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Magnetic shielding of trafo inside Leben amp - Page 2

post #16 of 25
Thread Starter 
Quote:
Originally Posted by jcx View Post
 

don't destroy the xfmr's bobin, insulation soldering the belly band - may even want a wrap of kapton tape to maintain creepage/clearance distances if it is a pcb pin mount style

 

 

mu metal is not needed/useful anywhere near a line power transformer - mu metal saturates easily - only used to case very sensitive components - knock the mag field down by shorting with cheap iron 1st

 

while a box with more sides is better for shorting the leakage mag field - just a strap bent in a U as much taller than the xfmr as fits should help a lot

 

1) Kapion tape as a layer between the copper and the trafo to protect it, will it take the heat?

 

2) Are you suggesting a upside iron U over the trafo?

 

Sorry my ignorance - but I am a total novice at this stuff :) But if we sort this out, the new Leben mod will be legendaric :D

post #17 of 25
Quote:
Originally Posted by ardilla View Post

1) Kapion tape as a layer between the copper and the trafo to protect it, will it take the heat?

Kapton tape is often used as a masking material during wave soldering, so yes, it will take the heat from a transformer. biggrin.gif

se
post #18 of 25

I am more worried about electical insulation between the pri-sec pins if the belly band comes close and also about the heat from soldering the belly band - the wide, heavy copper will soak up and spread a lot of heat - especially if you don't have a big enough soldering tool and experience in soldering big stuff

get it hot enough while soldering the ends together and it could ruin the bobbin, wiring insulation

 

base of a U magnetic shield would be between the power and output xfmrs, blocking them from "seeing" each other as much as possible, arms paralleling the power xfmr body - do leave air space


Edited by jcx - 10/22/13 at 8:14pm
post #19 of 25

Hi ardilla

1.I am impressed by the amount of generous advices you have managed to extract from some of the big names and experts in this area!

2. Since you live in a country with symmetrical net supply (or whatever it is called), have you tried to turn the contact 180 degrees? It COULD have some influence on the hum level. ( I am notoriously lazy, so I always try such simple things first of all).

3. Since there is some space to the left of the mains transformer, maybe a simple “wall” consisting of a piece of  ordinary iron would be enough to deflect the waves enough to reduce the hum to below audible levels.

4. You are welcome to take contact (I live rather close*). I have copper foil and soldering equipment etc, and am always somewhat entertained by trying to solve this kind of problems.

 

 

*Bare noen få kvartal, for svingende!


Edited by chetlanin - 10/23/13 at 8:50am
post #20 of 25
Thread Starter 
Quote:
Originally Posted by chetlanin View Post
 

Hi ardilla

1.I am impressed by the amount of generous advices you have managed to extract from some of the big names and experts in this area!

2. Since you live in a country with symmetrical net supply (or whatever it is called), have you tried to turn the contact 180 degrees? It COULD have some influence on the hum level. ( I am notoriously lazy, so I always try such simple things first of all).

3. Since there is some space to the left of the mains transformer, maybe a simple “wall” consisting of a piece of  ordinary iron would be enough to deflect the waves enough to reduce the hum to below audible levels.

4. You are welcome to take contact (I live rather close*). I have copper foil and soldering equipment etc, and am always somewhat entertained by trying to solve this kind of problems.

 

 

*Bare noen få kvartal, for svingende!

 

Thanks a lot :) I will definetly take you up on number 4 there :D

 

I'll try the 180 fase trick - I think I have tried it before without any result. 

 

An iron wall was what I originally had in mind, and maybe I just should get hold of a fitting piece of iron and stick it down to see if it helps. 

 

Heres the inside f the amp, from underneath (bottom lid off - upside down)

 

post #21 of 25

Just an FYI, but you should terminate the tape and  grounded soldering joint on the laminations.  The heat transfer is sinked a bit better there.

post #22 of 25

looks to me like poor power supply wiring/parts placement - the black square "puck" is the bridge rectifier - the noisiest part - too close to the amp, wires not tightly twisted entering and leaving, no snubber parts soldered directly to its terminals

 

may even be a 2nd supply(V doubler?) with the discrete diodes and C over the vent hole pattern


Edited by jcx - 10/24/13 at 8:51am
post #23 of 25

The copper band goes on before the transformer bells.

 

If you can find a picture of an old dynaco 400, that is what

they had to do to prevent stray fields from getting into the left channel.

post #24 of 25

So, Ardilla, did you do the mod?

post #25 of 25
Thread Starter 
Not yet. Been too busy with less interesting stuff. But I am very tempted =D
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