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Old 16th October 2012, 07:25 PM   #551
redjr is offline redjr  United States
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ljm_ljm,

There have been allegations made that your L20-D boards (perhaps others) are inferior - both in design and parts usage. Claiming that the IRFI transistor and output inductor are fakes and that other parts used are recycled and therefore not new, or OEM.

I know counterfeit parts and boards are easily made and substituted for OEM parts, and this can be a real problem for uninformed buyers worldwide. You also stated earlier in this thread that the only two authorized ebay sellers of your products/design are zoe_tsang and along. I have dealt with both of these vendors through ebay and find them to be reputable and stand behind what they sell.

I recently purchased the L25D version of your design (from along) and find it to be made of the highest quality parts and superior PCB construction. I also find the amp performs flawlessly, and I'm very happy with the sound and its performance.

My question to you is... Are you aware of your 'L series' of class D amps being copied, counterfeited and marketed by unauthorized sellers? And, if so, do you have any knowledge of the eBay vendors (by name) that may be selling the inferior product(or kits)?
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Old 16th October 2012, 09:27 PM   #552
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My IRS2092/IRFI4212 amplifier.
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Old 17th October 2012, 05:15 AM   #553
skood is offline skood  Australia
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I too can attest to the quality and performance of the ljm_ljm modules L15D in my case, they are a solid performing, quality product
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Old 17th October 2012, 05:26 AM   #554
redjr is offline redjr  United States
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My concern is, how can we tell we're buying the genuine article and not some knock-off. What are the clear and distinguishable markings that separate the true original (authorized by ljm and his 2 distributors), or a fake? A lot of inductors are hand wound and often don't have any mfg markings. Is this a true telltale sign? Anyway, I was a little dismayed when I read to steer clear of ljm design. It may not be the audiophile's choice, but the price is right, and it does deliver on performance so I'm pleased.
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Old 17th October 2012, 08:04 AM   #555
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Default Buyer protection

Quote:
Originally Posted by redjr View Post
My concern is, how can we tell we're buying the genuine article and not some knock-off. What are the clear and distinguishable markings that separate the true original (authorized by ljm and his 2 distributors), or a fake? A lot of inductors are hand wound and often don't have any mfg markings. Is this a true telltale sign? Anyway, I was a little dismayed when I read to steer clear of ljm design. It may not be the audiophile's choice, but the price is right, and it does deliver on performance so I'm pleased.
I used the "buyer protection" function from Ebay 3 times now after receiving fake components and had my money refunded all 3 times . You have 30 days to lodge a complaint ( and find out if you got fake or dodgy components ), very usefull function ! and it works .

Cheers ,

Rens
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Old 17th October 2012, 10:56 AM   #556
alkasar is offline alkasar  France
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I guess RedJr question really is "are there some L15D/L25D copies and if yes, how to identify fakes ?".
A simple rule is to buy from Along or Zoe, they sell genuine kits.
Another hint is to look at the pictures to recognize the parts. I rekon it's almost impossible to know if a inductor or mosfet is real or fake before you listen to the amp.

As far as I can tell, kit components are of reasonnable quality. They were chosen to keep price low while not compromise board quality. Except some sensitive parts that really need an upgrade IMHO (input cap, filtering cap), the kit components are ok.

I built my two L25D with different parts : one mostly with kit capacitors, the second board with upgraded caps. I can not hear any difference! Have not measured yet, maybe instruments will find out


BTW, I wrote this mounting guide. The soldering is really easy! not much to say here. The guide summarizes some useful information, focuses on the upgrades and how to test amp at first power on. Recomandations valid for any amp actually.

