Will I need a transformer for this DIY Amplifier? - diyAudio
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Old 29th July 2009, 06:31 PM   #1
kizm0 is offline kizm0  United States
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Default Will I need a transformer for this DIY Amplifier?

http://cgi.ebay.com/NEW-LM3886TF-2X6...kparms=65%3A12|66%3A2|39%3A1|72%3A1234|293%3A1|294%3A50

This ad seems very deceiving to me. They say DIY, but the item shown in the photos is pre-made. They also don't say whether or not you need a transformer.

It might be a DIY kit that has been assembled already. I don't know.

What do you guys think? Will I need a transformer for the PSU of this?
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Old 29th July 2009, 06:51 PM   #2
Puffin is offline Puffin  United Kingdom
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The kit is for a stereo amp (2 power amp boards) and a power supply board.

You will need to supply a transformer. A twin secondary 18vac would do. You will need to know how to wire the transformer to the mains and the power supply board and house the amplifier in a case so that no-one gets electrocuted. Do you have the skills?
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Old 29th July 2009, 06:59 PM   #3
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No way to go without a transformer, typically 24V center tapped secondaries, approximately 200 - 300VA.
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Old 30th July 2009, 10:10 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
the PCBs look the same as some I bought from another seller.
I had my doubts about whether all the components were genuine or fakes.

The assembled PCBs play fairly well into 8ohm speakers using either 15+15Vac or 25+25Vac transformers.
I cannot vouch for the pre-assembled versions.

Be careful with dissipation of the TF chips. They need bigger heat sinks and are expensive to cool on 4ohm loads.

You need
chassis
heatsink/s
hardware
transformer

The budget for these four items is likely to be two to ten times the $40 of the PSU and 2amps.
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Old 30th July 2009, 05:54 PM   #5
kizm0 is offline kizm0  United States
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I was recommended a:

28V--0--28V

Does that mean

Parallel-Amperage-Series

??

Can somebody give me a direct link to Newark or Digi-key?

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Old 31st July 2009, 02:04 AM   #6
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Hi. 28v secondaries will be too high. Your chips will likely fry eventually. 28v will be 28 * 1.41 = 39.48v. +-40v is too much, with mains fluctuation your chips will explode. Those kits are fine. www.customaluminumboxes.com will create a custom encosure for you at an amazing price. just give them dimensions and general details. You should get an 18-0-18 VAC or 18-0 18-0 VAC transformer, rated at at least 200va to supply both of those chips. At (18*1.41=25.38VDC) your chips won't get very hot, affording you a heatsink that won't take up your whole chassis.
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Old 31st July 2009, 05:24 AM   #7
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Quote:
Originally posted by kizm0
Can somebody give me a direct link to Newark or Digi-key?
Are you joking?
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Old 31st July 2009, 09:49 AM   #8
Puffin is offline Puffin  United Kingdom
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Quote:
Originally posted by odysseybmx414
Hi. 28v secondaries will be too high. Your chips will likely fry eventually. 28v will be 28 * 1.41 = 39.48v. +-40v is too much, with mains fluctuation your chips will explode. Those kits are fine. www.customaluminumboxes.com will create a custom encosure for you at an amazing price. just give them dimensions and general details. You should get an 18-0-18 VAC or 18-0 18-0 VAC transformer, rated at at least 200va to supply both of those chips. At (18*1.41=25.38VDC) your chips won't get very hot, affording you a heatsink that won't take up your whole chassis.

I use twin 30vac trannys with my LM3875 monblocks. No problem.
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Old 31st July 2009, 10:05 AM   #9
kizm0 is offline kizm0  United States
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Sorry about asking for a direct link... lol
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Old 31st July 2009, 10:08 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Puffin
I use twin 30vac trannys with my LM3875 monoblocks. No problem.
tell us more.
I use 230:25Vac 225VA that gives +-37.7Vdc (when the mains is at 240Vac) into the amplifier when drawing quiescent current.
On the rare occasions that 254Vac may arrive I expect it to give ~+-40.5Vdc
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