Thanks Ashok from wherever?
I had just about made a decision to continue after source (digikey) replacements.
As to self inflicted wounds ,I had considered the possibilty but one board failed upon arrival unmoded and two other exhibited problems before mods.
Once mods were made later and measurements taken the amps actually ran for a while with my reserve speakers.I let the system run in for a few days before bypassing the dc blocking cap.In theory this could upset the bias? but the measurements showed very little change.
I am actually listening now in mono to the amp and have had one pair amps running with the big speakers for a few hours.(Allegro Volt/morel ) so I have a pretty good idea of their performance.
It was after a switch off that latest faults manifested themselves and I have a number of theories as to why that happened.It did not overheat.
Yes I had also considered the possibilty of the highly modded (clocks etc) Denon sacd players output upsetting the design.Much wider fq than CD.
The last and most serious blow got the heatsinks warm?..in seconds!.
It was akin to a short on the outputs.Could not find one but the possibility was always there.
As suspected the seller has now decided he wants ME to ship the amps back at my cost and he will repair them......LOL.
Im not likely to send the board and 50 odd vishays at £5 each off to someone else
to decide to charge me for something a pig could do if it had thumbs (joking)
As I had considered going active speakerwise , eventually. I may build the Mosfets as well and later decide which amp drives each speaker unit better.
As I am a serious music lover and former reviewer I am playing catchup on visiting concert halls (all around Europe) Hence a week in Sicily Catania to hear Korsakovas Strad and also an opera.Carmina Burana saturday .
Next month is a trip around Spain.Barca Madrid and 4 other cities.
So time is getting limited.
No cure yet for Diabetes or any of its side effects but Ive lived with it quite a while.
The other old joke applies.I dare not get into a swimming pool now.
Type one and you should be able work it out.
Once again thanks for posting and I will advise any progress.
I had just about made a decision to continue after source (digikey) replacements.
As to self inflicted wounds ,I had considered the possibilty but one board failed upon arrival unmoded and two other exhibited problems before mods.
Once mods were made later and measurements taken the amps actually ran for a while with my reserve speakers.I let the system run in for a few days before bypassing the dc blocking cap.In theory this could upset the bias? but the measurements showed very little change.
I am actually listening now in mono to the amp and have had one pair amps running with the big speakers for a few hours.(Allegro Volt/morel ) so I have a pretty good idea of their performance.
It was after a switch off that latest faults manifested themselves and I have a number of theories as to why that happened.It did not overheat.
Yes I had also considered the possibilty of the highly modded (clocks etc) Denon sacd players output upsetting the design.Much wider fq than CD.
The last and most serious blow got the heatsinks warm?..in seconds!.
It was akin to a short on the outputs.Could not find one but the possibility was always there.
As suspected the seller has now decided he wants ME to ship the amps back at my cost and he will repair them......LOL.
Im not likely to send the board and 50 odd vishays at £5 each off to someone else
to decide to charge me for something a pig could do if it had thumbs (joking)
As I had considered going active speakerwise , eventually. I may build the Mosfets as well and later decide which amp drives each speaker unit better.
As I am a serious music lover and former reviewer I am playing catchup on visiting concert halls (all around Europe) Hence a week in Sicily Catania to hear Korsakovas Strad and also an opera.Carmina Burana saturday .
Next month is a trip around Spain.Barca Madrid and 4 other cities.
So time is getting limited.
No cure yet for Diabetes or any of its side effects but Ive lived with it quite a while.
The other old joke applies.I dare not get into a swimming pool now.
Type one and you should be able work it out.
Once again thanks for posting and I will advise any progress.
Hi Dave,
Diabetes is a terrible thing. Several of my relations are afflicted with that. Wonder if I'll catch up with it sometime !
......if it is genetic !
Reading what you just said about your system raises some questions. You do know that like blood pressure, RF oscillation is a silent killer in power amps! Before you realise what's happening there is tremendous heating in seconds and you get the famous 'blue smoke'. Of course it doesn't smoke always but you can 'smell' it ! Fuses can blow , transistors can blow before you can even move !
It could come from upstream, the source. DC shift and RF oscillation must be a great way to kill an amp in fractions of a second !
