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Old 27th March 2004, 06:23 PM   #1
Wagener is offline Wagener  South Africa
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Default leach amp power supply

What is the best power supply setup to use for a four channel leach amp? Can I use one transformer? What VA rating will be sufficient for this?
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Old 27th March 2004, 09:17 PM   #2
kiwi_abroad is offline kiwi_abroad  New Zealand
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I have just finished my 4 channel leach amp!!!

I designed my power supply around two toroidal Transformers I already had, which involved some compromises, and perhaps some benefits. This won't answer your question (what is best) but will provide some info on something that works...

I had two transformers, one 530VA, the other 330VA, both 40-0-40 for a total of 860VA. A rough rule of thumb for transformer rating is double the max. power output. The Leach is 140W, so you need 140*4*2 = 1120VA Transformer. I'm not too far off with the 860VA.
Dr. Leach recommends a 40-0-40 at either 6 or 8 amps. This works out to 480VA or 640VA. Double these and you have a good guide for how big your transformer needs to be.

These were fed into seperate rectifier bridges (Hi-speed, soft recovery blah blah....) and then were joined together to form a single pair of voltage rails (+-58V). I couldn't have seperate rails because of the different power ratings. I belive this might have a benefit to the power rating, as potentially all 4 channels will not always be drawing high power at any one instant.

Filter caps. On my power supply board I used 22400uF (4x 5600uF) per rail, and on each Amplifier module, I used 11200uF (2*5600uf) per rail, for a total of 24x 5600uF caps (134400uF). This is somewhat more than Dr. Leach recommends.
I designed the PCB's myself so I put the filter caps on the Amp board as well. You might not do that.

Good luck...
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Old 27th March 2004, 11:19 PM   #3
BobEllis is offline BobEllis  United States
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I used a 950 VA transformer - two 42 volt windings and 39,000 uf per rail for my 4 channel Leach amp. The rating seems conservative since I get 61 volts on each rail and I've never seen them drop below 58 under load. I had two channels bridged driving my sub (that requires 6 dB of boost) and the others on the mains until I finished my A-75.

For normal music or HT use, anything over 750 VA ought to do the job. You wouldn't want to try to get max power out of all four channels continously though, the transformer would heat up a bit.
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Old 28th March 2004, 02:17 AM   #4
slowhands is offline slowhands  United States
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Default Re: leach amp power supply

Originally posted by Wagener
What is the best power supply setup to use for a four channel leach amp? Can I use one transformer? What VA rating will be sufficient for this?
I think Dr. Leach covers this on his website for pairs, just double the rating for 4 channels into 8 ohm loads, add 25% or more for 4 ohm loads. 800 watts feels about right, roughly double the output rating.

There is actually technical reason for that answer. Driven by a sine wave at full output, this amp will waste at least half its power consumption in heat, and deliver half to the load. Ergo, double the output power. But real music is not a sine wave, it's much more complex, so this is just a convenient computation for a starting estimate. If you share the iron over all 4 channels, statistically not all will pull max power simultaneously, so this is actually a very conservative estimate for that case.
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