| SkinnyBoy |
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... $130!?!?!? common!!!..... lol I mean.. its still a cheap amp... lol anyone made some PCBs for this chip yet? :rolleyes: |
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| tschrama |
Hi,
I think the LM4780 could be the perfect power-opamp. Two channel 60 Watt in one package.. or a 120W bridge amp .. I received them this morning. Since the have a relative large number of pins and small too, a PCB would be perfect. maybe someone is interested too. 2xLM4780 and a PCB = simpest 240 Watt stereo ever! :D
Someone designing such a PCB, or ahve a suggestion for a easy to learn PCB design program?
Greeting.
Thijs |
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| SkinnyBoy |
getting the boards made is the expensive part... unless we want a few dozen.... I personally want/need 4 or 5.... any one else want/need any? :)
and for those Australians who want some cheap toroidals.. :) go here.. :D www.oatleyelectronics.com (if ya can't find them, not my problem)
(NEW) 250VA TOROIDAL TRANSFORMER: 2 x 120V primary, 2 x 9V secondary. No mounting hardware available. The unit weighs 4Kg:
yes.... 9 volts... so.. you can get 12.5volt rails... 25volt rails... 38volt rails.... 50volt rails... (the more transformers... the merrier)
yep.... anyway... |
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| tlmadsen |
Hi
I am currently working on a PCB for 3 x LM4780 and a PSU (-trafo). It will be possible to configure it form 3 to 6 channels.
I don't mind "putting it into production", but the price is not low.
( I make doublesides PTH i FR4 standard with soldermaks and positionprint) Something like 30-45 US$ 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..........
$130 for heatsink is a lot, but they are expensive. If you need that kind of cooling maybe you should go for forced cooling with a fan. It is quite effective and it don't have to be noisy........well they are when you really need them, but then you most likely can't hear them anyway :)
Thomas |
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| SkinnyBoy |
| quote: | Originally posted by tlmadsen
Hi
I am currently working on a PCB for 3 x LM4780 and a PSU (-trafo). It will be possible to configure it form 3 to 6 channels.
I don't mind "putting it into production", but the price is not low.
( I make doublesides PTH i FR4 standard with soldermaks and positionprint) Something like 30-45 US$ 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 |
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... :p |
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| sangram |
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. |
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| tlmadsen |
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 |
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| agent.5 |
| May I suggest to make the board as a multiple of 2, such as 2 or 4 op amps per board. |
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| tschrama |
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 |
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| tlmadsen |
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 |
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| tschrama |
Thanks for the tip (and warning) .. I'll find something about eagle on google..
g,
Thijs |
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| Circlotron |
| quote: | Originally posted by sangram
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. |
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. ;) |
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| matjans |
tschrama
If you have a working pcb, i'd like a few -as long as it's a bridged version.
have my samples lying around but i'm too lazy to make a pcb. |
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| SkinnyBoy |
| quote: | Originally posted by sangram
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. |
| quote: | Originally posted by autoexec
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.s...duct/View/H3408
Thermal Resistance: 0.37 degrees C/W
Width: 300mm
Length: 75mm
Section Height: 48mm
they only cost $20 |
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... |
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| SkinnyBoy |
here are the capacitors in all their glory.. ;)
they were pretty cheap... ;) ;) ;) |
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| sangram |
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. |
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| tschrama |
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..:cool:
Cya,
thijs |
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| SkinnyBoy |
yeah.. but its so hard to use those heatsinks.. :p
but those would be really good... except how do I attach 2 of these chips to each heatsink.... and have a way so the fan does what it has too... |
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| SkinnyBoy |
yeah... those heatsinks seem best... 80mm fan per heatsink... fans mounted on the FRONT of a rack mount case... might even get clear fans with coloured LEDs... ;) could be interesting...
but a case... could be expensive.... I really don't wanna attempt my own... and I don't want raw aluminium.... seems like Jaycar has the best quality ones.... $109 for a 3 Unit case... hmmm but then I have the problem of cutting a CIRCLE the the 3mm thick aluminium front.... and I'm not sure if the heatsinks will fit in the case... need to go in there sometime and see if I can measure one.. :D but $109... thats the most expensive part out of everything....
SO FAR!!!
Filter Capacitors: 16 4700uF 100v chasis mount = FREE
Transformers: 3 X 18v CT 250VA = $75
Heatsinks: MF18-151.5 (0.11 C/W with fan) = $80 total
Fans: 2 X 80mm clear LED or plain black = $35-$45 total
Case: Jaycar 3 Unit rack mount case: $109
thats like $190 so far without the case....
