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Old 2nd June 2014, 09:08 AM   #21
AndrewT is offline AndrewT  Scotland
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While you are making modifications, ALWAYS use the bulb tester to Power ON.
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Old 2nd June 2014, 09:16 AM   #22
AndrewT is offline AndrewT  Scotland
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The TWO input interconnects are creating a LOOP.
That loop can only be broken by splitting the SOURCE common Ground.
That solution is generally impossible.

Instead you can build mono blocks. These are isolated from each other. That prevents the creation of the input loop.

A third method is to build a dual mono with isolated channels. This needs separate secondary windings to each channel.
This prevents creation of the input loop.
BUT !!!!!! you are required to add a link from Chassis to all exposed conductive parts. This creates a loop with the TWO input interconnects.

A fourth method is to build a stereo with a common ground for the two channels.
The solution here is not to break the loop, that breaks the two wire connection circuit.
Instead you add resistance into parts of the loop such that the interfering voltage drop on the signal wiring becomes low enough to not cause perceivable damage to the wanted signal.

This final method of adding resistance to some parts of the circuit or circuits is a very powerful technique. But you have to work out WHERE to place the added resistance so that you preserve the wanted signal.

There is a paper that describes exactly how to find these inadvertent loops and where to place the added resistances.
It has been linked a few times on this Forum.
I have downloaded it and printed it, but don't have the address. I'll see what I can find.
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Last edited by AndrewT; 2nd June 2014 at 09:19 AM.
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Old 2nd June 2014, 09:32 AM   #23
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Here are a few things that you could try:

1. Follow the users guide, it explains how to first connect the PSU board to the transformer, then measure, then connect the amp board, then measure, etc. If you had done this from the start you would not have made such a catastrophic mistake.

2. Best to build two mono amps or a stereo amp. Your two PSU boards connected to a single transformer is a configuration not often seen and it is not explained in the CHIPAMP.COM users guide. If you want to experiment when you have things working that it fine, but for now best to keep to the users guide.

3. Try different sources. A CD PLAYER would be best. You don't know what kind of signals (RF) are coming out of your telephone. My phone even uses the headphones as a radio antenna.

4. Place a stereo potentiometer or resistor network before the inputs of both amps. See the users guide. it will reduce noise from the source.

5. No instructions in the users guide on how to connect two amp boards to a single PSU board. You could try something like this:
lm3886-ground-safe1.GIF
Different mains plug of course.

Its important to keep the ground connections short, which in this case should not be a problem. I would recommend twisting supply and returns where possible.
If you want to build two mono amps just follow the users guide.

6. The heatsink seems to small, although it is larger than what is advised in the users guide. If you have the TF type chips, do not insulate the chips from the heatsink, fasten the chips directly to the heatsink. Don't place a plate between the chips and heatsink, it will only reduce the heat transfer.

7. Use the correct coloured leads and insulate all mains connections.



I hope some of this info was helpful.
Attached Images
File Type: gif lm3886-ground-safe2.GIF (56.1 KB, 96 views)
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Last edited by Mark Whitney; 2nd June 2014 at 09:40 AM.
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Old 2nd June 2014, 10:42 AM   #24
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Quote:
Originally Posted by dhanigan View Post
Maybe I'm an idiot but with AC does it matter which line off the mains I switch? One is always available to bite you if you are grounded correct? You're saying move the switch to the other AC terminal?
I'm not familiar with the the US mains wiring and how the A.C relates to ground but I would play it safe and use a two pole switch and switch both conductors

Even where I live where one of the A.C conductors (neutral) is at ground potential and only the other A.C conductor (phase) has voltage with respect to ground, I still use a double poll mains switch and switch both the phase and the neutral, mainly to guard against incorrect house or power cord wiring, however unlikely that may be. That way, I know when it's switched off, its all off

Only the safety earth should be permanently connected, it should have its own connection to the chassis
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Old 2nd June 2014, 11:13 AM   #25
AndrewT is offline AndrewT  Scotland
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The UK requires the mains switch to be two pole.
This is to ensure when OFF, that swapped Live & Neutral do not leave the equipment "Live".
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Old 2nd June 2014, 11:18 AM   #26
tomchr is offline tomchr  United States
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Quote:
Originally Posted by dhanigan View Post
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.
Good deal. The circuit should work then.

