Transformer placement

[zpyder]

Is placing two or more transformers close to eachother on a board a bad idea?  Or close to other components or wirse for that matter?  Noise bad... tone good...

zpyder

[Rafa]

Technically I have no idea but:

Cheers
Rafa

[zpyder]

bump...........

[petemoore]

  Me neither really
  IF they have a shield running across the top, from what I understand it's two of the sides which are better shielded so noise comes out in an angle pattern like   >l< with the 'l' being the core or shielding, the arrows indicating the angles at which the most activity takes place outside the transformer. I might have this a 1/4 backwards also..
  1/4 turn...as in the PT of an amp and the OT of the same amp are sometimes placed adjacent one another, or near, notice 1 of the two is often turned 1/4 turn when looking from the top, one field is bad, two fields interacting is worse...
  Positioning and orientation of PT/OT placements on tube amps has been explained once...on a 'new' layout as something that can be done testwise...leave the bolts loose, connect the tranny's and try orientations to 'tune' them for lowest noise...not something I'd recommend as safest HV method, but what I'd probably do w/insulated gloves 'n sneakers w/ left hand in back pocket..and 'grommet' around the tranny wiring hole.
  Otherwise I'd try orientations or just go with having one of them turned 1/4 turn from the other, looking down from atop.
  As to the other questions about noise, prototyping is the only real certain answer to them, but what circuit and how used may help sort it out too.
 

[R.G.]

Is placing two or more transformers close to eachother on a board a bad idea?  Or close to other components or wirse for that matter?

There is no substitute for knowing the details.

Case 1: both transformers transmitting the same signal. It largely doesn't matter, place them as you will.
This might be two power transformers. Or two signal transformers carrying the same signal to different places/levels.

Case 2: different signals in each transformer. This may be a disaster if the circuits following the transformers are sensitive to the same range of frequencies, or may not matter if the following circuits are insensitive to the frequencies carried by the opposing transformer.
(a) power and signal transformers - potential disaster; the power line stuff can be magnetically coupled into the signal to be further amplified
(b) power and RF transformers - doesn't matter much because following RF circuits are insensitive to power frequencies
(c) different audio signals - cautionary. You can get crosstalk if you are not careful.

Each style of transformer core has its own magnetic leakage field shape. For instance, in E-I transformers, it's worst in the direction of the middle tongue. This is what leads to the orientation of power, choke and output transformer tongues in three different directions in tube amps.

Toroids have lower leakage overall, and the leakage is along a radius of the donut.

[zpyder]

Thanks RG!  I'll go ahead and put those transformers for an isolated splitter right next to eachother on the layout then!

zpyder

[mac]

A PRIORI a guy named Ampere would say 'do not place them near each other' because the magnetic fields H1 & H2 will interact.
But it depends on how strong the Hs are, ie, the amount of current through the transformers T1 & T2, the geometry of the transformers and if they are shielded.
If vector H1 has a component perpendicular to the area enclosed by T2 wiring then it will generate a current in T2 modifying it own H1, which in turn can do the same thing with H2.
H1 -->     Area2 <--((-)) T2 wire.
And do not trust that placing some metal separator between them will isolate them completely. When a magnetic field H reaches the surface of a metal some or all of the energy is lost because it generates currents in the metal. It can be proven that H intensity decreases exponentially in the direction perpendicular to the surface. If the metal is thin enough some amount of H will leave the other face.
About the geometry, toroidal Ts keep most of H inside them being more 'efficient' than normal ones. You can check this by placing a screwdriver near them. You'll feel the 50/60hz in some directions and nothing in others. This can give you an idea of H's intensity and direction outside T.


mac

[petemoore]

  Silly hijack or idea?
  Each style of transformer core has its own magnetic leakage field shape.
  Maybe 'mag/audio' probing with a magnetic tape head [a'la cassette playback head?] connected to a monitor would be of some use to...say someone working out a different chassis layout on a tube amp?..and would show where the noise is 'output',
  A Reverse testmethod would be to wire up an unwanted noise proDucing tranny, and wave that around to see where/from what angles the signal transformer picks up that unwanted 'schtuff' best and worst...indicating where the transoformer works best as a 'pickup.
 

