Decided to make this thread to consolidate my ongoing progress and questions related to the LM3886 amplifier I'm building over the next month.
I ordered the stereo LM3886 kit from chipamp.com and should have it in a few days. I also ordered an Antek 300VA 2x25v toroidal transformer.
I ordered quality rca connectors, speaker binding posts and power connector from chipamp as well.
First question:
Brian doesn't sell a fuse holder and I am in need of one. I see 5 for like $7 on amazon, but these are just generic ones. Is there a particularly high quality fuse holder for my build that is on par with the quality of the other parts I just bought?
I ordered the stereo LM3886 kit from chipamp.com and should have it in a few days. I also ordered an Antek 300VA 2x25v toroidal transformer.
I ordered quality rca connectors, speaker binding posts and power connector from chipamp as well.
First question:
Brian doesn't sell a fuse holder and I am in need of one. I see 5 for like $7 on amazon, but these are just generic ones. Is there a particularly high quality fuse holder for my build that is on par with the quality of the other parts I just bought?
look into a IEC AC inlet with a built in fuse. compact and less wires to mess with
OK you shop Amazon , added link ( not sure if these are safety rated or not.
http://www.amazon.com/Inlet-Module-Switch-Socket-IEC320/dp/B00F4MFMXE
OK you shop Amazon , added link ( not sure if these are safety rated or not.
http://www.amazon.com/Inlet-Module-Switch-Socket-IEC320/dp/B00F4MFMXE
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Okay, just ordered that inlet/fuse/switch from Amazon for my LM3886. Makes for a great bench/testing setup as well. I might order more of these for other projects.. like a replacement linear power supply for my 1983 Commodore 64.
For things like that i have purchased from Apex Jr, Apex Jr.Home Page. They are in the vendors forum here. They have switched, fused IEC receptacles for $0.99
I received the parts the day before yesterday and spend all day yesterday working on this amp. So far it sounds great! This is my first power supply I've ever made and first amplifier ever 
It's a face panel from an old HP 400D vacuum tube multimeter (1/8" thick or so aluminum). And it is clamped to a piece of poplar.
An externally hosted image should be here but it was not working when we last tested it.
It's a face panel from an old HP 400D vacuum tube multimeter (1/8" thick or so aluminum). And it is clamped to a piece of poplar.
do not use multiple wires under the Safety Earth nut.
Use a dedicated bolt fixing for the Safety Earth.
Stick a couple of layers of insulating tape over the exposed MAINS terminals. You don't want to touch these nor drop a metal tool on them.
Change the label on the mains input. Either PE (Protective Earth), if that means anything to you, or "Safety Earth" if that sticks in your head better.
It is not GND. That is too easily confused with other parts of the audio circuits.
Use a separate bolt/lug for the Main Audio Ground. This can float as long as you can SEE that the mains transformer is not faulty.
Then after you have the amplifier working and tested you can take an extra wire (or Disconnecting Network) to the earthed panel with it's own separate fixing.
Are you using a single 4diode bridge rectifier? Or is that an 8diode dual bridge rectifier? Once I have this answer I am going to expand on Infinia's "twisted wires are great"
Have you built up a Mains Bulb Tester yet?
Do you know how to use it?
Do you know how to interpret the messages that the bulb gives you?
Use a dedicated bolt fixing for the Safety Earth.
Stick a couple of layers of insulating tape over the exposed MAINS terminals. You don't want to touch these nor drop a metal tool on them.
Change the label on the mains input. Either PE (Protective Earth), if that means anything to you, or "Safety Earth" if that sticks in your head better.
It is not GND. That is too easily confused with other parts of the audio circuits.
Use a separate bolt/lug for the Main Audio Ground. This can float as long as you can SEE that the mains transformer is not faulty.
Then after you have the amplifier working and tested you can take an extra wire (or Disconnecting Network) to the earthed panel with it's own separate fixing.
Are you using a single 4diode bridge rectifier? Or is that an 8diode dual bridge rectifier? Once I have this answer I am going to expand on Infinia's "twisted wires are great"
Have you built up a Mains Bulb Tester yet?
Do you know how to use it?
Do you know how to interpret the messages that the bulb gives you?
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8 diodes, dual bridge. One side provides positive voltage and the other is negative voltage.
Yes it is confusing, solely because so many refer to everything as ground. That is the confusion.
All these points in the circuit are generally doing a jog that has a specific purpose and each is usually doing a different job. If we gave each point it's specific title that described it's purpose much of this confusion would disappear.
A couple of examples:
Signal Ground is actually Signal Return to complement Signal Flow. It is NOT GND
Speaker Return is actually a return to complement to speaker current. It is not GND
Notice that in both of the above I used Signal or Speaker to describe the return route. Quite specific. No ambiguity.
Have you measured Hum plus Noise at the output yet?
Short the inputs with a shorting plug.
leave the speaker disconnected.
Measure the mVac using the 199.9mVac setting on your DMM
Measure the mVdc using the 199.9mVdc setting on your DMM.
All your testing should be completed and passed before you connect a speaker, yes BEFORE.
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The dual bridge rectifier uses TWO separate supplies from the isolated secondary windings.
Find one pair of tappings for one winding. Twist them together. Take this twisted pair to the two terminals on the PSU PCB.
Twist the other pair of tappings for the other secondary winding. Take this twisted pair to the other two terminals on the PSU PCB.
Look at the output side of the PSU.
There are 3 output terminals.
Attach 3 wires and twist them as a triplet. Take this triplet to the amp PCB and attach them to the correct power terminals.
Repeat for the second channel.
Use a colour code for your wiring that you can easily remember. Maybe attach a legend to the underside of the cover, so that you see a reminder in a few years time when you open it up again.
Many would use RED for +ve supply, Black for -ve supply, green for Zero Volts.
For AC choose two other unique colours, Blue & Yellow?
When you have a CT (centre tap) you need a third colour.
For mains try to use your countrie's standard colours. Even if you have to strip them out from a piece of redundant mains lead from a dead appliance.
I try to wrap the MAINS wiring in a double layer of RED sticky insulating tape. This double insulates the Mains wiring and gives an enhanced level of safety when you are poking around inside.
If you can find any, buy a rubber boot to fit over the IEC socket. secure it with a tight clamp. A Ty-Wrap is quite good.
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It provides a much enhanced protection for you and your project.
Read up and BUILD it.
Use it every time you power on a new project, or a modified project.
This provides an instant visual warning if you have made a silly wiring error.
I have twice blown up an amplifier when I did not use a Mains Bulb Tester.
eg.
3886 single channel power from a PSU located just 6" away. It was playing perfectly, but I wanted to alter the RF filter.
Unplugged, disconnect the PSU triplet (1/4" spades) and lifted out the chipamp. Reinstalled and connected up.
Power ON - explosion.
I had swapped the PSU Zero Volts for the PSU -ve at the amp PCB.
The renowned protection inside the 3886 does not protect from this silly mistake. Needed a new 3886, no other damage.
A Mains Bulb Tester would instantly light full ON and reduce the secondary voltages to a safe level (<<+-5Vdc), that allows the 3886 to survive.
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I can't to the back of the unit right now because it's in the shelf of my entertainment center. Enjoying listening to some Bob Marley right now -- I shot the Sherrif.
I'll do those tests when I get it back on the bench.
It's sounding pretty nice right now. But Im thinking a 10K pot might sound better.
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