OT Placement Headphone Trick

Bitsleftover

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I’ve read several write-ups regarding the headphone trick where the advice is to connect ONLY the PT primaries direct to the mains and the OT secondaries to the headphones, scope or meter.
My (probably stupid) question is-
Why not hook up the PT secondaries to the 5Y3 and say the first B+ filter cap? Or at least the tube heater wires which would be drawing current?
It seems logical to me to include as many of the noisy components as possible? And connecting the chassis ground seems like a no-brainer as a safety measure, But both go against every set of instructions I’ve found.
I’m not arguing against a tried and tested method. I’m just interested in the whys and what-for”s etc that make up the education process.
Thanks as always for any guidance or light shedding.
Mick
 

tubedude

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It's magnetic coupling of the transformer fields that you're trying to minimize. The other components don't figure into the positioning much, being on the other side of the chassis, and electrostatic or electrodynamic, rather than electromagnetic.
Hooking up other components to the secondaries may not be safe either, as the power transformer position is not set in stone yet, and the leads are not fixed. This is part of the process.
Place the magnetic components on the chassis, power the PT primary, and move them all around to get it silent. When they carry more current, the field's might be larger/hummier, but the alignment of your iron is still optimized for the lowest possible hum, and the amp would be noisier in any other alignment.
I tape off the PT secondary leads hook up the primary then move the PT and OT all around to get the lowest level of hum. Then looking at where this will roughly require the rectifier and filters to be, i set down the choke in a likely spot and rotate it in all axis for minimum hum. Placing the choke will move the magnetic field and will require a slight readjustment of each piece of iron to re-acquire the null. Mark mounting holes for drilling.
Sometimes the OT has to be rotated in the Z axis.. this requires a piece of angle aluminum to secure it to the chassis.
My amps are point to point so I have great flexibility in moving everything around. Using turret/fiberboard or another construction style may impose limits on the placement of your iron. Adjust the best you can.
 

Mongo Park

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Connect your op transformer ground to your multimeter and the other lead to the 16 ohm tap or less if you don’t have 16. Set the meter to mili volts. This is way better than headphones trick
But not really what you asked.
 

wabashslim

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Dear OP - DO NOT DO ANY OF THE THINGS YOU WROTE ABOUT!!!!!!!
None of it makes any sense, first of all, and second you will blow yourself and all your equipment and possibly your house sky high.
You're not ready yet. Just play your guitar, get good, and get somebody who knows what they're doing to turn the screwdrivers. Of course, if you don't know anything about this stuff how can you judge somebody else's know-how? The world is full of B.S.'ers. Even the Beatles got taken in by Magic Alex, a nimrod if there ever was one.

And the rest of you guys - shame on you.
 

owlexifry

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Dear OP - DO NOT DO ANY OF THE THINGS YOU WROTE ABOUT!!!!!!!
None of it makes any sense, first of all, and second you will blow yourself and all your equipment and possibly your house sky high.
You're not ready yet. Just play your guitar, get good, and get somebody who knows what they're doing to turn the screwdrivers. Of course, if you don't know anything about this stuff how can you judge somebody else's know-how? The world is full of B.S.'ers. Even the Beatles got taken in by Magic Alex, a nimrod if there ever was one.

And the rest of you guys - shame on you.
ease up turbo..
he’s only asking questions, however silly they may be.
the whole point of him and us being here is to discuss amps in a DIY context.
nobody learns anything from being correct all the time.
we all have to start somewhere and ask the dumb questions. i do all the time.
a bit over a year ago my only soldering experience was modifying guitar pickup/wiring configurations.
my first amp build was a 2204/JCM800 clone.
despite hesitation and advice i’d read about it being a bad idea to attempt a high gain amp with no experience, it was a complete success.
and so were the other amp builds that followed.
had i listened to someone like you i would have never even attempted it.
 

MarshallHeart

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I’ve read several write-ups regarding the headphone trick where the advice is to connect ONLY the PT primaries direct to the mains and the OT secondaries to the headphones, scope or meter.
My (probably stupid) question is-
Why not hook up the PT secondaries to the 5Y3 and say the first B+ filter cap? Or at least the tube heater wires which would be drawing current?
It seems logical to me to include as many of the noisy components as possible? And connecting the chassis ground seems like a no-brainer as a safety measure, But both go against every set of instructions I’ve found.
I’m not arguing against a tried and tested method. I’m just interested in the whys and what-for”s etc that make up the education process.
Thanks as always for any guidance or light shedding.
Mick

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tubedude

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Y
Dear OP - DO NOT DO ANY OF THE THINGS YOU WROTE ABOUT!!!!!!!
None of it makes any sense, first of all, and second you will blow yourself and all your equipment and possibly your house sky high.
You're not ready yet. Just play your guitar, get good, and get somebody who knows what they're doing to turn the screwdrivers. Of course, if you don't know anything about this stuff how can you judge somebody else's know-how? The world is full of B.S.'ers. Even the Beatles got taken in by Magic Alex, a nimrod if there ever was one.

