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chipamp.com 3886 amp power supply questions

Started by Top Top, April 10, 2011, 05:25:33 PM

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J M Fahey

From what you say, may I guess you don't have a Bass player either? (that part being played by a Synth?)
In that case the "PA" amp would carry only 2 Keyboards (one of them sequenced, as a background track) plus a single mic.
Well, that lightens the load a bit.
Sending the guitar to its own amp, even a 15W one, will help anyway.
Pity you told us so late, or we would have suggested the 160VA transformer instead, which would have allowed the future addition of another 3886 driving an extra box.
That would *sure* increase clean headroom.

joecool85

Sounds like you might be ok.  Especially if you decide to utilize both the new amp and the old Radio Shack one.  Let us know how it works out.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Top Top

#17
Quote from: J M Fahey on June 03, 2011, 03:15:56 AM
From what you say, may I guess you don't have a Bass player either? (that part being played by a Synth?)
In that case the "PA" amp would carry only 2 Keyboards (one of them sequenced, as a background track) plus a single mic.
Well, that lightens the load a bit.
Sending the guitar to its own amp, even a 15W one, will help anyway.
Pity you told us so late, or we would have suggested the 160VA transformer instead, which would have allowed the future addition of another 3886 driving an extra box.
That would *sure* increase clean headroom.

My setup is not exactly "normal." It's not really rock music at all. My setup is nord micromodular with trigger-able sequences/sounds stored in it, guitar w/some FX, guitar to midi converter into a synth, home made synth/sequencer thing, home made sampler, banjo, microphone.

Usually the nord plays "backing" sequences and I play guitar or banjo parts on top, whistle, and guitar->midi into old yamaha FM synth for some other sounds, and then the other stuff for between song transitions. There's some bassy sounds in there and occasional synth percussion parts, but it's not a standard drums/bass/guitar kind of thing. More melodically based.

I have my home made TDA2005 based 2 output channel space-heater amp (which landed me this 3886 kit when I won the contest way back a couple months ago). I could start putting my guitar through that again, and keep the 3886 for the synths stuff. My main concern is keeping equipment hauling from getting totally out of hand.

This is kinda what this whole mess looks like at the moment:
http://www.youtube.com/watch?v=g2WVlSKIbLg

J M Fahey

Well, if it's a kind of one-man-band, no drums, no real bass, then you can plug everything into that single multi-amp.
In this very particular case you don't benefit that much from putting that guitar through an external amp , specially since half of the time it's not "a guitar" but "a synth".
Pity you didn't state all this at the beginning.
It's as if I asked for dessert and cakes recipes at a cooking Forum, I received many sent by members with their best intentions , and after some time I stated : " thanks .... but I'm diabetic .... ".

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#19
Here's the thing: I already have the amp kit. Asking for a transformer to power it was not misleading at all. I am going to start by just building it regardless (not planning on building a double 3886 at the moment). So I am happy for the info provided so far  8) Also there is a 100 watt PA head/mixer sitting at my favorite mom and pop music store for $60, so there is a limit I am willing to spend on transformers and amp kits to make it myself.

Moving on...

My transformer arrived at my door today. I am going to check out the wiring to get it up and running. This is where I am going to need some help - I looked at RG's post in the thread linked by joecool in the beginning of this thread, but the description is a bit confusing to me because it refers to everything by terms I don't yet know, ie: "You can connect two identical secondaries into one centertapped secondary."

There's two sets of blue wires, two sets of green (two pairs outputs according to the label), and two sets of red, and two sets of black (inputs according to the label).

I've got this thing about death (not really my thing) so I want to make sure I understand how to wire it correctly even at the risk of appearing completely dense.

That's 8 wires that all have to go somewhere. Is there a diagram somewhere for what to do with these 8 wires?

Top Top

#20
OK... going to prod this one on a little bit with some pics.

After looking at the power supply diagram from that other thread, I wired up the secondaries (?) to the board in what I think is the right configuration.



PS diagram:


Got a box to put it in, still need to pick up a heat sink tomorrow.



