Quick update. Replaced the three resistors checked around again.Nothing obvious wrong.
Reconnected and both went up in smoke very quickly.ie into a short circuit?
.Output devices measure ok so do Q5/7/9/
Holiday cannot come quick enough but plenty to do when I return? .Even if it is only looking for alternative boards.
dave
Reconnected and both went up in smoke very quickly.ie into a short circuit?
.Output devices measure ok so do Q5/7/9/
Holiday cannot come quick enough but plenty to do when I return? .Even if it is only looking for alternative boards.
dave
Hi,
agree, the fault doesn´t look like a resistor problem, but one or meanwhile several faulty transistors.
I´d say, You bought fake amps in first place.
You might think about using those for some spare parts (resistors
) and purchase new ones from a trustworthy source alltogether
At Taobao for example along assured in the text to be using genuine parts and also showed pics of rolls of genuine parts ... so far I had not one single issue with those amps.
After my experience the amps work from out of the box, but the idle current varies considerably from amp to amp and can´t be changed/trimmed.
A easy fix to this is, to replace the 1k Bias resistor R19 by a parallel of 1k5 and a 5k-pot (a multiturn Poti 64W, or -Y; at a wiper position of 0.7 or ~3k the combined resistance equals 1k, the original value), btw. a more sensitive tuning than putting hyped boutique parts just everywhere without really knowing (there´s no guarantee that these are necessarily the best parts for that application, nor good parts at all .. the Elma Lytics for example are rather mediocre caps by their specs).
jauu
Calvin
agree, the fault doesn´t look like a resistor problem, but one or meanwhile several faulty transistors.
I´d say, You bought fake amps in first place.
You might think about using those for some spare parts (resistors
) and purchase new ones from a trustworthy source alltogetherAt Taobao for example along assured in the text to be using genuine parts and also showed pics of rolls of genuine parts ... so far I had not one single issue with those amps.
After my experience the amps work from out of the box, but the idle current varies considerably from amp to amp and can´t be changed/trimmed.
A easy fix to this is, to replace the 1k Bias resistor R19 by a parallel of 1k5 and a 5k-pot (a multiturn Poti 64W, or -Y; at a wiper position of 0.7 or ~3k the combined resistance equals 1k, the original value), btw. a more sensitive tuning than putting hyped boutique parts just everywhere without really knowing (there´s no guarantee that these are necessarily the best parts for that application, nor good parts at all
.. the Elma Lytics for example are rather mediocre caps by their specs).jauu
Calvin
I can't remember exactly but I did it couple of months ago and I managed to get to the other side.
With the buttons, highlight them and copy them out. I believe the browser picks up the description of the button in the html which comes out as text when you paste it.
I do recall a number of translation breaks along the way but none as bad as being greeted with the final site totally in Chinese.
And yeah, there's a habit in Asia to use text in pictures which of course causes havoc for translation efforts.
With the buttons, highlight them and copy them out. I believe the browser picks up the description of the button in the html which comes out as text when you paste it.
I do recall a number of translation breaks along the way but none as bad as being greeted with the final site totally in Chinese.
And yeah, there's a habit in Asia to use text in pictures which of course causes havoc for translation efforts.
Thanks again for response. It may be that these are fakes but with a feedback of 20600 plus I though I would be safe.They look identical to genuine pics.
I am not the only person who has purchased this amp from this seller.
Now that I Have returned from holiday and will be giving the repair some attention this week .It may be I have misjudged the original failure and these output devices are indeed suspect. This may ? explain the blown transformer on first pair of amps ,I suspected the 250 VA was overloaded and caused the fault ? After receiving poor soldered 3rd amp which later blew and I still need to check reason,The fifth amp has certainly the worst fault.Fourth still running ok.
It may well be my big speakers are being a difficult load,? time and measurement will tell.
I certainly have very little confidence in this amp now .My last kit amp lasted 12 years.
Will report back later.
1 per cent vishays resistors only improve quality of sound compared to metal film cheapos.
There are many obvious reasons.Sadly they are expensive and unless you have tried them over a considerable number of years you will not appreciate their performance.Elna Silmics may be middle of the road ? ,they were used in this case to balance out the sonic problems I believe caused by other cheap parts on the board.
