Bought a XY LM3886 Kit.

[pacificblue]

I'll have to aks Jason for a share of that donation.

[AndrewT]

Originally Posted by Aguilabrava

...............
I am still confused with the Zobel and Thiele networks and how to implement them in these PCB's.

I understand that what AndrewT calls the R+C Zobel is basically a resistor and capacitor connected in series, and the R//L Thiele is basically a resistor and inductor connected in parallel.

Now, he says to use the space left empty in these boards for R1, which I don't need to use. The space for R1 has two holes, one at the top close to Pin #3 of the LM3886TF and one at the bottom close to the Output + terminal. Is it OK to install the 10 Ohm resistor in the R1 location two holes, then attaching the 220nf capacitor in the bottom hole of R1 space and the Output + terminal right next to it?. Then, I will take the speaker connection (Output +) from the bottom of the PCB, and the Output Ground will go from the chassis speaker terminal to the common ground where ALL grounds will join the amplifier chassis, is this right?.

Not quite.
The R1 bottom hole takes the lower end of the Zobel resistor.
The R1 top hole takes the copper lead. Make the lead about 12mm long. 4mm below the PCB and 7mm above the PCB. Attach the speaker output cable to the 4mm of copper lead below the PCB.
Attach the Zobel resistor to the 7mm of top side copper lead.
The Zobel capacitor connects to PCB instead of the speaker terminal block.
One leg of the cap connects to the trace of R1 The other leg of the capacitor connects to the Ground trace.
That 7mm of copper lead is left long to allow you to bend it to an L shape. The short leg of the L gets soldered to the leadout of the chipamp.

At the same time, the chassis speaker terminal will have the 10 Ohm resistor with the 1.5H inductor connected in parallel attached to the Output +, correct?.

No. The R//L is located off the PCB. That part goes into the cable connection between PCB and chassis mounted speaker output terminal.

if someone here could help me understand his quote above where he mentions using a copper wire as a terminal,

Hopefully this is more clearly stated.

[AndrewT]

Originally Posted by Aguilabrava

I have another question. My kit calls for a 22uF capacitor in the C4 space, and a Wima 1.0uF in location C5 in the PCB. All other locations on the board call for 100uF capacitors.

After doing some research, I think I've seen some other kits that use a 47uF capacitor for what I think is C4, instead of the 22uF that my kit calls for. What would be the difference if I replace the C4 22uF with a 47uF?.

They still use the same 100uF 50V in all other locations.

I am already replacing the C5 Wima 1.uF with a Audiophiler MKP 4.7uF 400V.

Thanks again.

C4 & C5 values are determined by the Low Frequency response you require from the Power Amplifier.

C5 sets the input high pass filter frequency. 4.7uF may be a bit too big for the matching resistor R5.
Decide what F-3dB frequency you want. Determine the C5 value from F-3dB & R5 using the formula F-3dB = 1/2/Pi/R/C. Rearranged to be C5=1/2/Pi/F-3dB/R5

[AndrewT]

C4 should be chosen so that in normal operation it has virtually zero DC voltage across it and virtually zero AC voltage across it.

Choose C4 value by using the equation
C4 >= C5 * Sqrt(2) * [R5+R6] / R4

The bigger you choose for C5, the bigger that C4 becomes.

[AndrewT]

post48.
There are some errors in that layout.

[Aguilabrava]

Thank you very much, Andrew, we really appreciate your help. I have almost everything to start working on the assembly process, the speaker protection board I thought had been lost in the mail showed up today. I decided to order some more capacitors for the amplifier PCB's, I ordered Nichicon and Elna Silmic, I have the Nichicon but I'm still waiting on the Silmic, they should be here by monday.

As soon as I start, I will produce good pictures so you won't have to be answering these questions each time someone decides to get a XY LM3886 kit.

[fabricated]

Right on

I have also found that the inner copper core of tv coax cable fits in the pcb holes really well.

[Aguilabrava]

Hi:

Here are some pictures of the modification made to the XY LM3886 boards to include the Zobel R+C network, a very clever way of doing it, all credits go to AndrewT who gave me all the instructions and component values.

I just hope I got it right...!

You can also see the RF filter capacitor on top of the R5 resistor. That is a 0.01uF polyester film capacitor.

The resistor used in R1 for the Zobel is a 10 Ohm resistor. The rest are 22K Ohm and 1K Ohm, I just upgraded to 1/2 watt resistors instead of using the microscopic ones that came with the kit.

The capacitor located in the speaker output connection is a 0.22uF polypropylene capacitor.

The rest of the capacitors (C1, C2, C3, C4 and C5) are missing, I am still waiting for them, they should be here either monday or tuesday. I will post more pictures as soon as I have the boards totally finished.

The bare copper wire that goes in the top of R1 location is a piece of 18 AWG solid core wire I got at Radio Shack, it fits the hole perfectly. I know I have to cut it, it is too long now, but I want to finish the boards to see how I am going to solder the speaker + output to it. The soldering in the "shorter L shaped end" that joins the copper wire, resistor and pin #3 of the LM3886 is kind of hard because of the location, one has to be extremely careful not to hit something else with the hot tip of the soldering iron, perhaps it might be a better idea to solder the copper wire to the leg of the LM3886 before installing it in the board.

I have included more pictures in the next few posts, I couldn't upload them all in this one.

I have more questions, but I'll save them for later, for now, I just want to know I got this right, and again, thank you very much to all of you that have been here sharing your time and your knowledge so generously, specially AndrewT, Pacificblue, Fabricated and all others.

[Aguilabrava]

Here, I'm posting more pictures....

[Aguilabrava]

Here is the rest of the pictures, I had to do it this way because I couldn't upload them all in one post.