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Old 12th November 2011, 02:09 AM   #1
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Default switching from UK to USA power

Hi - I built my chipamp in the UK. I'm pretty sure I've got one of these:

Technical notes: : Technical Information

How do I reconfigure the transformer to run on USA power? The original setup had the two secondaries going into two bridge rectifiers. DO I now have to turn those two separate secondary windings into one long winding?
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Old 12th November 2011, 03:53 AM   #2
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Usually the primaries are wired in series for UK and in parallel for the USA. Do you have dual primaries?
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Old 12th November 2011, 04:10 AM   #3
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I do not have dual primaries. I have one pair of primary wires, and two pairs of secondary wires.

If I wire the secondaries in series here in the USA, I should get a similar voltage to what I was getting in the UK, where they were parallel. Right?

This diagram describes my transformer:

http://www.airlinktransformers.com/prodpics/tech4-1.jpg

Last edited by darkczar; 12th November 2011 at 04:13 AM.
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Old 12th November 2011, 05:49 AM   #4
wwenze is offline wwenze  Singapore
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Won't work - the amp needs two separate secondaries, so you cannot combine them into one.

You'll have to reduce the number of turns on the primary side.
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Old 12th November 2011, 08:05 AM   #5
! is offline !  United States
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How much time, trouble or exactness do you need? What are the specific specs on the transformer and the minimum current, and maximum voltage the amp can tolerate? A description or schematic of the amp including the component ratings (voltage for example) might also help.

There may be a few different paths to get from point A to point B. One might include swapping out amp parts that can't tolerate the higher voltage. One might include reducing primary windings if the resultant current reduction stays acceptably high. One might include replacing the transformer. On the wilder side, one might include approximating where the middle of the primary winding is, cutting it there and turning it into a poorly regulated transformer that roughly retains the current capability but has steeper drops in voltage as current rises. Nobody including myself will like this last option much but it is the cheapest way to go and in some cases might not make an audible difference.

The shortest, easiest answer is to just replace the transformer... thinking that since it's a chipamp, it probably doesn't need a very high capacity transformer. Here are a few examples, Antek has one of the best selections at low price though you might find something cheaper at random with acceptable specs, like on ebay or various electronics surplus or audio component related websites:
Antek - Transformers - Grid View[]=0
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Old 12th November 2011, 08:32 AM   #6
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Got it backwards, sir. The amp is configured for 230 but he wants to run 115. Everything will be 1/2 except the power which will be 1/4. His options are only 2. Replace the power transformer with a 120V primary or use a step up transformer ahead of the amp. Personally I'd change the transformer and use a toroid from Antek as well.

G
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Old 12th November 2011, 09:36 AM   #7
! is offline !  United States
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haha, yes you are right about "tolerate the higher voltage"being backwards, but the similar reverse logic applies as it pertains to bias levels, minimal chip input voltage, minimal output power needed, etc. It would just be a lot easier to pick specifics if we had specific details to deal with since it is seldom a chipamp amp could only operate at one exact voltage.

Perhaps we should back up for a moment though. We could assume that based on the amp gain, speaker impedance and efficiency, and designed volume that the amp "needs" to be reconfigured but is this known for sure? What if the amp were powered and listened to at the required volume level, there is a possibility that nothing needs done to it... for example there's an amp in front of me right now that if it ran at 1/4 peak output, I'd have to throw a party to ever notice or need more.
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Old 12th November 2011, 11:31 AM   #8
AndrewT is offline AndrewT  Scotland
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The 220/240Vac transformer will run on a 110/120Vac system.
It will have half the output voltage.
It will have half the VA rating.
It will run cooler.
It will waste less electricity.

You have three options:
1.) wire up the two half phases of your 110/120Vac supply to give you a 220/240Vac supply.
2.) wire up an autotransformer to step up your existing 110/120Vac to a 220/240Vac supply
3.) buy a suitable transformer rated for 110/120Vac.
__________________
regards Andrew T.
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Old 12th November 2011, 05:14 PM   #9
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Wow - thanks for all the info.

FWIW - I ende up wiring the secondaries in series. It's working. I'm not getting the power I got before...I think. I'm using different speakers, so who knows. I'm only using one bridge rectifier now, feeding both channels.

This is all for a musical performance. I'm a big fan of the band Chrome, so lo-fi is a plus. We're playing this evening at a party, so I needed to get something sorted out ASAP. The speakers are from Salvation Army.

Thanks again for all the help!
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Old 12th November 2011, 05:32 PM   #10
! is offline !  United States
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^ Maybe we are missing details about this amp? Wiring secondaries in series might cause problems.

What's the schematic look like now for the PSU and amp config?

Last edited by !; 12th November 2011 at 05:44 PM.
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