What should the surface temp be of the chip or heatsink be when cranking it up loud say for 30 minutes? I have an infrared thermo.
I tested a pair of 3886 chipamps for use as an active amplifier. One was passing 1W to an 8r0 resistor load, the other was passing 2W to an 8r0 resistor load.
I thought that would be equivalent to very loud music.
The chips on the big heatsink (~1.1C/W) got too hot to touch within a couple of minutes. I'd guess they were >60°C
I think that proved me wrong, reproducing very loud music into reactive speaker loads must be a lot less than my assumed 1W + 2W
Have a look at the datasheet graph Figure 35. & Figure 36.
You will see that @ 2W output the chip dissipation is not low, it's quite high and that explains my finger burning moment.
If you want to keep the current limiter off more of the time, then you need cool chips. Higher chip temperatures will result in more frequenct triggering of the current limiters.
Keep your chips cool.
If you can keep your heatsink below 40°C and your Tc below 50°C, then I would class that as cool.
I thought that would be equivalent to very loud music.
The chips on the big heatsink (~1.1C/W) got too hot to touch within a couple of minutes. I'd guess they were >60°C
I think that proved me wrong, reproducing very loud music into reactive speaker loads must be a lot less than my assumed 1W + 2W
Have a look at the datasheet graph Figure 35. & Figure 36.
You will see that @ 2W output the chip dissipation is not low, it's quite high and that explains my finger burning moment.
If you want to keep the current limiter off more of the time, then you need cool chips. Higher chip temperatures will result in more frequenct triggering of the current limiters.
Keep your chips cool.
If you can keep your heatsink below 40°C and your Tc below 50°C, then I would class that as cool.
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Almost done. All that's left is to hook the dc supply to the amp boards and to hook up the speaker terminals. Is solid core wire okay (preferable?) for both the dc supply and speaker terminals?
An externally hosted image should be here but it was not working when we last tested it.
Don't take my word on this as I haven't actually done it (I have seen results though) and you can get this laser cut with nice edges that are rounded or whatever. Other idea might be the thing PC moders did back in the day and use this rubber stuff over the edges so it has that clean look. (google 'u channel rubber' )
You *MIGHT* be able to get the screw holes to be flush with some engraving magic (ie you do engraving and get the surrounding area deep enough to make the screw flush) I have seen the sorta funnel like v shape holes on laser cut stuff to have screws flush too. No clue the process how that works. you might also be able to do this with some careful drill or dremel work.
Personally I don't mind the screws sticking out.
If you have a makerspace, or something in your city you might be find someone to pick their brain and or get access to a laser cutter (my city's public library actually has laser cutters which I have been meaning to use) orther wise there are lots of Chinese fabs that cut acrylic to what ever design you need (seeedstudio offers this)
Jennifer G,
This looks great - nice job!
I would used stranded 18ga copper wire for internal hookups of DC power and speaker outs. 16ga is too big and not needed as it adds mechanical stress to the connections. And TBH, even 20ga stranded works well enough for the short runs in here. The solid core is also too stiff and adds stress.
Looks like the solid aluminum plate you added works well. I noticed you use bolts going all the way thru - you should get a 4-40 drill and tap (for IC tabs) and 6-32 or 8-32 for the larger bolts - much cleaner and really easy to use on this aluminum. Use 4-40 hex cap screws to give a nice clean look.
This looks great - nice job!
I would used stranded 18ga copper wire for internal hookups of DC power and speaker outs. 16ga is too big and not needed as it adds mechanical stress to the connections. And TBH, even 20ga stranded works well enough for the short runs in here. The solid core is also too stiff and adds stress.
Looks like the solid aluminum plate you added works well. I noticed you use bolts going all the way thru - you should get a 4-40 drill and tap (for IC tabs) and 6-32 or 8-32 for the larger bolts - much cleaner and really easy to use on this aluminum. Use 4-40 hex cap screws to give a nice clean look.
Read all the threads - guess you solved the front plate issue
How did you make the adhesive label for the IEC outlet? (like what's it made out of is it something you print from a normal laser printer?) Looks very nice.
0) Used "Pages" application on Mac OS X to design the label. I suppose Microsoft Word, Libre Office, or OpenOffice would work as well.