[Ronsonic]

In general, the best location for a pair of transformers where you want to avoid interaction is as far away as possible and at an angle to one another that will be determined by monitoring one of them on your oscilloscope. This is usually a somewhat funky angle. You can also monitor with an AC meter of some sort. Usually the issue is a power tranny and an output. There you apply power to the, uhhh, power tranny driving a dummy load and look at the primary of the output as you move it around. If it's practical you can also do the whole build except for drilling and mounting the output tranny and monitor the output. This is a lot of work for building one amp.

Here's where it gets interesting: you want the power tranny as far from the high gain input circuitry as you can get. You also don't want the opt parked right over the inputs either. so you compromise. Also the thing has to balance and most people want the handle of their amp somewhere near the middle.

So now you have other criteria, balance and keeping both trannies away from the inputs. There's also a design aesthetic, people think it's funny to have their trannies at weird angles. SO..... on the gripping hand, the universal, second-best position that you don't need a scope or any particular planning to get a good result from is to have the trannies at a 90 degree rotation from one another in at least one plane. The traditional use of a laydown power tranny and a standup OPT gives you two planes. Having two standups, like an old Marshall or two laydowns like an old ampeg also works, just have them rotated at 90 in either case.

Hope this helps.
Ron

[R.G.]

A PRIORI a guy named Ampere would say 'do not place them near each other' because the magnetic fields H1 & H2 will interact.

A bigger "if" is if they are carrying different signals - see Case 1. In zpyder's usage, they are both carrying the same signal, so if they interfere, it's impossible to tell, and does not matter.  This particular "A PRIORI" only matters when different signals are present and therefore can interfere.

Maybe 'mag/audio' probing with a magnetic tape head [a'la cassette playback head?] connected to a monitor would be of some use to...say someone working out a different chassis layout on a tube amp?..and would show where the noise is 'output',
  A Reverse testmethod would be to wire up an unwanted noise proDucing tranny, and wave that around to see where/from what angles the signal transformer picks up that unwanted 'schtuff' best and worst...indicating where the transoformer works best as a 'pickup.

Good idea, Pete. Both techniques are longtime standbys for old tube techs. You can do the pickup with a tape head or with just a loop of wire on a scope lead for some high-emissions power transformers and RF.

The other reason to snag a cassette tape head is that you can use it to trace shorted wires by putting a signal current through the wire. The tape head on a scope or just an ampliifer will let you follow the wire ... or PCB trace.

[Tubebass]

on the gripping hand

Been reading Niven and Pournelle, I see.

[mac]

There is a say in high precision measurement quantum physics labs: the best transformer is the one placed at the infinite in a big iron safe at 0ºK... and not conected!
I stick to my big A PRIORI



mac

[R.G.]

There is a say in high precision measurement quantum physics labs: the best transformer is the one placed at the infinite in a big iron safe at 0ºK... and not conected!

Yessir, that is absolutely correct - in a high precision measurement quantum physics lab, that is absolutely the best place for a transformer.

The rest of the world must make do with figuring out how to use the poor, sick, weak, interfering transformers that we have to use. 

[Ronsonic]

on the gripping hand

Been reading Niven and Pournelle, I see.

Any kind of design decisions, you just run out of hands, otherwise. So many conflicting desiderata.

It's a great, if somewhat nerdish way of boiling it all down. Kinda figured a bunch of pedal geeks and amp mechanics would get the ref.

Ron

[mac]

The rest of the world must make do with figuring out how to use the poor, sick, weak, interfering transformers that we have to use.

It depends on the lab's budget... I rememeber that any marshall had better transformers than the ones we had.
The only way to make them less poor, sick and weak was to put them into a portable oudoor freezer and keep them 'cool' with N2 or dry CO2...

I do not suggest to do this to increase the efficiency of your amp's Ts, your valves will not like it 


mac



mac