Hi guys. The fan on my amp ended its life last week so I ordered one from DigiKey with pretty much the same specs. I opened the case and when I was unplugging the connector, I noticed I had a bad cap, resistor and a dead transistor. They are items R120, C60 and T27 circled in the schematic. So I removed the board and replaced the components. Now I use this amp in my home theater to power my 18" sealed sub that is rated @ 1000 watts and 22mm xmas. The speaker is 2Ω x 2 voice coil wired in series to get the 4Ω. Now, I am sure I plugged back the myriad of wires that are on this power board but, my amp is heating up with a burning smell. I am by no means a tech but am handy around electronics as long as it is not to complicated. I set up a few 100 watt resistors wired to give me 4Ω and fired up the amp and input a 50Hz signal from my phone. The phone outputs about 275mV. Here are the readings I am getting with only channel 1 driven:
in stereo mode, I get into 4Ω load 14.63 volts @ 1.53 Amps. The draw from the wall outlet is 5.8 A @ 120 V.
In bridge mono mode (Which is what I was running my sub at) 4Ω load 33 V @ 8.04 A. Draw is 11.1 A
8Ω bridge 31.75V @ 3.87A
So after looking at everything, the front part of channel 1 heats up very rapidly. When I was blasting it in bridge 4Ω, it took only a few minutes before the fan rpm rose like it had too much voltage at which point, I shut it down. I also noticed that when connected to the lfe output of my receiver and playing music with heavy bass with the volume on the amp set at 24 db, the stereo mode barely moves the sub speaker while the bridge mode does move it to maybe 1/3 of its cone movement capacity. So all this to say, besides the burning smell, what do I look at next. I only attached the last page of a 3 page schematic. If you need it complete, let me know.
in stereo mode, I get into 4Ω load 14.63 volts @ 1.53 Amps. The draw from the wall outlet is 5.8 A @ 120 V.
In bridge mono mode (Which is what I was running my sub at) 4Ω load 33 V @ 8.04 A. Draw is 11.1 A
8Ω bridge 31.75V @ 3.87A
So after looking at everything, the front part of channel 1 heats up very rapidly. When I was blasting it in bridge 4Ω, it took only a few minutes before the fan rpm rose like it had too much voltage at which point, I shut it down. I also noticed that when connected to the lfe output of my receiver and playing music with heavy bass with the volume on the amp set at 24 db, the stereo mode barely moves the sub speaker while the bridge mode does move it to maybe 1/3 of its cone movement capacity. So all this to say, besides the burning smell, what do I look at next. I only attached the last page of a 3 page schematic. If you need it complete, let me know.
Attachments
Since no one replied, I have another question. I tested one of those cheap $25.00 Chinese LM3886 Stereo boards that I built from a kit a while back. How is it that, with the same resistor dummy load, I can get more voltage out of the 4 and 8Ω loads, with less draw from the wall outlet(120V). I did not try in bridge mode since the amp is not rated for it but I got
21.56V @ 5.06A with a draw of 2A from the wall outlet? I know that my testing method is far from scientific but, something must be clamping the EP2500 down to get such low voltage and high draw from the wall. Again, any suggestions as to what I could check next. I do have an Oscope if that helps but, have not used it much.
21.56V @ 5.06A with a draw of 2A from the wall outlet? I know that my testing method is far from scientific but, something must be clamping the EP2500 down to get such low voltage and high draw from the wall. Again, any suggestions as to what I could check next. I do have an Oscope if that helps but, have not used it much.
Well gentlemen, this is not amounting to much. Does anyone know where I can get a service manual for this? The techs around here charge $65.00 just to open it up and take a quick look at it and then its an hourly rate to repair. I don't think its worth it. I might just use it until it blows something and then to the dumpster if I can't repair it.
50 Hz at full blast is hard for any amp. No wonder it heats up.
Amps and speakers are usually tested with pink noise, not with sinusoidal waves.
Music isn't sinusoidal.
Check the speaker voice coils & play some music at moderate power and verify it doesn't distort or smells. Try one voice coil at a time.
Are You sure they are in series or are they cancelling themselves out of phase ?
Well I did connect them in series and when I checked with the ohm meter, it does give me a reading of 4Ω. I did check the supply rails and everything was OK at ±110 and 55V. Even checked the 15V and it checked out. I was asking because after replacing the components, there is a burning smell coming out of the amp. I will plug it to my sub and see what happens.
Thank you MAAC0. I ran the amp with music out of my av in my small 10.5 x 22 ft home theater. The music was quite loud at around 100 db c weighing, louder than the 80-85 db I usually listen too and this, is at my listening position. I shut off the other sub that I have to make sure that what I was hearing came from the sub powered by this amp. Although I am at a loss to why it still smells like components are burning, after 10 straight hours of play, the amp performed flawlessly with the heat sinks just barely warm to the touch. I never realized how much a sine wave could torture an amp this much. Maybe I will find a place in my HT for my small LM3886 amp to power just my 4 ceiling mounted Atmos speakers or by amp my mains since it gave good results in my torture test. Again, thanks.
Don
Don
If you smell something “burning” you may have some component that’s NOT on the heat sink overheating. There might still be a problem. Usually when thats happening it doesn’t behave normally, though. Some of the resistors normally do run hot, and they may just be off-gassing and quit smelling eventually.
Most modern power amplifiers have trouble dealing with full power sine waves. Even ones that cost eight thousand dollars. In normal operation they will never be called on to put out that much continuously unless you’re constantly blowing speakers. Even DJs who ‘blast’ their systems rarely put out over quarter power on average, maybe half for a minute or two before coming up for air. When doing that the distortion is so bad you can’t even tell what song is playing. If you DO need to run that hard you need one of the vintage amps that have the whole top made out of heat sink, and have a fan that sounds like a low flying plane. Those could do it. But they don’t make them like that anymore and if they did they would be super expensive.
Most modern power amplifiers have trouble dealing with full power sine waves. Even ones that cost eight thousand dollars. In normal operation they will never be called on to put out that much continuously unless you’re constantly blowing speakers. Even DJs who ‘blast’ their systems rarely put out over quarter power on average, maybe half for a minute or two before coming up for air. When doing that the distortion is so bad you can’t even tell what song is playing. If you DO need to run that hard you need one of the vintage amps that have the whole top made out of heat sink, and have a fan that sounds like a low flying plane. Those could do it. But they don’t make them like that anymore and if they did they would be super expensive.
I have an old Philips AH578 that I purchased new in 1978. One channel is blown and I somehow can't seem to get rid of it. I don't have the knowledge to repair it and it might be somehow cost prohibitive to repair it since the power supply caps are all bulging but, at the time, I really did like that amp. Coupled with my Altec A7-5oo my friends thought I had a pretty good sound system and I agreed with them.
Don
Don