I didn't change anything in the amplifier, I wanted to change it bias etc, but I saw that it sounds good and so
The modifications I was thinking of are these: Verstarker - Leistungsverstarker - calvins-audio-pages
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I wanted to change the amplifier, bias, etc., but I saw that I was not taken into account, I gave up, I know you are staff, I am a little electronics
if I said what I was doing in the project, they would laugh at me, that's how I made audiophiles work
Hi I hope you don’t mind me posting on here but it is the closest I could find to the L20.5 amplifier boards as designed by LJM. I have a problem with one of the channels on this amplifier. One channel works perfectly but the other channel seems to have a fault and to be honest I haven’t a clue how to find out what the problem is.
I suppose I had better explain what the problem is I connected both boards to a power supply that I had been using to drive a pair of Quad 405 clones which were working perfectly. Prior to installing them I tested them individually on another very low power supply with cd player, mission speaker and Xiang 728A pre amplifier. Both boards appeared to be working fine I must stress this was at very low volume due to the small power supply.
When I installed the boards into the amplifier box I turned it on and let it run at low volume for a few minutes and all seemed to be well so I increased the volume a small amount to a level that would be akin to someone talking at a normal level. All seemed well but I could hear a little crackle on one channel I immediately turned off the amplifier and disconnected it. After a careful inspection and finding nothing wrong with connections etc and no sign of stress I connected it up again and the same happened. I then removed the board and heatsink and set up a test system in another room with a 100va transformer 18-0-18 to a power supply that I use only for testing purposes. It has 40,000 UF with 4 x 63 volt capacitors and a 50amp bridge rectifier.
At this point when I played music through it there was a constant hum a bit like an earth problem but when I turned the power off with the music still playing all of the hum stopped and until the big capacitors drained of power the music played perfectly. Has anyone any idea of the cause and better still how to fix.
I suppose I had better explain what the problem is I connected both boards to a power supply that I had been using to drive a pair of Quad 405 clones which were working perfectly. Prior to installing them I tested them individually on another very low power supply with cd player, mission speaker and Xiang 728A pre amplifier. Both boards appeared to be working fine I must stress this was at very low volume due to the small power supply.
When I installed the boards into the amplifier box I turned it on and let it run at low volume for a few minutes and all seemed to be well so I increased the volume a small amount to a level that would be akin to someone talking at a normal level. All seemed well but I could hear a little crackle on one channel I immediately turned off the amplifier and disconnected it. After a careful inspection and finding nothing wrong with connections etc and no sign of stress I connected it up again and the same happened. I then removed the board and heatsink and set up a test system in another room with a 100va transformer 18-0-18 to a power supply that I use only for testing purposes. It has 40,000 UF with 4 x 63 volt capacitors and a 50amp bridge rectifier.
At this point when I played music through it there was a constant hum a bit like an earth problem but when I turned the power off with the music still playing all of the hum stopped and until the big capacitors drained of power the music played perfectly. Has anyone any idea of the cause and better still how to fix.
Seller recommendations:
+ -35 to + -50 V, radiator 0.5 kg per channel
+ -40 to + -60 V, radiator 1 kg per channel
Current per channel 20 mA
Recommended Series Connection Bulb in 220V primary transformer for testing. Remove the lamp after normal use.
+ -35 to + -50 V, radiator 0.5 kg per channel
+ -40 to + -60 V, radiator 1 kg per channel
Current per channel 20 mA
Recommended Series Connection Bulb in 220V primary transformer for testing. Remove the lamp after normal use.
Hi OldDIY
many thanks for your reply I use two 300va 25-0-25 AC so after rectification I am within the sellers specs. The boards both worked fine with the above voltage at low volume. Do I need to replace the transistors?
many thanks for your reply I use two 300va 25-0-25 AC so after rectification I am within the sellers specs. The boards both worked fine with the above voltage at low volume. Do I need to replace the transistors?
In the amplifier, all transistors and parts are interconnected. Approximately they can be checked with a multimeter without dismantling (power is turned off). Resistance and diode junctions. You can compare the channels to find the difference.
There may be installation errors, poor soldering, jumpers - check visually.
If you have to change powerful transistors, you can first install one pair. You can drop one pair and see what happens.
You can check powerful transistors for breakdown, leakage separately. Connect the BE, and connect the 10 k limit resistor to the collector. Apply voltage in the correct polarity. The collector full voltage is normal.
