The advantage of LM3875, 3886 is the simplicity and all protection schemes. I think this is the main advantage.
Eventually I will make pcb's but so far I haven't heard a LM3886 live yet but I have no doubts that it's quite good. Technically it's also interesting because I believe it's the best monolithic non-class D power amp around. Apex is possibly better.
Eventually I will make pcb's but so far I haven't heard a LM3886 live yet but I have no doubts that it's quite good. Technically it's also interesting because I believe it's the best monolithic non-class D power amp around. Apex is possibly better.
A transformer like that cost $89,59 CAD (plus 15% taxes if bought locally). Shipping weight is 4kG. The lead time is probably 4 weeks. http://www.plitron.com/
There was a recent price increase, as I remember those were sold at around $ 70 previously.
There was a recent price increase, as I remember those were sold at around $ 70 previously.
Hi Peter;
>>>A transformer like that cost $89,59 CAD (plus 15% taxes if bought locally). Shipping weight is 4kG. The lead time is probably 4 weeks.<<<
How about the Avel Lindberg trafos? I see that Parts Express in the US has a 36vct, 250VA rated job for $42.26USD that's available without delay. Are the Plitrons really that much better (not stating an opinion, since I don't have one!), or could one "get away with" the Avel Lindberg toroidals?
Thanks in advance!
All the best,
Morse
>>>A transformer like that cost $89,59 CAD (plus 15% taxes if bought locally). Shipping weight is 4kG. The lead time is probably 4 weeks.<<<
How about the Avel Lindberg trafos? I see that Parts Express in the US has a 36vct, 250VA rated job for $42.26USD that's available without delay. Are the Plitrons really that much better (not stating an opinion, since I don't have one!), or could one "get away with" the Avel Lindberg toroidals?
Thanks in advance!
All the best,
Morse
I was buying 250VA transformers from Apex Jr for $25. They were pretty good and initially I thought they were even better than Plitron, but more tests shows 400VA Plitron was preffered.
I don't think Avel Lindberg would be a bad choice, it will work perfectly well in a GC. It's only if you want to gain tha last few percent of performance, you should become fussy about transformer chouces. I'm almost sure that 400VA vs 250VA toroid would be better.
I would assume that 400VA Lindberg converted to Canadian funds wouldn't much different regarding the price (comparing to Plitron). And then you add higher shipping cost when dealing with States vs local Canadian.
I would also assume that good quality R-core would be even better than toroid.
I don't think Avel Lindberg would be a bad choice, it will work perfectly well in a GC. It's only if you want to gain tha last few percent of performance, you should become fussy about transformer chouces. I'm almost sure that 400VA vs 250VA toroid would be better.
I would assume that 400VA Lindberg converted to Canadian funds wouldn't much different regarding the price (comparing to Plitron). And then you add higher shipping cost when dealing with States vs local Canadian.
I would also assume that good quality R-core would be even better than toroid.
Thanks Peter;
Good point about currency conversion and shipping - 'course if the USD keeps dropping, you guys north of the border may be buying cheap US goods soon!
BTW, my TDA2030's and LM4766's have all shown up, so it's just a question of finding enough 'quality time' in my workshop to wire up a little chipamp.
Do you think that a 4"x6" sheet of 1/8" thick aluminium will suffice as a heatsink for a (approx) 12wpc chipamp? I'll need to use a mica spacer with these, so that will cut into heat transfer. My current plan is to use the top plate of the chassis to mount everything (so it's going to hang upside down in there) and use it as a heat sink. Then the bottom plate can just be some thin alloy sheet stock I have laying around. Good or bad idea?
Thanks in advance!
All the best,
Good point about currency conversion and shipping - 'course if the USD keeps dropping, you guys north of the border may be buying cheap US goods soon!
BTW, my TDA2030's and LM4766's have all shown up, so it's just a question of finding enough 'quality time' in my workshop to wire up a little chipamp.
