The 1342v can handle much higher voltages. For 45v, the upc1225 works just ss well.
I have a couple of kits based on the 1225. These were pull outs from US designed amplifiers. Sonance Sonamp 1250. It uses the 2sc3519/ a1386 pair. With 45v rails, in bridge mode, 2 channels can put out over 250w with just 4 output devices. It’s ridiculous. Excellent SOA on those outputs.
I have a couple of kits based on the 1225. These were pull outs from US designed amplifiers. Sonance Sonamp 1250. It uses the 2sc3519/ a1386 pair. With 45v rails, in bridge mode, 2 channels can put out over 250w with just 4 output devices. It’s ridiculous. Excellent SOA on those outputs.
I know the datasheet says that however I put a large safety margin on any kits. I had D1047 output failures with several kits before I started applying a very generous extra safety margin. I would hope the uPC1342V are genuine but I have seen so many fake op-amps, output transistors and also capacitors that I am not going to make any assumptions.
I have also watched a few youtube videos about fake chip amps that can't handle the rated power and are missing the protection circuits.
Late last year I bought outputs from authorized distributors but I can't be sure about the uPC1342. Besides I don't need more power with my 4 Ohm speakers.
I have also watched a few youtube videos about fake chip amps that can't handle the rated power and are missing the protection circuits.
Late last year I bought outputs from authorized distributors but I can't be sure about the uPC1342. Besides I don't need more power with my 4 Ohm speakers.
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LJM doesn't publish schematics of his commercial products so whoever has one, will likely have drawn their own. The 2 obvious and essential 6-pin integrated LTP transistors are the only parts not commonly available but everything else, including the power supply, is quite standard, with discrete and relatively simple circuitry. Drafting a schematic with all resistor values from those images might be difficult but a little more image searching might help there, so why not exercise your ability to trace the tracks on a PCB and learn how simple this design actually is.
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I built the MX50 yrs ago. It works very nice and I like it. Then I built the 20SE and works great, NO problems with either amp. I run +-45 volts on the 20se. The hardest part was tapping the holes for the output transistors. I used the parts that came with the kits. Neither run very warm. Now I'm working on a KX amp. I fuse both +&- going to the boards.
I could trace this but it's a bit of work and I was just looking for an easier way. The schematic was for my curiosity and I was looking to replace the 50k pot with a 10k pot, I wanted to investigate what affect this may have on the circuit. I have a motorized 10k alps pot I'd like to use with this.
OK, perhaps for interest, you'd like to see LJM's own comments, specs and test results etc. You can find this and some of his other preamp schematics there in the commercial forum. https://www.diyaudio.com/community/threads/ljm-audio.180625/page-27.
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@Ian Finch
Thank you for providing that information, very helpful. You know this site quite a bit better then I do.
Thank you for providing that information, very helpful. You know this site quite a bit better then I do.
I know this theme is about the best Chinese amplifiers but I will present another extreme: the worst ever... and the last ever from China. Just look at the square wave measurements, I don't have to investigate this further. This is way the worst Chinese amplifier. It is now where it belongs: in the bin.
After the success with A60 amplifier I have had high expectations with this not so cheap amplifier. This has cost me slightly less than 360EUR, after taxes. I don't care too much for money, but disappointment hurts a bit. All these expectations and then... Crap.
Beware of this expensive garbage.
After the success with A60 amplifier I have had high expectations with this not so cheap amplifier. This has cost me slightly less than 360EUR, after taxes. I don't care too much for money, but disappointment hurts a bit. All these expectations and then... Crap.
Beware of this expensive garbage.
I'm back @kozard
Now, this is the Best Chinese amplifier board I've ever tested: A60+
Let me show you square wave response measured at 5Hz, 10Hz, 1kHz, 50 kHz and 150kHz. Also, THD is rather low, about 0,02%, with dominant 2nd harmonic. I think that great frequency response is the main reason for indeed great sound quality.