There may be installation errors, poor soldering, jumpers - check visually.
If you have to change powerful transistors, you can first install one pair. You can drop one pair and see what happens.
You can check powerful transistors for breakdown, leakage separately. Connect the BE, and connect the 10 k limit resistor to the collector. Apply voltage in the correct polarity. The collector full voltage is normal.
Hi OldDIY
I have almost no experience with checking for damage to amplifiers and to be honest I have been lucky in that almost all the kits I have built up have all worked once constructed. Where I have had problems I have tried to use a common sense approach to sort the problem, the one thing I have learned is most problems are created by using a poor or badly designed power supply. I have ordered replacement transistors and will try to do as you have said. Can you explain further on how to do the testing since I am not sure how much voltage you mean when you say "apply voltage". Building and connecting up amplifiers I am okay with fault finding I am a total novice. Thank you for trying to assist me. Bill
I have almost no experience with checking for damage to amplifiers and to be honest I have been lucky in that almost all the kits I have built up have all worked once constructed. Where I have had problems I have tried to use a common sense approach to sort the problem, the one thing I have learned is most problems are created by using a poor or badly designed power supply. I have ordered replacement transistors and will try to do as you have said. Can you explain further on how to do the testing since I am not sure how much voltage you mean when you say "apply voltage". Building and connecting up amplifiers I am okay with fault finding I am a total novice. Thank you for trying to assist me. Bill
Hi OldDIY,
Many thanks for the tips you were correct I replaced all the resisters and the power transistors and it is now working fine and probably sounds better than it originally did.
Bill
Many thanks for the tips you were correct I replaced all the resisters and the power transistors and it is now working fine and probably sounds better than it originally did.
Bill
Hi OldDIY,
Yes, I did it myself. I wasn't convinced you would be right but what you said made sense - so I bought new Power Transistors and changed the resisters on the edge of the board which I later learned were undamaged. I can't tell you how big the smile was on my face when it worked. Again thank you so much for taking the time to help I could not have repaired it without your help. No I should say I wouldn't have even tried. Ha ha! Can't stop smiling.
Bill
Yes, I did it myself. I wasn't convinced you would be right but what you said made sense - so I bought new Power Transistors and changed the resisters on the edge of the board which I later learned were undamaged. I can't tell you how big the smile was on my face when it worked. Again thank you so much for taking the time to help I could not have repaired it without your help. No I should say I wouldn't have even tried. Ha ha! Can't stop smiling.
Bill
Thanks. I've found 220V speaker protection board (easier for me).
I got my 2 amplifiers today. On Seller page I saw :± 50 V
45V should be OK ?
With my connexelectronic smps500RXE 45v I have a lot of distortion (lower frequencies).
Does anybody knows if I should try another voltage or something else?
Thanks
I own a an nother amp (classdaudio sds250) and everything is OK with my SMPS.
I also tried to feed one L12-2 with lithium battery (36v with 42v charger) = same problem, sound is okay with very low volume but when i try to raise it a little bit I meet a big distorstion amount.
I also tried to feed one L12-2 with lithium battery (36v with 42v charger) = same problem, sound is okay with very low volume but when i try to raise it a little bit I meet a big distorstion amount.
Pictures and link to the exact board you purchased might help.
how did you hook up a dual voltage amplifier to a single battery? You will need +/- 35V to get good clean sound. Looks like the SMPS should work fine, according to the website specs.
If it is connected correctly to your SMPS, then it sounds like you have a driver or output transistor that's bad. You could also have a capacitor that's bad.
how did you hook up a dual voltage amplifier to a single battery? You will need +/- 35V to get good clean sound. Looks like the SMPS should work fine, according to the website specs.
If it is connected correctly to your SMPS, then it sounds like you have a driver or output transistor that's bad. You could also have a capacitor that's bad.
Possible malfunction L12-2. Check, repair, tune.
+ -50 V means bipolar power supply + 50_0_-50 V. Requires 2 SMPS connected in series (in different polarity). If such an inclusion is permissible.
Capacitors may be needed in the power supply, which are not in SMPS.
The metal housing SMPS can be connected to 0 (-). This may be a problem.
+ -50 V means bipolar power supply + 50_0_-50 V. Requires 2 SMPS connected in series (in different polarity). If such an inclusion is permissible.
Capacitors may be needed in the power supply, which are not in SMPS.
The metal housing SMPS can be connected to 0 (-). This may be a problem.
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