Have spent too many years balancing out and tuning many amplifiers to date.
Cannot remember any amp, even those Cambridge disasters that come close to reliability of this one.Yet it did sound pretty damn good when tweaked,
I will give it another go.though I suspect a load of boards and bits may be going on ebay cheaply.very soon.
I am not the only person who has purchased this amp from this seller.
Now that I Have returned from holiday and will be giving the repair some attention this week .It may be I have misjudged the original failure and these output devices are indeed suspect. This may ? explain the blown transformer on first pair of amps ,I suspected the 250 VA was overloaded and caused the fault ? After receiving poor soldered 3rd amp which later blew and I still need to check reason,The fifth amp has certainly the worst fault.Fourth still running ok.
It may well be my big speakers are being a difficult load,? time and measurement will tell.
I certainly have very little confidence in this amp now .My last kit amp lasted 12 years.
Will report back later.
1 per cent vishays resistors only improve quality of sound compared to metal film cheapos.
There are many obvious reasons.Sadly they are expensive and unless you have tried them over a considerable number of years you will not appreciate their performance.Elna Silmics may be middle of the road ? ,they were used in this case to balance out the sonic problems I believe caused by other cheap parts on the board.
Have spent too many years balancing out and tuning many amplifiers to date.
Cannot remember any amp, even those Cambridge disasters that come close to reliability of this one.Yet it did sound pretty damn good when tweaked,
I will give it another go.though I suspect a load of boards and bits may be going on ebay cheaply.very soon.
Hi,
I don´t believe that the amps would blow up due to your speakers if You play them under typical HiFi conditions.
In fact they perform unusally stable into difficult complex loads.
I´d rather assume that the seller sells mostly crappy non-original editions/copies/fakes.
I´m very sorry for You that You lost so many amps and wasted time, but if You buy the original or from known good sources everything will be fine.
No pun intended, but what You call ´tuning´ rather sounds like parts rolling without the proper technical background to me.
It is not too unusual to find ´tuned´ assemblies working less well as the original or even failing.
Your judgement of quality seems to follow the price tag of the device not their effective technical quality.
For example are the Elna -by technical means- not outstanding parts.
Nichicon, Rubycon and others offer Lytics with better specs often at lower cost.
You probabely talk of Vishay CMF or BMF?
The degree of tolerance doesn´t say anything about the kind and quality of device, but just defines a value range.
1% tolerated pieces of good stuff is 100% fine, 1% of crappy stuff is 100% crap.
Some guys even prefer bulk carbon resistors even though those are technocally vastly inferior.
There are a (small) number of points on this amp where sensitive tuning may help.
The lytics at the input und feedback input may be bridged with small film caps, or replaced by improved caps.
And yes, the supply-lytics may be checked for quality and possibly be replaced, though the ones in the original are fully ok and you will add more capacitance with the rectifier/power-Caps board anyway.
And due to the wide variance of the bias currents the replacement of the fixed bias spreader by a variable one is wortwhile thinking of.
The amp doesn´t need much ´tuning´ to sound and behave very well from the start.
Don´t blame the original amp on failures of a copy or from the user.
jauu
Calvin
I don´t believe that the amps would blow up due to your speakers if You play them under typical HiFi conditions.
In fact they perform unusally stable into difficult complex loads.
I´d rather assume that the seller sells mostly crappy non-original editions/copies/fakes.
I´m very sorry for You that You lost so many amps and wasted time, but if You buy the original or from known good sources everything will be fine.
No pun intended, but what You call ´tuning´ rather sounds like parts rolling without the proper technical background to me.
It is not too unusual to find ´tuned´ assemblies working less well as the original or even failing.
Your judgement of quality seems to follow the price tag of the device not their effective technical quality.
For example are the Elna -by technical means- not outstanding parts.
Nichicon, Rubycon and others offer Lytics with better specs often at lower cost.
Well, Vishay -or precise the companies they overtook- also manufactures cheap metal films
You probabely talk of Vishay CMF or BMF?
The degree of tolerance doesn´t say anything about the kind and quality of device, but just defines a value range.
