Regards,
For the first time in my life (and I'm in my 50's) I assembled an audio amplifier, the LJM L12-2 V4. I have almost no experience in electronics, just the basics of measuring with a DMM and replacing some parts and such.
I used a 300 VA 25-0-25 toroidal transformer, which rectified to 34V DC, I recycled the chassis of an old Sony amplifier and put a speaker protection circuit on it. I plugged it into a bulb current limiter, no speakers, no preamplifier connection, no other audio signals connected and turned it on with no problem: no short circuit, no smoke, no strange noises or smells.
For the first minute I measured the DC output and it gave me between 6 and 7mv on each channel. All right!. After a minute it went up a bit to 7-8 mv. I didn't measure it anymore. I left it on, to wait for it to stabilize. So far so good...
But after 2 and a half minutes, the speaker protector activated for a second and then continued normal, but after 10 seconds the same thing happened again, and it was repeated like this every 10 seconds. All without connected speakers or sound source. I turned it off, as something was not right.
Please, I need help to identify what may be happening.
I did the following tweaks, prior to installation:
1. I put X7R capacitors in parallel for all lytics (except C5).
2. Increasing the high-current paths crossection by applying solder.
3. Replaced R19 per Calvin's recommendation, to make BIAS adjustments. I replaced 1K with 1.5K and added 5K potentiometer in parallel. I calibrated it to stay at 1K again, before the first power up.
I also disconnected one card at a time, to see if the problem came from one of them, but the same thing happened with both. I haven't used it without the speaker protection (which could be where the fault is…), but I don't know if this risks burning the boards. I could hook up cheap test speakers to it and see if it makes noise, but only if you tell me if it's safe.
I haven't measured the BIAS yet. I don't have an oscilloscope, just a DMM and a lot of goodwill.
Any idea what could be happening? Suggestions?
Thank you.
For the first time in my life (and I'm in my 50's) I assembled an audio amplifier, the LJM L12-2 V4. I have almost no experience in electronics, just the basics of measuring with a DMM and replacing some parts and such.
I used a 300 VA 25-0-25 toroidal transformer, which rectified to 34V DC, I recycled the chassis of an old Sony amplifier and put a speaker protection circuit on it. I plugged it into a bulb current limiter, no speakers, no preamplifier connection, no other audio signals connected and turned it on with no problem: no short circuit, no smoke, no strange noises or smells.
For the first minute I measured the DC output and it gave me between 6 and 7mv on each channel. All right!. After a minute it went up a bit to 7-8 mv. I didn't measure it anymore. I left it on, to wait for it to stabilize. So far so good...
But after 2 and a half minutes, the speaker protector activated for a second and then continued normal, but after 10 seconds the same thing happened again, and it was repeated like this every 10 seconds. All without connected speakers or sound source. I turned it off, as something was not right.
Please, I need help to identify what may be happening.
I did the following tweaks, prior to installation:
1. I put X7R capacitors in parallel for all lytics (except C5).
2. Increasing the high-current paths crossection by applying solder.
3. Replaced R19 per Calvin's recommendation, to make BIAS adjustments. I replaced 1K with 1.5K and added 5K potentiometer in parallel. I calibrated it to stay at 1K again, before the first power up.
I also disconnected one card at a time, to see if the problem came from one of them, but the same thing happened with both. I haven't used it without the speaker protection (which could be where the fault is…), but I don't know if this risks burning the boards. I could hook up cheap test speakers to it and see if it makes noise, but only if you tell me if it's safe.
I haven't measured the BIAS yet. I don't have an oscilloscope, just a DMM and a lot of goodwill.
Any idea what could be happening? Suggestions?
Thank you.
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First, sounds like you are almost there.
Second, post some pictures of the board and build, helps us locate a problem in the board, if there is one.
Next questions - before modifying any circuit, I would build as the designer intended and make sure it works, now you don’t know which upgrade caused or or if the boards weee faulty to begin with.
IMO, you don’t need the extra caps, but it’s DIY so do what you want.
Next, if you didn’t know how to measure bias, why put in another variable with the pot and resistor change?
FYI, bias is measured across one of the large resistors in line from the output transistor to the speaker output. Google is your friend for a picture of what I mean and how to do it. You only need a DMM and a calculator.
Last thing, taking out the speaker protection will have no impact on the amp, but I wouldn’t hook up any speakers until you sort out the issue(s) and put the protection back in and confirm it is working.
Second, post some pictures of the board and build, helps us locate a problem in the board, if there is one.
