Reading/understanding circuit - schemes. Mesa Boogie

SveinungL · Post by **SveinungL** » 27 May 2001 7:33 am

A while ago I posted a question on how to rewing a Mesa studio preamp from 150v to 230 v. I was told to request the AC wiring scheme from Mesa and I did. The other day it showed up!! Great!
Now I need som help from those of you who fully understand these schemes. Lok at the picture below: It describes two ways of wireing the transformer. One for 115V and one for 230V. Now: What doen "N.C." on some of the cables mean?

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Thanks SveinungL - Norway
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Kentucky Riders

[This message was edited by SveinungL on 27 May 2001 at 08:35 AM.]

Donny Hinson · Post by **Donny Hinson** » 27 May 2001 7:44 am

Normally, "N.C." means "no connection". In other words..."not used".

Blake Hawkins · Post by **Blake Hawkins** » 27 May 2001 9:51 am

As Donny said, "NC" means not connected.
The diagram shows that your power transformer has two primary windings. Only one is used for 100 to 120 volts.
Both windings are used and wired in series for 230 volts.
Be very careful to identify the leads from each winding and connect only what's called for and exactly as specified.
It looks as if you use a BLK (Black) and a
BRN/WHT (Brown-White) wire to connect to the mains for 230 volts. However, there are the ends of the two windings which are connected together to put them in series and they are not identified on the 230 volt section. Look at the other primary drawings to see if you can identify the colors of these wires.
If you have a low voltage AC source and a voltmeter you can check and verify your wiring before connecting the preamp to he mains.
Blake
[This message was edited by Blake Hawkins on 27 May 2001 at 10:56 AM.]

SveinungL · Post by **SveinungL** » 27 May 2001 2:02 pm

Thanks for great info!
Yes I thought of N.C. meaning not connected. The strange thing is that they actually were connected.......but the N.C.'s were connected in parallell to the other winding. Isn't it right that the resistance should be doubled when the trafo is winded for 230 v compared to 115 V? That's what it is now.

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Thanks SveinungL - Norway
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Kentucky Riders

Blake Hawkins · Post by **Blake Hawkins** » 27 May 2001 2:21 pm

Yes, the resistance should be double for 230 volts.
Sometimes windings are connected in parallel.
Of course the "NC" only applies to the particular mode in which the transformer is connected. In other modes, the "NC" wires may be used.
You must be sure that the windings are connected in series according to the diagram.
If one of the windings was reversed things would not work the way you expect. AC windings can be wired "series aiding" or "series opposed." If anyone tells you polarity does not matter in AC wiring, don't believe them.
Just be sure the color codes on the connected wires match the color codes on the drawing.
Blake[This message was edited by Blake Hawkins on 27 May 2001 at 03:23 PM.]

SveinungL · Post by **SveinungL** » 28 May 2001 3:25 am

Thanks for the advice!
I have rewired it and it works now on 230 V!

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Thanks SveinungL - Norway
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Kentucky Riders