I use my L12 without an input capacitor . I think it sounds 'slightly' better that way. However the DAC output has a capacitor . I have no idea what it is but it certainly sounds good.
But some input caps I have tried ( even simple electrolytic ones) are pretty close ! I've been trying some ordinary electrolytic coupling caps with a LM1875 amp which is currently running almost 24/7 for the past two weeks. The caps at the input seems to have gotten better ! These caps sound great right now. So maybe you can use a coupling cap and give it 2 weeks of use before you decide what it IS like.
Suggest you attack the faulty boards VERY slowly ! Think ten times before soldering or de-soldering lest you may inadvertently damage it . The boards are good so they deserve careful attention.
Have a great time.
Cheers.
From where ? Oh...from the Third Rock from the Sun ! That's very specific if you see how big our neighborhood is !
AND did you know we are having company soon ? Another planet some 4 or 5 times bigger than ours ? Is it true ? I'd love it to be true !
Imagine , they could be having maybe 5 times more DIYaudio guys and their technology could be amazingly different ! You'd NEVER want to die with so many new things to play with !
Diabetes is a terrible thing. Several of my relations are afflicted with that. Wonder if I'll catch up with it sometime !
......if it is genetic !Reading what you just said about your system raises some questions. You do know that like blood pressure, RF oscillation is a silent killer in power amps! Before you realise what's happening there is tremendous heating in seconds and you get the famous 'blue smoke'. Of course it doesn't smoke always but you can 'smell' it ! Fuses can blow , transistors can blow before you can even move !
It could come from upstream, the source. DC shift and RF oscillation must be a great way to kill an amp in fractions of a second !
I use my L12 without an input capacitor . I think it sounds 'slightly' better that way. However the DAC output has a capacitor . I have no idea what it is but it certainly sounds good.
But some input caps I have tried ( even simple electrolytic ones) are pretty close ! I've been trying some ordinary electrolytic coupling caps with a LM1875 amp which is currently running almost 24/7 for the past two weeks. The caps at the input seems to have gotten better ! These caps sound great right now. So maybe you can use a coupling cap and give it 2 weeks of use before you decide what it IS like.
Suggest you attack the faulty boards VERY slowly ! Think ten times before soldering or de-soldering lest you may inadvertently damage it . The boards are good so they deserve careful attention.
Have a great time.
Cheers.
From where ? Oh...from the Third Rock from the Sun ! That's very specific if you see how big our neighborhood is !
AND did you know we are having company soon ? Another planet some 4 or 5 times bigger than ours ?
Is it true ? I'd love it to be true ! Imagine , they could be having maybe 5 times more DIYaudio guys and their technology could be amazingly different ! You'd NEVER want to die with so many new things to play with !
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Ooops their goes another Rubber Tree Plant
Well in the words of the song all five have now blown.Last one in some style.
Sort of consistent? .This time its take a Volt 2208 bass unit with it.Despit protection.
Just making a cuppa and going to install a reliable half decent mosfet.
So its goodbye from me.
Some bits for sale or giveaway.
Dave
Well in the words of the song all five have now blown.Last one in some style.
Sort of consistent? .This time its take a Volt 2208 bass unit with it.Despit protection.
Just making a cuppa and going to install a reliable half decent mosfet.
So its goodbye from me.
Some bits for sale or giveaway.
Dave
Returning to the fold ?
So its goodbye from me. ?
Well its not quite goodbye as I have now reached a point in life that I am seriously missing the sonic benefits of a nice sounding amplifier.Whilst I have been absent for several reasons not connected to hifi but I am not happy with the several commercial units I have at my disposal.
So I have spent some time thinking about what caused my various failures with the LJM design and obviously there may have been several reasons but I am more than half convinced it was the sellers assembly . I am the only one who bought from Laz*******s and I am the only one using an sacd player.
It is possible that this sacd player misreads hi rez discs and sends out a white noise atnear enough full level which could have caused oscillation problems for the amp?.
I hope to sort this rare event out very soon.
Financially I am in a position that the loss doesnt bother me much but I would NOW like to progress and I am considering the L15 amplifier sourced from another Seller.
