power supply powering more tubes in the future so I am working with what I have at the moment.

I am taking a break but I suspect the very last source of hum (splitting hairs) is coming from the heater wires which is the grounded pin 9 with this 12vac heater design. The wires go back to the power supply board and I suspect I should make these as short as possible and perhaps isolate them from any other ground point.

Has anyone done the .1uf trick to quiet your B+X before? Any adverse effects I'm not thinking of besides taking up space?

[Guy77]

Ok, good news! I figured out where most of the hum/ground loop issues were. I also ended up grounding the input & output of the "B" loop if no jack was plugged in. This reduced one source of hum. I grounded the front pots but that didn't make much of a difference in my build.

Another source of hum/noise was coming from B+2 wire. It was super sensitive and the extra noise would magically disappear if I, safely, pinched the wire with my fingers close to V1. A trick I learned from building pedals is adding .1uF cap CLOSEST to the component that's consuming the voltage to eliminate any parasitic noise introduced along the wire routing. I added a .1uf 400v cap at the tube and the noise floor dropped dramatically and any weird noises while bringing the drive/recovery pots down to zero were also gone after this trick. I don't think it will affect tone with such a low capacitance value.

I also dropped my heater voltage from 14.4vac to 13.4 (within +/- 10% of 12.6vac) by using the opposing diode pair in series with one of the heater wires method. I probably need a weaker power transformer however, I have other plans with this power supply powering more tubes in the future so I am working with what I have at the moment.

I am taking a break but I suspect the very last source of hum (splitting hairs) is coming from the heater wires which is the grounded pin 9 with this 12vac heater design. The wires go back to the power supply board and I suspect I should make these as short as possible and perhaps isolate them from any other ground point.

Has anyone done the .1uf trick to quiet your B+X before? Any adverse effects I'm not thinking of besides taking up space?

Hi Ryan, congrats on your great looking build.
Regarding getting rid of the last bit of hum with a .1uf cap; I use a .1uf cap (orange drop) off the B+2 ,screen tap for power tubes. Its located right after my choke and I send this to the heater wires were the 2x100 Ohm heater resisters meet. It elevates your heaters with some DC voltage and this makes everything dead quiet. I lifted my mine with 40v and it was dead quiet. I believe you can experiment with anything form 10v - 70v. Just change the resisters size that connects across the .1uf cap to change your voltages.

Here is the post that describes it all.
https://ampgarage.com/forum/viewtopic.p ... 5&start=30

I was curious, what type of diodes did you use to drop the heater voltage?
Thanks

Cheers
Guy