I just re-read the chipamp.com instructions for this LM3886 amp. Brian says to run the mains "ground" (earth) to chassis ground. Then later he says to hookup the the CHG (chassis ground) on each amp PCB to "chassis ground".
So he's instructing me to put the amp/audio ground at the same location as the chassis ground from main. This is what I've done but AndrewT is telling me to use a different ground for audio--and it's confusing me that he says this can be "floating" (whatever that means).
Perhaps I shouldn't have the speaker terminals and rca inputs grounded immediately though as I have now... It only has a short run to the amp PCB before they both get sent to chassis ground by the CHG pad on the amp pcb. I have some neutrik rca's and speaker binding posts that are insulated from chassis ground -- I suppose I should use these in place of what I'm using now?
(Right now I am using the binding posts that came with the HP 400D vacuum tube multimeter faceplate which has the speaker signal return/gnd side connected directly to the faceplate/chassis ground. ANd I'm using some rca connectors from radioshack that aren't insulated so they get immediately grounded.)
So he's instructing me to put the amp/audio ground at the same location as the chassis ground from main. This is what I've done but AndrewT is telling me to use a different ground for audio--and it's confusing me that he says this can be "floating" (whatever that means).
Perhaps I shouldn't have the speaker terminals and rca inputs grounded immediately though as I have now... It only has a short run to the amp PCB before they both get sent to chassis ground by the CHG pad on the amp pcb. I have some neutrik rca's and speaker binding posts that are insulated from chassis ground -- I suppose I should use these in place of what I'm using now?
(Right now I am using the binding posts that came with the HP 400D vacuum tube multimeter faceplate which has the speaker signal return/gnd side connected directly to the faceplate/chassis ground. ANd I'm using some rca connectors from radioshack that aren't insulated so they get immediately grounded.)
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Hi Jennifer
Since you have followed chipamp.com directions, for the major items you are safety compliant towards Class I. Also you have reported no hum with RCAs tied to 'chassis' gnd, so you are finished with the temporary build. Sometimes depending on the music source their directions can cause hum with stray AC ground loop currents, this is a big subject and causes much debate on the forums. but if it's not a problem now don't fix it, right.
FWIW Chimpamp.com makes each amps "star gnd" on the PCB so they are independent. IMO some members rote instructions don't always consider that fact.
The light bulb tester thingy is used as mains current limit in case of transformer troubles, mis-wiring or other shorts, but thankfully you have successfully moved past that point, consider using one when / if you change things on your next build.
Since you have followed chipamp.com directions, for the major items you are safety compliant towards Class I. Also you have reported no hum with RCAs tied to 'chassis' gnd, so you are finished with the temporary build. Sometimes depending on the music source their directions can cause hum with stray AC ground loop currents, this is a big subject and causes much debate on the forums. but if it's not a problem now don't fix it, right.
FWIW Chimpamp.com makes each amps "star gnd" on the PCB so they are independent. IMO some members rote instructions don't always consider that fact.
The light bulb tester thingy is used as mains current limit in case of transformer troubles, mis-wiring or other shorts, but thankfully you have successfully moved past that point, consider using one when / if you change things on your next build.
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Thanks.
I have just now isolated both RCA's from the chassis by using insulated Neutrik RCA connectors.
However the source signal grounds and the speaker signal grounds are tied together on the chipamp boards at the CHG (chassis ground) solder pads -- which I run to chassis ground as instructed. My chassis ground point is close to where the 14 guage solid bare copper wire (from mains ground/earth) is bolted to the aluminum backplate. I simply solder the CHG wires from each amp board to this bare copper wire near the bolt (within an inch). I also solder the purple wire from the antek toroidal PS to within 1 inch of the bolt as well on this bare copper wire.
I have just now isolated both RCA's from the chassis by using insulated Neutrik RCA connectors.
However the source signal grounds and the speaker signal grounds are tied together on the chipamp boards at the CHG (chassis ground) solder pads -- which I run to chassis ground as instructed. My chassis ground point is close to where the 14 guage solid bare copper wire (from mains ground/earth) is bolted to the aluminum backplate. I simply solder the CHG wires from each amp board to this bare copper wire near the bolt (within an inch). I also solder the purple wire from the antek toroidal PS to within 1 inch of the bolt as well on this bare copper wire.
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I was thinking about getting a pair of these heat sinks ($5.16 a piece on Amazon) for my LM3886 amplifier. What do you think? Will they be large enough?
http://www.amazon.com/20mm-Aluminium-Heat-Diffusion-Cooling/dp/B0050MR8CG
They are 100mm x 40mm x 20mm .
I will have them standing alone in the MDF amplifier chassis (I think I"ll hot glue them onto the wood), about 1/2" from the back wooden wall.. ventilation screen opening above them for heat to escape upwards out of the chassis.