1) A good black and white normal laser printer would work well if it printed solid black -- usually need a pretty fresh toner drum for this (I buy mine for like $12 shipped from ebay for the toner drum for my HP laserjet 1022). I printed this on my color laser printer because it had a better drum and I have the heater set hotter on the color laser printer as well to bond the toner better.
2) After I print it out, I then cut out the square leaving about 1 inch margins/borders.
3) Then I glue that paper with Avery Permanent Glue Stick to 110 lb index card stock. Make sure to coat the entire back of the label including the margins, with the glue stick before adhering, so it can't come loose anywhere. EDIT: Come to think of it I probably could of used 3M adhesive spray instead of the glue stick.. might hold up better to heat? I dunno.
http://www.amazon.com/Neenah-Exact-Inches-Sheets-Bright/dp/B006P1Z59E
http://www.amazon.com/Avery-Permanent-Glue-Stic-98073/dp/B0000AQODQ
4) I then cut out some self adhesive Avery laminating sheet just bigger than the square and adhered that.
http://www.amazon.com/Avery-Self-Adhesive-Laminating-Sheets-73601/dp/B00007E7D2
5) After that's all done, I carefully trim all 4 sides with a paper cutter (I made the black box a little larger to be able to trim some off to ensure no white border shows.)
6) I forgot to do this next step but still turned out okay: use a sharpie along the cut edge to blacken it so you don't see the white cut edge -- doesn't really need it I guess (optional).
7) Then I used 3M spray adhesive putting the label face down in a large cardboard box with the front cut out (it's my spraying station). Then you let that dry for like 20-30 seconds before adhering -- it's pretty tacky by that time (it'll never come off by itself with that spray and can tolerate some heat).
And that's about it. Oh I used a razor sharp victorinox pocket knife to cut out the rectangle for the mains power inlet.
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My dc supply board has 8 pads for power.
1) Two x VE+ (both connected together on wide trace)
2) Two x VE+ GROUND (both connected together on wide trace)
3) Two x VE- (both connected together on wide trace)
4) Two x VE- GROUND (both connected together on wide trace)
Using 18 guage wire. Decided to make use of both pads and have more current capability (although probably not needed?). So for example VE+ will be two 18 guage wires running to the middle of the solid core wire connecting the stacked amp boards. I'll run each of the 4 pairs to the center of the respective solid core stabilizer.
VE+ GROUND and VE- GROUND on the dc supply board are independent of each other by the way.
So how do I twist them? You've mentioned twisting a triplet twice now, but I don't have a triplet, I have a quadruplet with independent grounds.
By the way, I want to say thanks for all your help -- you've been wonderful. Looking forward to getting this amp going in the next hour or so.
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are your two +ve and two grounds duplicates that are wired in parallel?
or
are they two separate supplies running to separate loads?
Are the -ve supplies running along with the +ve supplies creating a dual polarity supply?
A dual polarity supply pushes current out through the +ve lead and that returns via the Zero Volts lead when the halfwave to the load is +ve.
When the current to the load reverses, the -ve lead sucks current from the load and the zero volts supplies that current, again for only half the waveform cycle.
The two half currents when close coupled, mimic a whole cycle and the interference field can be cancelled by combining with the zero volts. The three wires +ve , zero volts and -ve form a self cancelling triplet. This minimises interference.
You twist the three wires as a triplet, instead of using 2wires.
or
are they two separate supplies running to separate loads?
Are the -ve supplies running along with the +ve supplies creating a dual polarity supply?
A dual polarity supply pushes current out through the +ve lead and that returns via the Zero Volts lead when the halfwave to the load is +ve.
When the current to the load reverses, the -ve lead sucks current from the load and the zero volts supplies that current, again for only half the waveform cycle.
The two half currents when close coupled, mimic a whole cycle and the interference field can be cancelled by combining with the zero volts. The three wires +ve , zero volts and -ve form a self cancelling triplet. This minimises interference.
You twist the three wires as a triplet, instead of using 2wires.
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Well it's playin' music now. Sounds great! Need to play more and enclose it in the case and do some other tests to see how it compares to the piece of wood I had it sitting on. It's hooked up right now as well.. wasn't before.
I'll figure out twisting the dc supply later.. right now I have all 8 wires twisted together. I need to replace the dc supply to amp board wiring anyways because I want a higher temp thicker jacket.
