High Quality Audio Preamp. - Page 2 - Electronic Circuits Projects Diagrams Free

audioguru · 20th April 2007, 08:23 PM

Where are you going to find a high quality 4.7uF non-polarized capacitor?
If the volume control is 100k and R2 is 1M then a very good 470nF metalized plastic capacitor can be used and the low frequency response will be the same as now.

The same for the output capacitor, use a 0.47uF metalized plastic capacitor. Then the whole preamp will be -6dB down at 3.4Hz and be flat down to about 30Hz.

mneary · 20th April 2007, 09:26 PM

VR1 will be incredibly expensive with 0.1% tolerance.

mneary · 20th April 2007, 09:29 PM

audioguru is right about the capacitors. DO NOT use crappy dielectrics like Z5U and X7R. They are fine for bypass but aren't for audio stage coupling. Speaking of bypass, where is it for this circuit?

Also use an np0 or c0g capacitor for C2. Don't trust people selling npo or cog, there is no such thing.

audioguru · 20th April 2007, 10:09 PM

A cheap ceramic disc capacitor as a coupling capacitor makes a lousy microphone. If anything bumps it then it makes a noise.

Ayne · 21st April 2007, 08:54 AM

Circuit Diagram has been changed accordingly..

But in my view,(need ur guidence)
Soundcard output impedence is low and our preamplifier input impedence is enough high. This impedence mismatching will cause the noise.. Am i right!!!.

Thanks.

**Nigel Goodwin** · 21st April 2007, 09:16 AM

Quote:

Originally Posted by Ayne

Circuit Diagram has been changed accordingly..

But in my view,(need ur guidence)
Soundcard output impedence is low and our preamplifier input impedence is enough high. This impedence mismatching will cause the noise.. Am i right!!!.

No, it's how it should be - you don't want impedance matching, it's a BAD thing! (exept for certain specific purposes).

Ayne · 21st April 2007, 09:57 AM

What u say! it's all right and ready for PCB???

Ayne · 21st April 2007, 04:10 PM

Finally PCb has been completed.
Put Suggestions and comments about my PCB and components layout.

Thanks.

audioguru · 21st April 2007, 08:59 PM

It looks good and it should operate good.

palesha · 22nd April 2007, 05:29 AM

Finally let us know what frequency response u got?
How u find the quality?
What software used 4 making nice pcb.

Ayne · 22nd April 2007, 10:22 AM

Quote:

Originally Posted by palesha

Finally let us know what frequency response u got?
How u find the quality?
What software used 4 making nice pcb.

I am using PCB123 for making PCB's. Many members of this web use Eagle(I think), But i like PCB123 becuse it is free and no restrictions.

audioguru · 22nd April 2007, 01:40 PM

The frequency response of a modern opamp like the TL072 with a voltage gain of only 7 is about 320kHz at low levels and 100kHz at high levels. An old 741 opamp has trouble above only 9kHz. An old LM358 or LM324 has trouble above only 6kHz.

The distortion is about only 0.003% up to 2kHz and less than 0.02% up to 20kHz. The old LM358 and LM324 have 3% crossover distortion with a gain of 1 and higher distortion at higher gain.

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20th April 2007, 08:23 PM	(permalink)
audioguru	Where are you going to find a high quality 4.7uF non-polarized capacitor? If the volume control is 100k and R2 is 1M then a very good 470nF metalized plastic capacitor can be used and the low frequency response will be the same as now. The same for the output capacitor, use a 0.47uF metalized plastic capacitor. Then the whole preamp will be -6dB down at 3.4Hz and be flat down to about 30Hz. __________________ Uncle $crooge

20th April 2007, 09:26 PM	(permalink)
mneary	VR1 will be incredibly expensive with 0.1% tolerance.

20th April 2007, 09:29 PM	(permalink)
mneary	audioguru is right about the capacitors. DO NOT use crappy dielectrics like Z5U and X7R. They are fine for bypass but aren't for audio stage coupling. Speaking of bypass, where is it for this circuit? Also use an np0 or c0g capacitor for C2. Don't trust people selling npo or cog, there is no such thing. Last edited by mneary; 20th April 2007 at 09:39 PM.

20th April 2007, 10:09 PM	(permalink)
audioguru	A cheap ceramic disc capacitor as a coupling capacitor makes a lousy microphone. If anything bumps it then it makes a noise. __________________ Uncle $crooge

21st April 2007, 08:54 AM	(permalink)
Ayne	Circuit Diagram has been changed accordingly.. But in my view,(need ur guidence) Soundcard output impedence is low and our preamplifier input impedence is enough high. This impedence mismatching will cause the noise.. Am i right!!!. Thanks.

21st April 2007, 09:57 AM	(permalink)
Ayne	What u say! it's all right and ready for PCB???

21st April 2007, 04:10 PM	(permalink)
Ayne	Finally PCb has been completed. Put Suggestions and comments about my PCB and components layout. Thanks.

21st April 2007, 08:59 PM	(permalink)
audioguru	It looks good and it should operate good. __________________ Uncle $crooge

22nd April 2007, 05:29 AM	(permalink)
palesha	Finally let us know what frequency response u got? How u find the quality? What software used 4 making nice pcb.

22nd April 2007, 01:40 PM	(permalink)
audioguru	The frequency response of a modern opamp like the TL072 with a voltage gain of only 7 is about 320kHz at low levels and 100kHz at high levels. An old 741 opamp has trouble above only 9kHz. An old LM358 or LM324 has trouble above only 6kHz. The distortion is about only 0.003% up to 2kHz and less than 0.02% up to 20kHz. The old LM358 and LM324 have 3% crossover distortion with a gain of 1 and higher distortion at higher gain. __________________ Uncle $crooge