Now, first 5Hz (at this frequency all other amplifiers have horrible square wave response) followed by 10Hz, 1kHz, 50 kHz and 150 kHz. The best square wave response I've ever measured.
EDIT: I forgot to mention: this amplifier simply doesn't attenuate at any low frequency, including DC (built-in speaker protection prevents disaster in this extreme case). Also at the upper side, at 20 kHz, attenuation is vanishingly small. This amplifier attenuates after many tens of kHz beyond audible region, and it is stable, like a rock.
Now, this is the Best Chinese amplifier board I've ever tested: A60+
Let me show you square wave response measured at 5Hz, 10Hz, 1kHz, 50 kHz and 150kHz. Also, THD is rather low, about 0,02%, with dominant 2nd harmonic. I think that great frequency response is the main reason for indeed great sound quality.
Now, first 5Hz (at this frequency all other amplifiers have horrible square wave response) followed by 10Hz, 1kHz, 50 kHz and 150 kHz. The best square wave response I've ever measured.
EDIT: I forgot to mention: this amplifier simply doesn't attenuate at any low frequency, including DC (built-in speaker protection prevents disaster in this extreme case). Also at the upper side, at 20 kHz, attenuation is vanishingly small. This amplifier attenuates after many tens of kHz beyond audible region, and it is stable, like a rock.
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My english is not so good. Excuse me if i write nonsense...
I have built a few amps with china clones.. the LJM L20.5 is better than the rest, in my opinion.. but some clones are really near by. My L20.5 has the KEC Transistors on its pcb. I haved changed nothing. Powered with Connex SMPS 500 Watt +- 55 volt, adjusted to +-52 Volt. A little less heat to the heatsinks. This amp never i never sell...
At first the "Goldmund Clone" from ali express https://de.aliexpress.com/i/1005003215766150.html?gatewayAdapt=glo2deu
Running with +-45 volts powered by a connex 500 Watt SMPS. Bias is set to 100 mA. Because of its name the amp was built in a golden case 🙂
The sound is amazing, warm, clear, wtith punch. If it gets more bias it will be a little bit darker. The case is not large enough...sounding is very near to the L20.5
The second amp is a Marantz Clone, i suggest. I call it GHX Amp. The GHX company offered this amp first. Very close to the L20.5 either. Amazing sound missing of nothing. It also ist powered by a 500 Watt Connex SMPS +- 45 Volt, Bias is set to 65 mA. https://www.aliexpress.us/item/3256804316070498.html?gatewayAdapt=glo2usa4itemAdapt
I put a coil 2,2 µH /10 Ohm 3Watt resistor to the output. "Blameless Amplifier " ?
LJM L12-2 another nice sounding amp. But not realy flat as i read here. It offers precision, very clear sound. I have made some hacks. On calvins audio page you can read about them. The bias is set to 40 mA. At first i used a transformator..awfull..humming in the speakers. No way to loose it. I choose a Connex SMPS +-35 volts 300 watt. Silence...
LJM L20SE..mhmm...not my sound. I cant say definitly what i am missing. Loveless to my ears...must hear one more time...
LJM MX50X2 is a nice sounding amp too. He has a little brother, the MX40X2. Both amps are rearly cheap and without difficulties you can built a good sounding amp. I use my MX50X2 for measurements on my Hypex DLCP.
Each of the amps would loose a shootout to the L20.5 in fact. But if hear them individually you will miss nothing. 🙂
I have made a few pictures.
I have built a few amps with china clones.. the LJM L20.5 is better than the rest, in my opinion.. but some clones are really near by. My L20.5 has the KEC Transistors on its pcb. I haved changed nothing. Powered with Connex SMPS 500 Watt +- 55 volt, adjusted to +-52 Volt. A little less heat to the heatsinks. This amp never i never sell...