1% tolerated pieces of good stuff is 100% fine, 1% of crappy stuff is 100% crap.
Some guys even prefer bulk carbon resistors even though those are technocally vastly inferior.
There are a (small) number of points on this amp where sensitive tuning may help.
The lytics at the input und feedback input may be bridged with small film caps, or replaced by improved caps.
And yes, the supply-lytics may be checked for quality and possibly be replaced, though the ones in the original are fully ok and you will add more capacitance with the rectifier/power-Caps board anyway.
And due to the wide variance of the bias currents the replacement of the fixed bias spreader by a variable one is wortwhile thinking of.
The amp doesn´t need much ´tuning´ to sound and behave very well from the start.
Don´t blame the original amp on failures of a copy or from the user.
jauu
Calvin
Well I repaired board number three (basically poor soldering ??? again )and That channel is up and running.Meanwhile I noticed that the only other working board (5 of the 5) started to show a drift upwards to .189 dc offset.
Then it stopped output of the signal and I removed and checked the resistance of the transistors and outputs. Once again C2837s showed up weird measurements.
So I salvaged the only other pair of good measurement C2837...BIG MiSTAKE.
This board then blew identical to board 4.
I am pretty sure NOW that I can guess the cause.
Resistors are bulk foil and from 1980 - 2000.If you havent used them yet, all the
top modders do.
Awaiting response from Lazerlands,,,They offered to send replacement output devices.LOL.
Might go back to top end amplifiers but these were good FOR THE PRICE.
Dave
Then it stopped output of the signal and I removed and checked the resistance of the transistors and outputs. Once again C2837s showed up weird measurements.
So I salvaged the only other pair of good measurement C2837...BIG MiSTAKE.
This board then blew identical to board 4.
I am pretty sure NOW that I can guess the cause.
Resistors are bulk foil and from 1980 - 2000.If you havent used them yet, all the
top modders do.
Awaiting response from Lazerlands,,,They offered to send replacement output devices.LOL.
Might go back to top end amplifiers but these were good FOR THE PRICE.
Dave
I bought a pair of L12-2 boards over 6 months ago. I bought it as a kit and soldered them myself. They worked perfectly right from the start. Very good sound and no problems at all so far. Bias is different for both boards due to the fixed resistors but makes no difference to the sound so I just left them as they are. I follow the policy of, if it ain't broke don't touch it !
I used a slightly larger heat sink than what we see in the original photo. I bought my heat sink locally. Shipping would have been expensive.
I think it's a great board and I don't see any strange behavior from it. Runs pretty cool at low levels. I made a new transformer for it and will be building a chassis shortly. Deserves to have it's own box !
Edit: I must be getting old. Looks like I already said many things about this board on this thread ! However , the board still works problem free today and sounds very nice.
I used a slightly larger heat sink than what we see in the original photo. I bought my heat sink locally. Shipping would have been expensive.
I think it's a great board and I don't see any strange behavior from it. Runs pretty cool at low levels. I made a new transformer for it and will be building a chassis shortly. Deserves to have it's own box !
Edit: I must be getting old. Looks like I already said many things about this board on this thread ! However , the board still works problem free today and sounds very nice.
Last edited:
yep unlucky to have bought from wrong supplier
Yes I agree Andrew.Very true remark especially from someone that may be Scottish.LOL.
It is my first ebay Chinese experience.
In hindsight I should not have been so easy going l upon arrival of these boards from the outset as I have now checked the quality of the soldering from underneath the boards and this may explain a lot.
Certainly a fair bit of flux which was clearly visible originally from on the top at the drivers. Quite a few of the legs of components are not fully soldered from the top and to some extent this may also have been a potential cause of the problem.However it worked but I had my suspicions.
Please note,
I have been around for 50 years into hifi and most of this time at genuine
hifi levels.Not with CD or run of the mill commercial designs.I am not a beginner and far from it.
I only reported my problem on this forum to help advise people away from this seller not really against this amplifier as I have previously stated its quite remarkable sonics for the design.I had also gone through an awful lot of thought and checking before I made this decision.Despite my advanced years into all sorts of electronics I am still learning.
