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Building a L20.5 Amplifier, what parts do I need?

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发表于 2020-9-21 06:09:36 | 显示全部楼层 |阅读模式
本帖最后由 DaveFred 于 2020-9-21 08:28 编辑

Hello,

Sorry to post in English, I hope that is okay.

I would like to build a two channel L20.5 Amplifier, but I am not sure what the best parts are that I need.

What power supply/recitifier board would you recommend?

And what transformer would you put with the power supply board?

Anything else you suggest? Speaker protection boards?

Links directly to what I should buy would be apprecaited.

What AliExpress or Ebay vendors are authorised to sell legitimate LJM products?

Taobao is hard to buy from when you are in North America.

From what I have been reading about this amplifier, I would like to run it at 48-52 volts, not higher.

This will be used on 110v, not 220v.

Thank you,

David, Canada.



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 楼主| 发表于 2020-9-26 09:20:42 | 显示全部楼层
本帖最后由 DaveFred 于 2020-9-26 09:28 编辑

Five days and no reply, let me make the options more simple.

I would like to build a stereo L20.5 Amplifier and I am trying to pick a power supply.

I read on one of the forums that LJM said not to use a switch mode power supply (SMPS), why is that?

An easy power supply would be this SMPS,

https://hifimediy.com/product/smps800re-50v-115v-power-supply/

Input: 115VAC
output: dual voltage +-50V DC (Minimum: ±46.5V Maximum: ±53.3V)
Current: 800W

Or this power supply in +-48v,

https://www.aliexpress.com/item/32810764650.html?spm=a2g0s.9042311.0.0.3a3e4c4dHrcm4K

KM-P800 High Power digital amplifier switching power supply DC +/-24V/36V/48V/55V/60V/70V/80V regulator 800W SMPS board

Introduction:This product uses LLC resonant half-bridge topology, with high conversion efficiency, interference, dynamic response speed, the output voltage stability, and integrated over-current, overvoltage, overheating, output short circuit protection, is the high-end amplifier products Best match. Can be used for 200-800W power amplifier, 25 degrees continuous heating power of 500W, peak power up to 1200W. ◆ Input voltage: AC 120V ◆ Output Main voltage/current:        ▲ DC +/-48V(8.1A)   ◆ Output auxiliary voltage/current: DC +/-12V (0.5A) ◆ Independent voltage/current: DC 12V (0.5A) ◆ Voltage accuracy: Main no-load +10%, Load +/-3%; Auxiliary no-load +/-20%, load +/-15% ◆ Continuous power: 400W-500W (25 Degrees Celsius ambient temperature can work continuously) ◆ Maximum power: 800W (25 Degrees Celsius ambient temperature can work for about 5 minutes) ◆ Instantaneous power: 1200W (dynamic signal generated when the impact of power, less than 100 hours of time) ◆ Conversion efficiency: Max 95% ◆ Use of the environment: -10 --- 40 Degrees Celsius ◆ Storage temperature: -30 --- 85 Degrees Celsius ◆ Size: 145mm * 80mm * 45mm (L * W * H)

If I went with a SMPS, I would add speaker proteciton boards.

The other option is to use a Power supply-transformer-rectifier filter board and toroidal transformer.

I was thinking of two of these boards



with two Toroidal transformers (one per board),

"Avel Lindberg Y236654 250VA 35V+35V Toroidal Transformer
AVEL's Y23 series power transformers offer exceptional value and performance for use in any high-quality power supply. All Y23 transformers are wound with heavy gauge copper and are wrapped with polyester tape. Meeting all major industry standards, these include double-insulated primary leads and a mounting kit with plate, pads, nut, and bolt. Other features include: 3% secondary tolerance at full load, 6" stranded copper leads with PVC insulation, and UL506/ CSA 22.2 and CE certifications

Specifications: • Primaries: 115V + 115V • Frequency: 50/60 Hz • Load Capacity: 250 VA • Secondary Voltage: 35V + 35V • Dimensions: 4.5" D x 2.0" H  • Weight: 4.9 lbs."

https://www.parts-express.com/av ... ransformer--122-635

Would this be a good choice?

LJM does not offer a soft start circuit board, I think I should use one if I go with a pair of toroidal transformers, any suggestions or recommendations for a good one?

Or would you choose something different?

Thank you,

David, Canada.


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发表于 2020-9-27 09:46:32 | 显示全部楼层
Switching power supply is not as good as traditional linear power supply
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发表于 2020-9-27 09:49:50 | 显示全部楼层
DaveFred 发表于 2020-9-26 09:20
Five days and no reply, let me make the options more simple.

I would like to build a stereo L20.5 A ...

How did you find the LJM forum
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 楼主| 发表于 2020-9-27 12:38:41 | 显示全部楼层
haizhongmu 发表于 2020-9-27 09:49
How did you find the LJM forum

I don't recall how I found the forum.

I have been searching the Internet from top to bottom to try to find examples building a L20.5 amplifier where they list what they used so I had an example to follow.

It could have been from Aliexpress, Taobao, looking at pictures of your circuit boards, in the descriptions, or some other forum.

Are you able to help me pick a power supply for a pair of L20.5?

Let's start with this, if I want to use a 35v-0-35v toroidal transformer, how many VA should I have?

Thank you,

David.
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发表于 2020-9-27 14:12:25 | 显示全部楼层
DaveFred 发表于 2020-9-27 12:38
I don't recall how I found the forum.

I have been searching the Internet from top to bottom to tr ...

I've already contacted LJM himself and he should give you a reply later
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发表于 2020-9-29 23:39:28 | 显示全部楼层
DaveFred 发表于 2020-9-27 12:38
I don't recall how I found the forum.

I have been searching the Internet from top to bottom to tr ...

It is better to use high quality ring transformer with 500VA or above
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 楼主| 发表于 2020-9-30 06:01:54 | 显示全部楼层
ding9488 发表于 2020-9-29 23:39
It is better to use high quality ring transformer with 500VA or above

I used an agent and ordered a pair of amps direct from LJM on Taobao last night along with two sets of capacitor/rectifier boards.

Not sure which ones I will use, but since shipping is going to be at least six weeks, I just wanted to get the order started.

These are the two types I ordered,



with 4 x 63v2200uf

and



Actually, now that I look closer, I think I might have made a mistake. This second board looks like it comes with 50V caps and not 63v caps. If that is true, I will have to replace them with 63v caps.

It is my plan to use two toroidal transformers and from what I have been reading, a pair of 300VA 36v-0-36v (one per board) should work well.

If LJM does post here, I would like to know which of the two boards would be best.

My choices for toroidal transformers is 200va, 300va, 400va, 500va, each.

Remember, it is my plan to use two.

Thank you,

David, Canada.
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发表于 2020-9-30 10:34:42 | 显示全部楼层
DaveFred 发表于 2020-9-30 06:01
I used an agent and ordered a pair of amps direct from LJM on Taobao last night along with two set ...

yes. This is LJM's website. It is estimated that he is very busy. I haven't seen him recently. The first rectifier board you choose is no problem. The second one is suitable for the amplifier with high damping coefficient.
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 楼主| 发表于 2020-9-30 18:48:40 | 显示全部楼层
haizhongmu 发表于 2020-9-30 10:34
yes. This is LJM's website. It is estimated that he is very busy. I haven't seen him recently. The ...

So the second power supply board is not good/suitable for the L20.5 amplifier?
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