And the rest of you guys - shame on you.

You suggest the OP isn't ready yet. If you had looked at his posts, you'd see he's built an amp already and has some experience. Your statement that "none of this makes sense" and that you will "blow up your house" indicates you are not ready, don't comprehend the basic physics involved, and don't belong inside an amp.
This is a time honored procedure in the amp design process. If you don't understand what we are doing, asking questions is the appropriate response, not submitting alarming, the sky is falling posts.
 

Paul-T

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Perhaps there more be more radiant fields with more parts connected but the vast bulk will come from the PT. I was surprised how well the headphones trick worked even with a cheap pair of buds and the difference from a minor realignment can be significant.
 

tubedude

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Perhaps there more be more radiant fields with more parts connected but the vast bulk will come from the PT. I was surprised how well the headphones trick worked even with a cheap pair of buds and the difference from a minor realignment can be significant.
There are not more fields of radiation, but the moved iron distorts the geometry of the lines within it, so the lines in the field shift positions. We are effectively reshaping the field so that our OT is intercepting a part of the field with a smaller number of concentrated lines of force.
Congrats on successfully doing this. No matter what else we do to eliminate or abate noise, if this isn't done first, that hum level will always be there. This is why well designed amps are silent and mass produced factory amps, that position iron in a line, will hum.
 

Bitsleftover

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Ok. Most of the time, I just bite my tongue and accept the Ill-informed and patronising internet criticism from guys who don’t really know what they’re talking about as a trade off for the few that issue quality advice!

But I’m a bit bored, so here we go…

The Ballzz- Sorry I didn’t reply to your original post. I’m not of a generation that can communicate purely via emoji. That’s why I post using words. Are you the Gene Ballzz that”s attached himself to JohnDH’s attenuator thread over on the Marshall Forum? If so, then nice work! I think I remember some questions you asked early on that made me go WFT?!? But some things that are obvious to some, need to be pointed out to others.

Tubedude! Thank you for the fullness of your complete answer to my question. You’re a proper geezer!


Mogopark- Thank you. Somewhere within the shockbrothers forum was a post of yours explaining this method which made perfect sense. I couldn’t find it via the search function. But now I have! Excellent tip! Thank you!

Wabashslim- Thank you for trying to prevent me from blowing myself up. I will NEVER ignore, nor discourage anyone from shouting “STOP” if they think I’m going to do something stupid!
Rest assured though… Ive built a few amps, repaired quite a few and modded several. Ive done an awful lot of guitar repairs and mods. In my day job, I work on very HT systems as an aircraft engineer. Such as HT ignition systems, HF Radios and weather radars. (Non of them tube based these days regrettably, but all certainly much more capable of turning me or my lads to carbonthan a 50 watt guitar amp!
Ive twisted screwdrivers for over 40 years professionally, and maybe 50 years or so as an amateur.
Incidentally, Ive been playing guitar for nearly as long. I’m not sure what from my post made you assume that I’m a beginner… But Ive played as a gigging musician for quite a good few years in a number of styles and several bands. In fact… been there-done to-got bored of it, and stopped doing it.

Owlexifry- Thank you for jumping to my defence.
The ‘Silly’ element of my question is yet to be discussed, interestingly enough! I, like you, pressed ahead with a build that everyone told me was ridiculous, but following the very wise advice issued by the regulars of this group turned out, like your build….. perfectly.

Brave heart- What? If you don’t understand…. Don’t join in!
I’d send you some patronising emojis back, if I was a teenage girl. But I’m not. So…..**** it dude!

Corliss1 - You sum up the general ethos of this forum perfectly.

I occasionally instruct students during the course of my professional career.
One of my entry level ground rules is… There is no such thing as a stupid question,,,, only stupid answers.
I guarantee, that in a class of 100, if one person asks a (stupid) question…10 others are thinking the same thing. As a result,I welcome the stupid questions…They save time. And occasionally lives.

I often precede my TDPRI questions with “sorry if this is a stupid question” simply because of the superior knowledge level in the group I am asking. I know my questions must be tedious.
But if people are discouraged from asking quesations…especially safety related questions, simply for fear of being ridiculed, then I think the entire forum should be shut down!

Paul-T - Always nice to hear from you. Thanks for the PT! Encouraging to hear you experienced some good results from this process! You are a Gent!

Anyway…In. The spirit of the season….Peace and good will to all men.
 




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