Do you think that a 4"x6" sheet of 1/8" thick aluminium will suffice as a heatsink for a (approx) 12wpc chipamp? I'll need to use a mica spacer with these, so that will cut into heat transfer. My current plan is to use the top plate of the chassis to mount everything (so it's going to hang upside down in there) and use it as a heat sink. Then the bottom plate can just be some thin alloy sheet stock I have laying around. Good or bad idea?
Thanks in advance!
All the best,
Thanks Peter!
Sounds like it's a 'go' on my current chassis design....
BTW, IIRC I can freely use a 115VAC 60cps rated PS trafo for 100VAC 60cps, right? In which case I can expect a reduction in Vout from the thing, but so long as I stay above +/-10VDC on the rails the 4766 should be happy. I'd like it to work on either power standard, so if need be I could wire in a 6.3VAC trafo and use it as an autoformer with a DPDT switch to select between the two configurations.
Or is any of that wrong? Thanks in advance!
Hi Ron; you wouldn't happen to be "Ron" at the Fullrange Forum, would you? Anyway, yep, I'm looking forward to getting something up off the ground (pun intentional) - it's been too long since my last new amp was finished and I'm going through "DIY amp withdrawl"!
Thanks again!
All the best,
Morse
Sounds like it's a 'go' on my current chassis design....
BTW, IIRC I can freely use a 115VAC 60cps rated PS trafo for 100VAC 60cps, right? In which case I can expect a reduction in Vout from the thing, but so long as I stay above +/-10VDC on the rails the 4766 should be happy. I'd like it to work on either power standard, so if need be I could wire in a 6.3VAC trafo and use it as an autoformer with a DPDT switch to select between the two configurations.
Or is any of that wrong? Thanks in advance!
Hi Ron; you wouldn't happen to be "Ron" at the Fullrange Forum, would you? Anyway, yep, I'm looking forward to getting something up off the ground (pun intentional) - it's been too long since my last new amp was finished and I'm going through "DIY amp withdrawl"!
Thanks again!
All the best,
Morse
> Do you think that a 4"x6" sheet of 1/8" thick aluminium will suffice as a heatsink for a (approx) 12wpc chipamp?
VERY ROUGH rules of thumb:
A surface runs about 100°C per watt per square inch.
So 4"x6" with both sides exposed is about 100/(2*4*6)= 2°C per watt.
A class B amp at full sine power dissipates about half its output power (and much less with unclipped speech/music signals).
Two 12W amps is 2*(12/2)= about 12 watts. I would round-up since chip-amps sometimes have 4-7 volt losses, so working at lower voltage they are not near theoretical efficiency. 20 watts dissipation is surely conservative.
20W*(2°C/W)= 40°C temperature rise. Is that OK?
The old habit for glass-seal transistors in commercial class B music service was to keep temperature rise down to 50°C rise, because the constant hot/warm/hot/warm cycling with the musical beat would fatigue the seals even though the continuous-duty rating was 100°C or so. Seals are better now, and the epoxy seals seem to beat the old glass-seal TO-3, and you are probably not going to abuse your amp as hard as a commercial sound system. 40° rise is quite safe. (And the National chips have a thermal-cutout to control temperature cycling, and IIRC it is set much higher than 50°C. I'm sure they thought about this and tested their seals, so my old 50°C rule is old-dog trivia.)
If the heat has to flow a long distance, it needs a fat conductor. The thickness to length ratio of heatsinks should be held to 1:10 or maybe 1:20. 1:10 is nice for parallel-flow as in fins; 1:20 is OK with radial-flow as for a small chip in the middle of a large area. With 0.125" plate, you would like the longest heat-path to be 20*0.125= 2.5".
