Hi guys,
I'm new to this stuff <mostly>, but have contructed 2 amps. 1 a sterio lm3876 non inverting <esp> and 1 sterio LM3886 non inverting using Brians boards. Both sounded ok, but looked very bad. Since improving my DIY electronics skills, as well as wading through tonnes of gainclone sites I've decided to run with 2 LM4780 <each in paralell, giving me my 2 channels out of 4 LM3886's> using audiosectors gold boards.
Anyhow, I have a couple of questions before I begin construction, so if anyone out there can help it will be well recieved.
So:
1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate?
2/ Do said sinks have to be isolated from the chassis?
3/ I have 2 toroidal 25x25 300va transformers, which gives me roughly 36 volts, with 4 ohm speakers, would this give me a decent output?
Any help would be awesome!
Scott.
I'm new to this stuff <mostly>, but have contructed 2 amps. 1 a sterio lm3876 non inverting <esp> and 1 sterio LM3886 non inverting using Brians boards. Both sounded ok, but looked very bad. Since improving my DIY electronics skills, as well as wading through tonnes of gainclone sites I've decided to run with 2 LM4780 <each in paralell, giving me my 2 channels out of 4 LM3886's> using audiosectors gold boards.
Anyhow, I have a couple of questions before I begin construction, so if anyone out there can help it will be well recieved.
So:
1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate?
2/ Do said sinks have to be isolated from the chassis?
3/ I have 2 toroidal 25x25 300va transformers, which gives me roughly 36 volts, with 4 ohm speakers, would this give me a decent output?
Any help would be awesome!
Scott.
Hi wotsascott, I just made one of these amplifiers using BrianGT boards.
That is you said-
Answer- No, Mine are about the same size but are very heavy/massive and are only adaquate because I am also using a fan to bring cool air over the sinks. They don't get hot in normal use but when the vol. goes up they need the fan.
Answer- Depends. The back of the chip is the negative power supply rail voltage and you don't want to shock anyone who touches your chassis. So you MUST electrically isolate the chip from the heatsink OR isolate the heatsink from both the chassis and from being touched by anybody or anything. Its normally easier to isolate the chip from the sink, and its much safer practice. Also, if you are going to use 1 transformer per chip each negative rail will not be identical, and you don't want DC (even a little offset) going from one heat sink to the other, which would be very bad. I think you really need to have the sinks isolated from the chips. If so, don't need to isolate from the case but it never hurts.
That is you said-
So I take this to mean 1 LM4780 per channel (2 parallel LM3886 per channel, 4 total), which is what I did.
Answer- No, Mine are about the same size but are very heavy/massive and are only adaquate because I am also using a fan to bring cool air over the sinks. They don't get hot in normal use but when the vol. goes up they need the fan.
Answer- Depends. The back of the chip is the negative power supply rail voltage and you don't want to shock anyone who touches your chassis. So you MUST electrically isolate the chip from the heatsink OR isolate the heatsink from both the chassis and from being touched by anybody or anything. Its normally easier to isolate the chip from the sink, and its much safer practice. Also, if you are going to use 1 transformer per chip each negative rail will not be identical, and you don't want DC (even a little offset) going from one heat sink to the other, which would be very bad. I think you really need to have the sinks isolated from the chips. If so, don't need to isolate from the case but it never hurts.
Answer- YES! I have used a single 330 VA 25x25 and you have two 300VA, so yours are better. Mine is very powerful and drives 4 ohm speakers quite well; I would not worry about this aspect of the design, make sure you use some good filter caps. Note that you will get quite a bit of heat because you are at 36 volts (see the datasheet) so this is another reason why your heatsinks are too small.
Ta very much
Hi one and all!
Thankyou for your help, it is much apprieciated.
Does anyone know where I can get the correct heatsinks?
I've got a 12 dc fan which is standard 80mm size, but I'd rather get the right sinks?
Extra thanks to 'lgreen' and I'd like to say how effective and cool looking some of the creations on said website are; nice one!
What gauge thickness shielded wire for the internal connects do you guys use? Can someone give me the site for 'decent' diy hifi supplies?
Until the next time?
Hi one and all!
