single stage common-drain amplifier

Music_Sg · 3rd July 2006, 03:34 PM

Hi

I'm trying to create a lush and rich sound to my music.

Hence I create this common-drain single-stage amplifier to connect to my Toshiba DVD player's output (2V rms). This circuit will then output the signal to a 30K input impedance pre-amp. I found the signal from the DVD player to average around 1V.

Is everything ok with this circuit. From the graph, is the 2nd harmonic at 2.7%? I calculated it by using the peak of the 2KHz (0.005V) divided by the peak of the fundamental 1kHz (0.185V) and use this value *100 to get 2.7%.

I tested using a 1000hz 0.5V input signal.

Thanks

MikeB · 3rd July 2006, 07:40 PM

Yes, your 2nd harmonic is at 2.7%, but it is very likely that you have far more harmonics, your circuit is already clipping the negative waves.
You shouldn't drive that circuit with more than ~250mv, with 2 volts you will get heavy clipping, not nice to hear and bad for your tweeters.
C1 is way too big, 4.7uf should be enough.
These distortions shouldn't scale with music level.

Maybe you can select a jfet with a vgs threshold below -2v.

Mike

lumanauw · 4th July 2006, 05:31 PM

Maybe you can use higher voltage? Like +/-15V? Rs=14000 is that Rs=14K resistor? Unless your rail voltage is very high (far more than 9V), you can consider CCS in the position of Rs for your application.

Christer · 4th July 2006, 06:12 PM

I think there are several issues here, but I think we have to start with the question: What do you really want to do?

Do you just need a buffer?
or
Do you want to deliberately distort the sound?

MikeB · 4th July 2006, 06:45 PM

I assumed that he wants a harmonizer, adding plenty of 2nd harmonics.

Mike

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3rd July 2006, 07:40 PM	#2
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	Yes, your 2nd harmonic is at 2.7%, but it is very likely that you have far more harmonics, your circuit is already clipping the negative waves. You shouldn't drive that circuit with more than ~250mv, with 2 volts you will get heavy clipping, not nice to hear and bad for your tweeters. C1 is way too big, 4.7uf should be enough. These distortions shouldn't scale with music level. Maybe you can select a jfet with a vgs threshold below -2v. Mike

4th July 2006, 05:31 PM	#3
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	Maybe you can use higher voltage? Like +/-15V? Rs=14000 is that Rs=14K resistor? Unless your rail voltage is very high (far more than 9V), you can consider CCS in the position of Rs for your application.

4th July 2006, 06:12 PM	#4
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	I think there are several issues here, but I think we have to start with the question: What do you really want to do? Do you just need a buffer? or Do you want to deliberately distort the sound?

4th July 2006, 06:45 PM	#5
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	I assumed that he wants a harmonizer, adding plenty of 2nd harmonics. Mike

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