So the wall AC part, I am still a little stumped about. Four connections on my transformer, two in the diagram.  Do I tie something together? Leave two of them unconnected?

Not wanting to die, set my house on fire, or kill a $20 transformer, I have not touched them yet. Also there should probably be a fuse wired in there somewhere as well I assume.

Edit: Actually, looking at that diagram again, I notice those two connections crossed to opposite coils. So I am assuming this means I tie something together... but still not sure how. Do I tie the black from one coil to the red from the other, on both sets?

phatt

Hi toptop,
It looks like you have dropped the extra diodes as per advice on the other thread?
In which case I have a hunch it won't work.

That PSU is insane and is overkill in the extreme and only serves to confuse a hobby person with little understanding of what is needed.

Yes the complex PSU design makes sense if the PSU was for a 400 Watt Monster Bass Amp
but for a 40 watt chip amp? *Then NO*.

The LM3886 chip is worlds away from serious hi-end power amps but just perfect for what you need.

Just Go find a simple split supply and build that instead.

You need a Transformer that has clearly marked windings printed on it,, or data for such.
Two mains wires for primary input.
3 wires for secondary,,called 50VAC CT (Or 25-0-25VAC)
VA rating is not super critical (again unless you want full power at 10hZ you won't hear
anymore watts at guitar freq that will make the extra expense worthwhile.

If you can't fully understand the PSU board I'd stop now.
Go work out some PSU basics and learn to understand them before you embark on the harder ones.
It is perfectly feasible to rewire the Board you have to work as a simple supply BUT as it's
a double sided affair it could turn out to be more trouble than it's worth. :loco

One more thing,, The Case is PLASTIC!! Bad move chum :trouble Try a Steel case instead.
I'm all for making things cheap but not that cheap.
The steel case becomes the ground plane which helps to reduce unwanted hums and buzzes.

The CT of your PSU secondary is often tied to a grounded metal chassis and the EARTH wire
from the *Primary Mains plug* is/Should be well connected to same via a bolt on the chassis in case
of a major meltdown/failure the short runs to ground Not Through YOU 0:)
Remember your guitar has steel strings and is connected to the electrical circuit so if something
goes really wrong the *Grounded metal Case* will help to save you from getting the full jolt back to ground.
It may just save your life. winky.  0:) 0:) 8|

Go learn first; http://sound.westhost.com/project27b.htm
halfway down that page is *Figure 3* That is all you would ever need for the Amp you wish to build.

Without knowing the voltages on your transformer and as no voltages are given on the schematic
it's near impossible to help you.
Phil.

Top Top

#22
ok... need to step back a second here.

The board was assembled by JoeCool and was tested by him as well to be working (hope he can jump in here and throw down a word about how he connected it).

My problem is that I do not know how to hook up a power transformer to it. It was my impression that all I needed was a power transformer.

Several people have suggested the power transformer I have bought (see earlier posts in this thread), so I am wondering why that is the case if it will not work.

Thanks for the tip about the chasis. I may install large metal plates inside of it to act as a ground plane.


joecool85

The board does work the way it is and does only need a transformer, not sure why anyone would think otherwise.  I know it works because I played my guitar through it for a few hours before sending it out.

I used a 18 - 0 - 18 transformer and it worked fine.  A center tapped transformer will have 3 output wires and two input wires.  The two input wires go to the ac line as expected.  2 of the output wires will be "hot" and one will be center tapped.  Put one hot one on AC1, one of AC2 and the center tap on the ground.  Done.

Not sure about your transformer since it has all these extra leads.

That said, there is NO REASON to build a PSU for this amp when this works just fine the way it is.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

joecool85

#24
Ok, you did wire it wrong, but it's no big deal.   8)

Your transformer is different because it is a toroidal and setup to take 110 or 220 on the primary - this gives you "extra" wires.

Here is the spec sheet for your transformer: http://www.antekinc.com/pdf/AN-1225.pdf

**edit**
Ok, you will need to connect the two black wires together and the two red wires together.  This is how you hook it up to 110v primary.  Connect the red and black to neutral and hot on your mains voltage.  Make sure you connect your chassis to ground for safety reasons.  Also connect your board's ground to chassis ground, same reason.  