Thankyou for your help, it is much apprieciated.
Does anyone know where I can get the correct heatsinks?
I've got a 12 dc fan which is standard 80mm size, but I'd rather get the right sinks?
Extra thanks to 'lgreen' and I'd like to say how effective and cool looking some of the creations on said website are; nice one!
What gauge thickness shielded wire for the internal connects do you guys use? Can someone give me the site for 'decent' diy hifi supplies?
Until the next time?
Re: Ta very much
Hi, good luck with his; glad you like my odd constructions. I'm not in England so cannot help on the heat sinks and parts. Here I spent a lot of time looking for electronics surplus stores and they have saved me a lot of money for parts, things like wire, and hardware screws, bolts, cases etc...
Lets see if I can answer some of your build questions- I have found that big wire is not necessary in these gainclones, 18 gauge is fine for mostly everything and 20 or 22 or 24 works for most non-powerline situations. I have bought a lot of silver-teflon wire on ebay and its perfect for the job.
wotsascott said:Hi one and all!
Thankyou for your help, it is much apprieciated.
Does anyone know where I can get the correct heatsinks?
I've got a 12 dc fan which is standard 80mm size, but I'd rather get the right sinks?
Extra thanks to 'lgreen' and I'd like to say how effective and cool looking some of the creations on said website are; nice one!
What gauge thickness shielded wire for the internal connects do you guys use? Can someone give me the site for 'decent' diy hifi supplies?
Until the next time?
Hi, good luck with his; glad you like my odd constructions. I'm not in England so cannot help on the heat sinks and parts. Here I spent a lot of time looking for electronics surplus stores and they have saved me a lot of money for parts, things like wire, and hardware screws, bolts, cases etc...
Lets see if I can answer some of your build questions- I have found that big wire is not necessary in these gainclones, 18 gauge is fine for mostly everything and 20 or 22 or 24 works for most non-powerline situations. I have bought a lot of silver-teflon wire on ebay and its perfect for the job.
I get most of my heatsinks from ebay, buying new is very expensive.
http://electronics.search.ebay.co.u...atrefZC12QQfromZR8QQfsooZ1QQfsopZ1QQsacatZ293
The top two would be ideal for a 4780
http://electronics.search.ebay.co.u...atrefZC12QQfromZR8QQfsooZ1QQfsopZ1QQsacatZ293
The top two would be ideal for a 4780
Hmmmm
Well, I'll check out ebay for wire and heatsinks and let you know how I got on!
My enclosure for the project arrived today, a standard 19 in, 2u, black type which I think I'll spray once I've cut the holes I need.
I'm having serious problems cutting sheet metal accurately and neatly; any idea's? The only sure fire way is to go get it done at the local metal worker, but is very expensive and I've already faced the wrath of 'she who must be obeyed' for spending too much; yikes?
It seems to me that the electronics part is a lot easier that the cosmetic part of the diy amp? Anyone else feel like this?
Anyway, thanks again guys, see ya!
Well, I'll check out ebay for wire and heatsinks and let you know how I got on!
My enclosure for the project arrived today, a standard 19 in, 2u, black type which I think I'll spray once I've cut the holes I need.
I'm having serious problems cutting sheet metal accurately and neatly; any idea's? The only sure fire way is to go get it done at the local metal worker, but is very expensive and I've already faced the wrath of 'she who must be obeyed' for spending too much; yikes?
It seems to me that the electronics part is a lot easier that the cosmetic part of the diy amp? Anyone else feel like this?
Anyway, thanks again guys, see ya!
sivan_and said:
Yes, but the back of the chip carries the negative power supply rail, and if its touching the heat sink, which is touching the case, the case will also carry the negative power supply rail. This must be avoided to avoid the risk of shock.
And yes, the mechanical part is much more difficult than the electrical part.
In Business!
Thanks once more to 'lgreen' for the advice! Ordered some of the silver teflon wire of ebay and found some sinks matching the one's on the LM4780 data sheet. I now have all I need to start the project!
Still stuck on the metal cutting bit though?
Any suggestions as to what sort of speakers to use?
Cheers, ta ta!