At first the "Goldmund Clone" from ali express https://de.aliexpress.com/i/1005003215766150.html?gatewayAdapt=glo2deu
Running with +-45 volts powered by a connex 500 Watt SMPS. Bias is set to 100 mA. Because of its name the amp was built in a golden case 🙂
The sound is amazing, warm, clear, wtith punch. If it gets more bias it will be a little bit darker. The case is not large enough...sounding is very near to the L20.5
The second amp is a Marantz Clone, i suggest. I call it GHX Amp. The GHX company offered this amp first. Very close to the L20.5 either. Amazing sound missing of nothing. It also ist powered by a 500 Watt Connex SMPS +- 45 Volt, Bias is set to 65 mA. https://www.aliexpress.us/item/3256804316070498.html?gatewayAdapt=glo2usa4itemAdapt
I put a coil 2,2 µH /10 Ohm 3Watt resistor to the output. "Blameless Amplifier " ?
LJM L12-2 another nice sounding amp. But not realy flat as i read here. It offers precision, very clear sound. I have made some hacks. On calvins audio page you can read about them. The bias is set to 40 mA. At first i used a transformator..awfull..humming in the speakers. No way to loose it. I choose a Connex SMPS +-35 volts 300 watt. Silence...
LJM L20SE..mhmm...not my sound. I cant say definitly what i am missing. Loveless to my ears...must hear one more time...
LJM MX50X2 is a nice sounding amp too. He has a little brother, the MX40X2. Both amps are rearly cheap and without difficulties you can built a good sounding amp. I use my MX50X2 for measurements on my Hypex DLCP.
Each of the amps would loose a shootout to the L20.5 in fact. But if hear them individually you will miss nothing. 🙂
I have made a few pictures.
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![IMG_20231214_214948[1].jpg](/community/data/attachments/1154/1154639-b888a95162e83b5796c3aff5e4c187dd.jpg?hash=uIipUWLoO1)
![IMG_20231214_215153[1].jpg](/community/data/attachments/1154/1154640-9e38be66768f5c656f7699317b3cc3a9.jpg?hash=nji-ZnaPXG)
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I have forgotten to write my name to you...🙄
Greetings
Peter
Greetings
Peter
Hi Kleinhorn,
Thank you for the summary on the amps you have made. I am interested in the LJM L20.5 using the SMPS. Did you modify or add any additional capacitance to the Connex power supplies?
My speakers are 4 ohm and I am considering using a lower voltage, perhaps +/- 35 vdc. Do you think I am being too conservative?
Your advice is greatly appreciated.
I hope you are doing well - AZ
Thank you for the summary on the amps you have made. I am interested in the LJM L20.5 using the SMPS. Did you modify or add any additional capacitance to the Connex power supplies?
My speakers are 4 ohm and I am considering using a lower voltage, perhaps +/- 35 vdc. Do you think I am being too conservative?
Your advice is greatly appreciated.
I hope you are doing well - AZ
I changed nothing at the Connex SMPS. I chose a 500 Watt because of the 4700 µf per rail. You can choose +-35 Volt, why not. I you order L20.5 boards have a look to the transistors which are offered. Choose the KEC ones. The MJE Boards are newer and i dont know where the transistors come from. In China the MJE types are rare.
BTW my speakers have 4 ohm too 🙂 with +-52 Volt no problem. In the DIY Audio Forum the user Saarmichel has powerd with nearly +-60 Volt. He had shown pictures and measurments here in this forum...
I am no electronic technican...no plan...just hobby. i am learning every day... 🙂
Greets
Peter
BTW my speakers have 4 ohm too 🙂 with +-52 Volt no problem. In the DIY Audio Forum the user Saarmichel has powerd with nearly +-60 Volt. He had shown pictures and measurments here in this forum...
I am no electronic technican...no plan...just hobby. i am learning every day... 🙂
Greets
Peter
Thanks for the information Peter. One question. Do you have 4ohm speakers? Are all amplifier you mention capable to drive 4 ohm?