LM3886 questions

[Makk]

I'm planning to build LM3886 based amplifier and got couple of question.
I'm planning to use Feuerbacher Copper Amp scheme because it is so simple. In that scheme PSU is 18-0-18 doubled mono. I would like to use single 30-0-30 260VA toroid, because I have one. Is this possible? Planning to use MUR860 scheme as shown in copper amp site. If using 30-0-30 does copper amp scheme need any value changes of components?

Also wondering what Cs means when it says 2200uf electrolytic; || 100nF polypropylene. What this "||" means?

Info about copper amp -> Mick Feuerbacher Audio Projects

[peranders]

2 x 28 VAC is max.

|| = in parallel

[pacificblue]

Originally Posted by Makk

... because it is so simple.

In Germany we have a saying: if it costs nothing, it's worth nothing.

Originally Posted by Makk

In that scheme PSU is 18-0-18 doubled mono. I would like to use single 30-0-30 260VA toroid, because I have one. Is this possible?

Depends on the load impedance. With 4 Ohm speakers use 18-0-18. With 8 Ohm you can go higher. 30-0-30 is definitely pushing it. Although as long as you only use 2200 µF of smoothing capacity the voltage will sag sufficiently under load that it might even work.

[Makk]

Originally Posted by pacificblue

In Germany we have a saying: if it costs nothing, it's worth nothing.

Heh, maybe true, but I think it's ears that tell, not the costs. That's why I like to try something simple like gainclone. I built one amp using 2SK1058 and 2SJ162 pair. That's where I have 30-0-30 260VA toroid left. I would like to use it because toroids are the most expensive part of the project and after building a new amp witout it I don't see any usage for that 30-0-30 toroid.

Is there any recommendations what should I try then? I want it to be enough simple. I listen mostly CD's and I'm thinking that if amp has volume pot, there is no need for a preamp. I think volume pot is like passive preamp (?).

[richie00boy]

Originally Posted by Makk

Info about copper amp -> Mick Feuerbacher Audio Projects

Oh dear another chipamp implementation that is likely to smoke and kill speakers of unsuspecting beginners. Please don't build this.

[nightanole]

Dont know about smoke and kill, but what happens when Mr. pot looses contact? Id add the extra resistor and use a 20k to ground and a 25k pot.

[Makk]

Hmm, I think I'm going for the briangt's Non-inverted LM3886. It looks pretty and simple. And I have read at least something good about it. Because UK is far a way to order premade pcb's I'm thinking of building them my shelf. If I use same kind of component assembly as in those pcb's is there any major copperlines which cant be next to each other, or have to kept short. Ground is usually as "big/wide/long" (don't know the word) as possible. Am I right?

[ampimp]

Hi all
I built a LM3886 amplifier last year using the toroid from a nad 320bee
The dc psu rails with the amp at idle where approx 42 volts.
I took it easy for the first week but after that gave it some stick
and to my surprise no smoke. i have now removed some of the windings from the transformer and the dc rails are now approx 24 volts at idle.
The amplifier now sounds so much better as i found it souded very glassy with higer supply volts.
I also tried a few other ei transformers and notice they make a big diffrence to sound.
Also i noticed that too much capacitance on the res caps dont help the sound either.
im now running 2000 uf junkbox caps the amp now sounds faster less harsh very nice
Ian

[asbjbo]

Originally Posted by Makk

Hmm, I think I'm going for the briangt's Non-inverted LM3886. It looks pretty and simple. And I have read at least something good about it. Because UK is far a way to order premade pcb's I'm thinking of building them my shelf. If I use same kind of component assembly as in those pcb's is there any major copperlines which cant be next to each other, or have to kept short. Ground is usually as "big/wide/long" (don't know the word) as possible. Am I right?

The cost of shipping a few PCBs from anywhere to anywhere else is almost zero, so I don't really see the problem. However, if you really want to make your own PCBs, pay close attention to the grounding scheme to avoid instabilities. Searching diyaudio for threads related to chipamp grounding would be a good start. Using a star ground with separate return paths to the star point for PSU bypass return, feedback loop return, and Zobel return (if used) seems to be the consensus solution. Or, if you really want to go guerilla, why not hardwire the thing with no PCB at all? Again, you will find many examples by searching diyaudio.

[Mankysteve]

i Ordered some of PB kits and they came very quickly and had no problem despite coming from the other side of the pond.