"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets

[Stammheim]

No, "clipping" stays the same, from zero to the max.
Both voltages are at +-43V.

 

[astx]

Hi guys,

after the Mosfet's got burnt I also replaced the LME-IC and measured the output of the LME49830 WITHOUT the Mosfets using a sine signal. The negative amplitude looks like it is clipping (flat amplitude), so I made a short clip of it, while increasing and decreasing the singal voltage.

What is strange is that both new amps show the same behaviour, unfortunatelly I cannot compare with other amps anymore.
Please could you watch my clip and give me a hint??

https://youtu.be/pAG_khKDSxk

Both channels are connected, so Pout and Nout are visible and are equal btw...

Schematic of your test scenario? Have you had a minimum load during this test?

BR, Toni

 

[scottjoplin]

Thanks, that's put my mind at rest. Just checked data sheet, my sink should be ok. Still...I'm tempted to drop the chip voltage a bit, I don't need that much power.

Hi,astx. I dropped the voltage to the chips to about +/-43V with 1k resistors in the chip power rails, much cooler now. Do you see any problem with this?

 

[Clockworktent]

Hi guys,

after the Mosfet's got burnt I also replaced the LME-IC and measured the output of the LME49830 WITHOUT the Mosfets using a sine signal. The negative amplitude looks like it is clipping (flat amplitude), so I made a short clip of it, while increasing and decreasing the singal voltage.

What is strange is that both new amps show the same behaviour, unfortunatelly I cannot compare with other amps anymore.
Please could you watch my clip and give me a hint??

https://youtu.be/pAG_khKDSxk

Both channels are connected, so Pout and Nout are visible and are equal btw...

Have you tried measuring the LME output with the mosfets connected?

 

[Boss1920]

I'm looking for a spice model LME49830. Can anyone help me ?

 

[Wimshurst]

Strange thing. I get random a very loud pop at high level. I'm afraid it will damage the woofer(s). Very hard to find the reason because it happens only once a week or so. Tapping the PCB doesn't help. Bad PSU or input cap? It started after I soldered the protection diodes over the mosfets. Could one of the diodes have this effect? I'm sure it is the amp because there was no input connected when it happened the last time. I'm not sure if it is one or two channnels. The amp worked perfect for more then a year or so.

 

[multisync]

remove one end of the diodes and see what happens.

 

[Wimshurst]

remove one end of the diodes and see what happens.

Going to do that and get my hands on some coldspray.

 

[Trollet]

Hi.
Does anyone know if there is a PCB made for LME49830 and SJ55/SK175 -TO3 ?
...and yes, I'm to lazy to watch all pages in the thread....

Regards

Figge

 

[scottjoplin]

^ I've used these 100W Lateral TO3 package MOSFET Power Amp PCB DIY - Audiomodule.eu if you email him he may have some boards made up for you, he did for me, he was very helpful

 

[Trollet]

Thank's scottjoplin. I will take a look into that. I would prefer 2 or 3 pairs of output devices, my speakers are down to 3.6 ohm, but it could be a good prototype.

Regards

Figge

 

[IanAS]

I get random a very loud pop at high level.......I'm sure it is the amp because there was no input connected when it happened the last time.

It might be via the mains supply. From, eg, a fridge switching on/off. Or heating.

 

[Wimshurst]

It might be via the mains supply. From, eg, a fridge switching on/off. Or heating.

Yes, this was the first thing I was thinking of but after the pop I hear the DC protection relais resetting. I will check the groundings of the house system soon.

 

[Wimshurst]

Freeze spray does nothing. Amp is quiet.

 

[Wimshurst]

Took out the zener protection. Connected everything to another mains group. After 15 minutes: BAM! Loud thumb. DC protection comes in. Goes off and the amp is playing again without a problem. Could play for hours and then suddenly BAM! Bad capacitor? Very hard to find out if it is one channel or both.

 

[IanAS]

Does it happen when you replay the same few seconds of the music that was playing when it did it?

My Meridian 605 amplifiers operate their DC protection relays due the low frequency content of some music.

 

[Wimshurst]

No, even with no music it happens. I have to do some more tests with some old speakers, so I won't blow my woofers. See if it is in one channel. = amp problem or two channels = psu problem. DC protection can be activated due to the low thumb, I guess. Or the output is a short moment close to railvoltage. = bad cap or so. Nasty problem.

 

[Wimshurst]

After another nasty loud pop the amp stopped playing. Both PSU railfuses blown. Speaker relay right channel welded (!), but the speaker itself survived. Left channel still works ok. I replaced the LME49830 right channel, which seems to be blown. Nowhere smoke. The Semelab fets survived! Wow. Everything is working. No pops untill now, so I think the LME was the culprit. Very strange, some weird internal LME problem or maybe a bad (invisible) solder joint or a little crack in the opamp.....
Fingers crossed.

 

[scottjoplin]

Yes, fingers crossed, the chips are obsolete now and I have 4 amps that use them. You wouldn't have anymore spare by any chance?

 

[multisync]

Whimshurst,

Just out of curiosity, what are your rail voltages and are the rails fused? Do you know the relay contact DC current and voltage rating?