I still have a half decent 54Vdc power supply at 500VA with 40k Caps and will now give some thought to re position within the casement to ensure minimal wiring.
As usual I have been reading whatever literature is available including their appears to be slightly different schematics/circuit for this board.
I am presuming the similarity with the L12 and also the L15 was the forerunner|?
Can anyone who has built bought or heard the L15 please pass any comments.
Especially sonicaly.
So its goodbye from me. ?
Well its not quite goodbye as I have now reached a point in life that I am seriously missing the sonic benefits of a nice sounding amplifier.Whilst I have been absent for several reasons not connected to hifi but I am not happy with the several commercial units I have at my disposal.
So I have spent some time thinking about what caused my various failures with the LJM design and obviously there may have been several reasons but I am more than half convinced it was the sellers assembly . I am the only one who bought from Laz*******s and I am the only one using an sacd player.
It is possible that this sacd player misreads hi rez discs and sends out a white noise atnear enough full level which could have caused oscillation problems for the amp?.
I hope to sort this rare event out very soon.
Financially I am in a position that the loss doesnt bother me much but I would NOW like to progress and I am considering the L15 amplifier sourced from another Seller.
I still have a half decent 54Vdc power supply at 500VA with 40k Caps and will now give some thought to re position within the casement to ensure minimal wiring.
As usual I have been reading whatever literature is available including their appears to be slightly different schematics/circuit for this board.
I am presuming the similarity with the L12 and also the L15 was the forerunner|?
Can anyone who has built bought or heard the L15 please pass any comments.
Especially sonicaly.
Being LJM's thread for L12-2s, I'll stay with that part of the question.
I bought several L12 modules and used 2 of course, for myself. I have learned over some years now that Chinese kits, even designed by member ljm-ljm, get pirated, copied, parts substituted and faked - all by his competitors and I guess customers too, as their boards look original. When you buy from reputable sellers (and I found a few) you get mostly genuine or at least genuine branded components and if you notice the original output devices are about the best Sanken LAPTs around - amazingly good sound.
One of the first replies in this thread bought a kit that came basic but with 2SC5200/A1943 output transistors and no heatsink. Others I know, received kits with obviously bad output transistors, where much of the parts cost would be and they failed within minutes of loading with speakers and powering up. The lowest prices have to be cut from somewhere and LAPTS are the obvious targets for fakes. Then again, assembling a PCB as tight as that one is not a doddle or with any guarantee of success - we can and I still do make assembly and testing mistakes - often repeated.
I didn't have the need to build so I bought ready built and tested kits on heatsinks for not much more from Along1986090 - a long time (bad pun) supplier with a good rap. No problem with hooking up a bench supply, power clips, input clips and speaker spade leads - Wow! all working absolutely great, very little sign of instability on the scope and a sound that grows on you as something you want to hear more of. The trick? buy it built so it works as it comes with bias already set even. Then it only remains to follow the pics earlier in the thread along the lines of activexp, for a great amp. - honest!
I can't say a lot about other popular LJM designs but I have listened to L20 & L15 - all seem to squeeze a lot of power into a small PCB at low cost but some are just too low cost and average sound for my interest.
I bought several L12 modules and used 2 of course, for myself. I have learned over some years now that Chinese kits, even designed by member ljm-ljm, get pirated, copied, parts substituted and faked - all by his competitors and I guess customers too, as their boards look original. When you buy from reputable sellers (and I found a few) you get mostly genuine or at least genuine branded components and if you notice the original output devices are about the best Sanken LAPTs around - amazingly good sound.
One of the first replies in this thread bought a kit that came basic but with 2SC5200/A1943 output transistors and no heatsink. Others I know, received kits with obviously bad output transistors, where much of the parts cost would be and they failed within minutes of loading with speakers and powering up. The lowest prices have to be cut from somewhere and LAPTS are the obvious targets for fakes. Then again, assembling a PCB as tight as that one is not a doddle or with any guarantee of success - we can and I still do make assembly and testing mistakes - often repeated.
