well that sucks. headphone trick issues

[wsaraceni]

i just did the "headphone trick" it seems the only place i don't get hum on the transformer is either right above the input jack or right above where it is in this picture.

the place where the chassis had a transformer spec'd is actually the noisiest place. no matter what the rotation is.

[img:764:1024]http://img.photobucket.com/albums/v217/ ... b5f69b.jpg[/img]

so i can place the OT here. it'll make me move that nice resistor i just mounted underneath while i was waiting for parts to come in, but thats no big deal, and only 3 holes. and i was thinking, to make the back panel a little nicer, i could just make the holes 16-16-8-8-4 instead of using a impedance selector.

but what do you guys think of this layout. really anywhere middle half worked but this place and right over the input jack worked best.

this does put it pretty close to the preamp tubes, no matter what the layout is.

[surfsup]

The OT induced hum is not going to be amplified, somit won't increase with the volume knob on the amp FYI. so if it is minimal somewhere away from the PT, you might want to mount it somewhere away from theinput jack. The OT is going to have basically all the amp current running through it, so it would be better to put it somewhere else, but ultimately its your build.

Lets see what some others say...

[wsaraceni]

Thanks. It,s very loud where the in the back corner of the chassis. If I put it near the other back corner it is close to v2. Not sure if that is an issue or not

[wsaraceni]

[img764]http://img.photobucket.com/albums/v217/ ... d0aa98.jpg[/img]

[img764]http://img.photobucket.com/albums/v217/ ... 76f932.jpg[/img]

[Cantplay]

Is there room to put it under the chassis? It might be quieter in that plane.

Or maybe on its side. Try lt lying down?

John

[wsaraceni]

can't put it underneath. i'll try it on it's side but not sure how that would work. i'd have to cut a hole for it and use brackets?

[paulster]

Do you have enough lead length on the PT to rotate it by 90 degrees if you still bring the wires up through the same holes? Then try the OT back behind it and see how it goes.

Try also using the OT at 45 degrees, if you haven't already, which can help sometimes.

[diagrammatiks]

you should turn the power transformer.

flux leaks perpendicular to the laminations.

[Jana]

I wouldn't put the OT right over the input jack--sounds like an oscillation disaster waiting to happen.

Maybe try taking a piece of sheet metal (ferrous material) about 4 by 5 inches and see if you can find the magic spot with that as a shield between the PT and OT. It will have to be in contact with the chassis while you do this. I have seen something similar done on Blues Junior amps to quiet the hum.

[Phil_S]

you should turn the power transformer.
flux leaks perpendicular to the laminations.

+1 on that. I didn't realize about flux leaks. I was going to say, just turn it and a you open up other possibilities.

[wsaraceni]

unfortunately i didn't realize it would be this big an issue and the PT doesn't have long enough leads now if i turn it 90 degrees. plus, even if i place the OT on the other side of the PT but still close to it, i get the same hum. its almost like i need a good 4 inches in diameter around it.

i should add, that in these pictures, its not above the input jack. it is just close to the tubes. i'll try a shield between the two.

how far should i be away from a preamp tube if i put it on the other side?

i can put it right where the choke is in the first picture. there is minimal hum there. then i'd have to figure out where to put the choke.

i guess this is a good reason not to buy pre-punched chassis in the future for unknown builds

[epis]

This is what I would do :

[diagrammatiks]

you know after you fire it up I doubt it'll be that much of an issue at all.

the pushpull power stage will cancel out most of the hum.

You just want to make sure you output transformer leads don't cross your small signal leads so just push them towards the other end of the amp.

But for future reference it's good to remember that transformers leak flux perpendicular to the core. This is why mounting the transformer perpendicular to the chassis like the old fender/vox/marshalls is a bit quieter so that put the laminations parallel to the amp and the leakage is only above and below the transformer.

In your case though, I don't see why having the ot where those other holes are already drilled would be noisy...

[xtian]

We should add to the Headphone Trick FAQ: The idea is to MINIMIZE the hum you hear, not eliminate it entirely, which is sometimes only possible by moving the OT off the playing surface entirely. YMMV!

[wsaraceni]

i have a few questions to see if i am doing this correctly.

does the metal from the OT and Choke need to be touching the metal from the chassis for it to work best?

does this sound ever get amplified? could i just hook an actual speaker cab up to the OT to determine how much hum is coming through. It may be a lot less than what i hear in a set of headphones.

how should the headphones be wired to the OT and to the Choke? should i have a mono jack hooked up so that i only hear the hum in one speaker? i think i have a stereo jack now and have one lead to the black of the OT and one to the 16ohm tap. on the choke, i get one lead into each.

sorry for the questions. it just seems weird to me that the hum is crazy loud when sooo many other amps have the same layout