But the fins run horizontally.. wouldn't it be better if they ran vertically for heat to dissipate better?
http://www.amazon.com/20mm-Aluminium-Heat-Diffusion-Cooling/dp/B0050MR8CG
They are 100mm x 40mm x 20mm .
I will have them standing alone in the MDF amplifier chassis (I think I"ll hot glue them onto the wood), about 1/2" from the back wooden wall.. ventilation screen opening above them for heat to escape upwards out of the chassis.
But the fins run horizontally.. wouldn't it be better if they ran vertically for heat to dissipate better?
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look at the Adcom you need at least half the size of that, noting they have chassis vents below as well as above. if it was me, I would find something about twice the size in your link with vertical fins and black anodizing. Consider mounting outside the wood walls it adds that certain aesthetic you cant get with a plain box.
Thanks, I was considering mounting them outside, but they'd both be on the back side of the amp to the right side--left side of amp is the ac line & then toroidal, diagonally across from amp boards. Since they'd both be in the back, you can't see them (to appreciate the looks of them) so I figured I'd take the easy route and mount them inside. But it would have better cooling if I did mount them outside as you point out.
maybe time to revisit the chip amp photo gallery for some inspiration. http://www.diyaudio.com/forums/chip-amps/79303-chip-amp-photo-gallery.html
Thanks I haven't seen this thread before. Very much enjoying looking through it.
My transformer is taller than that 70mm. And I guess I want a lot of room in my case with transformer to the far left towards the front. And the amp boards to the back to the right. 17" wide case by 11" deep (like an adcom). 4 1/2" tall.
I have built a number of PSUs using toroidals inside, not the 300VA monsters, but smaller. I have insulated the mains leads and connectors with heat shrink and tape. Two things have already happened.
1) The mains cable was pulled out / twisted resulting in the live wire to come off the connector inside and simply "float" around. Considering this now almost loose and floating wirte could have touched various electronics inside... I appreciate that the earth wire is the longest and the last one to go if you pull hard on the mains cable, however that was not pulled so hard resulting in just the positive wire coming out of its connector.
2) Another PSU must have been dropped resulting in the toroidal coming off the brackets as it was sandwitched with two metal plates with the bottom plate glued on the plastic enclosure's bottom. Now we have a loose toroidal banging inside creating all sorts of untold and potentially hazardous damage.
As the enclosures are tight and you have a lot of wires in a small space, I have tried my best to isolate mains from secondaries and mains from everything else, but it is not perfect. If you look at the toroidal you will see the mains wires are half an inch or so away from the secondaries, providing some degree of isolation. But in a very tight enclosure they all then get bundles together more or less.
Edit: I am writiting this after I just saw the first photo of the assembly.
1) The mains cable was pulled out / twisted resulting in the live wire to come off the connector inside and simply "float" around. Considering this now almost loose and floating wirte could have touched various electronics inside... I appreciate that the earth wire is the longest and the last one to go if you pull hard on the mains cable, however that was not pulled so hard resulting in just the positive wire coming out of its connector.
2) Another PSU must have been dropped resulting in the toroidal coming off the brackets as it was sandwitched with two metal plates with the bottom plate glued on the plastic enclosure's bottom. Now we have a loose toroidal banging inside creating all sorts of untold and potentially hazardous damage.
As the enclosures are tight and you have a lot of wires in a small space, I have tried my best to isolate mains from secondaries and mains from everything else, but it is not perfect. If you look at the toroidal you will see the mains wires are half an inch or so away from the secondaries, providing some degree of isolation. But in a very tight enclosure they all then get bundles together more or less.
Edit: I am writiting this after I just saw the first photo of the assembly.
As in a later post ("Since you have followed chipamp.com directions, for the major items you are safety compliant towards Class I.") you have followed a set of instructions and got to a successful conclusion. Well done. There are many here that cannot do that. I am one, I read how to type alphanumerics into my computer and it does not do what the instructions tell me to expect!
Grounding and Earthing are commonly used words in DIYaudio.
But they have VERY DIFFERENT purposes/meanings.
Earthing is a reference to using the Protective Earth (PE) to protect users from faulty equipment.
Grounding, as explained earlier, is a misnomer that gets everybody confused.
The mains powered equipment that you build must be safe to use. We build to ClassI standards.
That requires a Safety Earth to the major metal part, probably the enclosing Chassis. The Third Wire (Green/Yellow here in Europe) to be permanently and mechanically fixed to the Chassis. This fixing point is the Safety Earth, others may use a slightly different name for it, but hopefully, whatever they call it it should be clear it is a SAFETY related connection.
