Here, adding some details is required: Is it a bad design? Or is it a good design affected by a third party? The first and the second, are not the same at all.
We see a response and attempt to support at least.
Even if four transistors need to be replaced (prised as a can of cola), it is still much more attractive and reasonable than spending $3k for the brand, or $10+k on boutique gear.
the second feature of human reason: one wants to believe that very expensive = very good. Actually, it is mine feature of snakeoilephiles, and other obsessive-compulsive patients.
which of the features is more stupid and harmful?
if the price/performance ratio is good. Now I ordering those transistors, to get an answer if that amp is worth the price of the burger & chips & cola.
My 5 coins: the only those not making mistakes, who doing nothing. A real master is one, who can recognize, and fix his own mistakes. LJM agree that there is an issue, so now, just let's see if he recognises the cause of the issue correctly and if the solution proposed by LJM is working.
Remember, that Aliexpress targets auditory in ex-USSR/CIS, and there are a lot of dudes, that quite confident that a high-end system should cost less than a bottle of vodka. Personally, I think it is a good idea to add a premium version of amplifier modules, made of components, imported from reliable sources.
First, thanks for providing a link to the Douglas Selfs' Load Invariant Amplifier schematics which is supposed to be a blueprint for the present Ver5. Now, let me ask you a simple question: does this stripped-of design really belong to the same category or the oversimplification compromises the original design. With all due respect to LJM and Douglas Self - it remains to be verified.
I am perhaps the last person who advocates expensive Snake Oil products, quite the contrary - I am against Propaganda and I have sufficient technical background to decide.
I rely on the real world performance: tests and verifications. So lets wait and see. Despite the obvious deficiencies, I will order Ver 5. kit, just out of curiosity. All my LJM "amplifier" kits have ended up in the bin and this one will too, but just for fun I will test it.
Hi Berlusconi,
Good CFP amplifiers have the capacity to sound really excellent. I have designed a couple, serviced many over the years. As long as the layout is good, the original schematic accurately followed and decent parts used, you should appreciate it. Matching or selecting components really helps with these designs.
A CFP design is really nice, other types are also very good. Much depends on the voltage amp stage and layout of the PCB. I own and use various basic designed amplifiers. No snake oil involved, just good engineering.
Good CFP amplifiers have the capacity to sound really excellent. I have designed a couple, serviced many over the years. As long as the layout is good, the original schematic accurately followed and decent parts used, you should appreciate it. Matching or selecting components really helps with these designs.
A CFP design is really nice, other types are also very good. Much depends on the voltage amp stage and layout of the PCB. I own and use various basic designed amplifiers. No snake oil involved, just good engineering.
These amplifiers are actually not that expensive. Most expensive products are not related to their effectiveness.
I do not recommend purchasing expensive solutions. Or components. They won't be better.
For example, MX50SE is half the price of L12-2. And it doesn't look as HIFI in appearance. But in reality, their effects are the same.
There will probably be a sales boom as people come up with different solutions round the output stage oscillation , Beeny has just posted his.
As LJM has hinted, the output driver specs matter probably due to minimal output stage compensation , minimal output driver degeneration and overall amp gain
If the design asks for extremal solutions or components, it is a sign of engineering problems.
Alex Cavalli, Cavalli Audio founder.
My 5 coins: it is sign of greed also...
Exactly what it is! An engineering problem... Wait for the placebo version 5.1, or 5.2, or....Just a waste of time and money. If you want to sell product to the average Joe, stick with a proven design. Left the "Experimental" part for the lab.
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But, the stock of faulty product must be sold first...
Let’s Wait with faulty products and engendering problems. I ordered Toshiba transistors, that LJM suggested to replace. The answer what’s wrong here just on the way.
If after transistors replacement the amp will work as expected, so all ok with LJM and his design. Who does not agree, are welcome to buy FM Acoustics gear; those making measurements for each part, prior to assembly.
But if the parts replacement will not help, for me it’s a clear sign to go to Antony Holton amps, or wolverine, or upcoming amp of N Suchov
If after transistors replacement the amp will work as expected, so all ok with LJM and his design. Who does not agree, are welcome to buy FM Acoustics gear; those making measurements for each part, prior to assembly.
But if the parts replacement will not help, for me it’s a clear sign to go to Antony Holton amps, or wolverine, or upcoming amp of N Suchov
Just a word of warning for newbs and the unwary - Ver4.2 and Ver5 of the L12-2 have a dc coupled input ( i.e. no input capacitor ). Check the output offset voltage if your preamp has a dc coupled output; and add an input capacitor if you intend to put a volume control directly in front of the power amp. I'm currently tracing the L12-2 Ver4.2 schematic from the pcb and will post it here when I'm done.
I wonder how many faulty boards have been sold so far. I bet they are continued to be sold, not withdrawn as they should be. So, do all these people have to go and purchased more transistors? What about people that purchased completed boards. They might well have enough knowledge to wire them up but would not be happy making changes to the board.
