Bought a XY LM3886 Kit.

[lanchile]

Originally Posted by Aguilabrava

Hi Lanchile:

Yes, the whole thing looks like a mess, I knew that as soon as I'd post the pictures I was going to get a lot of criticism, I am ready for it...

Now, the amazing thing is that even though the cables are a complete mess, I didn't have any hum or noises of any kind. I introduced hum last night when I added the two pieces of aluminum foil to the gaps between the heatsinks and the sheet holding the switch and volume pot.

All this issues will be addressed when I put this thing in a enclosure, but I need you guys help in the meanwhile. Can you please tell me where the ground loops are?. Can you please tell me if soldering ground cables to the heatsinks will get rid of the hum I have now that I didn't have before?.

Thank you, Lanchile.

Remove the aluminum foil and see if you still have the noise! Please post pictures to see it better how you have it now. I would not use aluminum foil inside amp, because it can get loose and fall on boards and make some trouble with all those live voltages.

[Corpius]

Hi Aguilabrava ,

This is how I planned to build my amp. All parts are finished except for the amplifier boards. I need to add some parts of the Thiele network and also a 220 nf capacitor. It is fully remote controlled, but can also be manually controlled. There are going to be 4 inputs. It has a speaker protection against DC current. This protection board also has a switch-on delay to prevent pops and clicks when powering up the system. In the back (left side) you can see the inductors I made myself, just like peranders advised me (post #177). I'm not able to measure the inductance because I have no equipment for this, but I think they will do just fine.

[Corpius]

As I mentioned in my last post I'm going to use a speaker protection kit. According to the manual of this kit the speakers should be wired as in the image. Should I place the second part of the thiele Network (the parallel RL circuit). In front of the speaker protection board or after it?

[AndrewT]

The R//L can go before the spkr prot, or after the spkr prot. Both work equally well.

The Zobel half if fitted before spkr prot must go as close to the output pins and chip decoupling as possible.

If you fit the Zobel after the R//L, then the Zobel is directly across the Amplifier's spkr output terminals.

[pacificblue]

It is preferable to place both circuits on the amp side of the relay. That way their protective function remains in place even if the relay cuts the signal to the speakers. Oscillation or RF interference may not bother you when the speaker is disconneceted, but that is no reason to subject the amp to either.

You also avoid discharging or recharging the snubber capacitor each time the relay changes state. Voltage and current involved are small, but so is the capacitor and there is no need to age it faster than necessary.

Normally at least the snubber will be on the amp board and the protection circuit will be on a different board, so that issue usually solves itself.

If you fit the snubber behind the R//L circuit, you go from a 1st order to a 2nd order low pass with a highish Q that may just lead to the oscillation the snubber is there to avoid among other things.

It is important to understand that the RC circuit is not a Zobel network, i.e. it is not an impedance correction. The capacitor value is far to small for that. It is an RF snubber. It should be close to the amp, not close to the speaker.

[AndrewT]

The Thiele Network is in two forms.

Form1:
R+C across the amplifier output and R//L on the route to the speaker terminals.

Form2:
R//L on the route to the speaker terminals and the R+C across the speaker terminals.

Both these versions work. That is the way Thiele designed it.

Cherry followed up with a short paper explaining that there are an infinite number of intermediate versions that span from the two limiting forms that Thiele proposed.

I have posted the spreadsheet to allow the two Thiele forms to be calculated and for all the intermediate Cherry versions to be calculated.

[Corpius]

This is how I made it.

[pacificblue]

Originally Posted by AndrewT

Both these versions work.

Yes, but with different values.

Originally Posted by AndrewT

I have posted the spreadsheet

Nice. Where?

[AndrewT]

When an output inductor is needed???
Download the zip file. It is simply a compressed Excel XLS file.

[Pemo]

Hi guys, this is PEMO again.

I found this new board, similar to the ones we bought before. I can see some differences in it. One of course is a Zobel. And the other is an input filter.

By viewing these photos can you confirm this?

Thanks again, PEMO.

IMG_0123.jpg

IMG_0054-1.jpg