There is a second Safety requirement:
all exposed conductive parts should be connected to the protected chassis.
This is where I confused you with the "floating" reference and your instructions that you followed correctly.
The input and output terminals often have exposed metal work.
This exposed metalwork should be connected to the Protected Chassis.
You do that by connecting the Main Audio Ground to the Chassis.
That was the extra wire I referred to. The amplifier works without this extra wire. The amplifier can "float" with respect to it's surroundings. It will still work. Just like your mobile phone, or Laptop or portable radio. They all float and they all work.
But with Mains powered equipment we must meet that second requirement. That is where your instructions correctly told you to connect the Main Audio Ground to the Chassis. This is a SAFETY requirement only.
But complying with this can something cause some deterioration in audio performance. This can sometimes be improved by using a Disconnecting Network instead of that direct wire connection.
Grounding on the other hand is all about amplifier performance.
Shame that we use the same word for all the different purposes of the differing connections.
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oh darn I thought you had the 200VA* 2x25V Antek which should fit perfectly in the 60 mm inside height spec.
you might experiment the XFMR orientation /spacing around on your 'test bed' to check for stray hum pick up, if your worried about it. toroids are much better that EI cores.
200VA should be fine for 2x60W Class AB amps heat wise, the V regulation may droop a little more than bigger sizes, not a problem unless using sine waves on dual 4 ohm loads.
I wish I did have the 200va instead of 300va, but Antek was all out of stock. I just blew the slow blow 3A fuse again trying to turn this amp on. The in rush for this 300va needs more I guess. I tried to buy 4A fuse but the electronic store was out. Thinking about throwing in the 10A fuse I got with the connector temporarily.
you need ~ 3A SB (slow blow is key ) http://www.amazon.com/Qty-Slow-Blow-Fuse-250v-GDC3A/dp/B004TRPKXM
yeah > 300VA -400VA is borderline for inrush current and using slow start protection
yeah > 300VA -400VA is borderline for inrush current and using slow start protection
Well anyways, I just finished my little 10ohm passive pre with split to powered sub. (One goes to LM3886 and other to Polk Powered sub). This LM3886 SOUNDS AMAZING with it ! 
This is the best amplifier I've ever owned. But I'm just starting out, but at least I have something as a reference. Anyways I think this LM3886 sounds better than the $200 behringer that I had .. (it blew up..sounded great but was proprietary and I just threw it away instead of trying to figure out the undocumented schematic).
Really happy with this amp! These infinity RS2001 bookshelf speakers are great too (along with the powered sub). YOu can pick up a pair for like $25-50 and refoam the 6 inch woofers for around $15 (that's what I did). Perhaps someone can recommend an upgrade to these speakers but maybe an upgrade isn't really needed? These speakers were recommended to me by a studio sound engineer -- said they were cheap and good for the money.
This is the best amplifier I've ever owned. But I'm just starting out, but at least I have something as a reference. Anyways I think this LM3886 sounds better than the $200 behringer that I had .. (it blew up..sounded great but was proprietary and I just threw it away instead of trying to figure out the undocumented schematic).
Really happy with this amp! These infinity RS2001 bookshelf speakers are great too (along with the powered sub). YOu can pick up a pair for like $25-50 and refoam the 6 inch woofers for around $15 (that's what I did). Perhaps someone can recommend an upgrade to these speakers but maybe an upgrade isn't really needed? These speakers were recommended to me by a studio sound engineer -- said they were cheap and good for the money.
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Here is a photo of the passive pre I quickly threw together. I didn't have a chassis so I fashioned a temporary one with chip board, cardboard & hot glue. Using greyhill input selecter but it isnt connected yet--I just have the DAC (to the left) running into it to the POT.
Using a 10K alps RK27 going to Neutrik RCA's. There is a duplicated set of outputs to the left of the rightmost (notice the little jumpers where I split it) -- this one goes to the sub.
The selector knob (the leftmost) that I put on the greyhill is from an old HP vacuum tube multimeter. The knob to the right on the alps came from some vintage equipment but I forget which.
Using a 10K alps RK27 going to Neutrik RCA's. There is a duplicated set of outputs to the left of the rightmost (notice the little jumpers where I split it) -- this one goes to the sub.
An externally hosted image should be here but it was not working when we last tested it.
The selector knob (the leftmost) that I put on the greyhill is from an old HP vacuum tube multimeter. The knob to the right on the alps came from some vintage equipment but I forget which.
^this is weird ,
I have 700VA and 4x 20K uF and no slow start (20mF) and I never blow fuses, but I rarely turn it off and on repeatedly.
I reckon not all SB fuses are created equal ( googled images tells me that.)
maybe you have to wait between on-off cycles for heat inside the glass fuse
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