Hello 
I build gainclone with LM4780 parallel. (mono 120w) (audiosector PCB)
I have good power supply when loaded I always have 75VDC
I don't have noise or hummm at speaker output but...
*first problem: When I put the sound loud it goes on PROTECTION Is it possible that my heatsink is too small ?
link to view my heatsink for each lm4780
http://cgi.ebay.ca/Aluminum-Heat-Si...ryZ80149QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
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*Second problem: I ALWAYS HAVE 166mVDC at the speaker output
I have only 1.0mVDC at the power supply output.
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*Third problem: I put ALPS 50K pot at input and at the POT output I add coupling cap 2.4uF SOLEN it's okay or not ?
Because when I turn the sound at minimum the lm4780 is very very HOT !
P.s. when I add 2.4uF coupling cap is it possible that it kills my low frequency.
thanks in advance for your hints
nicK
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My power supply is:
500VAC toroidal avel lindberg output 2x25vac
4x 100uF elna Cerafine CAP on power supply PCB
4x 5400uF elna LPO for audio
4x 4.7uF WIMA MKP non polarized
on PCB snubber is: solen 0.01uF non polarized + 0.5ohm 2W
the lm4780 have only audiosector standard parts.
I build gainclone with LM4780 parallel. (mono 120w) (audiosector PCB)
I have good power supply when loaded I always have 75VDC
I don't have noise or hummm at speaker output but...
*first problem: When I put the sound loud it goes on PROTECTION
Is it possible that my heatsink is too small ?link to view my heatsink for each lm4780
http://cgi.ebay.ca/Aluminum-Heat-Si...ryZ80149QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
---------------------------------------------------------------------------------
*Second problem: I ALWAYS HAVE 166mVDC at the speaker output
I have only 1.0mVDC at the power supply output.
---------------------------------------------------------------------------------
*Third problem: I put ALPS 50K pot at input and at the POT output I add coupling cap 2.4uF SOLEN it's okay or not ?
Because when I turn the sound at minimum the lm4780 is very very HOT !
P.s. when I add 2.4uF coupling cap is it possible that it kills my low frequency.
thanks in advance for your hints
nicK
_________________________________________________
My power supply is:
500VAC toroidal avel lindberg output 2x25vac
4x 100uF elna Cerafine CAP on power supply PCB
4x 5400uF elna LPO for audio
4x 4.7uF WIMA MKP non polarized
on PCB snubber is: solen 0.01uF non polarized + 0.5ohm 2W
the lm4780 have only audiosector standard parts.
pics
pics of my gainclone here :
http://profile.imageshack.us/user/gainclone/
I think the problem 2 and 3 was associated because when I put 50K POT at maximum I have 100mVDC speaker output and in minimum volume I have 166mVDC
nicK
pics of my gainclone here :
http://profile.imageshack.us/user/gainclone/
I think the problem 2 and 3 was associated because when I put 50K POT at maximum I have 100mVDC speaker output and in minimum volume I have 166mVDC
nicK
Am I allowed to say "******* Hell"!!!!! and that word starts with F and finishes with k.
But to be constructive:
where is the Safety Earth connection to all and every exposed conductive part?
Leave your parallel chipamp with separated PSU for now.
Get a simple chipamp with simple nearby PSU working and understand what you're trying to achieve.
Then maybe you can progress to this abortion.
But to be constructive:
where is the Safety Earth connection to all and every exposed conductive part?
Leave your parallel chipamp with separated PSU for now.
Get a simple chipamp with simple nearby PSU working and understand what you're trying to achieve.
Then maybe you can progress to this abortion.
I don't understand ??? MY POWER SUPPLY HAVE EARTH GROUND !!!
and my amplifier section TOO !
the problem is my ALPS 50k POT and the LM4780 PROTECTION.
THAT'S IT !
read my first post I don't have HUMMM trouble or noise in speaker or in power supply ! it's AMPLIFIER section trouble.
thanks !
I search for answers please
nicK
and my amplifier section TOO !
the problem is my ALPS 50k POT and the LM4780 PROTECTION.
THAT'S IT !
read my first post I don't have HUMMM trouble or noise in speaker or in power supply ! it's AMPLIFIER section trouble.
thanks !
I search for answers please
nicK
all right, I'll ask the question again, but in more detail.
How many metal parts are exposed on the outside of your two box mono amplifier?
How many of these exposed parts are permanently connected to the Safety Earth?
Are there any non metal parts that can conduct electricity to the outside of the cases?
How many metal parts are exposed on the outside of your two box mono amplifier?
How many of these exposed parts are permanently connected to the Safety Earth?
Are there any non metal parts that can conduct electricity to the outside of the cases?
