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PostPosted: 11 Nov 2009, 18:10 
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Location: Duesseldorf, Germany
Hej Olof,

now - i would say that the PCBs are really very good (keeping in mind that it's your second try!) The solderings aren't bad too. Congrats to ma ;-).

Just a little tip:
The copper leads / rails appear slightly oxidated, caused through the Natriumpersulfat (u used it - right?). The other thing is, that a small ammount of the photoresist has left on the copper - just a little bit. For the next time, i would suggest to clean up the copper leads with Acetone or Alcohol (not the good one from the V&S distillery in Åhus). Then clean it with a rough kitchen sponge and water to get the copper shiny. It helps a lot and is a good base for the solderings. Once the copper is clean, you also can seal the copper with solder and then(!) drill the holes... This makes sure, that the components can be soldered very clean and fine and also that the copper can not oxidate.. You'll love the next boards ;-)

OK - i think that you've measured the PSU (power supply) without a load connected.
The "+" rail has the right potential of +26Volt DC (measured to ground) and the "-" is NULL from "-" to ground. That's ok, because there are no currents that can flow without a load. Without a current flow, the PSU is not able to provide the proper ground. That will say, that the both potentials "+" and "-" can not build the ground, because there is no current flow through the capacitors... And the ground is provided by the capacitors.

If you measure the voltage between "+" and "-" your DMM (Multimeter) MUST show +54VDC (Volt DC).
A measuring from "-" to "+" must show -54VDC on the DMM (regarding that the black DMM lead is "com" and the red "+").
If not - there is something that went wrong! Maybe you have a pic from the PSU?

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 12 Nov 2009, 02:22 
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Joined: 04 Nov 2009, 01:45
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Thanks again, you must be the god of DIY!

I just checked the voltage between (+) and (-) rail and had 25V then I found out a bad solder on the brigde and resoldered it. And now I have 53,6V between (+) and (-)! :)

Image


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PostPosted: 12 Nov 2009, 02:59 
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By the way, is this the correct way to connect the potentiometer?

Image

The middle pin to the RCA connecter and the two others to input on the amp chip and gnd?

Another question came up; is this the correct way to ground the circuit?

Image


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PostPosted: 12 Nov 2009, 04:24 
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The potentiometer scheme is nearly right. Should look like:
Attachment:
whittj.GIF
The black coloured wire from the potentiometer should be connected to the ground point at the left side from the board (next to Vi). This point is especially for the input signal grounding. All other ground connections can be connected to the PSU ground on the right side from the board (the gnd point between (+) and (-). That one is the PSU ground, speaker ground and also the "AUX" ground. Just change the ground connection from the pot by connecting it to the signal ground point...
The signal ground shouldn't be connected to the PSU ground with the orange wire.
That's all ;-)


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


Last edited by tombethe on 12 Nov 2009, 04:36, edited 2 times in total.

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PostPosted: 12 Nov 2009, 04:31 
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So in other words I just have to switch positions on the player source and GND?


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PostPosted: 12 Nov 2009, 04:34 
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Plz see above ;-)

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 12 Nov 2009, 08:05 
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Joined: 04 Nov 2009, 01:45
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Alright, good news It worked for a while and played surprisingly good! Then I accidentally swaped potitions on the Vs+ and Vs-, note that It was only pluged in like this for 1 or 2 sec, both fuses triggered.

Now when I corrected the error, I just hear a load humming sound as soon as I plug it in. What could have happend?

Too bad that this occurred when I just got it to work!


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PostPosted: 12 Nov 2009, 08:42 
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Joined: 04 Nov 2009, 01:45
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You guys may ignore that last post! It was a bad soldering on the potentiometer, wtf again? :)

Now it works pretty darn well! And I'm really suprised of the sound, I was NOT expecting it to be that good :)

And that little chip doesn't even produce much heat, although I do have a pretty big heatsink.

Well, thanks tombethe for the great schematics and all help. And thanks everyone else who helped me out!

Now I'm gonna listen all day out on my own work =) Have a nice day!


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PostPosted: 12 Nov 2009, 12:20 
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Joined: 04 Nov 2009, 01:45
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Sorry for the tripple post, I'm currently building the second amp circuit and I just noticed I'm out of 22uF 50V caps can I use a 22uF 25V?

Cheers,
Olof


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PostPosted: 12 Nov 2009, 12:54 
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Joined: 27 Aug 2009, 15:19
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Location: Sweden
Hej Olof,
If you run 25V at rails and use a 25V cap u have 99% chance that they will blow up on you so
get atleast 35V at minimum or best 50-63V cap's.
Do a calculation in this by take tranny voltage and multiply with 1.141 and then that voltage with
1.25 to get a safe voltage for capacitors.

Regards,
Kjell.


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