Quote:
Originally Posted by dhanigan View Post
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.
I'm guessing you're using a 3.5 mm headphone jack to RCA cable to connect to your phone. What happens if you plug in both RCAs but leave the 3.5 mm end floating? Still hum?

Do you have a voltmeter? With the input cable disconnected, try measuring the voltage (both DC and AC) between the outer ring ("ground") on the two RCA jacks. I.e. touch the outer ring of one jack with the (+) lead of the voltmeter and the outer ring of the other RCA jack with the (-) lead. There should be no voltage here (neither DC or AC). If you have voltage here, I bet you accidentally swapped the transformer windings between the two boards.

If you're dealing with a ground loop, you should be able to make the amplitude change by moving the wires around. If you bundle all the wires tightly, the amplitude should go down. Likewise if you make the RCA cable shorter (you could emulate that by touching the outer ring of the two RCAs with a piece of wire - after confirming that you don't have voltage between them), the hum amplitude should be lower.

Personally, I think the problem is with the hookup of the power transformer. One thing you can try is to hook the transformer to only one rectifier board and use the output from that board to supply both channels. I don't know if the rectifier board can handle that at max output power (probably not), but for a quick test at a few watt output power (still damn loud), it should be fine.

Quote:
Originally Posted by dhanigan View Post
It doesn't help that I'm doing all this in my garage in AZ, it's probably ~110*F in there all day.
Yuck. Here in Seattle, we consider 90 F (low 30ies C) to be very hot. 100 F (40 C) would be unbearable, "why didn't I get a house with air-conditioning" hot...

~Tom
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Old 2nd June 2014, 11:20 AM   #27
tomchr is offline tomchr  United States
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Quote:
Originally Posted by AndrewT View Post
The UK requires the mains switch to be two pole.
This is to ensure when OFF, that swapped Live & Neutral do not leave the equipment "Live".
Yep! +1 for two-pole mains switches.

~Tom
__________________
Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
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Old 3rd June 2014, 04:01 AM   #28
DUG is offline DUG  Canada
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Then the input should be fed first to a two-pole ganged breaker.

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Old 3rd June 2014, 05:36 AM   #29
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Quote:
Originally Posted by AndrewT View Post
The TWO input interconnects are creating a LOOP.
That loop can only be broken by splitting the SOURCE common Ground.
That solution is generally impossible.

Instead you can build mono blocks. These are isolated from each other. That prevents the creation of the input loop.

A third method is to build a dual mono with isolated channels. This needs separate secondary windings to each channel.
This prevents creation of the input loop.
BUT !!!!!! you are required to add a link from Chassis to all exposed conductive parts. This creates a loop with the TWO input interconnects.

A fourth method is to build a stereo with a common ground for the two channels.
The solution here is not to break the loop, that breaks the two wire connection circuit.
Instead you add resistance into parts of the loop such that the interfering voltage drop on the signal wiring becomes low enough to not cause perceivable damage to the wanted signal.

This final method of adding resistance to some parts of the circuit or circuits is a very powerful technique. But you have to work out WHERE to place the added resistance so that you preserve the wanted signal.

There is a paper that describes exactly how to find these inadvertent loops and where to place the added resistances.
It has been linked a few times on this Forum.
I have downloaded it and printed it, but don't have the address. I'll see what I can find.
Quote:
Originally Posted by Mark Whitney View Post
Here are a few things that you could try:

1. Follow the users guide, it explains how to first connect the PSU board to the transformer, then measure, then connect the amp board, then measure, etc. If you had done this from the start you would not have made such a catastrophic mistake.

2. Best to build two mono amps or a stereo amp. Your two PSU boards connected to a single transformer is a configuration not often seen and it is not explained in the CHIPAMP.COM users guide. If you want to experiment when you have things working that it fine, but for now best to keep to the users guide.

3. Try different sources. A CD PLAYER would be best. You don't know what kind of signals (RF) are coming out of your telephone. My phone even uses the headphones as a radio antenna.

