Would it kill me to not use these caps and resistors

MC · 30th December 2003, 10:03 PM

I just recieved two LM3875T's today and I really want to test one out but I a bit short on resistors and capacitors. I've attached a schematic with some stuff circled and I was wondering if it's absolutely necessary to include them in this schematic or if I should buy everything I need before I attempt anything.

Thanks

Richard C · 30th December 2003, 10:13 PM

Most of those components are essential.

theChris · 30th December 2003, 10:34 PM

Rin is a volume control
Rb is to reduce DC offset
Cs is supply filtering
Rfi and Ri are gain setting resistors and Rfi/Ri > 10
Ci is to reduce DC offset

GregGC · 30th December 2003, 10:35 PM

Quote:

Originally posted by MC
I just recieved two LM3875T's today and I really want to test one out but I a bit short on resistors and capacitors. I've attached a schematic with some stuff circled and I was wondering if it's absolutely necessary to include them in this schematic or if I should buy everything I need before I attempt anything.

Thanks

C1 not needed and RL is your speaker. The rest of them, unfortunatley ablolutely have to be there.

SkinnyBoy · 30th December 2003, 10:42 PM

you could exclude the volume control if you are able to run the amp from the headphone socket of something....

jean-paul · 30th December 2003, 10:44 PM

If you omit the parts you describe you better omit the LM3875 too

Dxvideo · 31st December 2003, 10:50 AM

Rfi and Ri are to determine voltage gain. Its OK! But What Ci makes? If we ommit that what happens?

Nuuk · 31st December 2003, 10:51 AM

In the UK, the first day of April is called April Fools day when people play a lot of silly pranks. Reading some of the posts here this morning it looks as though the last day of December is the equivalent in the US!

Circlotron · 31st December 2003, 11:05 AM

Quote:

Originally posted by Dxvideo
But What Ci makes? If we ommit that what happens?

If you replace it with a short circuit then the amp will have flat response down to DC. Normally you would want to reduce the gain to 1 below a few Hz.

Edit: I have left off RB before with no obvious problem.

GregGC · 31st December 2003, 04:48 PM

Quote:

Originally posted by Circlotron
If you replace it with a short circuit then the amp will have flat response down to DC. Normally you would want to reduce the gain to 1 below a few Hz.

Edit: I have left off RB before with no obvious problem.

You will have quite a DC offset if you short Rb and short C1 at the same time. If C1 is there, Rb is not that critical.

30th December 2003, 10:34 PM	#3
theChris diyAudio Member Join Date: Dec 2001 Location: SIUE, Illinois, USA	Rin is a volume control Rb is to reduce DC offset Cs is supply filtering Rfi and Ri are gain setting resistors and Rfi/Ri > 10 Ci is to reduce DC offset __________________ if only it could be used for good, not evil...

30th December 2003, 10:44 PM	#6
jean-paul diyAudio Moderator Emeritus Join Date: Sep 2002 Location: The Netherlands	If you omit the parts you describe you better omit the LM3875 too __________________ It's only audio

31st December 2003, 10:51 AM	#8
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	In the UK, the first day of April is called April Fools day when people play a lot of silly pranks. Reading some of the posts here this morning it looks as though the last day of December is the equivalent in the US! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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30th December 2003, 10:13 PM	#2
Richard C diyAudio Member Join Date: Jul 2003 Location: Nottingham, England	Most of those components are essential.

30th December 2003, 10:42 PM	#5
SkinnyBoy Banned Join Date: Nov 2002 Location: Adelaide, Australia	you could exclude the volume control if you are able to run the amp from the headphone socket of something....

31st December 2003, 10:50 AM	#7
Dxvideo diyAudio Member Join Date: Nov 2003 Location: Turkey	Rfi and Ri are to determine voltage gain. Its OK! But What Ci makes? If we ommit that what happens?

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