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Old 26th April 2014, 08:14 AM   #1
diyAudio Member
 
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Default Advice for new DIY Ampli

Hi to all.....
I have 2 toroidal trasformer (500v each), output 54-0-54v each toroidal...
I want make an DIY ampli, I will use it to play a pair of self-built speakers (2 or 3 way, 350w/400w rms in 8 ohm), unpretentious, just make a bit of noise in some party (I already have a MACKIE powered speaker system, this new DIY would be a reserve or for small parties)...
now i have read various post on this forum, and my ideas might be these modules:
http://www.aliexpress.com/item/LJM-H...729677992.html
http://www.aliexpress.com/item/2pcs-...286935592.html
http://www.aliexpress.com/item/YJ-Ne...868265207.html...
What would you do if you had my transformer and my needs?
another doubt it would be enough if a single transformer to power the two modules (perhaps using a power supply like this http://www.aliexpress.com/item/4-100...704465796.html so I will have in output +-75V //54*1,41//) or if is better to use two trasformer and two power supply board....
thank you for help me....
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Old 26th April 2014, 12:32 PM   #2
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75V rails could permit much more than the L25 design's advertised 250W/8R rating. There can't be proper assessments without a schematic but it may be OK if 8R loads or greater only are used. I would not rely on that being the case, given the modern speaker units available for this power level. You should always allow for real load impedances of half the nominal rating or even less, since loudspeakers vary greatly across the audio frequency spectrum. 8R nominal speakers can drop lower than 3.5R at around 300 Hz and there is usually a high amount of audio program energy concentrated there.

Another problem is that 2SD1047/B817 have a Vceo of only 140V. That leaves no SOA margin to use full power at what may often be >150V total supply voltage. It will require carefully designed VI limiters to run safely at high power.

Either rebuild the modules with higher rated components and risk further stress to the PCB/copper foil, or use lower voltage transformers that will have a higher current:voltage ratio, allowing use at lower impedance, such as with 45-50VAC windings.

The L25 product may meet the ratings shown, but I'm not convinced that the power supply options are thought through for the many inexperienced users who may try them. The YJ product is class D and without without details, is an unknown - perhaps the class D forum guys are the ones to ask about such commercial offerings.
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Last edited by Ian Finch; 26th April 2014 at 12:34 PM.
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Old 26th April 2014, 12:33 PM   #3
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http://www.diyaudio.com/forums/vendo...amplifier.html
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Old 26th April 2014, 05:34 PM   #4
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ok..thank you for reply...
being my first project was looking for something simply and inexpensive that's why I'm headed to the amplifiers in class D.
+-74V rails are actually many .... now I'll try to ask for help users in the class D section ..
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Old 26th April 2014, 05:35 PM   #5
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Join Date: Apr 2011
Default New DIY Ampli

Hi to all.....
I have 2 toroidal trasformer (500v each), output 54-0-54v each toroidal...
I want make an DIY ampli, I will use it to play a pair of self-built speakers (2 or 3 way, 350w/400w rms in 8 ohm), unpretentious, just make a bit of noise in some party (I already have a MACKIE powered speaker system, this new DIY would be a reserve or for small parties)...
now i have read various post on this forum, and my ideas might be these modules:
http://www.aliexpress.com/item/LJM-H...729677992.html
http://www.aliexpress.com/item/2pcs-...286935592.html
http://www.aliexpress.com/item/YJ-Ne...868265207.html...
What would you do if you had my transformer and my needs?
another doubt it would be enough if a single transformer to power the two modules (perhaps using a power supply like this http://www.aliexpress.com/item/4-100...704465796.html so I will have in output +-75V //54*1,41//) or if is better to use two trasformer and two power supply board....
thank you for help me....
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Old 26th April 2014, 07:02 PM   #6
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Join Date: Jan 2010
I would recommend your first link, because this lookes like a clone of an IRAUD amp. This has several advantages:
-on IRF.com you find the data sheet and complete circuit diagrams
-hints to customize to different supply voltages
-it is a class d-amp, so cooling is uncritical
-I built an amp with similar modules from sure-electronics:
they cost <30Euro and work like a charm since then.

The second link is a class AB-amp, this will require big heat sinks, not shown on the photograph.

The last is class d, based on the same technique as the first one. I do not know it, but it does not look too bad.

so my vote would be definitely the first one.
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Old 26th April 2014, 07:42 PM   #7
jcx is offline jcx  United States
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its cheaper to buy Behringer or similar PA - cheaper than the ps iron, case, heatsink bought in hobby quantity - you could consider the working amplifier electronics as thrown in as a freebie

or turn a pair of fleamarket/used/junked Home Theater amps into bridged/parallel monoblocks...

buying discrete parts new in small qty will cost more - diy is not cheap

Last edited by jcx; 26th April 2014 at 07:50 PM.
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Old 26th April 2014, 08:35 PM   #8
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Join Date: Apr 2011
thank you friend...
I also had some preference on the modules LJM L25d ..
something I wanted to ask, I have two toroidal transformers, you should use a transformer with a power supply module and two modules L25d board or two transformer 2 power supply board and two 2 modules L25d?
Pros and cons?
It's my first project....
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Old 26th April 2014, 09:28 PM   #9
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Join Date: Apr 2011
I thought about a DIY because usually the things that cost the most are the transformers, and I saw that I have recovered a few powerful enough without spending anything, I thought I can use them to build a discrete power amplifier...sure if I had to spend 150 Euros for the two transformers plus another hundred for the amplifier modules, not to mention the rest (power supply board, connectors, soft start, protection modules, etc..) then you sarebbemolto more convenient to take a good final type behringer etc ...
I already possess a final GEMINI, if I'm not mistaken it should deliver about 180w rms per channel into 8 ohms ... this DIY is just a whim that I had for some time and now that I have given these two toroidal I was going to accomplish. ..
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Old 26th April 2014, 09:36 PM   #10
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Join Date: Jan 2010
The power Modules are single channel, for a stereo amp you will need two of them. There are even stereo modules for less money on the market.

Normally I suppose a single transformer is good enough for a stereo amp. On the other hand, you can avoid some irking problems with ground loops and crosstalk if you choose two separate power supplies. In that case there is no point in buying stereo modules.
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