Ok
update..I have just gone over the board known as (5) after completely resoldering and circuit checking board 3.It will be interesting to see IF this and the next board I redo will actually stay stable.Yep I could now describe this circuit in my sleep.again LOL
The DC offsets were very low and different on every board.Even different as they were run in but that was to be expected. I only had one opportunity to spot a rising offset prior to a main fault/loss of output.
Again I can only suspect the cause as everything happened to quickly
to take ongoing measurements.
Even now I am not sure if there was yet another bad soldering joint at R14.
So despite everything It may well be that a DIY job from a decent supplier is the answer.
It just seemed a good time saving idea at the time to buy ready made boards that ???? should have been better checked.Thugh they did in fact work from the off but a character change (reported) did take place.
This was both before and after Bulk foils were introduced which obviously made it easier to identify.
At least NOW I do have a little more time on my hands to sort it out but its been an experience I wanted to share.
Not one I wanted.
Just hope it saves some one else.
Ironically I bought 5 boards and seller is now showing only 3 sold?>>>
Maybe he is going to refund me for two...
No I cannot be that lucky....
Yes I agree Andrew.Very true remark especially from someone that may be Scottish.LOL.
It is my first ebay Chinese experience.
In hindsight I should not have been so easy going l upon arrival of these boards from the outset as I have now checked the quality of the soldering from underneath the boards and this may explain a lot.
Certainly a fair bit of flux which was clearly visible originally from on the top at the drivers. Quite a few of the legs of components are not fully soldered from the top and to some extent this may also have been a potential cause of the problem.However it worked but I had my suspicions.
Please note,
I have been around for 50 years into hifi and most of this time at genuine
hifi levels.Not with CD or run of the mill commercial designs.I am not a beginner and far from it.
I only reported my problem on this forum to help advise people away from this seller not really against this amplifier as I have previously stated its quite remarkable sonics for the design.I had also gone through an awful lot of thought and checking before I made this decision.Despite my advanced years into all sorts of electronics I am still learning.
Ok
update..I have just gone over the board known as (5) after completely resoldering and circuit checking board 3.It will be interesting to see IF this and the next board I redo will actually stay stable.Yep I could now describe this circuit in my sleep.again LOL
The DC offsets were very low and different on every board.Even different as they were run in but that was to be expected. I only had one opportunity to spot a rising offset prior to a main fault/loss of output.
Again I can only suspect the cause as everything happened to quickly
to take ongoing measurements.
Even now I am not sure if there was yet another bad soldering joint at R14.
So despite everything It may well be that a DIY job from a decent supplier is the answer.
It just seemed a good time saving idea at the time to buy ready made boards that ???? should have been better checked.Thugh they did in fact work from the off but a character change (reported) did take place.
This was both before and after Bulk foils were introduced which obviously made it easier to identify.
At least NOW I do have a little more time on my hands to sort it out but its been an experience I wanted to share.
Not one I wanted.
Just hope it saves some one else.
Ironically I bought 5 boards and seller is now showing only 3 sold?>>>
Maybe he is going to refund me for two...
No I cannot be that lucky....
As pointed out in earlier posts, genuine Sanken 3SC2837 and 2SA1186 are probably the best LAPT types available - amazing parts. I tried to buy them outside the Allegro Sanken distributorship and found there are at least six makers of inferior (non-LAPT) copies. Some, clearly marked as ISC (Inchange), PMC and KEC product are reasonable generic audio power transistors but those looking very similar to and branded as Sanken product are definitely not power transistors. Most failed at normal household levels for me too. One set of six pairs all failed at less than 3 watts maximum rms audio output. Perhaps this is the type of product that was supplied in your kits.
Fakes abound where consumers make their supplier and product choices blind. I now deal with only a few suppliers who are widely acknowledged as honest and careful to supply genuine parts the first time where possible or at least reasonable and honest substitutes where necessary.
I resolved some years ago to never buy electronics from unknown stores. Seek confirmation from frequent buyers here first if you need to try someone new. A cheap price or free replacements is no compensation for the grief you get with a pile of low grade junk or fake components.
Fakes abound where consumers make their supplier and product choices blind. I now deal with only a few suppliers who are widely acknowledged as honest and careful to supply genuine parts the first time where possible or at least reasonable and honest substitutes where necessary.
