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Old 1st June 2014, 01:49 AM   #11
DUG is offline DUG  Canada
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Quote:
Originally Posted by AndrewT View Post
Dug,
you are shown as Canada. May I presume you have adopted the british convention of Grn/Yel for PE?

...
The company where I work has...maybe because we ship to EU, US,etc., maybe it is CSA requirements...I don't know...I am just cct design and board layout guy.

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Last edited by DUG; 1st June 2014 at 01:52 AM.
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Old 1st June 2014, 01:50 AM   #12
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Update:
Hum goes away when either RCA is disconnected (no hum or heat with only 1 RCA connected to input, I'm using a 3.5mm to RCA)

Moved ground closer to mains input, used green wire

Reflowed input solders on the channel that was getting hot. This required removing the heatsink and separating the two channels from each other (physically). Because there was no heatsink I was able to feel the heat generated much better. Only one channel was getting hot (too hot to touch in <5 sec).

SWITCH RCA (black to red, red to black), OTHER chip gets hot. WTF? played around with RCA cables for a while, used 3 different sources, finally figured out my chassis insulated RCA jacks weren't so chassis insulated...I think. I think this solved that problem.

However, both chips still get hot, doesn't seem like either gets hotter than the other but I have the heatsink back on now so it's a little hard to tell. Hum is still there, hasn't changed a bit.

Hum does NOT go away if I removed chassis grounds.

I do not have a pot inline for the time being.

I haven't upgraded to Coax for inputs yet.

Does this help anyone? Thanks for all the help everyone.
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Old 1st June 2014, 02:00 AM   #13
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forgot to mention, I get slightly different measurements across R2. R1 and R3, using an Ohmmeter, I get what they are supposed to be (1K and 660). For R2, I get 4-8K (unstable) and 16K for each individual channel. What gives? This should be a 22k Ohm resistor but obviously I'm getting flow through somewhere with less resistance. No surprise since it goes to ground....but why are they different?
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Old 1st June 2014, 03:56 AM   #14
Dinithm is offline Dinithm  Sri Lanka
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problem of your circuit, POWER GND (0v) planes

i recomend,
1.do not use two power supply circuits
connect two amplifire circuits to one power supply circuit
*connect (ps V+,amp1 v+,amp2 V+)
*connect (ps V-,amp1 v-,amp2 V-)
*connect (ps PG+,amp1 PG+,amp2 PG+)
*connect (ps PG-,amp1 PG-,amp2 PG-)

2.remove eart wire.

make it simple
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Old 1st June 2014, 04:01 AM   #15
tomchr is offline tomchr  United States
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Quote:
Originally Posted by dhanigan View Post
Ci was omitted as it was optional. I completely forgot about that decision until just now. Could that be the issue?
What do you mean by "omitted"? You obviously didn't stuff the cap, but what did you do with the empty footprint on the board? Leave it open?

You can go without Ci, that's fine. You'll get slightly higher offset (DC) voltage on the output, but that's usually not a problem. However, if you don't populate Ci, you must ground R3. If the footprint for Ci on the board is currently open, connect the two pads of the footprint for Ci by a piece of wire.

Quote:
Originally Posted by dhanigan View Post
There are three 0.1uF caps used in the PSU schematic, which one? and why?
I count four. I'd use a film cap, but the exact type doesn't matter that much. That's not the source of your problem.

Quote:
Originally Posted by dhanigan View Post
Because there was no heatsink I was able to feel the heat generated much better. Only one channel was getting hot (too hot to touch in <5 sec).

SWITCH RCA (black to red, red to black), OTHER chip gets hot. WTF? played around with RCA cables for a while, used 3 different sources, finally figured out my chassis insulated RCA jacks weren't so chassis insulated...I think. I think this solved that problem.
Now we're getting somewhere. So the problem follows the cable. Have you tried playing with just one channel connected? Say, you connect the black RCA and have no issues with hum. One channels plays fine when connected to the black RCA. Then move the black RCA to the other channel. Does the other channel play? Leave the red disconnected (assuming it's the red that causes trouble).

Have you tried with a different cable?

Quote:
Originally Posted by dhanigan View Post
However, both chips still get hot, doesn't seem like either gets hotter than the other but I have the heatsink back on now so it's a little hard to tell.
An LM3886 burns around 50 mA at idle. With a 30 V supply, that's 3 W. That should make the chip quite hot (close to the thermal limit, in fact).

Quote:
Originally Posted by dhanigan View Post
I haven't upgraded to Coax for inputs yet.
That won't solve your hum issue anyway. There is something fundamentally wrong with your circuit or setup. Figure out what it is, then "upgrade" and modify.

See if you can get one channel to work at a time.

~Tom
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Old 1st June 2014, 07:45 AM   #16
AndrewT is online now AndrewT  Scotland
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Default EU and UK colour coding for Mains wiring

Tom, you recall correctly.