Optimal chip location and heat-flow distance: To a rough approximation, you locate two chips as-if you had sawn the plate in half and centered each chip on its plate. So draw a line down the center of the 6" dimension (2" from each long edge), then divide it in quarters. Put a chip at the 1/4 and 3/4 mark, or 1.5" from each short edge. Each chip is then 2" from a long edge and 1.5" from a short edge, and 3" from a corner. We see that the corners are less effective because they are more than 20*0.125=2.5" from the chip, but not much more, and a lot of area is inside the 1:20 thickness/length rule of thumb, which is only a crude guide to begin with. (And if other layout factors suggest off-centered location, it will still be pretty good.)
I think you could get away with half this area. But if you have the plate and it fits your box, use it. It is always better to over-cool than under-cool.
VERY ROUGH rules of thumb:
A surface runs about 100°C per watt per square inch.
So 4"x6" with both sides exposed is about 100/(2*4*6)= 2°C per watt.
A class B amp at full sine power dissipates about half its output power (and much less with unclipped speech/music signals).
Two 12W amps is 2*(12/2)= about 12 watts. I would round-up since chip-amps sometimes have 4-7 volt losses, so working at lower voltage they are not near theoretical efficiency. 20 watts dissipation is surely conservative.
20W*(2°C/W)= 40°C temperature rise. Is that OK?
The old habit for glass-seal transistors in commercial class B music service was to keep temperature rise down to 50°C rise, because the constant hot/warm/hot/warm cycling with the musical beat would fatigue the seals even though the continuous-duty rating was 100°C or so. Seals are better now, and the epoxy seals seem to beat the old glass-seal TO-3, and you are probably not going to abuse your amp as hard as a commercial sound system. 40° rise is quite safe. (And the National chips have a thermal-cutout to control temperature cycling, and IIRC it is set much higher than 50°C. I'm sure they thought about this and tested their seals, so my old 50°C rule is old-dog trivia.)
If the heat has to flow a long distance, it needs a fat conductor. The thickness to length ratio of heatsinks should be held to 1:10 or maybe 1:20. 1:10 is nice for parallel-flow as in fins; 1:20 is OK with radial-flow as for a small chip in the middle of a large area. With 0.125" plate, you would like the longest heat-path to be 20*0.125= 2.5".
Optimal chip location and heat-flow distance: To a rough approximation, you locate two chips as-if you had sawn the plate in half and centered each chip on its plate. So draw a line down the center of the 6" dimension (2" from each long edge), then divide it in quarters. Put a chip at the 1/4 and 3/4 mark, or 1.5" from each short edge. Each chip is then 2" from a long edge and 1.5" from a short edge, and 3" from a corner. We see that the corners are less effective because they are more than 20*0.125=2.5" from the chip, but not much more, and a lot of area is inside the 1:20 thickness/length rule of thumb, which is only a crude guide to begin with. (And if other layout factors suggest off-centered location, it will still be pretty good.)
I think you could get away with half this area. But if you have the plate and it fits your box, use it. It is always better to over-cool than under-cool.
Thank you very much PRR!!
That is a lot of REALLY useful info - just what I was looking for, in fact!
To maximise cooling along the length of the heat sink, I could mount a separate sheet of .125" stock underneath (frankly I've got enough plate stock left to double 'em up to .25" for the whole top deck, if that's desireable...).
Do you think there'd be a problem with using a mica spacer between the chip and the heat sink (i.e. will it change the numbers on heat transfer significantly)? I was planning on using some Radio Shack heat sink compound.
Thanks again! Your help is greatly appreciated!
All the best,
Morse
That is a lot of REALLY useful info - just what I was looking for, in fact!
To maximise cooling along the length of the heat sink, I could mount a separate sheet of .125" stock underneath (frankly I've got enough plate stock left to double 'em up to .25" for the whole top deck, if that's desireable...).
Do you think there'd be a problem with using a mica spacer between the chip and the heat sink (i.e. will it change the numbers on heat transfer significantly)? I was planning on using some Radio Shack heat sink compound.
Thanks again! Your help is greatly appreciated!
All the best,
Morse
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