power supply section and the right way to wiring the GND-Earth (lm3886)

[madapj]

Here we go with this topic.
I wanna try to figure out how to wire and connect my future ampli+pre (effect) project.
I saw a lot of suggestions and ideas, but i'm not figure out how to wire and do a good project.
Compost of a LM3886 and other other pre and effect to change to seek the right sound (?)...
Everything with homemade PCB.
My goal is to draw a final schematic so i can start to make the pcb and enjoy the project.
In final i wanna have a stable power sections, a stable ampli and the possibility to change the effect that i wanna try(+15 -15 supply) .
So, in my mind, a stable PCB for the supply for the amp board(+35, -35), including also a little circuit to generate the supply for the preampli (+15, -15), a stable PCB for the LM3886, and in the end  the effects board that i'm going to change until i try all the possible effect in this world!!!!
First of all, i read some topic in here, from ESP Audio pages forum and some i check the Carlo Filipe suggestion.
So...
Just a few firsts suggestions that i need to know to draw this schematic and maybe posted for the people that is interested:

1. for the LM3886 is better to use the carlos felipe design (two bridge, some resistor and some small caps) o is enough the ESP site suggestion in the famous 27 project with only one brighe and only two caps? are 4700uF caps enough?
2.   I saw in the ESP pages that is used a little "2 diode - 1 resistor - 1 cap" section from the Circuit GND to The Earth plug in the chassis. I have to use it?
3. About the Output from the ampli board to the speaker. i have to take the GND throw a 0,1Ohm 5W resistor or i can plug it directly to the center GND?

Here the firsts questions, as soon someone answer me back i'm going to draw right the way the sch to understand better what i'm talking about...
I'm thinking that a lot of people, looking from this pages, remain a little bit confused about this things, a lot of different SCH over around and a lot of suggestion, and in the end the problems remain, and i know for sure, one of the easy and cheap project can be the LM3886...
I know that there is the ground section in the beghinning of  the site, but i wanna try to do something right for what i have in my mind!
Thank for everyone interested!!!

MArco

[phatt]

Hi madapj,
              http://sound.westhost.com/project27.htm
The Preamp Power Supply is derived from the main Voltage rails of P27.
Shown (though not clear for beguiners) at the bottom left of the preamp schematic.
(R18 R19)

The 680 ohm resistors will run quite warm,, I suggest 5watt will run very cool.
The Zener Diodes clamp the voltages to 15VDC.
Simple ,, works quite well, though If you want better than this you need to use Reg chips,, but more complicated.
Phil.

[madapj]

so the single rail supply is enough for the LM3886....
I have to follow right the way what is suggest on the this ESP pages?

[phatt]

OK lets get a few things sorted,,
I assume you wish to follow the ESP P27 preamp BUT use an LM3886 poweramp chip?

I've never been interested in chip amps and quite frankly using two transformer windings with two Bridge rectifiers to drive a single or dual 60 watt amp is just plain insane overkill.
If you where building a 400watt RMS @8 ohms power amp then YES it's worth the extra effort and expense.

Most of these poweramp chips can run a single supply rail but dual supply generally gives better perfomance.

Now unless I'm mistaken the red PSU board from *Chipamp* does not join the *Common pcb track* right at the Main Filter Caps. From what I've read this is poor design.

Side note; Thank *Teemu* for pointing out that hidden gotcha on PSU filter caps:). It had not dawned on me until I read his book. Good on yah Teemu

Sounds like you should download teemu's PDF book and take the time to read it as it may help you come to terms with building an amp. The link can be found right here on SSGA.

Sadly all the overrating of parts is probably going to waste if you don't have good pcb layout.

Reading right off the Data sheet,
LM3886 is rated at 50 watts RMS @ 8 ohms from a 50 volt CT Tr delivering 35-0-35VDC.

Now the psu for ESP's P27 which states a 150 VA rating on a 50 volt CT secondary is
driving a 100watt amp,,  Humm, then I'd say it's perfectly capable of driving a little LM3886 to full output and beyond.

I'm not the chip amp expert here but a quick look at the workings tells me this chip uses all NPN output drivers which from what I understand is well out dated being that use of
both N and P drivers is now commonly accepted as being better.

I'm adding a small schematic to help get your head around the power supply.
this should power most small chip amps like you propose and deliver a split rail for preamps.
Cheers, Phil.

[madapj]

No, i think that i explain myself really bad...
Forget everything that i said and we start again.
Sorry i'm italian and is a little bit difficult to explain myself.


So, here we go:

I'm going to use only one transformer, a 150VA, 18-0-18 output. Maybe not enough for the full output power, but anyway good for my needs.

I'm going to use a LM3886, for the amp section, i wanna built it following a sch that i find in this post. here:
http://www.elektronika.lt/_sys/storage/2004/11/30/pic1.gif
I wanna do that in a standalone board, with the input for the power (from the powerboard), input for signal (from the preampboard) and output to the speaker.
Everything until now is easy and clear!!!

The powerboard, have to give the 25/-25 to the amp, and also the 15/-15 to the preamp. 
The image that you post, is perfect. I decide to put also the two fuse there.
You said that the single bridge way is enough, so i'm not going to use the schematic suggest in here http://sound.westhost.com/project04.htm (Figure 1- +/-35V Dual Power Supply).
I saw also, in the ESP page that is used another "little" bridge with a resistor and a capacitor in parallel to prevent loop. (Figure 3 - power supply) from http://sound.westhost.com/project27.htm.
My question is, i have to use it?

And another question, this time for the output jack to the speaker.
I saw that there's a 0,1Ohm 5W resistor in series to the GND center, in my case on the powerboard. I have to use it?

I hope i explain myself a little bit better, anyway, i'm going to draw this thing down, so maybe i can explain my issus better.