I didn't have the need to build so I bought ready built and tested kits on heatsinks for not much more from Along1986090 - a long time (bad pun) supplier with a good rap. No problem with hooking up a bench supply, power clips, input clips and speaker spade leads - Wow! all working absolutely great, very little sign of instability on the scope and a sound that grows on you as something you want to hear more of. The trick? buy it built so it works as it comes with bias already set even. Then it only remains to follow the pics earlier in the thread along the lines of activexp, for a great amp. - honest!
I can't say a lot about other popular LJM designs but I have listened to L20 & L15 - all seem to squeeze a lot of power into a small PCB at low cost but some are just too low cost and average sound for my interest.
many thanks again Ian
Yes Its mostly likely (probable) that I chose the wrong supplier at cost saving?
To be honest all the 5 boards fired up and ran without problems for a while.
In hindsight I may have jumped to conclusions incorrectly as each failure was different each time .None of which I was actually a witness to them blowing.
So its guess work.
One comment from a long standing connection in the hifi world suggested over tightening the screws, bolting the outputs down.Even on good devices.?
Its now partly a lack of confidence after the history plus the supplier you mention no (a)longer selling these boards.As at May 2016.
It is easier to replace with L120s rather than fit L150s but I am slightly curious of the difference in design.ie 0.22 resistors being the most obvious addition.
Specs are slightly better but that is of lesser concern.
Dave
Yes Its mostly likely (probable) that I chose the wrong supplier at cost saving?
To be honest all the 5 boards fired up and ran without problems for a while.
In hindsight I may have jumped to conclusions incorrectly as each failure was different each time .None of which I was actually a witness to them blowing.
So its guess work.
One comment from a long standing connection in the hifi world suggested over tightening the screws, bolting the outputs down.Even on good devices.?
Its now partly a lack of confidence after the history plus the supplier you mention no (a)longer selling these boards.As at May 2016.
It is easier to replace with L120s rather than fit L150s but I am slightly curious of the difference in design.ie 0.22 resistors being the most obvious addition.
Specs are slightly better but that is of lesser concern.
Dave
Hmm... with thick silicone washers, the leads end of TO3P transistors could lift a little, increase spreader and die temperature, etc. but the average dissipation would have to be fairly high, as in really loud audio, to be serious. The nagging doubt with CFP designs is stability and there are no output coils here to prevent excitation from interaction with the speakers. I have a few tame KEF reference speakers and local speaker products that I can't live without but I have no problems I'm aware of from 'scoping the output stage with them but that's not the same as music program. Who's to say that the speaker/output stage interaction has not tipped the balance to instability?
I think if you repaired these modules (check the output devices and drivers for shorts C-E, and Vbe or diode drop - the drivers are rather fragile for 2 pairs) then fitted some decent TO3P outputs like NJW3281/1302 or NJW0281/0302 then add a parallel air-core output coil plus resistor combination of 1uH/6,8R, in the +lead to the output terminals, you would stand a better chance of success. Even so, I would be watching the temperature of the transistor tops with a pyrometer etc. to see what's happening heatwise, if you can't use an oscilloscope to check for oscillation with a sinewave signal. A square wave would be more telling but not so simple to distinguish the cause.
At least you will learn a little and get closer to the problem - no need to tackle more than one module for testing - hope there is some encouragement for you here
I think if you repaired these modules (check the output devices and drivers for shorts C-E, and Vbe or diode drop - the drivers are rather fragile for 2 pairs) then fitted some decent TO3P outputs like NJW3281/1302 or NJW0281/0302 then add a parallel air-core output coil plus resistor combination of 1uH/6,8R, in the +lead to the output terminals, you would stand a better chance of success. Even so, I would be watching the temperature of the transistor tops with a pyrometer etc. to see what's happening heatwise, if you can't use an oscilloscope to check for oscillation with a sinewave signal. A square wave would be more telling but not so simple to distinguish the cause.
At least you will learn a little and get closer to the problem - no need to tackle more than one module for testing - hope there is some encouragement for you here
PS.