Changing these transistors will not correct the very poor PCB layout. Remove the track to no ware! Unstable bias and way to hot thermally linked bias circuit.
Overhigh gain and FETs that are not FETs.
Add a QI pot to the V4.2 you have a much better solution.
I'm asking myself do I spend more money and time replacing transistors, re testing. I think it's time to move on.
Changing these transistors will not correct the very poor PCB layout. Remove the track to no ware! Unstable bias and way to hot thermally linked bias circuit.
Overhigh gain and FETs that are not FETs.
Add a QI pot to the V4.2 you have a much better solution.
I'm asking myself do I spend more money and time replacing transistors, re testing. I think it's time to move on.
@michael beeny sir after watching your videos I have assembled the amps but I have a persistent hum from both speakers.
I am using:
The wiring is as per the option 1 diagram here: https://www.diyaudio.com/community/threads/ljm-l12-2-ver-4-2-help-me-wire-this-plz.421972/
Speaker negative to amp ground
Amp ground to PSU ground
The issue occurs as soon as I connect a source to BOTH RCA inputs. With source turned off or on I get the hum. It doesn't seem to amplify, just there like an annoying itch.
I have tried to:
What can I do guys??
I am using:
- L12-2 version 4.2 amps
- 500va 30-30v transformer1
- 5000uf x 6 PSU board
- 220v speaker protect
- slow start module
- topping d50s as source with volume control and dac
The wiring is as per the option 1 diagram here: https://www.diyaudio.com/community/threads/ljm-l12-2-ver-4-2-help-me-wire-this-plz.421972/
Speaker negative to amp ground
Amp ground to PSU ground
The issue occurs as soon as I connect a source to BOTH RCA inputs. With source turned off or on I get the hum. It doesn't seem to amplify, just there like an annoying itch.
I have tried to:
- Float the signal ground for one rca = no change
- Adding capictor in series to signal ground=no effect
- Testing each amp individually I get no hum
- Removing the RCA input I get no hum
- Removing one RCA I get no hum
What can I do guys??
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Sir, could you please take a look at my hum issue and help me if it's related to what you posted
What I meant by floating the RCA ground was that on one of the RCA inputs I simply removed the ground connection. The other RCA had both ground and signal connected.
I also removed all RCA inputs and removed power. And measured the resistance across the signal ground and signal input. Both at the RCA inputs and also at signal input jack on the amp board.
I get:
Left: 0.854 k ohm
Right: 0.631 k ohm
Does this imply that version 4.2 indeed doesn't have any DC coupling caps?
I also tried a different input source and I get exactly the same behaviour.
I also removed all RCA inputs and removed power. And measured the resistance across the signal ground and signal input. Both at the RCA inputs and also at signal input jack on the amp board.
I get:
Left: 0.854 k ohm
Right: 0.631 k ohm
Does this imply that version 4.2 indeed doesn't have any DC coupling caps?
I also tried a different input source and I get exactly the same behaviour.
Update
I have fitted 2.2uf capacitor (audiophiler mkp, 400vdc) to both RCA input signals. The buzzing is slightly reduced but it's still there, albeit 80% of before.
With the system turned off I get infinite resistance across both RCA inputs after I installed the caps.
With the system turned on and no music playing at source.. I get a DC reading of
4.6mv at both the amp signal terminals. This is after the capictor has been put inline at RCA input.
Speaker terminals have a DC reading of:
DC -52mv and DC -45mv
The buzz is still there:
Summary of what i have so far tried:
- 2 alternative star grounds (details here) Thread 'LJM L12-2 ver 4.2 - help me wire this plz' https://www.diyaudio.com/community/threads/ljm-l12-2-ver-4-2-help-me-wire-this-plz.421972/
I have fitted 2.2uf capacitor (audiophiler mkp, 400vdc) to both RCA input signals. The buzzing is slightly reduced but it's still there, albeit 80% of before.
With the system turned off I get infinite resistance across both RCA inputs after I installed the caps.
With the system turned on and no music playing at source.. I get a DC reading of
4.6mv at both the amp signal terminals. This is after the capictor has been put inline at RCA input.
Speaker terminals have a DC reading of:
DC -52mv and DC -45mv
The buzz is still there:
Summary of what i have so far tried:
- different input source
- different RCA cables
- different PSU
- twisted cables
- only 1 amp connected (no hum)
- only 1 RCA connected (no hum)
- no RCA connected (no hum)
- source off, both RCA connected (hum)
- source on, both RCA connected (hum)
- DC blocking capacitor on RCA (hum)
- NO DC blocking capacitor on RCA (hum)
- 2 alternative star grounds (details here) Thread 'LJM L12-2 ver 4.2 - help me wire this plz' https://www.diyaudio.com/community/threads/ljm-l12-2-ver-4-2-help-me-wire-this-plz.421972/