Next questions - before modifying any circuit, I would build as the designer intended and make sure it works, now you don’t know which upgrade caused or or if the boards weee faulty to begin with.
IMO, you don’t need the extra caps, but it’s DIY so do what you want.
Next, if you didn’t know how to measure bias, why put in another variable with the pot and resistor change?
FYI, bias is measured across one of the large resistors in line from the output transistor to the speaker output. Google is your friend for a picture of what I mean and how to do it. You only need a DMM and a calculator.
Last thing, taking out the speaker protection will have no impact on the amp, but I wouldn’t hook up any speakers until you sort out the issue(s) and put the protection back in and confirm it is working.
I bought two LM L2-2 ver 4 amplifier boards on Aliexpress and two boards on EBAY.
I decided to create a voltage map of the amplifier. I used the scheme from the Calvin website. Many thanks to Calvin!
I noticed one discrepancy with the scheme on my boards. Transistor Q12 is connected differently. On my boards, the base of the transistor Q12 is connected to the resistor R19, and the collector to the base of the transistor Q17. I made a change in the circuit.
I decided to create a voltage map of the amplifier. I used the scheme from the Calvin website. Many thanks to Calvin!
I noticed one discrepancy with the scheme on my boards. Transistor Q12 is connected differently. On my boards, the base of the transistor Q12 is connected to the resistor R19, and the collector to the base of the transistor Q17. I made a change in the circuit.
Attachments
Maybe I was too hasty.
"It turned out that for 2N5551 there are different schemes of arrangement of contacts. Chinese KEC is different from all others, such as Fairchild, OnSemi, etc. EB CE CB standard."
I will need to remove the Q12 transistor from the board and check the contacts.
"It turned out that for 2N5551 there are different schemes of arrangement of contacts. Chinese KEC is different from all others, such as Fairchild, OnSemi, etc. EB CE CB standard."
I will need to remove the Q12 transistor from the board and check the contacts.
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Hi Bullisttang:
Yesterday I removed the X7R capacitors, checked each connection and turned it on again. It worked!. Speaker protection is no longer activated. I waited an hour and everything seems fine.
I adjusted the BIAS as you indicated and left it at 8mv on both channels (about 36mA). I aslo measured the DC at the output, and stay between 6 and 7 mv in one channel and between 7 and 9mv in the other. I think it's okay.
Today I will do audio tests.
Thank you very much for the help!
I removed the transistor and checked the location of the contacts.
The location of the contacts differs from the standard European one. Now it is clear where the L12-2 amplifier circuit with an incorrect Q12 connection came from on the Internet.
How do I remove the wrong schema?
The location of the contacts differs from the standard European one. Now it is clear where the L12-2 amplifier circuit with an incorrect Q12 connection came from on the Internet.
How do I remove the wrong schema?
Attachments
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105 The capacitance can measure whether it is damaged.Regards,
For the first time in my life (and I'm in my 50's) I assembled an audio amplifier, the LJM L12-2 V4. I have almost no experience in electronics, just the basics of measuring with a DMM and replacing some parts and such.
I used a 300 VA 25-0-25 toroidal transformer, which rectified to 34V DC, I recycled the chassis of an old Sony amplifier and put a speaker protection circuit on it. I plugged it into a bulb current limiter, no speakers, no preamplifier connection, no other audio signals connected and turned it on with no problem: no short circuit, no smoke, no strange noises or smells.
For the first minute I measured the DC output and it gave me between 6 and 7mv on each channel. All right!. After a minute it went up a bit to 7-8 mv. I didn't measure it anymore. I left it on, to wait for it to stabilize. So far so good...
But after 2 and a half minutes, the speaker protector activated for a second and then continued normal, but after 10 seconds the same thing happened again, and it was repeated like this every 10 seconds. All without connected speakers or sound source. I turned it off, as something was not right.
Please, I need help to identify what may be happening.
I did the following tweaks, prior to installation:
1. I put X7R capacitors in parallel for all lytics (except C5).
2. Increasing the high-current paths crossection by applying solder.
3. Replaced R19 per Calvin's recommendation, to make BIAS adjustments. I replaced 1K with 1.5K and added 5K potentiometer in parallel. I calibrated it to stay at 1K again, before the first power up.
I also disconnected one card at a time, to see if the problem came from one of them, but the same thing happened with both. I haven't used it without the speaker protection (which could be where the fault is…), but I don't know if this risks burning the boards. I could hook up cheap test speakers to it and see if it makes noise, but only if you tell me if it's safe.
I haven't measured the BIAS yet. I don't have an oscilloscope, just a DMM and a lot of goodwill.