4. Place a stereo potentiometer or resistor network before the inputs of both amps. See the users guide. it will reduce noise from the source.

5. No instructions in the users guide on how to connect two amp boards to a single PSU board. You could try something like this:
Attachment 421707
Different mains plug of course.

Its important to keep the ground connections short, which in this case should not be a problem. I would recommend twisting supply and returns where possible.
If you want to build two mono amps just follow the users guide.

6. The heatsink seems to small, although it is larger than what is advised in the users guide. If you have the TF type chips, do not insulate the chips from the heatsink, fasten the chips directly to the heatsink. Don't place a plate between the chips and heatsink, it will only reduce the heat transfer.

7. Use the correct coloured leads and insulate all mains connections.



I hope some of this info was helpful.
I'm building this amp off of the BOM of someone else. I don't know if DIYAudio allows to post external links, but it's a small desktop amp over at PE. I didn't realize this was such an uncommon setup, I will PM the original builder and see how he/she wired things. Also, yes, I am stupid for not using a bulb tester the first time around. I use one now. I actually did test voltages as in the manual, but had things wired differently.

Quote:
Originally Posted by tomchr View Post
Good deal. The circuit should work then.



I'm guessing you're using a 3.5 mm headphone jack to RCA cable to connect to your phone. What happens if you plug in both RCAs but leave the 3.5 mm end floating? Still hum?
no hum.

Quote:
Originally Posted by tomchr View Post
Do you have a voltmeter? With the input cable disconnected, try measuring the voltage (both DC and AC) between the outer ring ("ground") on the two RCA jacks. I.e. touch the outer ring of one jack with the (+) lead of the voltmeter and the outer ring of the other RCA jack with the (-) lead. There should be no voltage here (neither DC or AC). If you have voltage here, I bet you accidentally swapped the transformer windings between the two boards.
Will check.


Quote:
Originally Posted by tomchr View Post
If you're dealing with a ground loop, you should be able to make the amplitude change by moving the wires around. If you bundle all the wires tightly, the amplitude should go down. Likewise if you make the RCA cable shorter (you could emulate that by touching the outer ring of the two RCAs with a piece of wire - after confirming that you don't have voltage between them), the hum amplitude should be lower.
Amplitude does not change. I've shuffled around the amps, twisted the wired, moved them around while it's humming...nothing. Always the same.

Quote:
Originally Posted by tomchr View Post
Personally, I think the problem is with the hookup of the power transformer. One thing you can try is to hook the transformer to only one rectifier board and use the output from that board to supply both channels. I don't know if the rectifier board can handle that at max output power (probably not), but for a quick test at a few watt output power (still damn loud), it should be fine.
I'll check one last time. Right now, I have each secondary paralleled to both amps. Here is a pretty good picture of how they are wired. AC1 and AC2 are in parallel with the opposing PS board.



Quote:
Originally Posted by tomchr View Post
Yep! +1 for two-pole mains switches.

~Tom
Well, I hate the switch I have because of the way it mounts so I will purchase a 2 pole.

Last edited by dhanigan; 3rd June 2014 at 05:38 AM.
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Old 3rd June 2014, 06:06 AM   #30
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Quote:
Originally Posted by tomchr View Post
Good deal. The circuit should work then.


Do you have a voltmeter? With the input cable disconnected, try measuring the voltage (both DC and AC) between the outer ring ("ground") on the two RCA jacks. I.e. touch the outer ring of one jack with the (+) lead of the voltmeter and the outer ring of the other RCA jack with the (-) lead. There should be no voltage here (neither DC or AC). If you have voltage here, I bet you accidentally swapped the transformer windings between the two boards.


Personally, I think the problem is with the hookup of the power transformer. One thing you can try is to hook the transformer to only one rectifier board and use the output from that board to supply both channels. I don't know if the rectifier board can handle that at max output power (probably not), but for a quick test at a few watt output power (still damn loud), it should be fine.


~Tom
~14mv DC, no AC with RCA hooked up to inputs but not plugged into source. ~5mvDC, no AC when hooked up to source. Does that tell you anything?

I started looking at my wiring to make sure it matched the diagram I posted but I chickened out, too hot.
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