Interesting that you have 75 V DC under load. With a 2x25V transformer you should get something like 2x33..34 V with no load, and about 2x30..31 V under load.
According to the design guide you need 0.86 K/W for 8 Ohm speakers and 0.05 K/W (!) for 4 Ohm speakers with the 2x37.5 V. Your heatsink doesn't look that efficient.
If you have 75 V and use 4 Ohm speakers you might also reach the current limit.
Concerning the DC voltage at the output and the heat issue at low volume: did you respect the recommendation on page 16 in the datasheet to use 0.1% tolerance resistors for the gain setting (Ri and Rf)?
According to the design guide you need 0.86 K/W for 8 Ohm speakers and 0.05 K/W (!) for 4 Ohm speakers with the 2x37.5 V. Your heatsink doesn't look that efficient.
If you have 75 V and use 4 Ohm speakers you might also reach the current limit.
Concerning the DC voltage at the output and the heat issue at low volume: did you respect the recommendation on page 16 in the datasheet to use 0.1% tolerance resistors for the gain setting (Ri and Rf)?
hi nickthevoice,
Heatsinks should have their fins vertical. Think of the air flowing over the fins and imagine where it goes. Mounting the heatsinks like you have will more than double the size required.
If you can't mount them vertically, the next best is to have the heatsink horizontal with the fins pointing up.
Having said that, I think you may have another problem and when you solve that your heatsinks may be OK for normal volumes if you speakers are 8 ohms and reasonably efficient
Did you short the inputs to ground to make DC offset measurements? If you didn't you will find your measurement will drop considerably.
Andrew is talking about the safety earth not ground earth. I measure the resistance between all metal surfaces and the earth wire on the back of the IEC socket. It looks (in your picture) that the front and back panels are metal and are not connect to safety earth. It seems to me people in 230V/240V countries are a lot more concerned about safety earthing issues, rightly or wrongly.
BTW: What is the supply voltage in Canada?
regards
Heatsinks should have their fins vertical. Think of the air flowing over the fins and imagine where it goes. Mounting the heatsinks like you have will more than double the size required.
If you can't mount them vertically, the next best is to have the heatsink horizontal with the fins pointing up.
Having said that, I think you may have another problem and when you solve that your heatsinks may be OK for normal volumes if you speakers are 8 ohms and reasonably efficient
Did you short the inputs to ground to make DC offset measurements? If you didn't you will find your measurement will drop considerably.
Andrew is talking about the safety earth not ground earth. I measure the resistance between all metal surfaces and the earth wire on the back of the IEC socket. It looks (in your picture) that the front and back panels are metal and are not connect to safety earth. It seems to me people in 230V/240V countries are a lot more concerned about safety earthing issues, rightly or wrongly.
BTW: What is the supply voltage in Canada?
regards
problem
First 75VDC is pushing that top 10% supply range, dissipation goes up as voltage goes up, check Nationals design notes and dissipation figures.
Two the heat sinks are way way to small for a lm4780, again check Nationals app notes on heat sinks.
Third the pot if not separated by a cap will introduce DC into the input. A 4.7uf should not kill your bass at all?? should be smooth to around 5Hz. Get bigger heat sinks, and run the cap between your pot and the amps 1K feeder and 22K shunt, if your designs is built around the data sheets common values.
First 75VDC is pushing that top 10% supply range, dissipation goes up as voltage goes up, check Nationals design notes and dissipation figures.
Two the heat sinks are way way to small for a lm4780, again check Nationals app notes on heat sinks.
Third the pot if not separated by a cap will introduce DC into the input. A 4.7uf should not kill your bass at all?? should be smooth to around 5Hz. Get bigger heat sinks, and run the cap between your pot and the amps 1K feeder and 22K shunt, if your designs is built around the data sheets common values.
As far as I understand your first post, you already use a 2.4µF decoupling capacitor after the poti. So you should not be getting any DC from the input. The DC noise must come either from the chip itself or from some grounding loop. If you bought a PCB from Audiosector we can assume that the layout does not allow for the latter.
The chip has of course a small DC offset at the input, and that leads me to the resistors. It may be an issue, because with higher resistor tolerances you may get different gains per amplifier channel, resulting in currents running from one channel to the other to establish an equilibrium. This could explain excessive heating at no load as well as a high DC offset at the output.
As an example take 1k for Ri and 20k for Rf with 10% tolerance each. In a worst case scenario you have 1k -10% = 0.9k for Ri1 and 20k +10% = 22k for Rf1, resulting in a gain of 25.44. Then you have 1k +10% = 1.1k for Ri2 and 20k -10% = 18k for Rf2, resulting in a gain of 17.36. You see, what happens, when you imagine e. g. 10 mV of noise at the input? Channel 1 will deliver 254.4 mV, channel 2 173.6 mV. The result will probably be an output voltage of 214 mV at the speaker terminal. But of course both channels are trying to reach their corresponding 254.4 and 173.6 mV, so they are constantly wrestling against each other and heat up even under no load.
