Slight hum at all times

[Gaz]

I totally believe that rotating the transformer solved your hum issue, but I don't see how rotating the OT 90 degrees would change anything according to Paulster's diagram?

[paulster]

The PT will still generate a field the same but the susceptibility of the OT to it will vary dramatically with orientation and placement.

Read up on the 'headphone trick'. It's a great method for finding the sweet spot for transformer orientation when designing new amps.

[Gaz]

Yeah, I always use the headphone trick, but do orient my transformers like in your diagram for lead dress convenience.

It seems then, like the diagram you posted is overly simplistic, seeing as the OP's hum-free setup now still reflects the drawing. Can you explain why put the secondaries closer to the PT may have helped? I genuinely curious because I've always done it the OP's original way, only with the transformers spread mch further apart.

[amplifiednation]

Nicely done. Shielded coax on the input and getting the 33k off the board helped with my hum.

[paulster]

Consider that if a transformer leaks magnetic flux in one orientation it is also likely to be most sensitive to having magnetic flux coupled to it in the same orientation. So that's why having one at 90 degrees to the other helps.

This isn't really having the secondary side facing the PT at all, as both the primary and secondary will be interleaved on the same core. It just happens that the secondary leads exit on this side of the core.

If the OP actually means he rotated the transformer 180 degrees (since 90 degrees would mean he had it in the wrong orientation in the first place) then it's down to the particular winding pattern and construction on this transformer and also probably being placed a little further from the PT within the confines of the mounting bracket slots, which can make a reasonable amount of difference.

[M Fowler]

I truely believe that if your follow the build guide and place your PT/OT the way Ken F. did then there shouldn't be noise.

If you rotated your OT 90 degrees then you had the laminantions facing each other to begin with which is a no-no.?

Mark

[paulster]

I truely believe that if your follow the build guide and place your PT/OT the way Ken F. did then there shouldn't be noise.

There will be some, but it won't be bad, and certainly nowhere near the level of the hiss.

It's been reported on originals and clones, and is down to the confines of the small chassis and the big PT.

Having the OT core parallel to the PT core is really asking for trouble though.

[Gaz]

Paulster, no confusion actually - I read 90 degrees, and thought 180 because it sounded like the OP had his trannies placed like a Wreck to begin with, with the laminations at 90 degree angles. I guess he was much worse than your diagram to begin with.

I'm going to have to try turning both transformers on my next build 90 degrees, so it's not like the diagram with headphones attached. Very interested to see if there's a difference. If so It seems like one could get away with moving the iron a little closer together.

[M Fowler]

There is not much room for moving trannies around on a traditional TW build.

The front wood valence means you have to be back at least 3/4 from the front of the chassis unless your using thinner wood there and you need to watch the side spacing as well.

The PT and OT are darn close on a TW.

[keewee]

Hey, I don't mean to barge in on the thread but I have the same or similar problem on my rocketBUT when I rotate my chassis with control knobs up nearly all humm dissapears!! I'm thinking about maybe building a vox style cabinet. I am nothing close to an engineer/scientist and find this interesting. Any ideas??

[paulster]

when I rotate my chassis with control knobs up nearly all humm dissapears!!

If you don't have a bottom plate on then repeat the experiment with the bottom plate on and if it's fine then you've solved the problem.

You've got a source of noise somewhere in the room that the amp is picking up. CRT monitor perhaps? Or something with a reasonable sized transformer in it?

[keewee]

Thanks for the info Paulster, yeah havn't got the pale yet, I was kinda suspecting that. Thanks again

[solderstain]

Here's something that no one really mentioned, but it's a possibility that some of us deal with: the quality and age of the wiring in your house/rehearsal room, etc.

I live in an older house, and the wiring was done when wiring codes were different. Every amp I own has a little background hum, and it drives me NUTS! And... it comes and goes, sometimes it's worse than others, and sometimes it's gone altogether. Amps I've owned for years in different areas of the country buzz here. Sometimes when I play on a Saturday afternoon, the buzz is virtually gone, and playing on a Tuesday night becomes torture.

It drives me nuts as a builder! I've been building amps since 1978, so I know what I'm doing and have good build practices. But every time I build something new, I drive over to a friend's house who lives in a much newer neighborhood and play it there, just to satisfy myself that I didn't accidentally do something silly (even when I 'know' I didn't). And yes, my recently-completed Express build buzzes here, and other than the expected tube amp 'hiss', it's quiet as a church mouse at my buddy's house.

This won't be a problem for everyone, but some of us here have to deal with that.

[bandade]

Good point on the AC Power. I have experienced this when plugging in at certain locations other than my own. I believe a power conditioner may solve the problem but I dont know for sure because I don't own one.

[RJ Guitars]

Do we think this is a power ground issue or more specifically, a ground issue in your home wiring?