LM3886 questions

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Makk

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#1
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
 
#3
Makk said:
... because it is so simple.
Click to expand...

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

Makk said:
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?
Click to expand...

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.
 
#4
pacificblue said:
In Germany we have a saying: if it costs nothing, it's worth nothing.
Click to expand...

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 (?).
 
#7
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?
 
#8
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
 
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#9
Makk said:
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?
Click to expand...

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.
 
#11
pacificblue said:
In Germany we have a saying: if it costs nothing, it's worth nothing.
Click to expand...

you Germans should really come to my country, where genuine and fake items are nearly impossible to notice from their costs nor their appearances.

so if it costs you a headache, then it worths a headache :lol

what i'm trying to say is,
the original GainCard was made based on simplicity.
the zen approach of Kimura's San was proved legend by the failure of ourselves to build the clone of GainCard so we just called it "chip-amps" today

so think to it again;
"maybe only the simplest can accommodate the most complex"
(as quoted from 47 laboratory page)
 
#12
I ordered a kit from LM3886 chipamp.com.

In manual for that kit it says "one diyer has used 2x30vac transformer without issues, 2 x 25vac should work best for a wide variety of loads." My speakers are now CHR-70, one element per side. Hope 30V works!
 
#14
Is the transformer 220:30+30Vac , or 230:30+30Vac, or 240:30+30Vac?
What is the regulation of the transformer?
What is the maximum voltage from your supplier?

That one diyer may have used a 4% regulation 240:30+30Vac transformer on a 220Vac mains supply with a 5% voltage tolerance.
The specification says that 84Vdc is the maximum when a signal is present.
and 92Vdc is the maximum when no signal is presented.
 
#18
HSF is heat sink fin,
usually made of aluminium or cooper where you attach your chip to spread its heat🙂

hey since you already have your transformer...
why don't you give it some AC and DC measurement with a multitester, just to make sure😉
 
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