I'll report temperatures soon.
I'll figure out twisting the dc supply later.. right now I have all 8 wires twisted together. I need to replace the dc supply to amp board wiring anyways because I want a higher temp thicker jacket.
I'll report temperatures soon.
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Well the aluminum bar is doing a great job, even better than the fins connected to it!
LM3886 IC temp: 120F
Aluminum Bar Temp Near IC: 120F
Fins -- back outer edge even -- 122F
So I am very happy I added the aluminum bar to the heatsink.
65% power gets IC to 120-122F (50C). I don't listen to the stereo any louder than that either. It's fairly loud for me.
Should I put a fan in it?
By the way, one time when turning the amp on it blew both 3A fuses at the same time (AC inlet has 2 fuses for some weird reason). I've had this happen with this transformer many times before as well when sitting on wood. I guess 3A fuse just isn't enough for the 300VA 25V transformer startup. Need to look into softstart thing? AFter that can I put a 1.5A fuse in? Right now I have a 4A fuse in there.
LM3886 IC temp: 120F
Aluminum Bar Temp Near IC: 120F
Fins -- back outer edge even -- 122F
So I am very happy I added the aluminum bar to the heatsink.
65% power gets IC to 120-122F (50C). I don't listen to the stereo any louder than that either. It's fairly loud for me.
Should I put a fan in it?
By the way, one time when turning the amp on it blew both 3A fuses at the same time (AC inlet has 2 fuses for some weird reason). I've had this happen with this transformer many times before as well when sitting on wood. I guess 3A fuse just isn't enough for the 300VA 25V transformer startup. Need to look into softstart thing? AFter that can I put a 1.5A fuse in? Right now I have a 4A fuse in there.
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The amp definitely sounds clearer than before. It's properly setup in a case vs. not configured properly sitting on a piece of wood. (Had speaker returns, signal returns, v- ground, v+ ground all, transformer screen all connected to the same point as mains protective earth -- lol).
Corcom filter didn't get rid of the popping noise when turning on the bathroom light.. put the case cover on and screwed it down as well.
There is less hum/noise when cranking up the volume with nothing playing.. was worse before.
Corcom filter didn't get rid of the popping noise when turning on the bathroom light.. put the case cover on and screwed it down as well.
There is less hum/noise when cranking up the volume with nothing playing.. was worse before.
Having a weird problem. I hold the amp up off the entertainment center shelf it's on and move it forward out of the cabinet and back in all the way. At a certain point when it's about 1/2 way in it starts making popping noise and hum .. hum like a guitar amp and a popping noise like you unplugged the guitar with the guitar amp cranked up. Push it in far enough and it goes away but there is a quiet hum in the background.
I moved the a 12v DC supply, dac and pre amp (which are on the shelf above) around and it didn't seem to affect it. I know it's not the cabling connections.. nor inside the amp, because I am holding it very steady and moving back and forth in and out of the shelf and it makes the popping and intense hum in the same coordinates every time. Could it be something above in the attic? Or could it be the surge strip it's plugged into? It's above and about 2 inches behind the amp (mounted to the back of the entertainment center).
It's sharing a cheap surge protector strip (plastic) that the 12V 3a dc supply (pyramid) is on.
I moved the a 12v DC supply, dac and pre amp (which are on the shelf above) around and it didn't seem to affect it. I know it's not the cabling connections.. nor inside the amp, because I am holding it very steady and moving back and forth in and out of the shelf and it makes the popping and intense hum in the same coordinates every time. Could it be something above in the attic? Or could it be the surge strip it's plugged into? It's above and about 2 inches behind the amp (mounted to the back of the entertainment center).
It's sharing a cheap surge protector strip (plastic) that the 12V 3a dc supply (pyramid) is on.
I wiggled every chord/cable on the back of the unit and didn't get any hum or popping when I did that.. THen I carefully moved the amp in and out and heard the hum and pop. (This is holding it 1 inch above the shelf -- no friction). I was thinking it was maybe a connection inside but I've banged the front of the amp several times and not once heard hum or pop.. only when repositioning the amp)
Here is a photo of it powered up:
Note: the dc supply to amp board wiring will be replaced with stranded 18 guage, well insulated with hi temp jacketing if possible (recommendations?). I agree solid core puts way too much mechanical stress on the pads.. I tried to be as careful as possible though but I am not comfortable with it.