This will of course also happen under normal operation. Your music signal will also be amplified with those different gain factors, and the currents between the two channels will be accordingly higher. This could also be a reason for the chip protection to trip.
If you want to check that idea you need to measure the current from pin 7 or 25, meaning you would have some soldering to do.
Or, what is easier, you could take the Ris and Rfs out and measure their absolute values. Then you either buy 0.1% tolerance types or you measure several resistors from your stock and use pairs that fit better than the ones you are currently using. Don't worry about the absolute values. The interesting point is that they have little difference between each other. You want Ri1 = Ri2 and Rf1 = Rf2 as closely as possible.
The heat sink might become an issue at high listening levels. Can you measure the temperature of the LM4780 or the heat sink next to the chip, when the protection kicks in? Or could you try with a steady signal (e. g. sine wave) to increase the volume and measure the output current at which the protection kicks in? So you could find out, if the heat protection or the current protection are the reason for switching off, and so can close in on the trouble maker.
Please download the "Overture Design Guide" from http://www.national.com/appinfo/audio/. There you can fill in your values and you get a heatsink recommendation and also the output current. You will see that you reach a current limit with your supply voltage at 4 Ohms. And keep in mind that those values are for a pure resistive load. A real speaker might have 20 % less impedance at certain frequencies (3.2 Ohms for a nominal 4 Ohm speaker) resulting in even higher output current or in reaching the current limit at a lower output voltage.
The chip has of course a small DC offset at the input, and that leads me to the resistors. It may be an issue, because with higher resistor tolerances you may get different gains per amplifier channel, resulting in currents running from one channel to the other to establish an equilibrium. This could explain excessive heating at no load as well as a high DC offset at the output.
As an example take 1k for Ri and 20k for Rf with 10% tolerance each. In a worst case scenario you have 1k -10% = 0.9k for Ri1 and 20k +10% = 22k for Rf1, resulting in a gain of 25.44. Then you have 1k +10% = 1.1k for Ri2 and 20k -10% = 18k for Rf2, resulting in a gain of 17.36. You see, what happens, when you imagine e. g. 10 mV of noise at the input? Channel 1 will deliver 254.4 mV, channel 2 173.6 mV. The result will probably be an output voltage of 214 mV at the speaker terminal. But of course both channels are trying to reach their corresponding 254.4 and 173.6 mV, so they are constantly wrestling against each other and heat up even under no load.
This will of course also happen under normal operation. Your music signal will also be amplified with those different gain factors, and the currents between the two channels will be accordingly higher. This could also be a reason for the chip protection to trip.
If you want to check that idea you need to measure the current from pin 7 or 25, meaning you would have some soldering to do.
Or, what is easier, you could take the Ris and Rfs out and measure their absolute values. Then you either buy 0.1% tolerance types or you measure several resistors from your stock and use pairs that fit better than the ones you are currently using. Don't worry about the absolute values. The interesting point is that they have little difference between each other. You want Ri1 = Ri2 and Rf1 = Rf2 as closely as possible.
The heat sink might become an issue at high listening levels. Can you measure the temperature of the LM4780 or the heat sink next to the chip, when the protection kicks in? Or could you try with a steady signal (e. g. sine wave) to increase the volume and measure the output current at which the protection kicks in? So you could find out, if the heat protection or the current protection are the reason for switching off, and so can close in on the trouble maker.
Please download the "Overture Design Guide" from http://www.national.com/appinfo/audio/. There you can fill in your values and you get a heatsink recommendation and also the output current. You will see that you reach a current limit with your supply voltage at 4 Ohms. And keep in mind that those values are for a pure resistive load. A real speaker might have 20 % less impedance at certain frequencies (3.2 Ohms for a nominal 4 Ohm speaker) resulting in even higher output current or in reaching the current limit at a lower output voltage.
It's much worse than that.pacificblue said:
Many agree that the peak current can be upto around double the sinewave peak value into a reactive load, but some argue that the transient peak current can approach three times the sinewave peak into a nominal impedance.
Your 4ohm reactive speaker can hit [Vpk/4/0.35]amps. This will cause Spike to limit and cause heating that makes Spike limit even earlier.
For a 79Vdc supply the rails will be +-39.5Vdc, subtract about 4V to obtain transient peak output voltage and we have 35.5V across your 4ohm reactive load. That is a potential peak current approaching 25Apk on a fast starting or fast stopping transient.