In the EU, yellow/green is earth/ground, brown is hot, blue is neutral as I recall.
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Old 1st June 2014, 07:52 AM   #17
AndrewT is online now AndrewT  Scotland
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Quote:
Quote:
Originally Posted by AndrewT View Post
Shorten the Protective Earth (PE) wire and bolt it next to the mains cable entry hole.
This Safety Earth is permanent and should never be dismantled.
Is Green/yellow sleeving available in the USA?
But ONLY use it on the PE wire, no where else.
Quote:
Should I use this as a star ground still? or star ground elsewhere and run wire between SE chassis connection and star?
The Safety Earth/ Protective Earth is a SAFETY ONLY connection. It is there PERMANENTLY.
Do not dismantle it.
Do not connect anything else to it.

The Main Audio Ground (MAG)/star ground is an AUDIO voltage reference for all the audio circuits. This has NOTHING to do with the PE/Chassis.
Create your MAG as a floating point in space. Somewhere between the PCB inputs and PCB outputs and near the Chassis mounted Speaker terminals is usually a good enough location. I prefer a bolted connection with sufficient solder tags for each connected wire.
A 4mm bolt through the tags gives a nice low voltage drop "star".

This MAG/Star needs to be connected to Chassis to comply with:
all exposed conductive parts should be connected to (a protected) Chassis
This is a single wire connection to the nearest Chassis panel, not to the Safety Earth which is located beside the mains cable entry hole.
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Old 1st June 2014, 09:40 AM   #18
Dinithm is offline Dinithm  Sri Lanka
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Last edited by Dinithm; 1st June 2014 at 09:50 AM.
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Old 1st June 2014, 12:11 PM   #19
AJT is offline AJT  Philippines
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you may want to look here....Help with LM3886 amp

please read up on other threads on th topic...
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Old 2nd June 2014, 02:51 AM   #20
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Quote:
Originally Posted by Dinithm View Post
problem of your circuit, POWER GND (0v) planes

i recomend,
1.do not use two power supply circuits
connect two amplifire circuits to one power supply circuit
*connect (ps V+,amp1 v+,amp2 V+)
*connect (ps V-,amp1 v-,amp2 V-)
*connect (ps PG+,amp1 PG+,amp2 PG+)
*connect (ps PG-,amp1 PG-,amp2 PG-)

2.remove eart wire.

make it simple
I bought the dual mono kit because I want to use separate power supplies. I could give that up yes, but I intend to do that only as an absolute last resort. This was recommended previously Here

As well as using two torroids, neither of which I believe to be an acceptable solution.


Quote:
Originally Posted by tomchr View Post
What do you mean by "omitted"? You obviously didn't stuff the cap, but what did you do with the empty footprint on the board? Leave it open?
There are 2 options for the leads on R3, one for if Ci is used, one for if it is not. I checked if it is grounded in the configuration, it is.

Quote:
Originally Posted by tomchr View Post
Now we're getting somewhere. So the problem follows the cable. Have you tried playing with just one channel connected? Say, you connect the black RCA and have no issues with hum. One channels plays fine when connected to the black RCA. Then move the black RCA to the other channel. Does the other channel play? Leave the red disconnected (assuming it's the red that causes trouble).

Have you tried with a different cable?
Tried two different cables yesterday and had the same result with both. With only either RCA connected to either channel, I get no hum. The problem arises when I connect the other RCA. No music playing, loud hum, music playing, quieter hum, slower frequency. Sounds similar to 60hz to my untrained ear. it changes pitch when I stop music playing. I have tried yet another source to no avail.

Quote:
Originally Posted by tomchr View Post
An LM3886 burns around 50 mA at idle. With a 30 V supply, that's 3 W. That should make the chip quite hot (close to the thermal limit, in fact).
It doesn't help that I'm doing all this in my garage in AZ, it's probably ~110*F in there all day.



Quote:
Originally Posted by AndrewT View Post
Quote:
The Safety Earth/ Protective Earth is a SAFETY ONLY connection. It is there PERMANENTLY.
Do not dismantle it.
Do not connect anything else to it.

The Main Audio Ground (MAG)/star ground is an AUDIO voltage reference for all the audio circuits. This has NOTHING to do with the PE/Chassis.
Create your MAG as a floating point in space. Somewhere between the PCB inputs and PCB outputs and near the Chassis mounted Speaker terminals is usually a good enough location. I prefer a bolted connection with sufficient solder tags for each connected wire.
A 4mm bolt through the tags gives a nice low voltage drop "star".

This MAG/Star needs to be connected to Chassis to comply with:
all exposed conductive parts should be connected to (a protected) Chassis
This is a single wire connection to the nearest Chassis panel, not to the Safety Earth which is located beside the mains cable entry hole.
These PCBs have all the grounds tied together in the "chassis ground" lead. My only option is to tie the chassis ground leads from the PCBs into the star ground, which leaves me without a dedicated MAG.

I goofed with it today for a couple of hours, still nothing. I removed the soft started from the circuit to make things simpler too. I blew up a couple of diodes originally wiring this thing wrong, but it should have only affected the diodes themselves. Is it possible that some of the others are damaged and are making some noise? There are only so many options with these PCBs and I'm really out of ideas.

Last edited by dhanigan; 2nd June 2014 at 03:07 AM. Reason: bad hyperlink
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