http://www.mpja.com/productview.asp?product=14674+HS
The above link is to the heatsink I am using. Ok, so I am concerned with the temperature I am getting for my Chip amp. I was under the impression that the amps ran cool to the touch, or rather, just a little warm. This amp is running warmer than my large main amp. I dont have a thermometer to test with yet, but I can get back to you with that. The chip and mounting screw is now staying to about the same temperature as the rest of the heatsink, probably slightly higher, but not like before, however now the hole heatsink is quite warm. Not too warm to touch, but quite warm. Is the heatsink too small, did I introduce some other problem? Is that one not large enough to have two amp modults mounted to?
The only other thing I could think of is the power supply, running to high of rail voltages. I am currently running the 330VA 25-0-25v Avel transformer, are my rail voltages going to be too high, I was under the impression this was within the safe range, but at the higher end. My rail voltage appears to be about 36 volts. Is that high?
The above link is to the heatsink I am using. Ok, so I am concerned with the temperature I am getting for my Chip amp. I was under the impression that the amps ran cool to the touch, or rather, just a little warm. This amp is running warmer than my large main amp. I dont have a thermometer to test with yet, but I can get back to you with that. The chip and mounting screw is now staying to about the same temperature as the rest of the heatsink, probably slightly higher, but not like before, however now the hole heatsink is quite warm. Not too warm to touch, but quite warm. Is the heatsink too small, did I introduce some other problem? Is that one not large enough to have two amp modults mounted to?
The only other thing I could think of is the power supply, running to high of rail voltages. I am currently running the 330VA 25-0-25v Avel transformer, are my rail voltages going to be too high, I was under the impression this was within the safe range, but at the higher end. My rail voltage appears to be about 36 volts. Is that high?
Need more info.
What IC are you using? Depending on what chip you are using and under what load that heatsink might not be big enough for two chips.
What is the impedence of your speakers (4ohm, 8ohm)? The LM3875 cannot drive 4ohm loads with the voltage levels you are using.
Have you checked the DC offset at the outputs? High DC offset can create added heat.
What about only using one chip on the heatsink. Does it still get hot?
What IC are you using? Depending on what chip you are using and under what load that heatsink might not be big enough for two chips.
What is the impedence of your speakers (4ohm, 8ohm)? The LM3875 cannot drive 4ohm loads with the voltage levels you are using.
Have you checked the DC offset at the outputs? High DC offset can create added heat.
What about only using one chip on the heatsink. Does it still get hot?
I am using an LM3875 chip into an 8ohm nominal impedence. The Speakers are JmLabs Electra 905's with the crossovers remaid using better parts, but all values were basicly kept the same. I would expect Impedence to have not changed from that modification.
With just one amp it gets less hot, but still warm, two amps is definatly making it hotter, but that would only be expected, two heat sources instead of one. Again, it doesn't get so hot it I can't keep my hand on it, I just was under the impression that the amps didn't run hot at all.
As for the DC Offset, how exactly do I measure that, I asked this once before and really didn't get an answer. Do I simply hook a load, like an 8ohm resister, and plug the amp in, then measure the dc voltage across the resistor. DO I have to short the input? Let me know, as I was intrested to measure the dc offset.
With just one amp it gets less hot, but still warm, two amps is definatly making it hotter, but that would only be expected, two heat sources instead of one. Again, it doesn't get so hot it I can't keep my hand on it, I just was under the impression that the amps didn't run hot at all.
As for the DC Offset, how exactly do I measure that, I asked this once before and really didn't get an answer. Do I simply hook a load, like an 8ohm resister, and plug the amp in, then measure the dc voltage across the resistor. DO I have to short the input? Let me know, as I was intrested to measure the dc offset.
To check DC offset you can connect a 10 ohm resistor to the outputs and measure the DC across the resistor. You do not short the input.
At +-36 volts the LM3875 will dissipate close to 35 watts of heat. Two of them on one heatsink would mean 70 watts to be dissipated. With out knowing how hot the heatsink is, it does not sound too abnormal what you are feeling.
I run my LM3875 amp from a +-25volt supply. With that voltage it barely gets warm with a smaller heatsink. The more voltage you apply for a given load, the more heat will be produced. You are suppling at the upper end of what the LM3875 can handle, therefore more heat.
At +-36 volts the LM3875 will dissipate close to 35 watts of heat. Two of them on one heatsink would mean 70 watts to be dissipated. With out knowing how hot the heatsink is, it does not sound too abnormal what you are feeling.
I run my LM3875 amp from a +-25volt supply. With that voltage it barely gets warm with a smaller heatsink. The more voltage you apply for a given load, the more heat will be produced. You are suppling at the upper end of what the LM3875 can handle, therefore more heat.
What is hot really? It's a little vauge description about your heat problems.
