LM3886 68W Amplifier

[Carel_Integrated]

Hi,
I've built an 18 x 2CH amp using a TA8205AH IC. Before I started building the basic amp, I tested the chip, with only a speaker, a PSU, wires and the chip itself. I knew that noise levels will be extreme and that it wouldn't work as intended, but after I saw that the chip does at least make noise, I started building it. I'm happy with it now, it just doesn't have enough volume. I used the circuit diagram as the one in the TA8205AH datasheet provided by Toshiba and it worked right away, although I had to make a few adjustments...

Now I'm trying to build an AMP with 2x LM3886 chips, but I have no idea where to begin. Also I don't really know where to find a decent diagram (basic)? I've found a basic one somewhere online & I tried to use the chip without other components (just to test if I can actually hear something, even if it's just noise), but nothing happened. Then I realized that I had tied up Pins 4 & 7 (GND and V-), which was wrong. I've corrected it now and now I have some other problem. The chip is constantly putting out 12V at the output stage, it doesn't even make noise (I'm temporarily using a Switching PSU, just to test with, the final project will use Transformers. The PSU has a -12V, GND & +12V pin). I've tried to use a -24V, GND and +24V supply, but then it's even worse as my speakers are getting 24V this time.
1.) I'm not sure why the chip sends 12V directly to the speaker?
2.) Is there a way to bypass the MUTE function completely? (connect the mute pin to V- maybe?)
3.) Where can I find other schematics / examples of how to just get a basic sound coming from the speakers...? I'll worry about the rest later, but It looks like this chip isn't very easy to configure, and also the datasheet is very difficult to read compared to Toshiba's TAXXXX series.

I've used the Diagram located in the LM3886T datasheet (Typical Application)
TA8205AH Datasheet: **broken link removed**
LM3886T Datasheet: **broken link removed**
ANY help will be gladly appreciated.

 

[MikeMl]

What's wrong with the one on page 1 of **broken link removed**?

 

[Carel_Integrated]

Well, I tried to connect the pins like in that diagram, but then as said, I have a problem with the chip sending the V+ straight to the speaker. It sends 24V straight to the speaker and I have no idea why? It's similar to this problem: https://www.electro-tech-online.com/threads/lm3886-problem.28421/
By the way, I think the problem has got something to do with the Power Input at V+, GND & V-. Aparently I can use this circuit with a single supply too?

 

[MikeMl]

I can use this circuit with a single supply too?

Not without putting a huge electolytic capacitor (+ to amp out) in series with the speaker. Fig 2 in the link I posted shows single supply operation.

The chip is designed to be used with split supplies; Converting it to run on a single supply is not trivial.

 

[Carel_Integrated]

According to the last post in the link I provided above, LM_Gabriel says that the chip doesn't have a DC Ground? I've discovered that if I disconnect the GND pin, then the chip doesn't send 12 / 24V directly to the speaker. Well, the chip isn't defective, because I've tested it with 2x chips and they seem to do the exact same thing. I think National Semiconductor's engineer who designed the circuit used terms or pin names that are confusing, because the pinout, exactly as in Fig 1 doesn't work at all an the chip heats up immediately (which eventually can lead to damage if not turned off). If I connect the GND pin to my PSU's GND, then the Protection circuitry immediately activates, but if I don't connect the GND pin, then it doesn't, but then the chip seems dead... Can I maybe just connect Pin 8 (the MUTE pin) directly to the V- pin to disable the mute function?

In this image https://www.electro-tech-online.com/attachments/lm3876-jpg.43182/ the chip's GND (as seen in the datasheet), isn't connected to the PSU's GND... I think National Semiconductor have designed a crap layout of the diagram they provided, their symbols are also not very descriptive and the datasheet are not very descriptive, it sucks a bit...

 

[MikeMl]

Let me ask you this. Have you connected the chip as shown in Fig 1 (with spilt power supplies)?

If not, you need to understand what is going inside the chip.

 

[Carel_Integrated]

I've just used a temporary PSU (one that's not strong enough to provide lots of power, but enough for testing purposes). I've used a Switching power supply. -12V, GND / 0V & +12V. I asume I should connect the +12V to the V+, the GND to the PSU's GND / 0v & the -12V to V- of the chip. But then the speaker receives the full amount of +12V / 24V. Another type of Diagram: https://www.diyaudio.com/forums/att...4787-lm3886-schematics-pcb-apex-gainclone.jpg

 

[Carel_Integrated]

Isn't it maybe caused by the fact that I don't have:
Ri connected: Inverting input resistance to provide AC Gain in conjunction with Rf1.
Rf1 connected: Feedback resistance to provide AC Gain in conjunction with Ri.
?????

 

[MikeMl]

Your diyaudio link requires registration to see anything.

Refer to fig 1 on National's data sheet. Everything I read there suggests that GND must be connected; if you look at the transistor equivalent circuit, GND is used as a source for the entire bottom half of the amplifier. Leaving the GND terminal float may "fix" the output railing problem, but I suspect that you have a screw up in how the amp is biased.

Note that the input to the + input is DC referenced to GND (halfway between V+ and V-). The feedback from output to the -input sets the AC gain to 20, while the DC feedback is unity for DC, meaning that the output pin is actively driven near the GND voltage. If the amp is railing, then you have hooked it up differently to what is show in Fig 1.

 

[ariaaudiocraft]

I was succeed using LM3886T for my GC project but failed using LM3886TF: on the output rail appears DC voltage exactly as half-high as voltage supply in (-) polarity. Desperate for quite a while, then I checked the pins number 1&5 (+), 7 (ground/as reference) and 4 (-) individually; and for both chip amp for a compare. Using an Ohm meter I found that in LM3886T, pin number 1, 5, and 4, giving resistance to pin number 7 around 10megaohms. But in LM3886TF, pin number 5 doesn't give any reaction (0). I assume that the TF series (probably) has internal damage, because all my (new) 5 pieces of those chips tested and gives the same results.

 

[ronv]

I tried to use the chip without other components (just to test if I can actually hear something, even if it's just noise), but nothing happened.

??????