I'm looking for ideas for an 4ch. amp to power a pair of bi-amped near field monitors. They are supplemented with a powered sub woofer and are high passed at around 70hz. The two amps I have been using are huge (both take up 6 rack places) and would like to get all 4 channels of power into about 2 rack spaces.
Requirements are pretty simple. 4ohm stable and around 30 to 35 watts/channel. 20wpc would work but I want some headroom.
I was looking at maybe a pair of LM4780 chips. Would these work at 4ohms?
Any other ideas???
Requirements are pretty simple. 4ohm stable and around 30 to 35 watts/channel. 20wpc would work but I want some headroom.
I was looking at maybe a pair of LM4780 chips. Would these work at 4ohms?
Any other ideas???
The LM4780 is an excellent choice as it is basically two LM3886's on one die.
Do run it at a lower voltage for 4 Ohms as suggested as this will help to keep the heat lower for your target power level.
Some have complained about its ability to dissipate the heat because because of the smaller die area per power so make sure that you have enough heatsink area or you can use a small fan as well to help.
One DIYer used a few CPU heatsinks suck as from Coolermaster or Ximatec that have heat pipes and they worked out nicely.
A compounded opamp design such as the MY REFdesign may yield you a better sound as others have claimed since you are using it for nearfield monitors.
jer
Do run it at a lower voltage for 4 Ohms as suggested as this will help to keep the heat lower for your target power level.
Some have complained about its ability to dissipate the heat because because of the smaller die area per power so make sure that you have enough heatsink area or you can use a small fan as well to help.
One DIYer used a few CPU heatsinks suck as from Coolermaster or Ximatec that have heat pipes and they worked out nicely.
A compounded opamp design such as the MY REFdesign may yield you a better sound as others have claimed since you are using it for nearfield monitors.
jer
I am looking at the AudioSector kit and configuring each LM4780 for stereo mode. For PCBs, it either that or something from China. I'm not setup for doing my own etching.
Given no more power than what I need or would push it, what VA transformer would I need?
Given no more power than what I need or would push it, what VA transformer would I need?
Last edited:
Anything of at least 200watt range will be good.
At best a class AB amplifier is only about 78% efficient so you have to have at least that 22% more plus a little more for headroom is always good.
Remember that these are for maximum output ratings and not for average listening level.
Although, You don't want to be limited on the current draw as this will cause clipping of the peaks.
Even though you may only be using 5 watts rms your peaks can be as high 10db higher(10X) or in the 50 watt range for most music.
As you know clipping is not good for tweeters and is the major cause of the death of them when using low power amplifiers.
A 5 watt amplifier that is clipping will kill a speaker quicker than a non-clipping 50 watt amplifier will.
jer
At best a class AB amplifier is only about 78% efficient so you have to have at least that 22% more plus a little more for headroom is always good.
Remember that these are for maximum output ratings and not for average listening level.
Although, You don't want to be limited on the current draw as this will cause clipping of the peaks.
Even though you may only be using 5 watts rms your peaks can be as high 10db higher(10X) or in the 50 watt range for most music.
As you know clipping is not good for tweeters and is the major cause of the death of them when using low power amplifiers.
A 5 watt amplifier that is clipping will kill a speaker quicker than a non-clipping 50 watt amplifier will.
jer
Last edited:
Currently, I am using a Kenwood Basic M2A on the woofers. If the front panel VU meters are to be believed, I can play something like Steely Dan - Black Cow (something that has alot of dynamics) and the peak hold on the meters shows 35-40 watts at volumes louder than I would ever normally play. A loud "normal" shows about 5 watts as peak. The woofers have a 91db watt/meter efficiency and the tweets at 90db. My listening position at my DAW is right at or maybe a bit less than 1 meter.
I saw in your profile than you have a studio. This is for just a small home studio. This may give you a better idea as to what I am after.
I saw in your profile than you have a studio. This is for just a small home studio. This may give you a better idea as to what I am after.
Cool....I know exactly what levels you are talking about.
I use nearly the same levels as well in my near field setup.
I can get well over +105db at .5 meter at about 80 watts or so using my DIY Desktop ESL.
But even at about 95db is plenty and more than enough for an average listening level using something like 10 to 25 watts when you are that close to the speakers.
I have some Lm4780's and Lm3886's but I have not built them yet and will be very shortly.
However I have been planning on doing the My Reference design due to the great reviews I have read.
I will be using either LME49860's (dual) or the LME49740's (quad) for the front end an crossovers as well.
Anyhow the LM4780 should work very nicely for you!!
I think that they where used in the Mackie monitors my Friend had and they sounded very good to me for the short time I was around them.
jer
I use nearly the same levels as well in my near field setup.
I can get well over +105db at .5 meter at about 80 watts or so using my DIY Desktop ESL.
But even at about 95db is plenty and more than enough for an average listening level using something like 10 to 25 watts when you are that close to the speakers.
I have some Lm4780's and Lm3886's but I have not built them yet and will be very shortly.
However I have been planning on doing the My Reference design due to the great reviews I have read.
I will be using either LME49860's (dual) or the LME49740's (quad) for the front end an crossovers as well.
Anyhow the LM4780 should work very nicely for you!!
I think that they where used in the Mackie monitors my Friend had and they sounded very good to me for the short time I was around them.
jer
Last edited:
Cool. Looks like from here I need to look at enclosures and all the other parts that will go with it.