Enjoy, and please provide feedback
http://alkasar.free.fr/docs/Mounting%20guide%20L25D.doc
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Old 17th October 2012, 11:24 AM   #557
Cristi is offline Cristi  Europe
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Quote:
Originally Posted by redjr View Post
My concern is, how can we tell we're buying the genuine article and not some knock-off. What are the clear and distinguishable markings that separate the true original (authorized by ljm and his 2 distributors), or a fake?
I guess the question should be if the so called genuine are indeed genuine. It's very common in this part of the world to do a design initially with reasonable quality components for advertising purpose, then cut the price as much as possible no matter what parts are used. Sometimes entrepreneurs without too much experience are submitting designs to factories to assembly large lots and they have the freedom of choice for the components and unless careful supervision from the one who ordered them, fake parts are very likely to be used.
There are several pictures in this thread where can see details of components which are used. some of these posts are: 320, 402, 412, 469, 471. can see very clear that the inductor has no marking at all, and on one of the pictures can barely see the marking of the transistor, similar with the one which I mentioned in the other thread. A cheap inductor will have less saturation current (possible damage at high power, low impedance or shorted output) higher core losses (higher temperature) and will be less linear (higher THD level) of course we can't hear the difference because the human ear can't tell the difference between 0.1% and 2-3% THD, because it's higher TDH threshold and also speakers are usually having much higher THD than amplifiers, so is easy to pick up any THD values and declare them knowing that very few can measure them, and those who have equipment to do so, will not buy these boards.
Regarding the layout, is a poor layout even for a class AB amplifier, and terrible for a class D amplifier. there are no close placed decoupling capacitors near the D-S of the power transistors, no GND copper pour and the only reason why the transistors are not flying away is that they use larger DT setting, leading to slower transitions but higher THD. and probably the biggest flaw is the lack of protections anything but what's included in the chip. with 100-220uF caps on each rail, if someone would be tempted to use a minimal capacitance on the power supply, these modules will be damaged instantly once the volume is cranked up.

I am surprised why peoples are so amazed by so called "very low price" while fail to understand that for this price they get less that minimum necessary for a reliable amplifier, and for the similar price others offer more.
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Old 17th October 2012, 02:40 PM   #558
redjr is offline redjr  United States
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Quote:
Originally Posted by Cristi View Post
I guess the question should be if the so called genuine are indeed genuine. It's very common in this part of the world to do a design initially with reasonable quality components for advertising purpose, then cut the price as much as possible no matter what parts are used. Sometimes entrepreneurs without too much experience are submitting designs to factories to assembly large lots and they have the freedom of choice for the components and unless careful supervision from the one who ordered them, fake parts are very likely to be used.
There are several pictures in this thread where can see details of components which are used. some of these posts are: 320, 402, 412, 469, 471. can see very clear that the inductor has no marking at all, and on one of the pictures can barely see the marking of the transistor, similar with the one which I mentioned in the other thread. A cheap inductor will have less saturation current (possible damage at high power, low impedance or shorted output) higher core losses (higher temperature) and will be less linear (higher THD level) of course we can't hear the difference because the human ear can't tell the difference between 0.1% and 2-3% THD, because it's higher TDH threshold and also speakers are usually having much higher THD than amplifiers, so is easy to pick up any THD values and declare them knowing that very few can measure them, and those who have equipment to do so, will not buy these boards.
Regarding the layout, is a poor layout even for a class AB amplifier, and terrible for a class D amplifier. there are no close placed decoupling capacitors near the D-S of the power transistors, no GND copper pour and the only reason why the transistors are not flying away is that they use larger DT setting, leading to slower transitions but higher THD. and probably the biggest flaw is the lack of protections anything but what's included in the chip. with 100-220uF caps on each rail, if someone would be tempted to use a minimal capacitance on the power supply, these modules will be damaged instantly once the volume is cranked up.