Any idea what could be happening? Suggestions?
Thank you.
Measure with the resistance gear of the multimeter. If the resistance is small. This capacitor may be damaged.
It can be replaced with an aluminum electrolytic capacitor. Or do not install any capacitor. There will be no difference.
If there is no DC output. OUT。 There may be a problem with the protection circuit.
Does anyone has experience with those L12-2 (v4) amp kits from Aliexpress (JOJOHIFI Store)?
I am a bit worried if those are indeed supplied with genuine SANKEN devices?
Maybe I`m a bit paranoid but buying any semiconductor (audio) related stuff is no fun anymore these days...fakes everywhere.
I have read somewhere that the thread starter and designer of this amp "ljm_ljm" is selling at Taobao.
Would likely be the best bet to get genuine parts but I have absolutely no clue about how to buy there.
Would prefer the kit version as I want to a.) rely only on my own soldering and b.) want to use my own choice of parts (for example I certainly would not use the electrolytic caps that are supplied with the kits).
Even better would be only to buy bare PCBs + corresponding sets of (genuine) SANKEN output transistors but I can not find this offered anywhere
Only ready soldered amps or complete kits.
Any ideas where to buy in order getting the "real thing" (maybe PCBs + SANKENs only)?
I am a bit worried if those are indeed supplied with genuine SANKEN devices?
Maybe I`m a bit paranoid but buying any semiconductor (audio) related stuff is no fun anymore these days...fakes everywhere.
I have read somewhere that the thread starter and designer of this amp "ljm_ljm" is selling at Taobao.
Would likely be the best bet to get genuine parts but I have absolutely no clue about how to buy there.
Would prefer the kit version as I want to a.) rely only on my own soldering and b.) want to use my own choice of parts (for example I certainly would not use the electrolytic caps that are supplied with the kits).
Even better would be only to buy bare PCBs + corresponding sets of (genuine) SANKEN output transistors but I can not find this offered anywhere
Only ready soldered amps or complete kits.
Any ideas where to buy in order getting the "real thing" (maybe PCBs + SANKENs only)?
Hello everyone.
I bought 2 boards of this amp on ebay from seller with nickname "toplasers2016", it's ver4 and there is 🐼 in corner and now I would like to know couple questions.
First is there any easy way of testing boards with only multimeter are they legit or I got some fake ones ?
I was measured DC offset on outputs and 1 board is around 12mV and other around 20mV and I was wondering for modification could I just replace R19 with 2k pot without parallel connection with 1.5k resistor and 5k pot and also could I just try to replace some resistors to get on normal DC offset ?
Thanks and please keep in mind I have only multimeter and soldering iron and just a lot of love for electronics and I'm steel noob. 🤓
I bought 2 boards of this amp on ebay from seller with nickname "toplasers2016", it's ver4 and there is 🐼 in corner and now I would like to know couple questions.
First is there any easy way of testing boards with only multimeter are they legit or I got some fake ones ?
I was measured DC offset on outputs and 1 board is around 12mV and other around 20mV and I was wondering for modification could I just replace R19 with 2k pot without parallel connection with 1.5k resistor and 5k pot and also could I just try to replace some resistors to get on normal DC offset ?
Thanks and please keep in mind I have only multimeter and soldering iron and just a lot of love for electronics and I'm steel noob. 🤓
Thank you tu100, you save my life... I am making this amplifier by myself (PCB, components, and others) and I did not understand the pinout of this 2N5551. You give me the answer "The transistor with the kit come from India (NCC 5551 = Make by CDIL Continental Device India Limited) And it is the only one with pinout BCE. All others have EBC...".
I did the same mistake - I wanted to be "clever" - but components from the kit are good. Just measure and use the components from the kit. Don't apply the proposed mods except: (1) change the C5 capacitor for something better and (2) (perhaps) adjust the bias with potentiometer. Nothing else.
L12-2 kit is good as-is.
I agree with you for the mods, and that's what I just want to do. For the other things, I want to use 1w resistors, better capacitors, a larger headsink for Q5, Q6 and Q9, a better PCB (larger tracks and 4oz thickness) and separated PSU for the channels. It's this thread (that I have read from the first page) that makes me begining this fine amplifier. I hope it will replace my old amplifier (a NAD C325 BEE) with happiness. Thank you for your advice Sir Berlusconi (I will go in the begining of june in Italy and I will sleep near san Siro in "Milano". It's a land where your name is famous...).
Didier
Didier
This pcb looks like the one designed by ljm ljm version 4. Be careful with the power transistors (theirs back faces are linked to the collector).