Since the LM3875 is a class AB amp normal theories applies. I recommend that you read the following documents where heatsink issues are described.
http://www.national.com/ds/LM/LM3875.pdf
http://www.national.com/an/AN/AN-1192.pdf
http://www.national.com/appinfo/audio/files/Overture_Design_Guide13.xls
http://www.national.com/appinfo/audio/files/Using_Overture_Design_Guide.pdf
Since the LM3875 is a class AB amp normal theories applies. I recommend that you read the following documents where heatsink issues are described.
http://www.national.com/ds/LM/LM3875.pdf
http://www.national.com/an/AN/AN-1192.pdf
http://www.national.com/appinfo/audio/files/Overture_Design_Guide13.xls
http://www.national.com/appinfo/audio/files/Using_Overture_Design_Guide.pdf
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Joined 2002
Yes I used thermal paste, though maybe not enough, but I dont see it causing this problem.
As for what is heat, I dont know, I need to measure, this may be normal. As for the remark about if it gets hot with no load, yes it does, but not as hot, or even what I would call hot hot. It gets warm to the touch, but easily something I can place my hand on comfortably. However, again, this is still quite a bit warmer than my very cool running Acurus amp. I dont see any shorts, I can't imagine I have any, but anything is possible, any thoughts on a place where a short would not strongly effect sound, but would cause such heat. One thing was my power wires, I didn't have wire of small enough guage without being way too small, so I simply trimmed the wire to fit into the hole, and so the edges were a bit scraggly, but I dont believe I had any loose ends that could have touched anything they shouldn't. I will look it over, or posisbly redo it with better wire.
As for the heatsink, it looks like it says its just bare aluminum. I think I read somewhere, maybe on the ESP sight, that anodized aluminum works much better. Something about black oil even better. Not sure what Black Oil is, but for the anodized, if it says bare aluminum, is it probably not anodized, should I consider doing that? Thanks.
As for what is heat, I dont know, I need to measure, this may be normal. As for the remark about if it gets hot with no load, yes it does, but not as hot, or even what I would call hot hot. It gets warm to the touch, but easily something I can place my hand on comfortably. However, again, this is still quite a bit warmer than my very cool running Acurus amp. I dont see any shorts, I can't imagine I have any, but anything is possible, any thoughts on a place where a short would not strongly effect sound, but would cause such heat. One thing was my power wires, I didn't have wire of small enough guage without being way too small, so I simply trimmed the wire to fit into the hole, and so the edges were a bit scraggly, but I dont believe I had any loose ends that could have touched anything they shouldn't. I will look it over, or posisbly redo it with better wire.
As for the heatsink, it looks like it says its just bare aluminum. I think I read somewhere, maybe on the ESP sight, that anodized aluminum works much better. Something about black oil even better. Not sure what Black Oil is, but for the anodized, if it says bare aluminum, is it probably not anodized, should I consider doing that? Thanks.
I take back the comment about it getting hot with no load, it was hooked to the speakers when I said that, sorry. It does not with no load.
As for the DC offset, I measured it with a 8ohm resistor, its all I had, it was left over from a crossover. With that, I get 52mv, that seems high, but if you mostly measure with a 10ohm load, is that my problem. Well anyway, now how do I go about lowering my dc offset?
As for the DC offset, I measured it with a 8ohm resistor, its all I had, it was left over from a crossover. With that, I get 52mv, that seems high, but if you mostly measure with a 10ohm load, is that my problem. Well anyway, now how do I go about lowering my dc offset?
Nothing to worry about.
Sorry, just to recap, were you saying you had one of these amps on a heatsink, but it didn't realy heat up until you added a second amp to it....
Well do consider that these 2 amps together are putting out close to the heat that a PC CPU would, and they have huge heatsinks with 80mm+ fans....
Interested on your opinion as to how it sounds, being driven that hard and all....
P.S., no, you don't want to put too much paste on, just a spec, like part of a rice grain size, I add alot of the stuff to PC's , I use a plastic freezerbag, streched around my finger, which allows me to smear it so thin, its nearly transparent... remember the paste doesnt transfer heat, it just fills microscopic airpockets which would have prevented the proper flow of heat... to the heatsink
Well do consider that these 2 amps together are putting out close to the heat that a PC CPU would, and they have huge heatsinks with 80mm+ fans....
Interested on your opinion as to how it sounds, being driven that hard and all....
P.S., no, you don't want to put too much paste on, just a spec, like part of a rice grain size, I add alot of the stuff to PC's , I use a plastic freezerbag, streched around my finger, which allows me to smear it so thin, its nearly transparent... remember the paste doesnt transfer heat, it just fills microscopic airpockets which would have prevented the proper flow of heat... to the heatsink
No I wasn't saying that it didn't get hot until I added the second amp, I was just saying that I would expect logicaly that the amp would get hotter by having the second on, but it still gets warm. I knew I was going to be driving it up there in voltage, but didn't think it would be that unique. Should I consider using a different transformer?
