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Old 21st April 2007, 09:20 AM   #1
Ayne is offline Ayne  Pakistan
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Default High Quality Audio Preamp(PCB Soon).

want to take audio signal from PC sound card..

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It's gain should be flat from 30Hz To 22KHz.. Low noise..

Neeed improvement??

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Old 21st April 2007, 10:44 AM   #2
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R2 is superfluous. Divide R3, R4 by 10 for lower noise.
Divide pot by 10 for lower noise.
I think your gain is too high for sound card into power amp. What's the sound card output level?

Jan Didden
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Old 21st April 2007, 11:27 AM   #3
Ayne is offline Ayne  Pakistan
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If i divide all resistor by 10 then
VR1 = 10k
R1 = 1K
R2 = 100K
R3 = 1K
R4 = 6.2K

AND C1 should be equal to 4.7uF for flat responce down to 30 Hz. Which type of capacitor(C1 = 4.7uF) i should use for goodresult??

I am assuming Output of sound card is 200mVolts and this circuit have Gain of 7.

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Old 21st April 2007, 11:53 AM   #4
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Have investigated how much the output voltage is? Probably more than 200 mV.
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Old 21st April 2007, 11:57 AM   #5
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Quote:
Originally posted by janneman
R2 is superfluous.

Jan Didden
Jan, this resistor can be wise to have sometimes if you have a scratchy pot and in particular an opamp with bipolar transistor input stage. If the pot is bad and you don't get any base current you will get a quite nasty output signal. JFET inputs are less sensitive to floating inputs (in short term).
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Old 21st April 2007, 12:52 PM   #6
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Quote:
Originally posted by peranders

Jan, this resistor can be wise to have sometimes if you have a scratchy pot and in particular an opamp with bipolar transistor input stage. If the pot is bad and you don't get any base current you will get a quite nasty output signal. JFET inputs are less sensitive to floating inputs (in short term).

OK I see what you mean, but in my book, the only right thing is to replace the pot . No scratchy pots in my hifi!

Jan Didden
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Old 21st April 2007, 12:53 PM   #7
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Quote:
Originally posted by Ayne
If i divide all resistor by 10 then
VR1 = 10k
R1 = 1K
R2 = 100K
R3 = 1K
R4 = 6.2K

AND C1 should be equal to 4.7uF for flat responce down to 30 Hz. Which type of capacitor(C1 = 4.7uF) i should use for goodresult??

I am assuming Output of sound card is 200mVolts and this circuit have Gain of 7.

Thanks for reply.

R1 was ok as it was.
Yes 4.7u seems OK. a good foil cap would do. Many will advise 100$ designer caps, but that's your taste.

I would think sound card output is 1 to 2 V. Google the brand/type and look it up to be sure.

Jan Didden
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Old 21st April 2007, 05:32 PM   #8
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If the source is a soundcard, you know that it will be capacitively coupled already, so there is no need at all for C1.

I can think of about a 100 better op amps than a TL071.

The size of the resistors probably doesn't matter that much in this circuit since the input level is high. Johnson noise is probably irrelevant. I would still scale down the resistors however as recommended. If nothing else, it minimizes the effects of stray C.

If the resistors are relatively small, you can consider a BJT input op amp as an alternative. You may not need an output C either if the input offsets are reasonably low.

You don't show power supply details. Make sure you decouple the op amp properly.

Al Clark
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Old 22nd April 2007, 09:30 AM   #9
Ayne is offline Ayne  Pakistan
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Default PCB compeleted

PCB done.

C1, C2, C3, C4, C6 are added for decouple the op amp properly.

Suggest me any thing more to improvement.
What u say input Coupling capacitor should be ommited??

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