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Old 16th January 2006, 06:56 AM   #1
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Default Will this transformer work with the ChipAmp kit?

American Science & Surplus has a 18 volt @ 2.5 (Approx. 45VA) amp transformer for 1$. Would these be suitable for a GainClone PSU, if three were wired in paralell? (I'm using the PCB from chipamp.com).
Also, is the listed 18v voltage before or after rectification?

It's the third down on the page:
http://www.sciplus.com/category.cfm?...3&category=138
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Old 16th January 2006, 07:56 AM   #2
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hi 'teapot,

I think you need 4 at a bare minimum. Don't forget you need 18-0-18. That's 2 for each channel, 18-0-18 @ 90VA. I'd think about paralleling all 4 to give 180VA. A lot of wiring, but they are cheap. The 18 volts is before rectification, so after 18 x 1.4 is approx. 25 volts.

Good luck.
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Old 16th January 2006, 03:12 PM   #3
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I thought that rectification dropped the voltage. I guess that shows what I know.
Would larger-than-normal caps (13,000 uF vs. 10,000 uF) adversely affect the amp?
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Old 16th January 2006, 03:30 PM   #4
Nordic is offline Nordic  South Africa
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You may be confused with regulation.
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Old 16th January 2006, 03:45 PM   #5
Macaba is offline Macaba  United Kingdom
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Quote:
Originally posted by Spasticteapot
I thought that rectification dropped the voltage. I guess that shows what I know.
You are correct, it just has been badly explained to you.
An 18V AC transformer gives an RMS value of 18V's. When rectified (converted from AC to pseudo-DC) it is 'unRMS-ed' by multiplying the RMS voltage with 2^0.5 (About 1.4) to give 25V. Now there is a DIODE voltage drop in a rectifier of about 0.7V, but overall, the voltage seems to increase, but thats only because its been converted from RMS AC Volts to DC Volts.

This then goes through the CAP bank which smooths out the 'bumps' in the signal. Then optionally, it goes through regulation, which you can think of as just 'chopping' of the top of the voltage to get rid of any 'ripple' that occurs when the PSU is under load.
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Old 16th January 2006, 06:10 PM   #6
Tweeker is offline Tweeker  United States
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With 3 per channel you could get 37VDC rails. If going dual mono paralleling would not be necessary.

Apex Jr. has great deals on psu parts.
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Old 16th January 2006, 08:42 PM   #7
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Quote:
Originally posted by Spasticteapot
I thought that rectification dropped the voltage. I guess that shows what I know.
Hi 'teapot,

I should have mentioned, it seems to be a default that we use full wave bridge rectification using 4 diodes and this does increase the voltage. There is also half wave with 1 diode and full wave with 2 diodes rectification that produce different and from memory lower output voltages and different current capabilities.

So we were all right.

BTW: The voltage reading I mentioned, 25v, will only occur after the smoothing capacitors. Without the caps, and measuring at the output of the diode bridge with a DMM you will not get a 25 volt reading.

regards
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Old 18th January 2006, 04:52 AM   #8
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Thanks for all the help.
It looks like these are an acceptable option, and the price is hard to beat. (4$ for the lot!) However, they're obviously rather cheaply made, as well. How much would they negatively impact sound quality?

Also, ApexJR has a toroidial transformer for 25$ that looks good. However, they did'nt list the amperage, and I can only afford one for the both of them. It's got 2 20v outputs.
Item #: Basler 16-16431
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Old 18th January 2006, 10:58 AM   #9
Bazukaz is offline Bazukaz  Lithuania
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They won't have impact on sound quality , but may not be good(hum,high no-load current,etc).
Recently i purchased three little cheap ~2 W transformers.They consume 30 mA of current without a load , thats ~7 watts and heat a lot.

Toroid transformers usually produce less hum , what is one of consideration factors.

The power supply should be about twice as powerful as your amp's output.
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