$299 with the case.. :)
theres a few more components I need... bridge rectifier... some smaller value capacitors... probably a power switch and speaker and RCA sockets... looking at less than $400 total.. :) |
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| SkinnyBoy |
hmm... hmm.. hmm.. hmm..
but what component goes where??
lol |
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| Circlotron |
| quote: | Originally posted by tschrama
I just spend a hour or so trying to learn the 'Eagle' PCB layout program... but I am not impressed .. |
I never got excited about it either. Try Easytrax (simpler) or Autotrax. (Both DOS). They used to be commercial products by Protel (now Altium) before being put out to pasture as freeware.
http://www.protel.com.au/resources/downloads/index.html bottom of page. |
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| Tom McKay |
Don't make PCBs. Use two rows of "machined contact" type IC socket on solderable perf board, and then run flying leads from there. It's far more rugged and adaptable than a circuit board. I put the big stuff on a tag strip.
Cheers man |
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| Upupa Epops |
| Are you using fuses on secondary AC lines ??? It is absolutely wrong !!! |
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| ukram |
| quote: | Originally posted by Upupa Epops
Are you using fuses on secondary AC lines ??? It is absolutely wrong !!! |
I'm using fuses on primary AC too. What is wrong with using fuses on secondary AC? For example they might save speakers in case there is lots of DC voltage for some reason.
Often the primary fuse is oversized because toroidal transformers tend to take lots of startup current, which blows correctly sized fuses. |
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| tschrama |
Hi all,
Just a small word about my progress this weekend..
while I'm typing this, my first bridged-LM4780 is being put through the first measurements...... :D
I made this one on a piece of veroboard, you know the old-fashion solder-test-board-with-many-holes... I like it soooo much.. so simple .. so small.. .. so cheap .. couple of supply caps, 8 resistors, 2 blocking caps, one LM4780 .. all on a piece of 4cmx3.5cm veroboard (about 1.6x1.4 inch)... ready to deliver 120Watt... well .. not with this Vsupply and this 5k/W heatsink.. but it works..:cool:
DC offset is 1.8mV non-inv, 12mV inverting.. I think that's because I connected the IN+ of the inv channel direct to ground .. should be through a resistor.. so Ibias comes in to play..
I really had to think long about how to solder it on a veroboard, but it can be done..relatively easy
think about it .. compared to the lm3875 Gainclone, this baby has:
almost 4x the slewrate
almost 2x the current capacity
can give 120Watt instead of 40Watt for a 30V GainClone...
Well it's late, I need some sleep.. bye,
Greetings,
Thijs |
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| SkinnyBoy |
| Transformers arived today.. :D YAY!!! hm... heatsinks, and a case... hmhmhm case needs to be big enough... and strong enough... transformers weigh 12Kgs total... they are like 130mm in diameter and 65mm high... I believe they are the same size as a 500VA transformer... the windings on them are very spread out... hmm |
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| SkinnyBoy |
do you guys think 32,600uF per rail will be enough for my amplifier?? or should I buy some more capacitors?
heres what I have so far... except there will be 2 rows of capacitors, one on either side of the transformers... :xeye:
yes, thats a CD sitting ontop.. :p |
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| SkinnyBoy |
and a side view... lol
I like pictures... do you like pictures? :D
I need money for heatsinks and case.. :( I think.... case will be last.. lol |
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| SkinnyBoy |
you selling PCBs? :D ;) or should I read your side abit more lol...
EDIT: yep... shoulda read it.. :p lol |
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| Upupa Epops |
| Why is it wrong ? By switch up high inrush current blow this fuse ( if have correct size ). If is oversized, is it for nothing, because by failure of amp all charge of capacitor " flow " without any limitation. Correct is fuse on primarily side of transformer and second fuse before voltage rail ( behind main capacitor ). |
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| sangram |
I doubt that in the case there is a large DC voltage on the output, fuses inserted in the rails of the amp will blow quick enough to prevent the demise of the speaker, or at least damage. However some people do it anyway, maybe more for psychological peace of mind. I do not like to put fuses in rails or speaker lines (this is also common in some amp designs and serves exactly the same purpose - to prevent the speaker blowing up on high amounts of DC at the output), so I avoid it completely.
In any case, putting a fuse in will definitely limit the kind of currents that pass through the output stages, in case of low impedance speakers the fuse can go off in the middle of the session, even if all the other components are capable of correctly handling the transients. A well-designed amp should have enough room to handle transients, and quite a lot more.
Catastrophic failure, say like failure of the output transistor will probably ensure the speaker dies before a fuse can blow. A better way to correct would be to use active protection. Increases complexity, but if you want protection it's better to be well-protected.
