Finally, an affordable CD Transport: the Shigaclone story

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dzuvela

Member
Joined 2007
jitter said:


There's indeed a good reason for that. The most important reason is the "appliance class" as specified by IEC. This has to do with electrical safety and depends on the strength of electrical insulation (please read this wiki for explanation). The boombox came with a 2 conductor power cord, and therefore will be class II (the label on the back will probably show the European double square symbol), no earthing is required.

Another good reason not to use earthing is the fact that protective earth (PE) can be very polluted, you don't want this pollution to find its way into the chassis. That's probably why most audio and video appliances are constructed for class II compliance. Note: class I appliances must be earthed for safety reasons, whether you like it or not.
The pollution of PE can be so bad that buildings in which electronics are manufactured have a separate earthing system for the EPA-zone (EPA = Electrostatic Protected Area). This earth is often called "clean earth". "Clean earth" and PE are connected at one point only (just like digital and analogue GND are also connected at one point only).

Note: earth (UK) = ground (US). Do not mistake "signal ground", "chassis ground" and "earth ground" for eachother, even though they may be connected.



It's the signal ground of the circuits, usually that is connected to the chassis.
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Hi Jitter. Feel that I have to place remark here.

Boombox is class II appliance this is true. Class II here is achieved by plastic case.
Once we take mains tranformer out from boombox or use any 3rd trafo which is mount in ours DIYs metal boxes, class II is not satisfied anymore.
Such appliance is class I now and we do need earth wire, polluted or not. Just as you point above.

Guess it is important that people here are aware of that fact.
 
jitter

jitter

Member
Joined 2004
No, not necessarily. Even a metal casing can be constructed to be class II compliant. Actually, nearly all audio/video equipment has a metal casing without earthing.

If you put the boombox transformer in a metal casing and route and/or shield the mains carrying parts in a such a way that the casing can never get mains potential, it will comply with class II.

I may still have a book about this stuff, if I can find it, I'll look up the precise regulations.
 
jitter

jitter

Member
Joined 2004
Complying with class II is not difficult either. Just take a look at your amp or CD player.

Not 100% sure but I believe a strain relief and a minimum distance of 6 mm between mains carrying parts and the rest (incl. casing) is all that's needed...

A class II aplliance is safe when plugged into an unearthed wall socket (of which there are still plenty is this country), a class I is not (unearthed class I appliances are essentially as unsafe as class 0 appliances!).
 
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leoparleur

Member
Joined 2007
jitter

jitter

Member
Joined 2004
leoparleur said:



Also, here is a picture of mine. Notice weldings in each corners.

http://cid-54ea5cde40dc26de.skydrive.live.com/self.aspx/Shigaclone/transformer voltage.jpg?ccr=1746
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I'm a bit surprised to see this, and at the same time I'm not. This will probably be a horribly inefficient transformer, but it was very very cheap to make (they even saved time by not using the screw holes). HP probably negotiated a very very very low price from the factory that made these transformers for them.
 
kevinkr

kevinkr

Administrator
Joined 2004
kta-hifi.net
Paid Member
jitter said:



I'm a bit surprised to see this, and at the same time I'm not. This will probably be a horribly inefficient transformer, but it was very very cheap to make (they even saved time by not using the screw holes). HP probably negotiated a very very very low price from the factory that made these transformers for them.
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I have actually tested very similar transformers with welded lams vs unwelded lams, (100 - 300VA) and the difference in efficiency I noted was pretty small. Contrary to popular opinion lams in most N.A. EI type power transformers (at least) are not really well insulated from each other, and while there are resulting eddy current losses, these losses did not seem to be particularly high in properly constructed transformers. (Interleaved and evenly stacked cores filling the bobbin window fully.) The quality of the material used in the laminations seemed to be more important than whether or not there was a shallow weld on the surface of the laminations. The welded cores tend to be quieter as the multiple welds are pretty effective in reducing the audible effects of magneto-striction in the core. Note that the welds are generally (supposedly?) perpendicular to the existing current loops in the core.

I suspect most of the objections raised to welded lams are practically irrelevant at line frequencies.
 
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leoparleur

Member
Joined 2007
jitter said:



I'm a bit surprised to see this, and at the same time I'm not. This will probably be a horribly inefficient transformer, but it was very very cheap to make (they even saved time by not using the screw holes). HP probably negotiated a very very very low price from the factory that made these transformers for them.
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Jitter, you're scaring the hell out of me! ...ok, ok I'll purchase the Hammond.:D

But since I'm hard headed, I'll probably give this runner a chance.

Thanks Kevinkr also.
 
jitter

jitter

Member
Joined 2004
kevinkr said:
I have actually tested very similar transformers with welded lams vs unwelded lams, (100 - 300VA) and the difference in efficiency I noted was pretty small. Contrary to popular opinion lams in most N.A. EI type power transformers (at least) are not really well insulated from each other, and while there are resulting eddy current losses, these losses did not seem to be particularly high in properly constructed transformers. (Interleaved and evenly stacked cores filling the bobbin window fully.) The quality of the material used in the laminations seemed to be more important than whether or not there was a shallow weld on the surface of the laminations. The welded cores tend to be quieter as the multiple welds are pretty effective in reducing the audible effects of magneto-striction in the core.
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I may have an explanation for this. I think most of my earlier reasoning was flawed. After looking again at the wiki drawing I noticed that the eddy currents are revolving around the magnetic flux at a 90 degree angle. The eddy currents do not circle in the long part of the laminate (that's the magnetic flux), but in the NARROW part (look at the drawing again)!
Since there is only a weld on the outside of the core, and none on the inside, the eddy currents have no choice but stay in their own laminate.

Theoretically welding the whole outside of the core together would still have no effect on the eddy currents.

Note that the welds are generally (supposedly?) perpendicular to the existing current loops in the core.
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It's perpendicular to the magnetic flux, not to the eddy currents. The weld is placed that way as it's the only way to weld the laminates together.

I suspect most of the objections raised to welded lams are practically irrelevant at line frequencies.
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If my above theory is true, then there should never be objections against welding, as long it's done on the outside of the core only (or on the inside only, but that would be impractical).

Actually, according to the wiki article it's low frequency that needs laminated cores. Solid cores are used for higher frequencies...
 
jitter

jitter

Member
Joined 2004
leoparleur said:



Jitter, you're scaring the hell out of me! ...ok, ok I'll purchase the Hammond.:D

But since I'm hard headed, I'll probably give this runner a chance.

Thanks Kevinkr also.
Click to expand...

Don't be scared, lower efficiency will probably only be noticed by some more heat production. I can't really imagine it having any effect on the sound quality. Maybe it's (unintendedly) actually quite good at filtering out HF rubbish...

I'm not trying to talk you into buying the Hammond, BTW. IMHO the stock transformer is fine.
 
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leoparleur

Member
Joined 2007
Hi fellows, questions again:

I've started to dismantle the boombox tonight, will get transfo tomorrow.

1.- Is it better to use the beads (ferrite cores) on the PS cords, if yes, where should it (they) be placed?

2.- With the suggested 91 and 390 resistors, do the Shigaclone provide 2 Volts as like the industry standard?

Thanks.
 
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