| wotsascott |
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.:D |
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| Leolabs |
| quote: | | 1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate? |
What's the weight???
| quote: | | 2/ Do said sinks have to be isolated from the chassis? |
Not all the time.But most sinks should be electrically isolated from the chips.
| quote: | | 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? |
It depends on the driving capability of the amp. |
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| lgreen |
Hi wotsascott, I just made one of these amplifiers using BrianGT boards.
That is you said-| quote: | | with 2 LM4780 <each in paralell, giving me my 2 channels out of 4 LM3886's> |
So I take this to mean 1 LM4780 per channel (2 parallel LM3886 per channel, 4 total), which is what I did.
| quote: | | 1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate? |
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.
| quote: | | 2/ Do said sinks have to be isolated from the chassis? |
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.
| quote: | | 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? |
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. |
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| wotsascott |
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?
:idea: |
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| lgreen |
| quote: | Originally posted by wotsascott
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?
:idea: |
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. |
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| sivan_and |
lgreen wrote:| quote: | | 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. |
????
SHOCK ? How ? Aren't we using a transformer ? |
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| wotsascott |
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?
:bawling:
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! |
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| lgreen |
| quote: | Originally posted by sivan_and
lgreen wrote:
????
SHOCK ? How ? Aren't we using a transformer ? |
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. |
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| wotsascott |
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!:D
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!!!! |
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| wotsascott |
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.:cannotbe: |
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| lgreen |
| that teflon wire is good stuff you don't need to shield it. If you get a lot of hum over the speakers you may want to re-route the wire away from the transformer or put in some shielding. However for me shielded wire in a GC has been unnecessary. |
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| wotsascott |
Hi guys,
Will do on the silver teflon and thanks.
Can you use a pre-amp with a lm4780 gainclone or is it better to build a seperate 'passive' out of a selector switch plus attenuator?
Cheers!!!:wiz: :wiz: |
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| jackinnj |
| quote: | Originally posted by wotsascott
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.:D |
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. |
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| wotsascott |
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!! |
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| Hara |
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/show...tnumber=122-640
or the 500VA version, or 2 of the 330VA
What is the recommended method of isolating chip from the heatsink? |
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| Hara |
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. |
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| wotsascott |
Hi,
I got away with 160va 25/0/25 for each psu on a 2 channel gainclone, sounds very good! |
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| flraer |
I also have one little question about the powersupply.
Can I use one withe these specs:
300VA, 2x24 Volt, 2x6.25A
/ Fredrik. |
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| Hara |
| I bet these questions are so common we should create a gainclone wiki. Anyone think this would be a good idea? |
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| wotsascott |
" I also have one little question about the powersupply.
Can I use one withe these specs:
300VA, 2x24 Volt, 2x6.25A "
This is perfect in my experience, with the standard 1.4 multiplier you should give you around 36volts ish. Don't use any voltage regulators as they have a maximum tolerance of 35 volts! I popped a few with my own PSU??
I've found that you can get 60 watts plus into a 8 ohm load with this setup. Personally, I would use two, one for each PSU/Chanel.
Although my recent gainclone only used 1 PSU and I got 50 watts plus into my 4 ohm Jamo giants! |
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| Hara |
| Because I'll be potentially bridging a 6.6 ohm driver (apparent 3.3 ohm when bridged) I decided to go with dual 250VA 18-18. |
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| flraer |
| quote: | Originally posted by wotsascott
This is perfect in my experience, with the standard 1.4 multiplier you should give you around 36volts ish. Don't use any voltage regulators as they have a maximum tolerance of 35 volts! I popped a few with my own PSU??
I've found that you can get 60 watts plus into a 8 ohm load with this setup. Personally, I would use two, one for each PSU/Chanel.
Although my recent gainclone only used 1 PSU and I got 50 watts plus into my 4 ohm Jamo giants! [/B] |
I'm not really sure if I know what you mean. Should I remove some components from my rectifier bord?
/ The noob :xmasman: |
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| wotsascott |
Hi Guys,[QUOTE]I'm not really sure if I know what you mean. Should I remove some components from my rectifier bord?[QUOTE]
What I meant is that if you are going to use any sort of voltage regulator chip then remember that most can only handle 35 volts before they are destroyed!
To be honest it is unlikely in a gainclone's PSU.
I gather the power supply you plan to use is something like this:
http://images.google.co.uk/imgres?i...6lr%3D%26sa%3DN
If so then this is ideal and no components should be removed!
I built one power supply for each channel on mine and a seperate 300va 25-0, 25-0 toroid transformer for each PSU.
The PSU's supplied a steady 35 volts! <25x 1.4= 35 ish>
See what I mean? |
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| flraer |
Now I understand!
Thank you very much for the help :)
It's ordered now. Can't wait for it to come.
/ Fredrik |
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| wotsascott |
Hi Again,| quote: | | It's ordered now. Can't wait for it to come. |
Have you ordered a kit? My first gainclone was one of Rod Elliots from ESP; worked around the LM3876! I used vero board and components I could "harvest" from junk at home, sounded as sloppy as it's construction. Rod's circuit is great though and I see he's finally added a "gainclone" < we all succumb to social terminology in the end> to the ranks of his other 100+ circuits!!
After that I bought one of Brian's kits at chipamp.com. The single power supply version of the LM3886 kit; it sounds awesome.
You'll find that you can't stop at one, the buzz takes hold; it is very rewarding.
A tip is that the electronics are the easy part <for me anyway>, it's the pigging cosmetics of the chassis that frustrates!! I find myself not happy every time I build one. So try and find a stopping point and keep it simple! I have made some monumental cockups from tinkering with minor unecesary changes.
When you first turn it on <and it works> you'll be hooked for sure!!!!
I've moved on to the LM4780 chip <2 LM3886's in one package> and am playing with 2 of them in parallel! 4 glorius 3886's!
Try Rod's site out:
http://sound.westhost.com/index2.html |
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| flraer |
Ooops, havenot been here for a while due to some personal reasons...
Yes I hav ordered a LM4780 kit from audiosector. I hope it wold work just fine when I put the pieces together.
You will probably see meny stupid questions from me from because I am a beginner att this :)
Edit: Since I have bought a kit from audiosector, should I ask questions about it in the thread at "Vendor's Bazaar" ?
/ Fredrik |
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| Netlist |
| quote: | Originally posted by flraer
Edit: Since I have bought a kit from audiosector, should I ask questions about it in the thread at "Vendor's Bazaar" ?
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A good starting point is to look at the thread starter's original post and see if you question or answer fits in the thread. Not that all threads are constantly on topic of course. :)
/Hugo |
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