Oh yeah, certainly don't want the chasiss linked to the negative rail, so I'll insulate the chips from the sinks, nice 1!!!!
Thanks once more to 'lgreen' for the advice! Ordered some of the silver teflon wire of ebay and found some sinks matching the one's on the LM4780 data sheet. I now have all I need to start the project!
Still stuck on the metal cutting bit though?
Any suggestions as to what sort of speakers to use?
Cheers, ta ta!
Oh yeah, certainly don't want the chasiss linked to the negative rail, so I'll insulate the chips from the sinks, nice 1!!!!
Don't know if you've tried this, but I found that high quality tin snips are great for cutting metal. There's an article on a computer modding site that I found really helpful: http://forums.silentpcreview.com/viewtopic.php?t=2307
Teflon Silver Wire
Hi 1 & all,
I got the silver teflon wire, however, it's not shielded? Do I need to buy some shielded cable? Or will it be sufficient?
Started mounting the power supplt components last night and have a good image in my head of the final amp!!!
Anyway, cheers and I'll keep you posted.
Hi 1 & all,
I got the silver teflon wire, however, it's not shielded? Do I need to buy some shielded cable? Or will it be sufficient?
Started mounting the power supplt components last night and have a good image in my head of the final amp!!!
Anyway, cheers and I'll keep you posted.
wotsascott said:
Hi guys,
I'm new to this stuff <mostly>, but have contructed 2 amps. 1 a sterio lm3876 non inverting <esp> and 1 sterio LM3886 non inverting using Brians boards. Both sounded ok, but looked very bad. Since improving my DIY electronics skills, as well as wading through tonnes of gainclone sites I've decided to run with 2 LM4780 <each in paralell, giving me my 2 channels out of 4 LM3886's> using audiosectors gold boards.
Anyhow, I have a couple of questions before I begin construction, so if anyone out there can help it will be well recieved.
So:
1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate?
2/ Do said sinks have to be isolated from the chassis?
3/ I have 2 toroidal 25x25 300va transformers, which gives me roughly 36 volts, with 4 ohm speakers, would this give me a decent output?
Any help would be awesome!
Scott.
The heat sink you describe has a thermal impedance of about 3 C/W -- with +/- 36V -- the heat you have to dissipate is 65 watts -- this is the heat not going into the load -- if the device temperature is to rise only 75 degrees from ambient, you need a much, much larger heat sink. Sorry, that's how the math works.
Much appreciated info on the sinks! I now have four of said sinks. Is there anyway I could link them together, making 4 into 2?
After talking about the silver teflon a friend of mine had 20ft of shielded lying in his shed!! This I pinched most quickly.
So, shielded or not shielded that is the question???
Anyone wishing to give me some feedback on the pre-amp thing??
Cheers and happy halloween for tomorow geezers!!
After talking about the silver teflon a friend of mine had 20ft of shielded lying in his shed!! This I pinched most quickly.
So, shielded or not shielded that is the question???
Anyone wishing to give me some feedback on the pre-amp thing??
Cheers and happy halloween for tomorow geezers!!
Hello,
Still working on my audio sector kit and have some questions:
You say 330VA 25-25 is good for parallel amps but what about both on stereo for 4 channels, and another possibiility of one on stereo and the other bridged?
I was debating of getting this
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=122-640
or the 500VA version, or 2 of the 330VA
What is the recommended method of isolating chip from the heatsink?
Still working on my audio sector kit and have some questions:
You say 330VA 25-25 is good for parallel amps but what about both on stereo for 4 channels, and another possibiility of one on stereo and the other bridged?
I was debating of getting this
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=122-640
or the 500VA version, or 2 of the 330VA
What is the recommended method of isolating chip from the heatsink?
Scratch the isolation question, I think I'll have the chip attached directly to an isolated heatsink for better thermal coupling.
As for the transformer question I'm still curious because I recall some posters saying there are disadvantages to large transformers because of noise and surge protection. Also I do not know effect on the audibility when having seperate transformers for each chip.
As for the transformer question I'm still curious because I recall some posters saying there are disadvantages to large transformers because of noise and surge protection. Also I do not know effect on the audibility when having seperate transformers for each chip.
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