I am surprised why peoples are so amazed by so called "very low price" while fail to understand that for this price they get less that minimum necessary for a reliable amplifier, and for the similar price others offer more.
The pictures of the ljm amp you show in this thread looks nothing close to the quality of the boards I'm using from along. Not sure where you purchased this one or how old it is, but I think it's an 'unfair' comparison to paint such a broad brush of inferiority for a reasonably good product. I have no delusions that this $50-$60 amp will perform like a $5k commercial product, but I see it for what it is. And I don't always search out the web for the lowest price products. I'm fully aware of the old adage, "you get what you pay for".
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Old 17th October 2012, 02:58 PM   #559
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Default Low price and quality with a bit of effort

Quote:
Originally Posted by Cristi View Post
I guess the question should be if the so called genuine are indeed genuine. It's very common in this part of the world to do a design initially with reasonable quality components for advertising purpose, then cut the price as much as possible no matter what parts are used. Sometimes entrepreneurs without too much experience are submitting designs to factories to assembly large lots and they have the freedom of choice for the components and unless careful supervision from the one who ordered them, fake parts are very likely to be used.
There are several pictures in this thread where can see details of components which are used. some of these posts are: 320, 402, 412, 469, 471. can see very clear that the inductor has no marking at all, and on one of the pictures can barely see the marking of the transistor, similar with the one which I mentioned in the other thread. A cheap inductor will have less saturation current (possible damage at high power, low impedance or shorted output) higher core losses (higher temperature) and will be less linear (higher THD level) of course we can't hear the difference because the human ear can't tell the difference between 0.1% and 2-3% THD, because it's higher TDH threshold and also speakers are usually having much higher THD than amplifiers, so is easy to pick up any THD values and declare them knowing that very few can measure them, and those who have equipment to do so, will not buy these boards.
Regarding the layout, is a poor layout even for a class AB amplifier, and terrible for a class D amplifier. there are no close placed decoupling capacitors near the D-S of the power transistors, no GND copper pour and the only reason why the transistors are not flying away is that they use larger DT setting, leading to slower transitions but higher THD. and probably the biggest flaw is the lack of protections anything but what's included in the chip. with 100-220uF caps on each rail, if someone would be tempted to use a minimal capacitance on the power supply, these modules will be damaged instantly once the volume is cranked up.

I am surprised why peoples are so amazed by so called "very low price" while fail to understand that for this price they get less that minimum necessary for a reliable amplifier, and for the similar price others offer more.
I totally agree with the low buffer caps on the rails in the LJM's modules , so I changed them to 820uf low esr's , but for the rest of your comment , I can say I have very good experience with LJM's amplifiers . You're referring to post 402 , that's my amp ( with your A1000SMPS), there's not one fake component in my system as far as I know and I'm very happy with the sound! it cost me only a couple of dollars to upgrade some components and like to remember all members to this THD measurement made on a L20D LJM amp . Distortion Tests - HifimeDIY T2 / LJM L20D / SURE TDA7498. dont forget to read post 23 and 24 .My ears don't fool me , I have 2 very expensive ( commercial) amps and this "cheap" EBay one sounds damn good !

Cheers ,

Rens

Ps I will order some of your Cxd250 soon for Christmas to try , always open for improvement
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Old 17th October 2012, 03:24 PM   #560
Cristi is offline Cristi  Europe
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The boards from the pictures I've posted were purchased by a customer of mine from the same "authorized" source. In fact he bought several modules, he's building multi-channel amps for public announcement and he had to try them. They failed the tests, 3 of them being damaged in less than 5 minutes. later on he bought few boards from my site and after successfully testing them, now I'm making a custom version for his multi-channel application. I asked him to send me two of these boards, I've been curious why they failed. If you notice, reading some older posts in this thread, I also had a good opinion about them till I got them in my hand.
I'll make some time next week and make some THD tests for the boards after (if I can) repair them and post the results. since I don't have an AP unit yet, only a Kenwood VA2230, accurate enough but no PC interface to save the graphs, it will take some time, and not sure is worth the effort while dealing with rigid attitudes.
Next I expect to be accused that I try to advertise my own boards, but before writing this, ask yourself's why I haven't opened a single thread at class D section trying to promote something. Even at Connexelectronic section (which I pay for) is quite silence and I'm also not inpatient to make more waves. Eventually everyone can do what he wants with his money and spend them more or less wisely. But keep in mind that while consciously purchase low-quality or substandard parts boards, you do nothing than to escalate the phenomenon.
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