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Old 24th January 2007, 03:03 AM   #1
hotscot is offline hotscot  Scotland
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Default Opinions on Options

I built my first Gainclone from Brians basic LM3875 kit and I'm very pleased with the results such that I now want to tinker more.

Currently I have the two amps and the transformer in one single very cheap metal case.

I'm interested in qualitative opinions on the improvement in quality by respectively,

1. Putting the transformer into a separate case.

2. Putting the single transformer and two amp boards into three separate cases.

3. Buying another transformer and going the monoblock route.

Regards
Alan
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Old 24th January 2007, 08:42 AM   #2
Nuuk is offline Nuuk  United Kingdom
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Option 3 is the only one likely to result in an audible improvement IMHO!
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Old 24th January 2007, 08:57 AM   #3
Nordic is offline Nordic  South Africa
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I have had little lcuk bringing my EI core too close to the amp... toroids will work better.... but I think if you want to go full tilt, I would stick with 3 boxes keep one for the 2 power supplies... in one, and the monoblocks in the other two.
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Old 24th January 2007, 09:26 AM   #4
lineup is offline lineup  Sweden
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Quote:
Originally posted by Nordic
I have had little luck bringing my EI core too close to the amp...
toroids will work better....

but I think if you want to go full tilt, I would stick with 3 boxes keep one for the 2 power supplies... in one, and the monoblocks in the other two.
this is correct.
Old square EI type transformers have somewhat higher level
of electromagnetic radiation field around them
Toroid also radiate, but not as much.

1. No transformer should be put too close to Input of amplifier
or near unshielded input / supply wiringd
2. Especially old EI types, I would put at least 20-30 cm away
in a box:
put input circuit in one end .. and transformer in other end
3. Of course this is more important, The Bigger transformer is.

Small trafo - little radiation
Big Trafo - big radiaton .. evenso from Toroid!



Main 2 differences between EI-Type and Toroids:
EI-types: more electromagnetic radiation
Toroids: more peak inrush currents at Switch On and so initial Capacitor Loading currents


.. may be a few more differences,
but those are what I know are the main things to consider


Regards, lineup
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Old 24th January 2007, 10:49 AM   #5
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Default Toroid options, shielding.

I'm using an RFI and EMI shielded Plitron 300VA toroid for the given reasons. Also am shielding the trafo real estate of the enclosure with TI Shield and enclosing the mains and supply wires in copper mesh tubing. While paying attention to layout as is possible in a small enclosure, this combination works like a charm.

The Plitron is special order; don't know where else you can get the RFI and EMI options. The TI Shield and copper braid tubing can be purchased from Michael Percy.

George
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Old 24th January 2007, 01:36 PM   #6
CarlosT is offline CarlosT  United States
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Toroids biggest most magnetic field in the z axis or straight perpendicular from the center of the doughnut. This means that it's important to route wires around the tranny and not over them. You can prolly place a toroidal tranny very near an amp board side by side with little adverse effect. Matter of fact, I would think that long leads of any kind inside a chassis prolly cause more noise and grounding problems than sweating out where yoou place the tranny.

Now as far as RFI...a strict interpretation of that would mean radio frequency and that has little to do with a tranny operating at 50Hz/60Hz. If you truly worry about RFI, then consider the leads in your chassis (and your power cord externally) becoming antennae and picking up stray RFI from the air. Twisting the wires can help to reject RFI. Adding a Corcom power jack or a ferrite may also help for the power cord.
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Old 24th January 2007, 01:39 PM   #7
CarlosT is offline CarlosT  United States
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A metal belly band is recommended to cut down on EMI from toroidal trannies. This could be a simple piece of copper tape or something more elaborate made or beyllium or some other boutique metal. Overkill?
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