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Old 28th August 2010, 12:07 PM   #231
millano is offline millano  Czech Republic
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Default Pcb

hello, i made this PCB for LM1875. PCB is a little larger than a pack of matches. No problem can be used for the TDA2030 or 2040, etc.
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Old 27th September 2010, 05:46 PM   #232
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Hello.

I considering making the LM1875 for some practice. I've just been looking at the data sheet and more specifically the IC pins. According to the datasheet, pin 3 is Vee and Pin 5 is Vcc. Now I am a newbie but as I undrstand Vcc is the positive voltage rail and Vee is the negative voltage rail?

Looking at the PCB diagram above, specifically the + and - symbols at the bottom, and assuming that the IC pins run from 1 -5 left to right, the middle pin (3) track goes to positive voltage input and furthermost right pin (5) track goes to negative voltage input which is the opposite way round to the datasheet.

If I'm wrong about this then let me know, as like I said, I'm relatively new to this with only a couple of simple builds under my belt!

Thanks,

John
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Last edited by johnalexwarren; 27th September 2010 at 05:57 PM.
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Old 27th September 2010, 06:12 PM   #233
AndrewT is offline AndrewT  Scotland
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look again.
Vcc = most positive supply = +ve = pin5
Vee = most negative supply = -ve = pin3
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Old 27th September 2010, 06:26 PM   #234
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Hey Andrew.

I understand that but if you look at Millano's PCB layout diagram, the track marked as positive is running to pin 3 and the track marked as negative is running to pin 5...shouldn't the symbols be the other way round?

I'd also be interested what you think of the layout as a whole?

John.
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Old 27th September 2010, 06:39 PM   #235
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Well spotted. That is a typo. The smoothing caps are drawn the right way round.
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Old 27th September 2010, 06:43 PM   #236
AndrewT is offline AndrewT  Scotland
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Hi,
well spotted, the labels at the PCB edge have been accidentally swapped.

The proposed RF filter is set to cut some of the audio band.
RC time constant =1.5us (R=1k5, C=1nF).
This is F-3dB @ ~100kHz and F-1dB @ ~50kHz.
You may not like the sound of this. Leave the 1nF cap on very long leads or even temporary tacked onto the bottom side of the PCB and listen to it's effect.
Change it to 680pF and to 470pF to hear the difference. You might even prefer going to 330pF.

I don't like the RC (23.5ms) of the DC block (R=1k0, C=47/2uF). It is set to double the frequency of the input filter. I recommend that you try one 100uF and 150uF here. Link across the empty cap location. Measure the DC voltage on this cap once you have the output offset adjusted to near zero millivolts DC. Expect +-30mVdc to +-150mVdc. Fit a diode across the cap terminals (on the bottom side). Arrange the +ve of the diode to match the +ve of the capacitor. This prevents the capacitor becoming reverse biased if the amplifier ever fails.
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Last edited by AndrewT; 27th September 2010 at 06:50 PM.
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Old 3rd August 2011, 04:25 AM   #237
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Red face pls

Quote:
Originally Posted by danielwritesbac View Post
Pretty job there!!!
hey daniel!am a newvie...pls help me out with 5 watts tweeter amp with dc protection...am on a project for tri amping.....cud it de tda or 1875!??
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Old 30th October 2011, 11:42 AM   #238
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simple but useful
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Old 1st November 2011, 12:02 PM   #239
RaviRao is offline RaviRao  India
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Hi Milano,

That was a great PCB. Pls mail me the PCB files if U can as I would like to make this to replace my current 2.1 system in which one channel is dead. Although the PCB is relatively simple even to hand make , I would still prefer to get it made from a fab house in case I need to make some more. Thanks Andrew T , I belive I shall incorporate your suggestions too .
I notice this thread is quite old and Iam not sure if there is any further interest in the topic anymore... Anyway Iam posting this just in case Milano is still out there listening.

Thanks in Advance...
Ravi Rao ( ravi.rao.kumar@gmail.com )
Mumbai-India
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Old 26th October 2012, 10:50 AM   #240
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Hello! What is the schedule for the Nordic PCB ? Is different from the datasheet. Thanks.
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