Yes, I layered Mu-metal, copper, and galvanized metal for the main part of the shield. I should have mentioned that. It was by far easier to build another chassis for the power supply and be done with it.
In my junk box, somewhere, I must have a Realistic phono preamp, dating back from the early seventies. It was quite compact, including the mains transformer and everything in a very compact package.
It didn't hum at all; it had a severely elevated noise floor, due mainly to the germanium transistors of the time, but the hum issue was perfectly solved thanks to the thoughtful mechanical configuration.
This means that it is possible to reduce this type of interference using only "cost-free" solutions
It didn't hum at all; it had a severely elevated noise floor, due mainly to the germanium transistors of the time, but the hum issue was perfectly solved thanks to the thoughtful mechanical configuration.
This means that it is possible to reduce this type of interference using only "cost-free" solutions
I get that, and I bet that it didn't have any inductors involved in the phono circuit. Most Phono circuits use CR, but hardly any these days except for a few, use LR.
True, two tins with empty space between them will work better than one tin with double thickness steel. Empty space is a lousy conductor of magnetism.
Instead of making changes to the transformer configuration/shielding, it might more advantageous/simple to alter the filter coils setup. It should have the same result, with a lower cost and complications
If it is feasible for the required inductances, you could wind your own inductors on gapped potcores.
I'm not able to wind inductors. 100mH are needed with low series resistance.
I found one on eBay who sold me matched pairs of resonable priced customs inductors. But the matching wasn't good enough.
So I went back to what DigiKey and Mouser have in stock.
A GOSS band around the periphery of a toroid reduces the radiated field substantially (10-20 dB), so if you are getting one custom wound for a project likrvtjis, it will make a difference. If you then rotate the transformer by +-60 degrees you will potentially get another 3-6 dB reduction in noise pickup. EI transformers can also have GOSS bsndd specified but they are never as quiet as a toroid.
I use a print transformer. I already made some test with moving the psu board (as far as possible) and found that lifting it a few mm reduced hum a bit.
I will now buy some mu metal - the filter is on a piggy back board, so I can easily wrap the Metal tightly around it.
BTW, what's GOSS band?
I will now buy some mu metal - the filter is on a piggy back board, so I can easily wrap the Metal tightly around it.
BTW, what's GOSS band?
Hello,
This a pair of mono riaa LCR phonostages made by Pultec in the sixties. On one chassis there is the power transformer, the input transformer, the LCR network and the output transformer and no hum.
Most diy copies back then ended up with hum, usually coming from the power transformer.
Original one all heaters AC, no big caps but all 4 tubes had their own RC network.
SO it can be done.
Greetings, Eduard
This a pair of mono riaa LCR phonostages made by Pultec in the sixties. On one chassis there is the power transformer, the input transformer, the LCR network and the output transformer and no hum.
Most diy copies back then ended up with hum, usually coming from the power transformer.
Original one all heaters AC, no big caps but all 4 tubes had their own RC network.
SO it can be done.
Greetings, Eduard
Attachments
Best is to put the turntable a fair distance away, like in the closet, and then orientate your thinking towards a dac and digital music files.
Hello,
Good idea to save money for future medical expenses if you plan to get old.
Greetings, Eduard
Good idea to save money for future medical expenses if you plan to get old.
Greetings, Eduard
It’s a metal band that is tightly wrapped around the outside of the toroid and it ‘captures’ any stray mag field from the toroid.
Get secondhand lead floats for fishing. Beat them flat for shielding. Won't lead stop magnetisme? Maybe you can find a used car bettery?
Cheers!
Cheers!
Lead shields gamma rays, but that's not my issue 😉 I still have some kilos of lead from when I did scuba diving when I was younger...
GOSS is Grain Oriented Silicon Steel. It is used for magnetic shielding, similarly to Mumetal. Perhaps it is more effective, or less expensive.
The copper flux belt works differently, it cancels most of stray magnetic field. It is a one-turn short circuit winding outside the transfomer core.
I think Bonsai meant a Gauss band: it is a conducting band acting as a shorting turn for the stray fields (and only for the stray fields)