As for sound, I consider it still breaking in, though it probably is breaking in faster than normal. Last night I went to the Hector Jazz Festival and let it break in over that time. By the way, I got to jam out with a few pretty well know New Orleans Stars, Including one of the Nevilles groups.
Earlier however I was listening to some delta and classic blues as I needed to refamiliarize myself with it for a session. I was listening to Robert Johnson, John Lee Hooker, and Muddy Waters. All of them were fairly simple and small recordings, most of them were acoustic in nature as well. The sound was very pure and open, and the amp was not a let down. These recordings dont exactly have a huge dynamic range though, and I believe all of them are Mono, so Soundstaging was limited really to the depth, which was good, but not great.
This morning on the other hand I was ready to sit down and really listen again. So far I have listened to a wide arrange of strange things, but it is what I have on SACD. The First was a John Lee Hooker album on SACD, and compared with the greatest hits I have on cd, the recording sound seemed more inline with the records, though quiter, and with less flow and emotion, a less "You are there" experience. You all are going to chastise me for this, but I accidentaly bought, no really, that newer Journey album, Arrival. I thought the website said it was $1.29, but it was 12.99 with 10% off. The reason I wanted it was that it had good power rock guitar leeds with decent tapping technique, something I have been also trying to familiarize myself with so I can become better at it (I'm gonna be the first to start power rock revival bands, haha, no not really). This album has startolingly good sound. I really wasn't expecting much, but, setting aside the music for a moment, it has a very warm analogue like presentation. The soundstage is very central, it extends to the speakers, but I wouldn't say beyond them. However, the depth goes clear to my back wall, about 5-6 feet behind them. This is actually the first time I have heard this cd on my system, so that was more a review of the album than the amp, but compared to when I used it at an Instore Demo, its much more impressive in my own home, and on a far cheaper SACD player at that.
This amp has been suprising me with a somewhat warm overall presentation, good midrange sound, and pretty clear highs. The bass leaves something to be desired, but it seems to just subtract it rather than attempt it poorly, and I prefer that. I don't have big floorstanding speakers, so I can't say how it would do on those, but on my JmLabs Electra 905's (Two 5 1/4" midbass drivers in a slot ported enclosure), I usually get bass down to about 40-45hz, and it doesn't sound as deep right now. I will have to play some Pipe organ music to be sure of that. I am currently building a set of small efficient full range speakers, as I have heard these amps thrive on those, and I would be intrested to see how they sound that way, if they have that SET midrange magic at all.
As for sound, I consider it still breaking in, though it probably is breaking in faster than normal. Last night I went to the Hector Jazz Festival and let it break in over that time. By the way, I got to jam out with a few pretty well know New Orleans Stars, Including one of the Nevilles groups.
Earlier however I was listening to some delta and classic blues as I needed to refamiliarize myself with it for a session. I was listening to Robert Johnson, John Lee Hooker, and Muddy Waters. All of them were fairly simple and small recordings, most of them were acoustic in nature as well. The sound was very pure and open, and the amp was not a let down. These recordings dont exactly have a huge dynamic range though, and I believe all of them are Mono, so Soundstaging was limited really to the depth, which was good, but not great.
This morning on the other hand I was ready to sit down and really listen again. So far I have listened to a wide arrange of strange things, but it is what I have on SACD. The First was a John Lee Hooker album on SACD, and compared with the greatest hits I have on cd, the recording sound seemed more inline with the records, though quiter, and with less flow and emotion, a less "You are there" experience. You all are going to chastise me for this, but I accidentaly bought, no really, that newer Journey album, Arrival. I thought the website said it was $1.29, but it was 12.99 with 10% off. The reason I wanted it was that it had good power rock guitar leeds with decent tapping technique, something I have been also trying to familiarize myself with so I can become better at it (I'm gonna be the first to start power rock revival bands, haha, no not really). This album has startolingly good sound. I really wasn't expecting much, but, setting aside the music for a moment, it has a very warm analogue like presentation. The soundstage is very central, it extends to the speakers, but I wouldn't say beyond them. However, the depth goes clear to my back wall, about 5-6 feet behind them. This is actually the first time I have heard this cd on my system, so that was more a review of the album than the amp, but compared to when I used it at an Instore Demo, its much more impressive in my own home, and on a far cheaper SACD player at that.
This amp has been suprising me with a somewhat warm overall presentation, good midrange sound, and pretty clear highs. The bass leaves something to be desired, but it seems to just subtract it rather than attempt it poorly, and I prefer that. I don't have big floorstanding speakers, so I can't say how it would do on those, but on my JmLabs Electra 905's (Two 5 1/4" midbass drivers in a slot ported enclosure), I usually get bass down to about 40-45hz, and it doesn't sound as deep right now. I will have to play some Pipe organ music to be sure of that. I am currently building a set of small efficient full range speakers, as I have heard these amps thrive on those, and I would be intrested to see how they sound that way, if they have that SET midrange magic at all.
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