Transformer layout symmetry?

[Rogue]

I did a search but couldn't find anything, although I'm certain it exists on here somewhere. So, apologies.

Everything I read says transformers as far away from the input as you can get them....PT being the most important. Yet, my Jet City 20h has the PT and OT on opposite sides of the chassis. The OT is right one top of the input. The amp isn't particularly noisy. As far as I away so are the 100 watters, and certainly Soldano's have transformers on both ends and it has gain aplenty.

So, what's the deal? How are they able to get away with it? I Kind of like the whole symmetry thing for both the looks and balance. Is it a PCB benefit? What's going on here?

Thanks

[roberto]

It depends on where the OT wires passes inside the chassis.

On the SLO, front to back there's the input, then V1, then the PCB and then the OT wires plus power tubes, then output jacks.

[JMFahey]

Input circuitry is inside a metallic box (the chassis), transformer is on the outside; you have a thick steel plate between them which to boot is grounded.

That stops 99% of the problem

As`said above, you still have to be careful on how/where you run the OT wires.

FWIW in my own amps, I run them "outside" for as long as possible, often passing inside through rubber grommets just by the output jacks and just by the power tubes.

So the OT may be a couple inches from input in a physical way, but electrically 10 (or more) inches away

[Rogue]

Thanks for the responses.

That all seems curiously simply. I mean, wouldn't Fender and Marshall have figured it out instead of having a cumbersome, unbalanced head?

SLO's are pretty clean. My Jet City is PCB, so clean, but the wires going from the tubes to transformer aren't thought out. They just go there behind the board with a wire tie.

So, if it's just thoughful layout, then what do we look for to keep the noise down on a OT that is on the same end as the input?

Or, is it Occam's razor, and the old school guys were going on theory and people attempted a more symmetrical approach and didn't realize a downside?

[Malcolm Irving]

If we twist the three wires to the OT primary together and all the OT secondary wires together, that will minimise how much they 'couple' into sensitive input circuits. Also, if the OT wires and input circuits are unavoidably close, we can cross them over at right angles to each other, again to minimize coupling. (Best to keep them as far apart as possible though.)

[rp]

This might be a good place to ask something I've always been curious about:

Any reason to not stick OPT wires in metal braid/snake for shielding, grounded at one end? Braided signal wire can knock off some of the sparkle, I've experienced it, but curious about transformers. I'm thinking the signals in the transformer leads are too high to be affected by any capacitance created by inserting in a braid.

I ask as I'm (slowly) building an amp w/ a board and the OT wires will run under it. I have large enough diameter metal braid on hand. Odds are it'll be fine, but it would be much easier to insert the leads in a shield before hand, rather than taking stuff apart if a problem shows up.

I've never seen it done guitar or Hifi. So either it's a worthless effort or even has negative consequences to the sound.

[briane]

I ask as I'm (slowly) building an amp w/ a board and the OT wires will run under it.

not a problem - done it a thousand times. or at least as high as I can count.

[epis]

Here is an image of my SLO build. I had a problem with positive feedback at high volume settings until I covered the primary wires of OT.

[/img]

[Rogue]

Thanks again for the comments. It's probably safer to do it the old school way.

[Rogue]

Here is an image of my SLO build. I had a problem with positive feedback at high volume settings until I covered the primary wires of OT.

[/img]

Really? That little cover fixed it even though the wires are exposed at nearly the same place?

[epis]

[/quote]Really? That little cover fixed it even though the wires are exposed at nearly the same place?[/quote]

Yes, it did stop the squealing.
At the first I wanted to make small L shaped "fence", but I would have to remove the OT to drill a few mounting holes for it in the chassis, so I gave up and just used that transformer cover (I used it while troubleshooting, it was first metal thing I saw on my bench, when I put it over the wires, squeal stopped )

[Gaz]

Thanks again for the comments. It's probably safer to do it the old school way.

Look at Hiwatts where transformers are on opposite ends of the chassis, but still distanced from the input circuitry. I think it's totally possible (and sometimes even more ideal than having the OT under the board) if your chassis is deep enough. If you have a 'shallower' Marshall style chassis I would also be tempted to keep the xfrmr layout Marshall-style.

[Rogue]

Yes, it did stop the squealing.
At the first I wanted to make small L shaped "fence", but I would have to remove the OT to drill a few mounting holes for it in the chassis, so I gave up and just used that transformer cover (I used it while troubleshooting, it was first metal thing I saw on my bench, when I put it over the wires, squeal stopped )

I find that fairly interesting. It's just hole in the chassis the wires comes through, right? If so it would seem to suggest it was angle of wires at the bend, is that what you are thinking?

[Rogue]

Thanks again for the comments. It's probably safer to do it the old school way.

Look at Hiwatts where transformers are on opposite ends of the chassis, but still distanced from the input circuitry. I think it's totally possible (and sometimes even more ideal than having the OT under the board) if your chassis is deep enough. If you have a 'shallower' Marshall style chassis I would also be tempted to keep the xfrmr layout Marshall-style.

I'm moving forward the old way until I'm more confident in understanding how the ones that get away with it, get away with it.



Thanks for all the replies