Is this 3 X LM3886-design correct?!

[CJ900RR]

Hi all!

I've been hanging around here for a while now. I'm about to build a mono-glaincone to start with and have decide to use the popular LM3886. But i want a bit more power than just 50W in 8ohm so today i started working on the schematic.

The design is not mine at all, it was found at http://www.shine7.com/audio/bpa300.htm and i think it's alex88's website and design, but i will only use 3 paralleled circuts and no push-pull function.

Anyhow, the 3 first LM3886 is on its way and i need to leave the schematic to my companion soon if i want the pcb done (usefull to work at a electronic manufacter, lot's of components for free!).

So if you guys would look at the schematic found here; http://www.leetmaa.se/lm/3lm3886.png and post a comment if it's ok or not, it would be nice

With best regards, Carl-Johan...

[jaudio]

Capacitors7,8,and9 should be 220pf

Resister 5,7 and9 should be increase to 10K. I never seen mute resistor as low as 5k and I don’t know if there is any benefit with a resistor that low

Increase P1,P2 and P3 to 200K

You are may need to incease C1,C2 and C3. 2200uf is not enough for 3 lm3886

It might help to use a buffer at input.

One question , why the 5k mute resistors?

[lgreen]

Same comments as above.

With 3 in parallel you should use .1% resistors for R11, R12, R13.

When you build this please report back, its not something we see here very often. I think you can pull it off, looks like you have a good start and some practical intelligence. good luck.

[alexw88]

If your R2, R3, R4 is 10K, then your amp's input impedence would became 3k. Would that be too low for your pre-amp? You could consider adding a buffer to the input or increase R2-4 to 30k and R6,8,10 to 600k.

In my PCB, I only use one 5K mute resistor per 3 LM3886s. If you use one mute resistor for each 3886, suggest you to use 10k.

[tlmadsen]

Most have been said, but I noticed that you call it "150W". You will not get 150 W i 8 ohm wiht that design. Paralleling only gives you more current, so you will only get 150 W if you lower your load (sub 4 ohms I guess).

Have fun.

Thomas

[CJ900RR]

Originally posted by jaudio
Capacitors7,8,and9 should be 220pf

Resister 5,7 and9 should be increase to 10K. I never seen mute resistor as low as 5k and I don’t know if there is any benefit with a resistor that low

Increase P1,P2 and P3 to 200K

You are may need to incease C1,C2 and C3. 2200uf is not enough for 3 lm3886

It might help to use a buffer at input.

One question , why the 5k mute resistors?

Ok thanks for the tips. I will change those values. Regarding the mute-resistor (and every other values) its 5k because of the original design at alex88's website.

Originally posted by lgreen
Same comments as above.

With 3 in parallel you should use .1% resistors for R11, R12, R13.

When you build this please report back, its not something we see here very often. I think you can pull it off, looks like you have a good start and some practical intelligence. good luck.

Yes those 3 resistors will be 0,1%. Thank's

Originally posted by alexw88
If your R2, R3, R4 is 10K, then your amp's input impedence would became 3k. Would that be too low for your pre-amp? You could consider adding a buffer to the input or increase R2-4 to 30k and R6,8,10 to 600k.

In my PCB, I only use one 5K mute resistor per 3 LM3886s. If you use one mute resistor for each 3886, suggest you to use 10k.

Honestly i dont now if that to low i will check that.. or reconsider to changes those values...

Originally posted by tlmadsen
Most have been said, but I noticed that you call it "150W". You will not get 150 W i 8 ohm wiht that design. Paralleling only gives you more current, so you will only get 150 W if you lower your load (sub 4 ohms I guess).

Have fun.

Thomas

Well you can consider that as a type-o. It's suposed to say 4ohm at the speaker.. Thank's!

[peranders]

Mr Carl-Johan, I really recommmend that you dive into the "originals" sort of speaking. This only for reference because some designs out there are good some are less good and it's hard to tell which is which.

The Exel file is good, test it!

http://www.national.com/appinfo/audi...gn_Guide13.xls
http://www.national.com/appinfo/audi...sign_Guide.pdf
http://www.national.com/an/AN/AN-1192.pdf
http://cache.national.com/ds/LM/LM3886.pdf

The mute function is bescribed in the datasheet. Under a certain current value out of this pin you'll get attenuation. I use 33k + 100 uF in oder to get suffient startup delay. The reason why I don't use 10k is that I want to have only 100 uF. If you don't want this delay (which I reall recommend) you can take 10k and then not think more about it.

Some brave person here just shorted the pin down to V-, nothing I would do. The datasheet doesn't mention it, perhaps because they don't think it's safe.

No offence, but when you want to have three in parallel it shows that you don't have got _why_ you should connect in parallel in the first place. Have many you connect in parallel has to do with the load you plan to use.

[CJ900RR]

Originally posted by peranders
No offence, but when you want to have three in parallel it shows that you don't have got _why_ you should connect in parallel in the first place. Have many you connect in parallel has to do with the load you plan to use.

Hej Per-Anders!

I'm not offended at all. That's why i'm here. To learn. And as you say I was at the wrong track

So I have decided to leave that design and start with some old trusted design, the BR100, as shown in Nationals AN-1192.

So if you guys would like to look at this "brand new" schematic and post your comment's about faults (yes I dont trust my self). My biggest problem is that I'm kind of lost when it comes to calculation about values. I will do my homework to increase my knowledge in that but for now this is what i got: http://www.leetmaa.se/lm/2lm3886.jpg

So again, please have a look and comment's are welcome! The mute-function Per-Anders is "dissabled" for now, because i dont know how to make one to mute 2 LM3886 at the same time.

Best regards...

[jaudio]

Are you still going to use 4ohm speakers?

If you are it might be better to use lm3886 in parallel.
PA-100 on datasheet.

If you use the bridged circuit and 4ohms,stay near -/+20volts for 100watts. Remember each chip will only see 2ohms

[Mad_K]

Originally posted by lgreen

With 3 in parallel you should use .1% resistors for R11, R12, R13.

Good luck finding 0,1% 3W resistors
Anyway, they don't need to be 0,1 or even 1%. In fact, 5% units may even be used, especially if you match them or take them from the same batch as they tend to be more like 2-3% between themselves.
Worst case with 2,5% resistors there would be 5% difference in output current from the chips..