Dumble Bandmaster Gator UltraPhonix Build

[rccolgan]

Update: I fixed the trem tick by removing the trem-fix cap!! No idea why but this worked and I'm sticking with it. I also don't want to place another Mouser order so I added another 100k in parallel with the 100k cathode to get closer to the 56k spec. I like the way it deepens the vibrato.

Now it's just playing and getting to know her. A few shots of the Croc exterior and comparing to the Dumble I am attempting to emulate the look of. Note, the interior comparison pic is outdated with the latest mods

[martin manning]

Update: I fixed the trem tick by removing the trem-fix cap!!

Great! The tech note that Fender put out on the tick fix says to remove the cap, which was a previous fix, and adjust lead dress.

Do you have the filter cap grounds separated, i.e. is the preamp filter ground D separated from the others? In my Deluxe Reverb build I ran the trem tube cathode grounds direct to the B-C filter negative, and then ran a lead from there to the power tube cathode ground area. No ticking at all.

[rccolgan]

Update: I fixed the trem tick by removing the trem-fix cap!!

Great! The tech note that Fender put out on the tick fix says to remove the cap, which was a previous fix, and adjust lead dress.

Do you have the filter cap grounds separated, i.e. is the preamp filter ground D separated from the others? In my Deluxe Reverb build I ran the trem tube cathode grounds direct to the B-C filter negative, and then ran a lead from there to the power tube cathode ground area. No ticking at all.

That's great! I didn't catch that Fender's tech notes negated themselves afterwards.

No, I did not separate grounds between B/C & D but it makes total sense for ground partitioning. I got lucky that the lead dress was likely the cure in this case too. Next time I pull the chassis, I'll possibly separate out the grounds. Right now, I'm really, really happy with this build!

Anyone play around with 12AT7 vs 12AX7 PI tubes on the UP? I know the Bluesmaster has 12AX7. I'll play around with it myself, just curious.

[rccolgan]

My wife and daughter left the house for a bit to get a hair cut so I had some time to experiment with the UltraPhonix a bit today...

Unscientific tests and impressions through a 2x12 PRS closed-back JMOD cab loaded with G12-65H speakers. It's about the same dimensions as a Bassman cab.

12AT7 in the PI - Amp is big and bold but I found myself working the treble up near 7 or 8 to get anything sweet out of it. Notes release quickly.
12AX7MG (mid-gain) JJ tube in the PI - Now we're talking. More definition in the high end so I can roll it back a little. Overall much more fun to play.
12AX7 Sovtek in the PI - The amp is a fire breathing dragon! Cleans up nicely and when cranked, it turns into a tight SRV machine! Great sustain, gets your typical Fender bite even after rolling down the treble to 4.5. At loud levels, I turned the bass down to 0 much like how Kenny Wayne does with his. This makes me think that the circuit is accurate. FYI I'm using a 500k bass pot. I'll do some research what a 250k pot change would do but it's so good right now I am not really motivated. Plus the bonus that it matches KWS settings, makes me think I should just walk away and not get knob-position-paralysis.

Overall, this amp will be my #1 for a while! Covers so much ground with a single amp like my SSS #004 build. This is a little bit more fun to play (and carry at half the weight!)

Sound clips coming next once I practice up a bit.

[rccolgan]

Me again! I think I'm going to swap out the 500k bass pots to 250k after I played around with the online tone stack calculator. It looks like I can get a smoother sweep using the 250k on the low end which is exactly where this amp needs the fine tuning. The only down side is that the maximum bass will be less with the 250k but no one would ever use max bass on this thing.

6.4/10 500k bass = 10/10 250k bass

In the screen shot: Red = 500k, Green = 250k at the same midway position 5/10.

[Ariel Meyer]

Which might also explain the evolution to the skyliner tonestack, with 300k pots

[rccolgan]

Which might also explain the evolution to the skyliner tonestack, with 300k pots

Great point! I'm sure if I rolled off more bass via cathode bypass caps or something the 500k would be more interesting but 250k it is!

[Charlie Wilson]

What coupler value did you use for PI out?
CW

[rccolgan]

What coupler value did you use for PI out?
CW

2x .022uF on the PI out and .022uF after the mixing. I could probably lower this post-mix coupling to .01uF perhaps too

[Charlie Wilson]

Hmmm, I think you mean two .022 as the power tube couplers. I could be wrong. The output cap on the PI looks like a different sized cap than the two power tube couplers. I am guessing that you used a .1/200v? If so, use a .02. The cap across the trem roach is the same cap as the PI cap.
CW

[rccolgan]

Hmmm, I think you mean two .022 as the power tube couplers. I could be wrong. The output cap on the PI looks like a different sized cap than the two power tube couplers. I am guessing that you used a .1/200v? If so, use a .02. The cap across the trem roach is the same cap as the PI cap.
CW

Yes, you're absolutely correct. My apologies. I did use .1uf 200v there. 02uf makes way more sense in the trem tick fix and also would make even more sense on pi coupler spot. Time to update!

Thanks, Charlie! Will report back

[rccolgan]

What coupler value did you use for PI out?
CW

Hey Charlie, before I change out the part, are you referring to the AC Shunt capacitor in the PI feedback? .1uf 200v? I was reading up on that part and lowering the value will introduce more top end but also possibly cause more oscillation.. Just double checking. I'll dig through the original thread to see if I missed something about this component value too.

[Smitty]

Ryan,

Nice build and interesting thread. Can you share where you got the Ultra Phonix badge? Thanks.

Smitty

PS I had good success converting a few Bantam Bass Amps to UP. No tremolo to worry about.

[rccolgan]

Ryan,

Nice build and interesting thread. Can you share where you got the Ultra Phonix badge? Thanks.

Smitty

PS I had good success converting a few Bantam Bass Amps to UP. No tremolo to worry about.

Thanks!! And of course..
https://www.droplightind.com/products/badges

I asked them to scale down to 6" long and it's perfect. That's the same length of the fender logo I measured.

[Smitty]

Thx!