Tech Square Technical and speculative discussion of amps, cables and other topics.

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RE: Quizzle me this, techmeisters

Posted by shermanr@prw.net on October 9, 2010 at 13:47:29

In Reply to: RE: Quizzle me this, techmeisters posted by Lee of Omaha on October 5, 2010 at 17:10:17:

I think it's risky to proceed like this, the note could imply one of two things.

1) The factory would re-wire the primary of the already installed transformer. Lucky you!

2) The factory would swap the 220V transformer for a 120V version.

I would note down the wire configurations and de-solder the primary.

Then with an Ohmeter, measure the wires and see if you have a split primary (roughly equal DCR between one the wires and the other two).

Or a tapped primary to adjust for +/- mains voltage deviations from 220V.

This would result in un-balanced DC resistance readings.


If you had access to a signal generator and an oscilloscope, you could de-solder the transformer and apply a signal to reverse engineer the winding ratios to determine the AC Voltage parameters.

Another option is to replace the existing transformer for a close substitute that has a 120V Primary.

You can measure the secondary if you get hold of a proper step-up tranny.
The current capacity of the secondary must be a few amps DC. You can measure the rectified DC with an ammeter and reverse engineer.

Also the secondary AC voltage is simple to determine with an AC voltmeter.

The safest would be to buy a step-up transformer unit and be done with it, or borrow one for testing.

The saddest thing that can happen is that the preamp is broken and you find out only after applying power properly.

It's a preamp, so the current draw is steady. Shouldn't affect the sound or performance unless placed under a sonic microscope :)

Good luck!

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

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