As for the primary, the fuse should always be of the correct rating, but should be a slow-blow type to prevent fusing at switch-on, particularly for toroids. Upupa is right in saying that fusing the secondary AC is not advised, because the caps on the supply can pull some serious current, upto tens of amperes. Putting a 15-amp fuse on a gainclone will neither protect the gainclone, nor its speakers, nor the amp. |
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| SkinnyBoy |
| but the problem is 8 channels, and 750VA of transformers... if one channel get shorted or the chip dies, I don't think its going to take out the slowblow mains fuse too quickly... |
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| ukram |
| I used 250 VA toroidal tranformer in my LM3886 amp. I had to use at least 3A (230 V mains) "slow blow" fuse to avoid blowing it just with the transformer startup current. Then i used a current limiter on the primary AC, which softened the startup so much that a 500 mA fuse could be used on primary. 3A*230V = 690W into the speaker... |
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| SkinnyBoy |
| it all well and good for a 2 channel amp.. but with these 8 channels, I'd still want a 4 amp fuse..... which isn't going to protect much is one amp chip fries, and nothing more.. :p |
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| SkinnyBoy |
I think its time to find some heatsinks...
and fans.... and an enclosure, and some PCBS... :xeye:
grrrr.. PCBs... hmmmm
maybe I should just pay the cash and get the PCBs from ukram.....
:bawling:
EDIT: Thats $US100 for the 4 boards I need... thats $136.205 AUD
wow, the american dollar is doing really poorly.. lol
$140!!!! that would make it the most expensive part of the whole amplifier.... hmmm
:bawling: :bawling: :bawling:
maybe I'll just have to try p-p....
maybe I can try making my own PCBs... I mean, I'm sure I could set myself up and make the 4 PCBs for less than $140.... |
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| elizard |
This chip looks most interesting, and promising (although I don't have enough knowledge by any means to say that, but it looks good :p).
What sort of a transformer should I expect to use for one channel, bridged? to get around 100 watts, or possibly the full 120 watts?
I'm trying to decide on a project for next year, and this might be one possibility! Although I'm not sure if I should do 2 chip amps, or if I should go with somethin like aleph 5 (already got heatsinks for it!) or p3a.
Certainly looks interesting I must say, and VERY simple! |
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| elizard |
| Oh yeah, and the main thing, how does it compare to lm3875 in terms of quality? If it sounds worse, or about as good as 3875, no use for me to build it. I don't really need heaps of power (unless of course I decide to build a 5 or 6 channel HT amp, in which case this would be a PERFECT candidate!) |
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| MWP |
Skinny....
Where are you getting your components from?
Im here in Adelaide also :) |
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| SkinnyBoy |
| quote: | Originally posted by elizard
Oh yeah, and the main thing, how does it compare to lm3875 in terms of quality? If it sounds worse, or about as good as 3875, no use for me to build it. I don't really need heaps of power (unless of course I decide to build a 5 or 6 channel HT amp, in which case this would be a PERFECT candidate!) |
The quality should be the same as the LM3886.... or so the datasheet suggests....
| quote: | Originally posted by MWP
Skinny....
Where are you getting your components from?
Im here in Adelaide also :) |
what parts are you refering to? :) |
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| SkinnyBoy |
| wanna get a 3unit rack mount case? :) if we can find 4 people they are $97.95 each.... one would normally be $109... but if we can find 10 sales, they are only $86.95... :D |
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| MWP |
| quote: | | what parts are you refering to? |
Good quality caps, heatsinks, etc.
The harder to find stuff.
| quote: | | maybe I can try making my own PCBs... I mean, I'm sure I could set myself up and make the 4 PCBs for less than $140.... |
I make my own PCBs... i can do double sided (not plated-through hole tho), with accuracy of 7mil.
Anyone with a decent bubble jet printer can, no other special equipt needed.
| quote: | | wanna get a 3unit rack mount case? :) if we can find 4 people they are $97.95 each.... one would normally be $109... but if we can find 10 sales, they are only $86.95... :D |
Hmmmm.
Actually, i think i will be needing a new 3U case soon, and i do like the Jaycar units. |
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| SkinnyBoy |
| quote: | Originally posted by MWP
Good quality caps, heatsinks, etc.
The harder to find stuff.
I make my own PCBs... i can do double sided (not plated-through hole tho), with accuracy of 7mil.
Anyone with a decent bubble jet printer can, no other special equipt needed.
Hmmmm.
Actually, i think i will be needing a new 3U case soon, and i do like the Jaycar units. |
wow, netscape really sux.. lol and this keybord is just the worst, and why would anyone use Windows NT.. :p anyway.. lol
Good quality caps? ohh, umm.. lol I wasn't really going to bother... lol all I really need is power, my speakers are bad, if I apgraed them, I will ungrade the caps also.. :) (yeah right) the capacitors I do have came off ebay... heatsinks I will probably get from Conrad heatsinks or just Dick Smiths..... transformers came from www.oatleyelectronics.com thats about it... |
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| MWP |
| quote: |
wow, netscape really sux.. lol and this keybord is just the worst, and why would anyone use Windows NT.. |
If you want a good alternative to Nutscrape and IE, try Firebird:
http://www.mozilla.org/products/firebird/
| quote: |
heatsinks I will probably get from Conrad heatsinks or just Dick Smiths |
Woo, i didnt know about Conrad, thanks :) |
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