Thank again for your patience.

Marco

 

I'm going to use a toroidal that i have home, a 18-0-18, 120VA, i know, maybe not big enough but for now i think that is going to be fine.

[J M Fahey]

Your toroidal will be fine, because your amplifier is *not* going to put out 50W RMS, but closer to 30W into 8 ohms.
Build the simplest version of anything, it often is best, don't complicate yourself with dual bridges and the like.
Those +/-15V will power any op amp project you want to test, it's also easy to get +9V to test most pedal circuits.
I'd build a power amp+PSU block, *and* a front panel full of holes for pots, jacks and switches, and a couple protoboards semi-permanently fixed (velcro or double sided tape), to experiment at will.
Good luck.

[phatt]

I saw also, in the ESP page that is used another "little" bridge with a resistor and a capacitor in parallel to prevent loop. (Figure 3 - power supply) from http://sound.westhost.com/project27.htm.
My question is, i have to use it

No you don't have to use it Rod E is just covering all possible situations that his circuits may have to confront.
You will only need it with really big complex setups.

Re the .1 ohm resistor hanging off the speaker you mention.
Again NO. Until you become more confident with building just leave it out.

I my experience it only makes a very subtle difference to the end result,, but hey others claim great benifit. It gets many names ,, (Defined Impedence or Current Feedback)

From 18-0-18 secondary you should get at least 22watts.

Re elektronika circuit,,,play with different values for C1, I'd try lower even .5uF, but let your ears work it out.

Now back to PSU I posted, the problem you now face is those 680 Ohm dropping resistors will need to be changed.
You will need to mess around but at a guess ,, 470 Ohms might be a starting point.

Don't worry your english is obviously good enough to get the point across
I very much doubt I could write it all down in your language.

Arrh,, just noticed your post JMF,, thanks it all helps.
Yes bread board or protoboard EVERYTHING.
I've learnt that the hard way but it was all so long ago I forget to say it now.

Have fun with it Marco,,you will learn as you go,, Phil.

[madapj]

Thanks so much to everyone...
i think that i have understand everything i need for now...

When i'll finish to make the pcbs, i'm going to ask something about the speaker to buy.
I was thinking about two 8Ohm speakers to put in parallel, but i really don't know where i have to start to search...

For now... thank again!!!

[J M Fahey]

Speakers?
Italy makes some of the world's best speakers.
RCF is second to none in the PA field, and better than many "modern" JBLs, although very expensive.
Guitar legend Jensens are made right there, at the SICA factory.
*Maybe* they can't sell direct to you, because they make them under contract for an American distributor, or they must charge you the international price, but I know that Sica sells guitar speakers under its own trademark. I'm sure they are exactly the same.
Search a little and tell us.

[madapj]

thanks J M for the suggestion of the speaker... great.

I search in the web and I find some good start point... The problem is that most of them don't sell to private, but i think that i'm going to figure out something.
Another things...
I built the LM3886 amp. i have to tell that sound good. I drive an old speaker box of a old marshall ampli that i have.
Which preamp did you raccomand.
I'm don't know, something simple for the beginning, with volume, gain, and maybe controls for the tone. Something clean.
I don't care for the power supply.
Everything have to be ok for driving the lm3886.

Marco

[J M Fahey]

Rod Elliott (search) published a good guitar preamp.
You will even find some comments here, at SSGuitar.
It does not have much of a distortion, but you can use (or make) some good pedal for that.
Maybe a friend's shop may order a couple speakers from the factory, or a distributor.

[madapj]

yes, i look a lot in the ESP Elliot pages.

I'm wonder is you're talking about the preamp in the project27 or in the project27b.
If is so, whick one of the two do you raccomand? are they quite the same about sound or are they different?

[J M Fahey]

Hi madapj.
It's the newer Project 27.
It's a clean, quite Fenderish flavored preamp, also somewhat similar to what Roland Cubes and JCs, or old Yamaha G series tried to do.
Of course, as Teemuk already stated, the distortion is very weak, but that's what pedals are for.
To test it, mount a protoboard on a piece of wood and screw in front of it a piece of aluminum (preferably) or acrylic (cover its back with aluminum paper for grounding) full of holes for jacks, switches and pots.
That way you can experiment at will, and only commit to pcb design (or perfboard layout) after you are satisfied with your sound.
You can rehearse with that contraption and even play live once, if you are *very* careful about the transport.

[madapj]

Thank J M for your advice.

I've already done something like a test board, full of holes, jack and everything i need. i recover the board from a old dvd case player. It is in plastic, so is ok, i think.

Anyway, i check the sch from the project 27 (ESP):
http://sound.westhost.com/project27.htm
like you said, the new one.

here some question, that i have already ask, but i'm a little bit confused, about the capacitor.

I saw this capacitor, from the sch:
C3:   1uF
C8:   1uF
C10: 2,2uF
C15: 2,2uF
C14: 10uF

what i have to use? electrolitics or "normal"?
is i have to use electrolitic capacitor, can you tell me the right positive position, expecially the last three?
I ask you again this thing cause i wanna be sure about what i have to do and don't make any mistake.
thank again...

Marco

[J M Fahey]

Hi Marco.
1)They are all standard electrolytics.
2) They all handle only a few millivolts DC if at all. Conventional wisdom would be use bipolar or non polarized ones.
Years of bench practice by zillions hobbyists says: in that case just use conventional electrolytics.
If irrelevant I point all the same way, so if someday that does not work, I know I must invert that one.
Calling U:up; D:down; L:left; R:right:

C3 U
C8 U
C10 L
C15 L (the transistor base will be a few millivolts negative)
C14 R (the transistor emitter will be around 650 mV negative)
this is the only one that has some significative DC voltage)