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Author Topic: Reducing transformer voltage  (Read 990 times)

markorock37

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Reducing transformer voltage
« on: June 04, 2012, 08:23:11 PM »

Building a solid state guitar amp, everything is ready to go except my rail power is too high. I'm running 52 volts and would like to get around 25-30 volts. I'm using a 36 volt power supply w center tap into a full wave rectifier and two 2200uf 50v caps. What's my best solution? Thanks
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Roly

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Re: Reducing transformer voltage
« Reply #1 on: June 04, 2012, 09:23:17 PM »

Please sketch, scan and post your current power supply arrangement.  I can think of at least a couple of quite different arrangements that would fit your description.

The most obvious first thought has to be buy/scrounge/swap a more suitable transformer.

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Enzo

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Re: Reducing transformer voltage
« Reply #2 on: June 04, 2012, 10:23:45 PM »

I think so too.   I have been cleaning out the shop, and scrapping some old dead stereo recievers and stuff.  I been saving their power transformers for just such projects.  A dead smallish stereo receiver ought to provide you a reasonable transformer.  For free.


One possibility.  Is your existing transformer by any chance a 120/240v primary one?  You could probably wire the primary up for 240v operation, but feed it the 120v from the wall, and that would drop your 52v to 26v.
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J M Fahey

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Re: Reducing transformer voltage
« Reply #3 on: June 05, 2012, 12:23:51 PM »

Agree that description is not clear.
Please draw your PS as-is including voltages, polarity and whether they are AC or DC.
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markorock37

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Re: Reducing transformer voltage
« Reply #4 on: June 08, 2012, 06:20:21 PM »

I did find another transformer with the right voltage I can use if neccessary. But 'Ill draw up the current configuration and try to get that up here this weekend.
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Roly

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Re: Reducing transformer voltage
« Reply #5 on: June 09, 2012, 08:38:07 PM »

There is a trick using SCR's that can be used to reduce the voltage of a transformer for a power supply (see attached).

The gate trigger voltage is obtained from a divider between the transformer peak voltage and the output voltage.  When the output voltage rises there is a point where the voltage on the gates doesn't rise high enough to trigger the SCR any more, thus limiting the output voltage.

It has a few "gotchas" however;

- at higher voltages the gates may need to be protected by diodes

- the output voltage is a function of the gate trigger voltage which is itself a function of the SCR temperature, so this simple circuit may show a high temperature sensitivity

- SCR's and audio generally don't make for good partners and there may be considerable, and objectionable, high frequency buzz in the output
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