My 8 channel LM4780 power amplifier.. :D

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SkinnyBoy

SkinnyBoy

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Joined 2002
home.iprimus.com.au/jlstanley/Speakers/Index.html
#1
Just a progress report and a chance to put my ideas down somewhere... plus... I am tired.. depressed... bored... lonely... and I figure I should do something...

anyhow... I have the filter capacitors... sixteen 4700uF 100 volt chasis mount, even though I am only using +-38 volt rails... or so... My transformers have been ordered and should be here in a week... I am getting three 250VA transformers and connecting them in series... should give me enough power to run the amp to its fullest into 8 ohms... and give a fair whack of power into 4 ohms.. 🙂 but now.. I gotta find heatsinks... I have looked.. and it seems I'm gunna be slogged like $130 for heatsinks... :xeye: but so far, all I have spent on all the other parts... (transformers, capacitors, amplifier ICs 😉 ) is $75... but now.. heatsinks... $130!?!?!? common!!!..... lol I mean.. its still a cheap amp... lol anyone made some PCBs for this chip yet? 🙄
 
#2
Hi,

I think the LM4780 could be the perfect power-opamp. Two channel 60 Watt in one package.. or a 120W bridge amp .. I received them this morning. Since the have a relative large number of pins and small too, a PCB would be perfect. maybe someone is interested too. 2xLM4780 and a PCB = simpest 240 Watt stereo ever! 😀


Someone designing such a PCB, or ahve a suggestion for a easy to learn PCB design program?

Greeting.
Thijs
 
#3
getting the boards made is the expensive part... unless we want a few dozen.... I personally want/need 4 or 5.... any one else want/need any? 🙂

and for those Australians who want some cheap toroidals.. 🙂 go here.. 😀 www.oatleyelectronics.com (if ya can't find them, not my problem)

(NEW) 250VA TOROIDAL TRANSFORMER: 2 x 120V primary, 2 x 9V secondary. No mounting hardware available. The unit weighs 4Kg:

An externally hosted image should be here but it was not working when we last tested it.


yes.... 9 volts... so.. you can get 12.5volt rails... 25volt rails... 38volt rails.... 50volt rails... (the more transformers... the merrier)

yep.... anyway...
 
#4
LM4780 PCB

Hi

I am currently working on a PCB for 3 x LM4780 and a PSU (-trafo). It will be possible to configure it form 3 to 6 channels.
I don't mind "putting it into production", but the price is not low.
( I make doublesides PTH i FR4 standard with soldermaks and positionprint) Something like 30-45 US$ depending on how many we make.

It will most likely take about a month before I have the first prototype up and running. I will get back with some more information when that happens.

I also have an idear in my head about a 4 x LM4780 board incl. PSU (-trafo). This should be configurable as either two or one "BIG" channel. I think I have found a way to avoid the DC-servos. Personally I like them, but they do take up a lot of borad space and need quite a amout of components compared to the rest of the amp.
Comments on this idea/board are very welcome..........

$130 for heatsink is a lot, but they are expensive. If you need that kind of cooling maybe you should go for forced cooling with a fan. It is quite effective and it don't have to be noisy........well they are when you really need them, but then you most likely can't hear them anyway 🙂

Thomas
 
#5
Re: LM4780 PCB

tlmadsen said:
Hi

I am currently working on a PCB for 3 x LM4780 and a PSU (-trafo). It will be possible to configure it form 3 to 6 channels.
I don't mind "putting it into production", but the price is not low.
( I make doublesides PTH i FR4 standard with soldermaks and positionprint) Something like 30-45 US$ depending on how many we make.

It will most likely take about a month before I have the first prototype up and running. I will get back with some more information when that happens.

I also have an idear in my head about a 4 x LM4780 board incl. PSU (-trafo). This should be configurable as either two or one "BIG" channel. I think I have found a way to avoid the DC-servos. Personally I like them, but they do take up a lot of borad space and need quite a amout of components compared to the rest of the amp.
Comments on this idea/board are very welcome..........

$130 for heatsink is a lot, but they are expensive. If you need that kind of cooling maybe you should go for forced cooling with a fan. It is quite effective and it don't have to be noisy........well they are when you really need them, but then you most likely can't hear them anyway 🙂

Thomas
Click to expand...


you're putting the trafo on board??? umm.. thats like a 750 - 1000 VA transformers.... you did mean put it on the PCB... didn't you?? cos... that'll weigh like 10kgs... thats nearly $100 just for the PCB... :xeye: and I'm not sure how suitable it would be... 😛
 
#6
Sign me up for the 3x board immediately. 40 bucks seems OK but postage to India is quite expensive. But still worth it.

4x 4780 also seems good, and if it has the PSU on board it'll be convenient - but untweakable, I fear. Switching PS caps etc/ will be more difficult...

And if anybody is doing singles, sign me up for three of 'em. I need a 6-channel amp for a 6.1 system, and I have exactly three 4780s, which can be used as 3x on one board or three boards with one chip each...

SkinnyBoy, he said (-trafo), so I assume it's only the diode/bridge and caps, snubbers etc....

A fan really helps, and brings the required heatsink down to half or less, even with very quiet and lo-flow fans. I run 12 volt fans off about 6.5 volts. There is a very low grumble like you get if you put your ear to the amp case, but no noise at all. And it helps drops temps a lot. $130 is quite a bit for a heatsink. 20 bucks of heatsink and a couple of $2 fans keeps my hugely powerful STK 4191 amps cool, and they're doing 300 watts at peak dissipation.
 