I did a confusing thing posting the L12 schematic to explain that the L12-2 schematic on most sellers' sites had been deliberately screwed up to be unreadable and avoid easy copying. I did say that but still it confuses readers of the thread. The resistors are correct at 0.22 ohms for L12-2 as evenharmonics said in #24. (I doubt if 0.1 ohms is easily available in a dual ceramic package)
I did a confusing thing posting the L12 schematic to explain that the L12-2 schematic on most sellers' sites had been deliberately screwed up to be unreadable and avoid easy copying. I did say that but still it confuses readers of the thread. The resistors are correct at 0.22 ohms for L12-2 as evenharmonics said in #24. (I doubt if 0.1 ohms is easily available in a dual ceramic package)
Hmm... with thick silicone washers, the leads end of TO3P transistors could lift a little, increase spreader and die temperature, etc. but the average dissipation would have to be fairly high, as in really loud audio, to be serious. The nagging doubt with CFP designs is stability and there are no output coils here to prevent excitation from interaction with the speakers. I have a few tame KEF reference speakers and local speaker products that I can't live without but I have no problems I'm aware of from 'scoping the output stage with them but that's not the same as music program. Who's to say that the speaker/output stage interaction has not tipped the balance to instability?
I think if you repaired these modules (check the output devices and drivers for shorts C-E, and Vbe or diode drop - the drivers are rather fragile for 2 pairs) then fitted some decent TO3P outputs like NJW3281/1302 or NJW0281/0302 then add a parallel air-core output coil plus resistor combination of 1uH/6,8R, in the +lead to the output terminals, you would stand a better chance of success. Even so, I would be watching the temperature of the transistor tops with a pyrometer etc. to see what's happening heatwise, if you can't use an oscilloscope to check for oscillation with a sinewave signal. A square wave would be more telling but not so simple to distinguish the cause.
At least you will learn a little and get closer to the problem - no need to tackle more than one module for testing - hope there is some encouragement for you here
Power can use the + 15 v to + - 55 v. Dc voltage.
As for buying address I don't have.
I don't even know agent business.
But the picture is ok.
Hmm... with thick silicone washers, the leads end of TO3P transistors could lift a little, increase spreader and die temperature, etc. but the average dissipation would have to be fairly high, as in really loud audio, to be serious. The nagging doubt with CFP designs is stability and there are no output coils here to prevent excitation from interaction with the speakers. I have a few tame KEF reference speakers and local speaker products that I can't live without but I have no problems I'm aware of from 'scoping the output stage with them but that's not the same as music program. Who's to say that the speaker/output stage interaction has not tipped the balance to instability?
I think if you repaired these modules (check the output devices and drivers for shorts C-E, and Vbe or diode drop - the drivers are rather fragile for 2 pairs) then fitted some decent TO3P outputs like NJW3281/1302 or NJW0281/0302 then add a parallel air-core output coil plus resistor combination of 1uH/6,8R, in the +lead to the output terminals, you would stand a better chance of success. Even so, I would be watching the temperature of the transistor tops with a pyrometer etc. to see what's happening heatwise, if you can't use an oscilloscope to check for oscillation with a sinewave signal. A square wave would be more telling but not so simple to distinguish the cause.
At least you will learn a little and get closer to the problem - no need to tackle more than one module for testing - hope there is some encouragement for you here
Hi again.
The suggested failure was NOT related to bending or pulling( your) leg...It was actually internal stress due to over tightening thru the hole bolt.
To be honest all five of the amps started off ok. They all failed after a reasonable 30 hours plus of use.
Not all faults seemed the same and as I was not actually present at each failing It can only be guess work.
Not overheating seems to have been common.
To be honest I am not in the mood to re build something that MAY have a suspicious reliablity problem due to either my possibly? higher than normal output Denon 3910. Transformer under rated ? Or even possibly difficult speaker loads.?
Yes the previous amplifier I was using had that Zobel ? network resistor /inside Inductor (so have all my previous amps near enough)
So I am more or less decided to go for the L150 variation which uses the 6 driver Complimentry output design by LJM which seems to precede the later variation L120.
Ive narrowed it down to two suppliers (Along and Sepstore)
Prior to this I may test an old very simple Linsey Hood amp which uses the same outputs and Zobel.Though someone states 150 watt with two drivers?..
Thanks for reply and suggestions.
L12-2 is very easy to install.
Most of the users to use it, is the first time assembly power amplifier.
