Rocket 1x12

[HeeBGB]

OK So I am starting said build in a very small Blues Junior 1x12 format. Chassis space is at a premium. Obviously a total deviation from the original layout. I am trying to move things as little as possible and still make it work. I cannot put the transformers front and back of the chassis like the original because there is not enough space on the chassis to put them that way. Problem is I can't go too far to the side of the PT because the OT will interfere with the speaker.

My question is How close can the PT and OT be without risking any noise issues?

[xtian]

You can put them right next to each other and use the headphone trick to find the positioning for least induced hum. You can get nice and quiet this way. Don't forget to consider all FOUR axes of movement: X, Y, and Z axes, and Z rotation. Tiny changes can make a big difference.

One amazing thing I noticed last time I did this with a plexi build was that after I had positioned the PT and OT with a couple inches space between them, and then went to place the choke between the two, the Z-rotation of the choke influenced the hum a great deal, without being wired into the circuit! The copper in the choke was bending the magnetic fields!

[ampgeek]

I always do the headphone/external amp trick before finalizing PT and OT location.

Are you familiar with that gig? Thought I would ask before going into the long description.

Just let me know!

Cheers,
Dave O.

[HeeBGB]

I have no idea what the headphone/external amp trick is

[xtian]

You can find a thread or two on TAG. Basically, apply 120vac to your PT primary (make sure all other PT leads are taped off or wired into place so you don't shock yourself or short your PT. OT primaries should not be connected to an active circuit. Connect your OT secondary (any tap) to a set of headphones. Now, as you position the two transformers near each other, you will be able to hear hum in the headphones. Loudest when lams and coils are in the same orientation, and trending toward zero when one is rotated 90 degrees.

[ampgeek]

I have also fed the OT ouput into another amplifier with speakers for even better acuity.

As Xitan mentions, don't forget about the Z axis if you go this route. I once did an 18W amp that wouldn't pass the headphone test no matter how I arranged them in the X and Y planes. It wasn't unitil I accidently tipped the OT ~ 30 deg off of vertical and it went DEAD quiet that I learned that it can make a huge difference.

Good Luck!
Dave O.

[Blackburn]

Hey HeeBGB, you have an idea what speaker you're going to use? If you can spare the scratch, I'd look into an ASW Elegante for the single twelve setup. I really dig my AC30TB/Rocket through that one in my home built 1x12 cab.

[HeeBGB]

Hey HeeBGB, you have an idea what speaker you're going to use? If you can spare the scratch, I'd look into an ASW Elegante for the single twelve setup. I really dig my AC30TB/Rocket through that one in my home built 1x12 cab.

I would LOVE to try one but atm I have more speakers than cash. I will probably go with a celestion of some sort. I have a number of good choices. I have a Celestion 70th anny, a Fane AXA12 AlNiCo, Celestion Classic Lead 80's and assorted Sammi Sound 40's AND some Greenbacks (vintage recone and British made reissues)

[Blackburn]

It's cool you have a Fane Alnico. I did a thread a while back about my experience with it. I would've kept mine if it didn't have bad cone cry. Very nice tone and very easy to drive. That's one nasty speaker! In a good way.

I'd go with that one, if it's good.

[Cantplay]

You can dope the surround and edge of the cone to control cry.

John

[HeeBGB]

I've had mine for a few years and had no issues with it. It's reasonably well broken in also. I am gonna have to get the amp built first. I am notorious for taking WAY too long to finish a project. When it's done I am gonna play it with different speakers and see what floats my boat.

[LeftyStrat]

I have also fed the OT ouput into another amplifier with speakers for even better acuity.

This is what I do. I have insulated alligator clips I hook to the OT secondary and hook the other ends to a phone jack.

Though if you do it this way, you won't find a no-hum orientation if the amp you're feeding is turned up, you're just looking for a huge falloff in hum levels.

[Blackburn]

You can dope the surround and edge of the cone to control cry.

John

Wish I still had it so I could give that a try, but I returned it promptly, not wanting to make any hassle of it. Too much money for imperfection. It seemed to be an isolated problem, though, as I've not heard ANY others express an issue like I had. Maybe I'll get another one day, but I really love ASW's service and quality.... And they're in Texas. I compared their Elegante to the Fane and the Fane was more snarly and aggressive, which is not a bad thing, but for the sake of a single, really good AlNiCo, I decided I was fine sticking with my Elegante and using the money for something else.