AndrewT, now you can see what I am talking about regarding the 8 wires? By the way the matching colored wires on the dc supply board are connected together on the PCB with a 1/2 inch wide (or so) trace.. so I wanted to run both wires for extra current capability.
EDIT: leaving the speaker wire solid core because I want it to stay suspended over the heatsink without touching it.
An externally hosted image should be here but it was not working when we last tested it.
Note: the dc supply to amp board wiring will be replaced with stranded 18 guage, well insulated with hi temp jacketing if possible (recommendations?). I agree solid core puts way too much mechanical stress on the pads.. I tried to be as careful as possible though but I am not comfortable with it.
AndrewT, now you can see what I am talking about regarding the 8 wires? By the way the matching colored wires on the dc supply board are connected together on the PCB with a 1/2 inch wide (or so) trace.. so I wanted to run both wires for extra current capability.
EDIT: leaving the speaker wire solid core because I want it to stay suspended over the heatsink without touching it.
Here is the photo of the amp sitting in my entertainment center. I still need to polish the faceplate.
It's sitting below a passive attenuator (10K ALPS) with a greyhill 4 way switch to the left. Using vintage knobs from vintage 1960's Hewlett Packard vacuum tube multimeter. The enclosure for the pre is a cheap chinese aluminum one I got for $40 or so. Also, there are two outputs on the passive pre -- connected together as an internal Y splitter; one goes to LM3886 below and other to Polk Powered Sub. (My speakers are Infinity RS 2001). [Eventually the existing pre will be replaced with a Nelson Pass B1 Buffer -- have the board partially populated.)
To the left of the pre is a 12V power supply that's powering the DAC to the right of the pre. DAC is the Fiio with an internal 12V to 5V 7805 voltage regulator. (The Fiio is still in it's case within the DAC enclosure but the output wires are directly soldered to the RCA's on the back of the DAC. Artwork for the DAC is older than the black diamond I decided to go with on the aluminum enclosures. I want to get another $40 aluminum enclosure to match the pre for a new custom DAC then I'll sit it on top of the PRE and add a black diamond. The DAC currently is in an old galvanized steel radio shack enclosure (which they no longer make) with a chipboard/laser printed face plate screwed on.
Black diamonds printed on my color laser printer on some nice stock, with drum set for high heat so plastic melts very well -- very hard to scratch it off the paper. SO I don't need to laminate the labels. Used Avery glue stick to adher.. or could use 3M spray adhesive.
Please ignore the dusty shelf! sorry
It's sitting below a passive attenuator (10K ALPS) with a greyhill 4 way switch to the left. Using vintage knobs from vintage 1960's Hewlett Packard vacuum tube multimeter. The enclosure for the pre is a cheap chinese aluminum one I got for $40 or so. Also, there are two outputs on the passive pre -- connected together as an internal Y splitter; one goes to LM3886 below and other to Polk Powered Sub. (My speakers are Infinity RS 2001). [Eventually the existing pre will be replaced with a Nelson Pass B1 Buffer -- have the board partially populated.)
To the left of the pre is a 12V power supply that's powering the DAC to the right of the pre. DAC is the Fiio with an internal 12V to 5V 7805 voltage regulator. (The Fiio is still in it's case within the DAC enclosure but the output wires are directly soldered to the RCA's on the back of the DAC. Artwork for the DAC is older than the black diamond I decided to go with on the aluminum enclosures. I want to get another $40 aluminum enclosure to match the pre for a new custom DAC then I'll sit it on top of the PRE and add a black diamond. The DAC currently is in an old galvanized steel radio shack enclosure (which they no longer make) with a chipboard/laser printed face plate screwed on.
An externally hosted image should be here but it was not working when we last tested it.
Black diamonds printed on my color laser printer on some nice stock, with drum set for high heat so plastic melts very well -- very hard to scratch it off the paper. SO I don't need to laminate the labels. Used Avery glue stick to adher.. or could use 3M spray adhesive.
Please ignore the dusty shelf! sorry
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AndrewT,
You're right. I finally found out it was a defective RCA cable -- replaced and no problems.
Thank you!
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