The user more than 2000 people.
It does not require the output inductor, unless you are a capacitance, rather than by speakers as a load.
In the latest test, L12-2 has reached 0.0004% of THD + N 1 k HZ
I haven't heard the -l150, L120 this stuff.
I don't have a design of the model. I only L12-2, L15, L20.
I haven't heard the -l150, L120 this stuff.
I don't have a design of the model. I only L12-2, L15, L20.[/QUOTE]
The adverts on ebay DO vary in description.
ie. NEW LJM Assemble Dual channel L150W FET Power Amplifier Board IRFP240*6 J163 | eBay Clearly states LJM design L150 ?
several other versions also called L15
However I was happy with the performance when it was running until the tonal character changed and later its failures.
The 3 way 2nd order loudspeaker design is not IMO a highly capactive load.
and the alternative speakers that are 1st order were used on the first pair of amps that blew,
It is obviously easier for me to replace the two L12-2 boards onto the existing heatsinks designed for the boards so I will have yet another rethink.
I had to laugh at Lazerlands latest listings of these products.
Ie 4 sold. ???
Ive bought 5 from him and when I reported them faulty he assured me NO Other customers has had and problems...
Maybe arithmetic in China is different to mine. LOL.
Dave
I don't have a design of the model. I only L12-2, L15, L20.[/QUOTE]
The adverts on ebay DO vary in description.
ie. NEW LJM Assemble Dual channel L150W FET Power Amplifier Board IRFP240*6 J163 | eBay Clearly states LJM design L150 ?
several other versions also called L15
However I was happy with the performance when it was running until the tonal character changed and later its failures.
The 3 way 2nd order loudspeaker design is not IMO a highly capactive load.
and the alternative speakers that are 1st order were used on the first pair of amps that blew,
It is obviously easier for me to replace the two L12-2 boards onto the existing heatsinks designed for the boards so I will have yet another rethink.
I had to laugh at Lazerlands latest listings of these products.
Ie 4 sold. ???
Ive bought 5 from him and when I reported them faulty he assured me NO Other customers has had and problems...
Maybe arithmetic in China is different to mine. LOL.
Dave
The adverts on ebay DO vary in description.
ie. NEW LJM Assemble Dual channel L150W FET Power Amplifier Board IRFP240*6 J163 | eBay Clearly states LJM design L150 ?
several other versions also called L15
However I was happy with the performance when it was running until the tonal character changed and later its failures.
The 3 way 2nd order loudspeaker design is not IMO a highly capactive load.
and the alternative speakers that are 1st order were used on the first pair of amps that blew,
It is obviously easier for me to replace the two L12-2 boards onto the existing heatsinks designed for the boards so I will have yet another rethink.
I had to laugh at Lazerlands latest listings of these products.
Ie 4 sold. ???
Ive bought 5 from him and when I reported them faulty he assured me NO Other customers has had and problems...
Maybe arithmetic in China is different to mine. LOL.
Dave[/QUOTE]
B: yes. I have a L150W type power amplifier.
It USES six IRFP250 only
If I need a LJM L12-2, I would buy it at the sep_store store in eBay.
* New LJM DIY Stereo L12 2 Audio Two Channel Power Amplifier Kit J163 | eBay
* LJM Stereo L12 2 Audio Two Channel Power Amplifier Board J163 include Headsink | eBay
* New LJM Assembled DIY Stereo L12 2 Audio Power Amplifier Board J163 | eBay
* New LJM DIY Stereo L12 2 Audio Two Channel Power Amplifier Kit J163 | eBay
* LJM Stereo L12 2 Audio Two Channel Power Amplifier Board J163 include Headsink | eBay
* New LJM Assembled DIY Stereo L12 2 Audio Power Amplifier Board J163 | eBay
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First One - mosfet amplifier module - Side 3
- der bruger SMPS (+/-55V) fra brugeren "Cresnet". Denne kan kontaktes på Info @ micro-audio.com og oplyser:
"Price of the SMPS is 70 Euros + 50 Euros shipping for two SMPS units to your location via TNT 3-4 Days..."
- samt medsender PDF´s med data og in/output:
