Question for R.G. concerning power supplies

[donald stringer]

I am getting my power supply together for my lm 3886 guitar amp. I am pretty sure that I"ve done my homework on this so far, and this is such a trivial question but I have to ask. In the power supply.. transf[prim.] / secondaries/ into 25 amp fullwave rect/smoothing caps [two 3300 uf caps 50volts/ there are two res. 2.2 1 watt [could I use 1/4 watt here] ?   Where would I place the snubbing caps. if they are realy needed ?

[R.G.]

I am getting my power supply together for my lm 3886 guitar amp. I am pretty sure that I"ve done my homework on this so far, and this is such a trivial question but I have to ask. In the power supply.. transf[prim.] / secondaries/ into 25 amp fullwave rect/smoothing caps [two 3300 uf caps 50volts/ there are two res. 2.2 1 watt [could I use 1/4 watt here] ?   Where would I place the snubbing caps. if they are realy needed ?

The transformer secondary voltage should be no more than about 44Vac and center tapped. A 25A bridge is a good idea, as are the 3300uF. You could double up on that to good advantage. Actually, I would not use the resistors. I would put resistors across the filter caps to bleed them down. Something like 1/4W of dissipation in a 1/2W resistor across each filter cap. Build it without snubbers, then listen to it. If you think you need something more after listening tests, yell and we can discuss snubbers. Caps alone aren't snubbers, and can make things worse. See http://www.hagtech.com/pdf/snubber.pdf

[Brymus]

Ive heard about the lm3886 amp could you post a schematic?
And where are you getting your transistors?
Mouser shows a cross refarence of NTE something for 14$ apiece.

So is this supposed to be about a 100watt amp?
Wouldnt reducing the V down to about 25VAC  make it around 60watts?
SOrry for the dumb questions I want to build a decent SS amp too.

[donald stringer]

You can get them at national semiconductor. Go there and register, you can get two free samples but you pay 10.00 shipping and handling. Im going by the lm3886tf pdf just google for that/ then you can go to solid state guitar and read all of RDV post on his project. Another good place to read on them is elliot sound projects not to mention the thousands of gain clones on line. Google for that and you can get  more info than you could hope for. ..................In case anyone is interested and reading this among the thousands of am fm cd players bought and sold in the U. S. [you know you get the little square plastic case /glass enclosures/ two cheap speakers/ and as soon as the cd player quits working you either throw it in the trash or sell it at a yard sale for 10.00 if your lucky. The chassis /heatsink/ and transformer/ and in line fuse is what you want. I got one with a largish heat sink [vertical fins no less]. I"m not shooting for 100 watts. Just a good clean project.         Thanks R. G. I think I got  it  [you said to spend more qaulity time on the power supply  then go crazy with the amp and pre-amp thats what I"m working towards....just dont want any blue smoke or sparks got to go bend some sheetmetal

[R.G.]

You can also get them at apexjr.com.

If I were building an LM3886 amp, I would go to apexjr and buy
- Chia Yu Co Ltd toroidal transformer, 42Vct @80VA - $10.00
- two each 6800uF/80V Jun-Fu radial electro caps, $4.50 each
- one gold removed-from-RF-amplifier heat sink, $20. This is about twice as big as needed, so I would carefully hacksaw it in half and have two of them. It may be four times as big as needed, but getting too much heat sink is much, much better than not quite enough.
- LM3886T @ $3.50 each
- as many switches, fuse holders, knobs, wiring, etc, etc as you need.

[head_spaz]

Chipamp.com
Check out ChipAmp.com offers pcb boards and kits that are affordable, very well designed, and quite popular with the gainclone crowd.

DIYaudio.com has a large section of their site dedicated to the 3886 chip amps.
It's not as popular as it once was, but there is a lot of valuable information on that site.
You would do well to go back and check some of the older posts, before the economy crashed and the gurus left for other endeavours.

[Brymus]

Thank You all for the responses-the Apex Jr info was very appreciated,as was the rest.
Any chance someone has a verfied schematic as a base to work from?
I havent seen any completed ,verified ,and documented builds at SSguitar.com I went through the entire board.
I did download Teemuks SS amp book-(you guys should read this) and there are alot of posts by RG there as well as alot of helpful info.
You can find a million how to build tube amp articles and PDFs online but aside from the Ruby and the TDA 20xx amp.
I cant find anything detailing the construction of an SS amp.

[donald stringer]

 Hey brymus did you read this,http://www.ssguitar.com/index.php?topic=16.0   And if you go back to the amp. forum and read the top posts on heat sinks, etc. that will answer a lot of questions.  I know there arent a lot of complete amp. builds on that  subject but the main part is whats being discussed here the power supply. I let those things mystify me until I dug in and absorbed a little more of the learning curve. If  you can build  something like a simple stompbox circuit you can let your imagination go wild with the pre-amp portion and exterior cosmetics.   Hey R. G. If I were me I think I could spring for that toroid and caps thats a doable option this week.

[Brymus]

Hey guys after much searching I did find this http://www.national.com/ds/LM/LM3886.pdf It has alot of useful stuff I may just build off the 40watt amp info they give and use the tranny RG suggested that would be perfect I think.

I found this too http://www.tech-diy.com/Audio_Designs.htm they are building these as stereo units for hifi looks useful as well.

So let me know if I am right, but with a 36V bipolar supply you would see 50 watts at 8 ohms around .03 THD
or 100 watts at .1 THD

OH Yeah - thank you for the shopping list RG that helps alot!

[donald stringer]

I "ve built the power supply board. I couldnt double the caps with what components I"ve got but I added some to it. I had two 330 uf caps rated for 100 volts, I put in the bleeder res. I think this is a succes there about 36.70 volts dc. This is  kinda funny the question that I was going to ask was why I was seeing neg voltage on the pos. rail as I  glanced at the dmm I noticed the red plug in was in the common outlet on the dmm and its always been like that since I borrowed it. No wonder I have always read neg. volts on pos rails when I knew they where pos.I"m a little embarrassed. I did the math after I finished and there a little more dc than was expected. 24x1.44=34.56 and I" ve got  almost 37           If I have the proper diodes I think I gonna divide this down for an 15 vol + - pre-amp supply then I "m cooking with gas

[donald stringer]

http://sound.westhost.com/project43.htm this is the divider network I used but it didnt work. Whats the difference ? dc is dc I have used it before with wallwarts but it didnt work here it only transfered the 36.66 volts to another board. Does anyone have a clue about this ?

[donald stringer]

I know why it didnt work. I used the 36.66 plus and 36.66 minus and the ground, I should have only used the 36.66 and grnd.

[donald stringer]

Victory ! I have 18.59 pos. and 18.59 neg. Thats plenty of clean headroom. As soon as I get some thermal grease I ll do the power chip. In the mean time I"ll ponder about pre-amp.

[Thomeeque]

...
- one gold removed-from-RF-amplifier heat sink, $20. This is about twice as big as needed, so I would carefully hacksaw it in half and have two of them. It may be four times as big as needed, but getting too much heat sink is much, much better than not quite enough.
...

Hi!

I'm planning to build simple cca 50W/8Ohm power amp based on LM3886 and build it into old standard PC ATX power source case (I just want quick and simple PA build for Yamaha DG Stomp multi-fx preamp for band practises) - this case is made of ordinary thin 0.6mm sheetmetal (it was very cheap OEM PSU). Is there any chance that this case itself would made sufficient heat-sink (would active fan help?)? I assume that not, but maybe I'm wrong.. If not, would it be OK to mount LM3886 from the inside of the case and some proper heat-sink from the outside (so there would be that 0.6mm sheetmetal between chip and proper heat-sink, and some thermal grease of course), would it made sufficient thermal bridge? It would made construction a lot easier for me.

Thanks a lot!

T.