For the secondaries you will want to connect a blue and a green together - this will be your center tap and you will connect this to ground on the board.  Then connect the remaining blue to AC1 and the remaining green to AC2 (or vice versa, doesn't matter since it's still AC at this point).  That should do it for you.   :tu:

The other option would be to have me send you some more MUR860 diodes so you can have all 8 in there and then wire in all four of the secondary wires to the board.  Either way will work but this last way is overkill and more of a pain in the butt.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

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#25
So let me make sure I have this correct -- few questions:

1. the "AC1" & "AC2" with the line over them on the board stay unconnected? (the ones that currently have the green wires going to them)

2. I would want to take a blue and a green from separate secondaries (one from output 1 and one from output 2) to connect together, right? I assume so otherwise I am shorting the transformer, if I understand correctly. And they connect to that middle "GND" connection on the PSU side of the board?

3. The grounds can all go to the same chassis ground connection? (ie: Mains ground (prong 3 on 3 prong power plug), AC secondary ground (the green and blue tied together) and DC/audio/speaker ground)? Will it be the same for when I add a small preamp/mixer running at a lower DC voltage? (tapped/stepped down with a regulator off the DC voltage going to the amp chip)

I think that's all for now, I am sure I will have more questions later.

joecool85

#26
1.  As depicted in your picture, you need to remove the top left blue wire and the bottom right green wire.

2.  Correct you want to take a blue and a green from separate secondaries to connect.  Tie these two together and put those in the ground hole (labeled GND in the middle of the board). 

I should have said that before  :P  You should also have a fuse on the primary/mains voltage hot line.  This would blow if you accidentally shorted the secondaries.

3.  Grounds all to the same location regardless of voltage or function, this is called star grounding and I recommend it.

Glad you ask a lot of questions or you might have smoked your transformer if you connected the blue and green from the same section of the secondaries...not so much dangerous, but frustrating.  Always best to ask for clarification  ;)
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

phatt

Arrh tiss all good, it sounds like you have it sorted, wink.

@Joecool, Sorry if I come across as a cranky old sod but If these boards
had a simple straight forward supply setup the maker would likely sell many more units
because the most likely customer would be the home hobby builder who (more often than not)
is not up to speed on complex PSU design.

As has happened here,, Without your help toptop would be stuck with nowhere to turn. :'(

My guess is you could fit the whole thing on a SS board if you used a simple PSU.
I'd bet he would double his sales in a month,,  8).

Another point,
Unless I'm wrong the board layout has a common ground rail but is drawn on the schematic
as two separate rails. Again more confusion.

The owner would wise to correct that slight oversight as it would make life easier
for the end user.
Of course *Not having the board in front of me* I can't be certain but the Filter caps
seem like they all attach to a common ground rail.
See my schematic suggestions.

One could argue that a schematic does not have to represent the board layout exactly
but given such a simple circuit it is not hard to draw it as it is connected on the board.
Cheers, Phil.

joecool85

Phil, no problem.  And I think you are right about the common ground rail on this board.  That schematic was from his other PSU boards which are similar but much larger in physical size.  Actually, the PSU boards he normally uses are twice the size of this entire PCB I sent to TopTop! 

As far as sales go, he doesn't sell this board, it was a prototype.  This is what he sells: http://chipamp.com/lm3886.shtml
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

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#29
Ok got all this so far.

I am on the fuse now. the 3 prong power cord that I am using has black white and green wires. I know the green is ground (it goes to the center ground prong). I looked up online and it says black is usually hot and white is neutral. Does that mean I should hook the black wire from my plug to the fuse terminal?

And then from the fuse to the input of the transformer - do I hook the black or red wires to it? Or perhaps it doesn't really matter because ultimately it is just rectified to DC anyway?

EDIT: did a little research and found info that says you should connect hot to the fuse... so I did.

The main question then is from there into the transformer - does it matter if the "hot" from the wall goes to the red or black wires into the transformer? I would think the only difference will be that the AC is 180° out of phase one way vs the other, but shouldn't matter if it is being made into DC anyway, right?