Bought a XY LM3886 Kit.

[lanchile]

Originally Posted by AndrewT

Plumbers' copper pipe does not come ready tinned.
Yes, you have to clean it if the flux is not aggressive enough to remove some contamination.

That is very different from soldering pre-tinned electrical component leads.

it does not matter "professor", as long as is clean and shiny it will work.

[Aguilabrava]

Originally Posted by AndrewT

Have you drawn a schematic from the XY PCB you have in front of you?

Have you added to the schematic those modifications you have so far made to that PCB?

Have you compared your XY schematic to the various diagrams in the datasheet?

Have you looked at the purpose that National tell you each component has?

I suggest you do all of that before you think about powering anything up.

AndrewT:

I am trying to "draw a schematic" of the board in front of me, including the modifications made.

I have read the datasheet from National so many times that I am having dreams with it, the problem is that it is really hard to understand it since my knowledge in this matter is extremely limited.

I measured the voltage coming out of the mains few minutes ago, I got a reading of 120.7 volts, for the first time.

Thank you, Professor.

[Corpius]

Could anybody explain to me why one needs a tranformer with lower secondaries for 4 ohm speakers then with 8 ohm speakers?
I`m building the same amp also with the XY lm3886 ebay kit. I have a dual 24V tranformer lying around. Would this be OK for both 4 and 8 ohm speakers or just 8 ohm speakers?

[Aguilabrava]

AndrewT:

I connected the transformer and PSU, measured the voltage twice, last night I got 40 volts when measuring +V -V, and 20 volts when measuring +V GND or -V GND. Today I measured 38 volts and 19 volts when measuring +V GND, -V GND.

I have another question. I soldered a piece of wire to the copper on the PCB for speaker output. I have to add the Thiele to it, my question is, do I have to cut the wire and then solder the ends to the inductor and resistor in parallel, or I can just remove two little pieces of insulation and solder these components to the wire?.

Also, the speaker protection board has a connector block with GND and 12 V. I have four secondaries in the transformer, two produce 28 volts at 115 volts AC, the other two produce 15 volts at 115 volts AC. I have a LIVE and Neutral in each secondary. How do I connect the power from the transformer to the speaker protection board?. I thought it would have a connector block with +V GND -V like the PSU, but it only has GND 12V....?

Thanks again.

[AndrewT]

I don't understand your voltage measurements.
a 28+28Vac transformer should give two DC supplies. Each should measure ~40Vdc.
When these DC supplies are connected in series you should measure ~80Vdc.
If you are measuring 20Vdc and 19Vdc there is something wrong !
Is the bulb of the Tester ON/OFF/glowing/very dim?

[Aguilabrava]

AndrewT:

Thank you for the quick response.

Let me explain what I did. My transformer has 2 red wires and 2 black wires for the mains. From what I understand, to be used here in USA, those wires have to be connected in parallel. I did that, then used the Red//Red combination for LIVE and Black//Black for NEUTRAL. On the secondaries side I have 4 pairs of wires, blue and green, blue and green are each 28 volts, then brown and brown, orange and orange are the two secondaries that produce 15 volts each.

In the PSU, in the AC connection block, I have AC GND AC. I connected the 2 blue wires together in the AC located in the right side of the PSU, the 2 green in the AC in the left, and GND to the GND from the mains for now, just to test this contraption.

According to what I have read, one has to multiply the voltage of the secondaries, in my case 28 volts, by 1.414 to obtain what it is supposed to come out in the other end of the PSU. 28 x 1.414 = 39.52, so I thought I was OK.

I believed that to power each amp PCB, all I had to do was to connect the V+ GND -V in parallel to each amp PCB, so they both would receive 40 volts. Now I am confussed...

My dim lightbulb tester is not with me, I took it to a friend's house last weekend to test a LCD TV that he thought had a short circuit and I left it there, I will pick it up today.

Anyhow, the PSU has two LED's, one green and one red, they both light up brightly, once I disconnect the power from the mains, they remain ON for a while...

[AndrewT]

Originally Posted by Aguilabrava

............... transformer has 2 red wires and 2 black wires for the mains. From what I understand, to be used here in USA, those wires have to be connected in parallel. I did that, then used the Red//Red combination for LIVE and Black//Black for NEUTRAL.

Safer to connect just one red and one black via the tester, first. Power up Bulb OFF. Then connect the second red in parallel to first and connect the second blue, parallel to the first. Power up via the tester. During these two tests the bulb should remain OFF.

On the secondaries side I have 4 pairs of wires, blue and green, blue and green are each 28 volts, then brown and brown, orange and orange are the two secondaries that produce 15 volts each.

OK.

I connected the 2 blue wires together in the AC located in the right side of the PSU, the 2 green in the AC in the left,

NO NO NO !!

and GND to the GND from the mains for now, just to test this contraption.

According to what I have read, one has to multiply the voltage of the secondaries, in my case 28 volts, by 1.414 to obtain what it is supposed to come out in the other end of the PSU. 28 x 1.414 = 39.52, so I thought I was OK.

I believed that to power each amp PCB, all I had to do was to connect the V+ GND -V in parallel to each amp PCB, so they both would receive 40 volts. .............

[AndrewT]

The first thing I do is insert each transformer wire end into a separate receptacle of an insulated terminal strip. The screw down ensures you bite through any corrosion or enamel.

For 110/120Vac wire the mains into one primary pair.
Check voltages at all other pairs. Careful, one pair are at 110/120Vac.

Now wire the second pair of primaries in parallel to the first pair.
Measure voltages of all the remaining pairs. If any of the voltages on the secondaries has dropped to near zero, then check for a fault. If all the secondaries drop to near zero volts, then you have connected the primaries out of phase. The bulb should be brightly lit to confirm this.

Now find two pairs of secondaries. connect a single shorting link across one end from each pair. Is the voltage across the non shorted ends equal to the sum of the two individual pairs? You can mix 28Vac and 15Vac windings when doing this test.
If the voltage across the two non-shorted ends is less than either of the two individual windings then you have connected the secondaries out of phase. This time the bulb does not glow because you are not drawing current. Thus no warning. You must heed the voltages.

[Aguilabrava]

AndrewT:

That's what I am using, a terminal strip between the cable with the 3 prong male connector coming from the wall, and the AC GRD AC connector block in the PSU.

I still don't have my dim lightbulb test with me, I have to pick it up later on today at my friend's house.

Anyhow, last night, the first time I attempted to do this, I connected the two primaries in parallel, red with red and black with black, put them in two separate spots in the terminal block, then connected the mains in the opposite terminals of the 2 reds and 2 blacks. I connected the green GRD wire from the wall mains in the middle.

Then, in the AC on the left, at the PSU, I connected BLUE + GREEN together, the center GRD I connected to the green cable for GRD from the mains and in the AC on the right, another pair of BLUE + GREEN together.

When I plugged the connector into the wall's outlet, I heard a hum, and the light in the room went dim, I immediately removed the plug from the wall's outlet. Then I realized that what I had done was basically the same as connecting a wire in one side of the mains to the other, I had the LIVE and NEUTRAL together in both terminals at the PSU, so I removed them, and when I reconnected BLUE + BLUE in AC on the left, and GREEN + GREEN in the AC on the right (LIVE with LIVE, NEUTRAL with NEUTRAL), that's when the 2 LED's in the PSU illuminated, I didn't hear any hum and the light in the room remained normally bright.

I was so happy, I thought I had it right, but you now tell me this is not the proper way to do it...

Do you want me to post pictures?. Would that help?

[AndrewT]

Tell me, do you have one PSU?
How many wire connections is it expecting from the transformer?