I need to finish the linear PSU I am building for my Soundcraft Spirit. The original SMPS went out and thought it would be better to have a linear one like it's bigger,better brothers.
I need to finish the linear PSU I am building for my Soundcraft Spirit. The original SMPS went out and thought it would be better to have a linear one like it's bigger,better brothers.
Last edited:
OK....I'm within about a week or two from ordering a LM4780 kit from Peter (AudioSector) and the rest of the parts needed. I have been working on case design and am wondering about the heatsink. I have some 1.5" x 3" aluminum channel I was thinking about using for the sides and mounting the chips to. At about 9" long, what is the opinion about using them as heatsinks? One on either side for each chip. It's just simple channel without fins. But, it is a pretty good size (1.5" X 3" x 9"). If this is enough, I will go with it as I already have the channel.
Alternatively, I could go for 9" length of the 3.5" wide heatsink from Heatsinks USA. 3.500" Wide Extruded Aluminum Heatsink - HeatsinkUSA, LLC Store Surely this would be enough. If this is the route everyone thinks I should go, what would be a minimum length? Shrinking it down to about 7" would be helpful with case size.
Alternatively, I could go for 9" length of the 3.5" wide heatsink from Heatsinks USA. 3.500" Wide Extruded Aluminum Heatsink - HeatsinkUSA, LLC Store Surely this would be enough. If this is the route everyone thinks I should go, what would be a minimum length? Shrinking it down to about 7" would be helpful with case size.
No one?
On the other hand, I could go for a 3" length of the 7.28" wide heatsink from Heatsinks USA. This would give vertical fins which I know is a better orientation than horizontal.
I have tried to calculate the channel to see if it is enough but, The numbers are beyond what I can understand.
Here is a link to the datasheet for the LM4780
http://www.ti.com/lit/ds/symlink/lm4780.pdf
On the other hand, I could go for a 3" length of the 7.28" wide heatsink from Heatsinks USA. This would give vertical fins which I know is a better orientation than horizontal.
I have tried to calculate the channel to see if it is enough but, The numbers are beyond what I can understand.
Here is a link to the datasheet for the LM4780
http://www.ti.com/lit/ds/symlink/lm4780.pdf
It will burn up if you don't put some kind of heatsink on it !!!
Since the company of heatsink's that you are purposing to use don't have any data on them, you can calculate what you need to know using some on line calculators by their dimensions.
The links can be found here,
http://www.diyaudio.com/forums/chip-amps/236456-another-heat-sink-size-question.html#post3503083
Cheers !!!
jer
Since the company of heatsink's that you are purposing to use don't have any data on them, you can calculate what you need to know using some on line calculators by their dimensions.
The links can be found here,
http://www.diyaudio.com/forums/chip-amps/236456-another-heat-sink-size-question.html#post3503083
Cheers !!!
jer
Last edited:
I am planning to use 160x100 heatsinks, 40-60mm deep finned. From RS or poached from some junk i have. 2 4780s per sink, IF i can get away with it. Aiming for 0.6 C/W or lower.
I am also currently driving front end with 49740 xo, and input buffering/gain with 49710/49720 in to99.
The suggestion of CPU coolers is also a good one. Depends if you can get one large enough (silent cooler) or if you mind a bit of fan noise ( and can figure a control for it)
I am also currently driving front end with 49740 xo, and input buffering/gain with 49710/49720 in to99.
The suggestion of CPU coolers is also a good one. Depends if you can get one large enough (silent cooler) or if you mind a bit of fan noise ( and can figure a control for it)
Actually, I was being a bit sarcastic in my last post about not needing a heatsink and was hoping to provoke a response. Seems like it worked.
Looking at the specs from Heatsinks USA, they show thus....
"Extruded Aluminum HeatsinkAlloy: 6063-T6, Width: 7.280", Fin Height: 1", Base: .300", C/W/3": approximately 1.30, Weight per Inch: .37"
With some help from another source, I managed to calculate that the above 3" section of their 7.280" heatsink will cover a LM4780 putting out 65+ watts/channel. Of course, a LM4780 will only put out about 50wpc when powered by +/-25vdc on a 4 ohm load. So, in theory, I could run a sine wave at full power and still not have the protection circuit kick in. The math works out, roughly, 1.3C/W + .8C/W + .2C/W gives 2.3C/W. 150c / 2.3 = 65.21watts. The specs are sourced from the LM4780 datasheet and from HeatSinks USA.
AndrewT....MANY posts to the contrary. I know. I searched alot in the process of trying answer this question.
Looking at the specs from Heatsinks USA, they show thus....
"Extruded Aluminum HeatsinkAlloy: 6063-T6, Width: 7.280", Fin Height: 1", Base: .300", C/W/3": approximately 1.30, Weight per Inch: .37"
With some help from another source, I managed to calculate that the above 3" section of their 7.280" heatsink will cover a LM4780 putting out 65+ watts/channel. Of course, a LM4780 will only put out about 50wpc when powered by +/-25vdc on a 4 ohm load. So, in theory, I could run a sine wave at full power and still not have the protection circuit kick in. The math works out, roughly, 1.3C/W + .8C/W + .2C/W gives 2.3C/W. 150c / 2.3 = 65.21watts. The specs are sourced from the LM4780 datasheet and from HeatSinks USA.
AndrewT....MANY posts to the contrary. I know. I searched alot in the process of trying answer this question.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.