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Author Topic: debugging a small amp  (Read 31240 times)

J M Fahey

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Re: debugging a small amp
« Reply #90 on: August 30, 2011, 08:25:15 PM »
DearKin.
A few posts above I offered to make a board at home, even to document the job.
Problem is, when I checked the design you so kindly posted, I felt dismayed.
It's a relatively difficult board to home make  :(
I'm not saying it's a *bad* design, it can be commercially made with no problems. but for home made toner transfer, specially using not the real PNP but some ersatz equivalent, such as magazine paper ... ugh !!
Fact is, traces are unnecessarily thin, much worse rge pads are too small, with relatively large holes; that combination leaves a thin metal ring around component legs.
To further complicate things, the (unnecessary) ground fill areas, complicat the paper removal.
If it's a photo-board or a silkscreened one, no problem, but with thermal transfer ....
In fact I started to redraw it with twice thicker tracks and pads, using my trusty Protel Autotrax 1.61 freeware, but really don't have the time so I quit.
I also found a design error: Pin1 of IC1A sits at 4.5V DC , through R5 and R9 it applies DC voltage to the tone pot, you end having over 1V DC across it.
Instant scratchy pot, big way.
You should replace R6 with a 1uFx16V electrolytic, positive pointing left.
The range of the "Tone" pot is very subtle.
Maybe it's really that way, or it was improperly copied.
Oh well.

phatt

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Re: debugging a small amp
« Reply #91 on: September 01, 2011, 09:57:14 AM »
Thanks Mr Fahey,, You have given me some ideas to work with as I do find Eagle a pain. :tu:

I did have a copy of  Autotrax but was running Win Me at the time and it refused to work. :'(

Phil.

J M Fahey

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Re: debugging a small amp
« Reply #92 on: September 01, 2011, 12:31:21 PM »
Hi Phil of Nambour Australia.
Please let me remind you that using any software besides a Protel one (Easytrax or Autotrax are acceptable) will instantly strip you of your Citizenship.
You will be lashed, not with a 9 cat tail whip buy with an actual cat.

I hate Eagle, simple as that.

*Up to* XP you can run Autotrax if you start the machine in DOS mode *or* in software properties state parameters as DOS would. No "automatic" memory settings (it does not know how to ask for it) but you reserve the maximum for it in each little window *or* download the excellent DOS BOX program which takes a little setting up but then does everything for you *or* use any old machine you have rusting in the garaje .
 Win 3.1/95/98 will do, in any old hard drive (even a 500 Mb one).

I am running it in Dos Box in a Windows 7 netbook and "printing" to a PCX file, which later any graphics software can handle.

Something I forgot to mention, a modern program which does not need so many tricks to run:
I will experiment with Express PCB which is very similar in concept, "paper and pencil drawing board", and is available for any Windows.

It has no size or pin limitations, but being a proprietary program forces you to order the boards from them.
As you already know, there is not such a thing as a free lunch.
Anyway, for homemakers you can print the PCB design (using a little trick) and thermal transfer it.

phatt

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Re: debugging a small amp
« Reply #93 on: September 11, 2011, 10:09:41 AM »
Thanks Juan,

Yes I do now have an old clunky win98 machine and I might just have a fiddle with it and see what happens.

I did get a patchy grip on DOS quite some time back So I do have some ability to get things to work with older gear.
Lets just hope the old machine still works. (Yes it is in the shed collecting dust)

My main excuse for not getting boards to look pretty is I hate all the mucking around with printing the boards ready for etching.

I'm just using a pen and hand draw as I'm not in production I don't see the point in outlaying money to make sexy boards that no one will ever see. As long as they work it's valid for me.

Most of the stuff I've made is fairly simple by hand but now that I'm trying to bring a few ideas all into one unit I may have to rethink my whole approach.

Eagle just helps to get pins for opamps and like stuff in the right place.
Then lightly centre pop the holes, the rest is just joining the dots with an ink pen> etch> drill> done.

Of course,,,More than one or two opamps,,,you go nuts trying to keep track of all the dots.

Meantime time I'll keep an eye out for a strange man walking up my street with a cage full of angry cats.  :P
Phil.

J M Fahey

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Re: debugging a small amp
« Reply #94 on: November 06, 2011, 04:44:07 PM »
The real problem starts when he throws on you a bucket full of old fish ... and then leaves the cats free. :lmao:

You can do the exact same thing with Easy/Auto-Trax.
I used to test designs by printing the PCB artwork on regular paper, any printer will do, even a prehistoric Ribbon Dot Matrix one, tape said artwork over the copper board with a sheet of carbon paper (incredibly still available) in the middle, trace the tracks with a ball point pen (which leaves a trace on the copper) , pin through all holes with a sharp needle or similar, and then it´s very easy to handtrace with Sharpie pens.
The faint trace on copper helps a lot .

Now it´s faster and easier for me to thermal transfer, practice makes perfect.