I resolved some years ago to never buy electronics from unknown stores. Seek confirmation from frequent buyers here first if you need to try someone new. A cheap price or free replacements is no compensation for the grief you get with a pile of low grade junk or fake components.
My naieve return to the Kit Amp world.
Yes It seems after reading up reports for the last 24 hours that I should and could have made much better decisions.
So many things Ive learnt and relearnt....
I am guessing that only the output devices are suspect and I am pretty sure that Lazerlands will try to avoid sending replacements, somehow,time will tell..This doesnt really matter as I feel more confident in getting genuine parts from my previous usual sources within the industry.
The small cost is irrelevant.
It has been an interesting time and energy consuming journey so far.(The only bits I really could not have afforded)
Once again I shall be out of the zone for various reasons over the next few weeks.(Hospital) So will give some thought to whether to progress with these amps or possibly revert back to my reliable Dr White mosfets design.
Lesser of two evils springs to mind?.I may even do both ,energy levels permitting..
Re engineering casework?ugh.
Thanks for all the comments and I only hope I have prevented someone elses misfortune.
Dave
Yes It seems after reading up reports for the last 24 hours that I should and could have made much better decisions.
So many things Ive learnt and relearnt....
I am guessing that only the output devices are suspect and I am pretty sure that Lazerlands will try to avoid sending replacements, somehow,time will tell..This doesnt really matter as I feel more confident in getting genuine parts from my previous usual sources within the industry.
The small cost is irrelevant.
It has been an interesting time and energy consuming journey so far.(The only bits I really could not have afforded)
Once again I shall be out of the zone for various reasons over the next few weeks.(Hospital) So will give some thought to whether to progress with these amps or possibly revert back to my reliable Dr White mosfets design.
Lesser of two evils springs to mind?.I may even do both ,energy levels permitting..
Re engineering casework?ugh.
Thanks for all the comments and I only hope I have prevented someone elses misfortune.
Dave
Thanks for updating forum members with your problems with this board.
Considering that the thread on the L12 started sometime in 2011 , it's clear that there haven't been too many problems with the boards. Otherwise we would have had seen several complaints by now.....about 5 years !
You are really unfortunate with so many boards giving trouble. Either you have defective parts supplied to you or something went wrong while modding the parts. No one seems to have complained so far about bad parts. Maybe it's a combination of soldering from your supplier and subsequent parts changes that might have led to the disasters. Hope you will be able to get the boards working again.
They are worth being fixed. It's a great amp.
Wish you all the best with your hospitalisation . Trust your medical problems will be solved and you can get back to DIY again.
Cheers.
Considering that the thread on the L12 started sometime in 2011 , it's clear that there haven't been too many problems with the boards. Otherwise we would have had seen several complaints by now.....about 5 years !
You are really unfortunate with so many boards giving trouble. Either you have defective parts supplied to you or something went wrong while modding the parts. No one seems to have complained so far about bad parts. Maybe it's a combination of soldering from your supplier and subsequent parts changes that might have led to the disasters. Hope you will be able to get the boards working again.
They are worth being fixed. It's a great amp.
Wish you all the best with your hospitalisation . Trust your medical problems will be solved and you can get back to DIY again.
Cheers.
L-12-2 LJM
Hi
I have put together four channels of the L12 amp,and never had a problem with them.
2 of the (upgraded capacitors)) channels have been connected constantly to mains for about a year or two now.
Psu for 2 channels is 2x28V AC 500VA+220.000uF (+/-40V DC.)
Both channels 1-4mV DC offset.
Never had a problem with them.
No hum or noise.
Sounds great driving my 4 ohms (2.9)
mtm speakers
Seller zoe tzang
KM
Hi
I have put together four channels of the L12 amp,and never had a problem with them.
2 of the (upgraded capacitors)) channels have been connected constantly to mains for about a year or two now.
Psu for 2 channels is 2x28V AC 500VA+220.000uF (+/-40V DC.)
Both channels 1-4mV DC offset.
Never had a problem with them.
No hum or noise.
Sounds great driving my 4 ohms (2.9)
mtm speakers
Seller zoe tzang
KM