Absolutely right. That should of course only cause the chip to limit the current for that transient and not to switch off.
And oops, I didn't use the design guide correctly. As the two channels are in parallel at 4 Ohms, the calculation should be made for 8 Ohm per single channel. The numbers get a bit friendlier then. Ipeak at 4.2 A per channel should be enough safety margin, and the heat sink should be 0.86 K/W. So there must be something else.
Even so, listening at levels, where this becomes an issue, must be really unhealthy, if not unbearable.
BTW looking at your photos, it seems as if the heat sink is directly mounted onto the bottom and the back of your housing. Maybe there are holes that are hidden in the photo?
The heat sink should be mounted in a way that air can circulate freely around it. Holes in the bottom and the top of the housing are the least you should do. Or even better to move the heat sink to the outside, so that it forms the backwall, and the fins are entirely outside of the housing.
And oops, I didn't use the design guide correctly. As the two channels are in parallel at 4 Ohms, the calculation should be made for 8 Ohm per single channel. The numbers get a bit friendlier then. Ipeak at 4.2 A per channel should be enough safety margin, and the heat sink should be 0.86 K/W. So there must be something else.
Even so, listening at levels, where this becomes an issue, must be really unhealthy, if not unbearable.
BTW looking at your photos, it seems as if the heat sink is directly mounted onto the bottom and the back of your housing. Maybe there are holes that are hidden in the photo?
The heat sink should be mounted in a way that air can circulate freely around it. Holes in the bottom and the top of the housing are the least you should do. Or even better to move the heat sink to the outside, so that it forms the backwall, and the fins are entirely outside of the housing.
But is that "little" copper bar is connected to the case metal work?
Little it is not!
Your sink is far too small for two channels of chipamp and it is oriented the wrong way and it is obscured from an effective cool air flow.
I doubt it would work sufficiently with a single channel even if it were mounted correctly (it's nowhere near 0.86C/W).
Little it is not!
Your sink is far too small for two channels of chipamp and it is oriented the wrong way and it is obscured from an effective cool air flow.
I doubt it would work sufficiently with a single channel even if it were mounted correctly (it's nowhere near 0.86C/W).
it's standard digikey resistor !
but I try my system with 8ohm speaker and all work well if I put the amplifier at maximum volume it distortion but don't goes on PROTECTION.
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but my power supply is to high with 75volt DC for 4 ohm speaker.
look at national.com Lm4780
page 12
4ohm Clipping Voltage vs Supply Voltage
it's +/- 36V MAX = 72vDC
and
page 10
at 4ohm Output Power/Channel vs Supply Voltage
it's +/- 30V MAX = 60vDC
but at page 13
Output Power vs Supply Voltage, Parallel Mode (Note 19)
f = 1kHz, RL = 4Ω, 80kHz BW
the supply voltage runs until +/- 40volt = 80VDC
THANKS !!!
nicK
but I try my system with 8ohm speaker and all work well if I put the amplifier at maximum volume it distortion but don't goes on PROTECTION.
------------------------------------------------------------------------------------
but my power supply is to high with 75volt DC for 4 ohm speaker.
look at national.com Lm4780
page 12
4ohm Clipping Voltage vs Supply Voltage
it's +/- 36V MAX = 72vDC
and
page 10
at 4ohm Output Power/Channel vs Supply Voltage
it's +/- 30V MAX = 60vDC
but at page 13 Output Power vs Supply Voltage, Parallel Mode (Note 19)
f = 1kHz, RL = 4Ω, 80kHz BW
the supply voltage runs until +/- 40volt = 80VDC
THANKS
!!!nicK
Your system doesn't go into protection with an 8 Ohm speaker, because the current is lower. Consequently you have less heat.
The diagrams are all for the typical application (1 channel, 1 speaker). You are working with the parallel application. That means with a 4 Ohm speaker you use the 8 Ohm diagrams.
Your supply voltage is okay (page 3). You need to improve your cooling.
The diagrams are all for the typical application (1 channel, 1 speaker). You are working with the parallel application. That means with a 4 Ohm speaker you use the 8 Ohm diagrams.
Your supply voltage is okay (page 3). You need to improve your cooling.
- - Buy an adequate heat sink. (0.86 K/W or less)
- Use thermal grease between the chip and the heat sink, if you didn't already (I don't see anything like that coming out on the sides of your chip, like it usually would)
- Mount the heat sink in a way that it can actually dissipate heat, i. e. fins outside of the case or sufficient holes in the case around the heat sink.
- And change those resistors. It will help a little with your problem (though not solve it) and will also improve the sound, because it takes stress off the chip
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