#7
Hi

The on-board PSU is without the trafo !!

You can easely "bypass" the PSU-section and connected your own PSU directly to the amplifier-section if you feel the need to do so. (you a then paying a few bucks for some PCB-areal you don't use, but I think most people can live with that...)

Shipping to India is not that expensive and the statet prices of 30-45 $ where incl. shipmemt.

Please post all your findings with the LM4780 to the benefit of our all.

Thomas
 
#9
Hi, thanks for your response.

For my limmited budget the boards are just out of reach, but many thanks for the offer. Besides, I made up my mind : I want to learn to design PCB's. I've got some designs that 'could' make it as a commercial product, but I can't afford to hire someone to design the PCBs.

SO... I'm going to design a 1xLM4780 as a first learning project... might take a while because I have yet to find a PCB program.. and the LM4780 layout model, I think?


Regards,
Thijs
 
#10
tschrama

There is a PCB-program called Eagle. If I remember right they have a "student-version" for free (the board -area is most likely limited) and should be a good starting point for you.

Just remember. It might look simple to make a PCB, but it takes years to master that art perfect..........and I sorry to say that I am not there yet 🙂

Thomas
 
#13
sangram said:
A fan really helps, and brings the required heatsink down to half or less, even with very quiet and lo-flow fans. I run 12 volt fans off about 6.5 volts. There is a very low grumble like you get if you put your ear to the amp case, but no noise at all. And it helps drops temps a lot. $130 is quite a bit for a heatsink. 20 bucks of heatsink and a couple of $2 fans keeps my hugely powerful STK 4191 amps cool, and they're doing 300 watts at peak dissipation.
Click to expand...
I agree. I have measured a x6 increase in heatsink performance using a fan. Like Sangram says, run it at 5 or 6 volts normally where it will make virtually no noise at all (especially if it is a cheapo sleeve-bearing fan, ball bearing fans sound gritty) and bring it up to full volts when it is either hot or loud. Fans are good for impressing YL's too. 😉
 
#15
sangram said:
A fan really helps, and brings the required heatsink down to half or less, even with very quiet and lo-flow fans. I run 12 volt fans off about 6.5 volts. There is a very low grumble like you get if you put your ear to the amp case, but no noise at all. And it helps drops temps a lot. $130 is quite a bit for a heatsink. 20 bucks of heatsink and a couple of $2 fans keeps my hugely powerful STK 4191 amps cool, and they're doing 300 watts at peak dissipation.
Click to expand...


autoexec said:
not sure if this is what ur looking for (might be too big, or u might even want more than 1!)

http://www.dse.com.au/cgi-bin/dse.storefront/3fc32067069a185e2740c0a87f9c06eb/Product/View/H3408

Thermal Resistance: 0.37 degrees C/W
Width: 300mm
Length: 75mm
Section Height: 48mm

they only cost $20
Click to expand...


I know a fan would really help, except I was planning on mounting the heatsinks on the outside of the case to form the side panels... that makes fans a little hard.... the reason I chose external sinks in cos its somewhat hard to fit three toroidals, 16 large chasis mount capacitors, and everything else in the one case... the transformers I am using weigh in a 4kgs each... using side mounted heatsinks I JUST managed to get everything to fit in a (external) 150mm high, 450mm wide, and 350mm deep case... ok... so.. that IS BIG!! and I'm not sure if it would actually fit anyway... :xeye:

yes... thankyou.. I looked at those heatsinks, and was considering getting 4 and bolting an aluminium plate to them to make 2 larger heatsinks.. but it would be messy... unless I can come up with a better way...
 
#16
here are the capacitors in all their glory.. 😉
they were pretty cheap... 😉 😉 😉
 

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#17
Well if you have side heatsinks the issue may be closed, except if you mount it below the fins or just place it there blowing upwards, if you have room. If you have horizontal fins, you can also mount a fan at each end (long side) of the heatsink. If you have vertical fins, top is a good place. It won't look as good, but will run cool. Else passive all the way, if you don't have room, you don't have room.

tlmadsen, I will take you up on that offer. Let me know when you are ready with the 3X or singles (or whatever other configuration). The best way would be probably to make it modular - so that there are perforations where it is possible to break off extras, and a separate perforation for PS, attenuator, etc.

As of now my experience with the 4780 is - Oh my God, so MANY pins!! I'm not going to do P2P, my earlier bravery is now diminishing with every step. I have ordered the transformers - 3x 22 Volt Center-tapped 220 VA monsters. Frame transformers only, not toroids I'm afraid, but three of them at switch-on is gonna be tough. May have to use a relay. A poor switch can't take it.
 
#19
Hi all,

I just spend a hour or so trying to learn the 'Eagle' PCB layout program... but I am not impressed .. not 'intuitive' enough .. so I switched to 'Traxmaker'' another PCB layout tool .. same thing .. simple command like adjust grid, move with arrow, calculate distance are not availeble...

So .. I decided to use veroboard.. If you are carefull, you can bend the wires of the LM4780 to fit.. I did and it works... Gotta heat up the soldering iron soon..😎

Cya,
thijs
 
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